maf burn off relay info



maf burn off relay info

Postby grumpyvette » November 9th, 2008, 11:13 am

This is from the '86 manual:
Image

http://tpiparts.net/85_89_maf_sensors/

The MAF Power Relay is called the Mass Burn Off Control Relay in the schematic. The photos I have are too blurry to be of any use to you, but I can verify the schematic is correct. As raid's description does not match the schematic, I assume the 87 is different.

MORE USEFUL INFO
http://www.corvettefever.com/techarticl ... index.html

http://books.google.com/books?id=O2vA-v ... 1#PPA54,M1

http://www.corvettebuyers.com/c4vettes/maf.htm
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QUOTE
"Most of the C4 Corvettes used a MAF (Mass Air Flow) sensor to determine how much air is being pulled into the intake manifold. The exceptions are the 1984 Corvette that used a speed density system--a sort of predictive method of measurement---and the 1990 through 1993 C4 models which were also speed density based. In 1994, Corvette went back to the MAF based system but used the speed density approach as a back up. (1989 Bosch MAF installation shown at right).

A Mass Air Flow sensor has an extremely fine wire inside its bore. The 1985 through 1989 C4 engines used a Bosch MAF sensor that heated the wire to 100 C. The 1994 and later C4 models used a AC/Delco MAF that heated the wire to 200 C. The amount of current required to reach the temperature is measured in each case. (Note: the LT-5 engine used in the ZR-1 used a speed density system and continued to use that system in 1994 and 1995 since the engines had already been made prior to the last two years of production. The ZR-1 therefore has no MAF even after Corvette went back to the MAF based system).

Theory of Operation

As the air travels past the heated wire enroute to the intake manifold, it will cool the wire and additional current is added to again heat the wire to the design temperature. Since the amount of air moving past the sensor is directly related to the amount of cooling experienced by the heated wire, a feedback condition is established whereby the exact amount of moving air is directly related to the amount of current passing through the wire and the intake air is therefore precisely measured.

Once the amount of air is known, the computer controlling the engine can add or subtract fuel as required to maintain the magic 14.7:1 air-fuel mixture resulting in the cleanest burn possible from an emissions (pollution) standpoint.

It does this by varying the "on time" of the fuel injectors. The injectors are pulsed on and off and the width of the pulse is lengthened or shortened as required. When you first start a typical engine, the pulse width is around 4 milliseconds but as soon as the engine "catches" the pulse width is shortened to about 2.2 milliseconds for idle. During operation, the measured air flow through the MAF will cause the computer to increase or decrease the pulse width as explained above.

MAF Operating Conditions

The Bosch MAF is more complex than the AC/Delco version. Both measure the air flow but the Bosch MAF has a circuit called the 'burn-off circuit' that cycles on for about 2 seconds when you shut the engine down. This circuit heats the wire to a high enough temperature to burn off any residue that may have collected on the wire during operation. If you are in a quiet area, you can hear the relays click on and then off on a 1985-1989 C4 as the burn-off cycle occurs.

There are two relays involved with the Bosch MAF: A power relay that passes current to the MAF wire during normal operation and the burn-off relay that provides the current for the cleaning cycle. Both are located on the firewall in the engine compartment, just behind the battery on the drivers side. Bad MAF power and burn-off relays can cause hard starting problems and should be changed periodically as preventative measure and any time you experience hard starting conditions.

The AC/Delco MAF has a power relay but no burn-off relay. For this reason, you should pay even closer attention to the condition of your air filter on a later model C4 than normal since a contaminated wire in a AC/Delco MAF is going to stay contaminated for the most part and cause false signals to be passed to the computer.

Also, the Bosch MAF outputs its information as a analog signal to the computer but the AC/Delco sends its signal as a digital component of varying frequency. For this reason, you cannot measure it's operation directly.

A scan tool is generally the best way to troubleshoot engine problems and with the 1994 and later Corvette, it is virtually mandatory. (An oscilloscope will also work on the AC/Delco MAF but a regular test meter will not).

MAF Problems

Faulty MAF sensors will normally light the check engine light on the drivers information center if the problem is constant and store a trouble code. If intermittent, a trouble code will still be stored as long as the battery is not disconnected.

Normally, the problem is a poor connection at the sensor and wiggling the wires, unplugging and reinserting the connector will often cure the problem.

A faulty MAF will normally cause a no start or difficult start condition and although you can eventually get the car into the "limp-home" mode in most cases, you need to attend to the problem ASAP.

AC/Delco sensors can become intermittent or give false readings if the wires become contaminated as explained above.

The MAF is a critical part of the emission control system and as such will cause the computer to react to problems very quickly, setting trouble codes and reducing performance in ways that cannot be ignored for long.

MAF Mods

The Bosch MAF is often modified by removing the two screens that are present in the front and rear of the cylinder. Removing these screens significantly increases the air flow through them and this results in more horsepower. Removing the screens is an old trick from the Corvette Challenge days in 1988 and 1989. It does work but is illegal in many states so be advised not to do anything that will get you arrested for a pollution violation.

The AC/Delco MAF is not readily modified. It is what it is but since it is a larger diameter than the Bosch, it responds well to changing the air filter to a free flowing type such as the K&N filter."
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: maf burn off relay info

Postby grumpyvette » November 13th, 2009, 8:20 pm

C4 Sensor Check Information
http://www.chevythunder.com/maf_code_36.htm

http://www.chevythunder.com/maf_code_33.htm

http://www.chevythunder.com/maf_code_34.htm

http://www.chevythunder.com/Flow%20chart%20index.htm


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first check your shop manual for the fuse and fuse able link locations
fuses are located in several locations and fuse-able links near the battery
http://www.gmtips.com/3rd-degree/dox/ti ... screen.htm

The C4 Corvette makes use of numerous sensors that feed information to the ECM/PCM (Electronic Control Module / Powertrain Control Module) and to the instruments on the dashboard.

Even if the sensor is operated by vacuum or pressure, the output is converted into an electrical signal for processing by the ECM. Most faulty sensors will cause a trouble code to be set (resulting in a 'Check Engine/SYS ' Light) and also alter the performance of the automobile. When troubleshooting the reason for the code, the normal approach is to go straight to the sensor and assume that it is faulty. While this may be the normal practice, you are strongly cautioned that it is seldom the sensor but rather a connector, a power problem or a grounding issue that is actually causing the problem. Or, the sensor may simply be doing it's job and reporting an occurrence that is at variance with what is allowed or expected by the ECM/PCM. In any event, because the sensor really is the easiest thing to check, the following information is provided to assist you in determining if the device is operating properly.

You will need a D-VOM (Digital Volt-Ohm Meter) to check the items below. It should have at least a10 megohms per volt rating, something that will be shown in the specifications. For those sensors listed below that have ohms listed as the measurement item, disconnect the negative battery terminal and then the sensor harness connector and measure the sensor's terminals. For voltage measurements, you can obtain test harnesses from any of the Corvette specialty catalog houses. [Before beginning your efforts, print the page so you can cross reference the code information with the sensor information.]

Sensor Location Measured Value
Engine Coolant Temperature Sensor. Front of engine, below Throttle Body. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohm @39 F.
Oil Pressure Sender/Switch. Top, left hand rear of engine. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 6PSI.
Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear. 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.
Outside Temperature Sensor. Right side of engine, top right corner of radiator. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body. .4 Volts @ idle, 5 Volts @ Full Throttle.
Oxygen (O2) Sensor. Left side of engine, in exhaust pipe. .1 Volt Lean Mixture, .9 Volt Rich Mixture.
TPS (Throttle Position Sensor). Right side of throttle body at the front. .54 Volts Idle, ~ 5 Volts Full Throttle.
Assembly Line Communications Link (ALCL)
F E D C B A
G H J K L M
[The ALCL is located underneath the dashdoard, just below the instrument panel and left of center console.]
Top of page
Code Circuit or Sensor Possible Failures
13 Oxygen Sensor Circuit Check wiring and connectors. Bad Sensor
14 Coolant Sensor Circuit (High) Check wiring, connectors, thermostat. Monitor actual engine temperature. If within limits, and wiring and connector is OK, change thermostat and or sensor.
15 Coolant Sensor Circuit (Low) See above, particularly thermostat
16 Ignition Problems (Used only on 1992-1996 models) Direct Ignition (DI) Fault
21 Throttle Position Sensor (TPS) (High) Sticking or Misadjusted TPS. Also check wiring and connectors. Adjust or replace TPS.
22 Throttle Position Sensor (TPS) (Low) Sticking or Misadjusted TPS. Also check wiring and/ connectors. Adjust or Replace TPS.
23 Intake Air Temperature (Low) Measure sensor resistance with Digital Ohm meter. Must not be 0 ohms or infinite ohms. Replace if it shows one of these readings. Check wiring and/ connector of sensor. If OK, replace sensor.
24 Vehicle Speed Sensor (VSS) Only valid if vehicle moving. Check connections at ECM Check TPS setting. Possible ECM failure.
25 Intake Air Temperature (High) Measure sensor resistance with Digital Ohm meter. Must not be 0 ohms or infinite ohms. Replace if it shows one of these readings. Check wiring and connector of sensor OK.
26 Quad Driver Module Number 1 Check EGR, Canister Purge and AIR pump relays with a digital Ohm meter. A resistance of less than 18 ohms indicates a bad relay. If OK, potential ECM failure.
27 Quad Driver Module Number 2 Potential ECM or on a manual transmission car, potential upshift relay problem. Check relay, replace if less than 18 Ohms using a digital Ohm Meter.
28 Quad Driver Module Number 3 Air conditioning Clutch relay and/or cooling fan relays. Check with digital Ohm meter, replace if less than 18 Ohms. If relays OK, potential ECM failure.
32 Exhaust Gas Recirculation Circuit The most common cause of this code is a bad or intermittent EGR switch which is located on the EGR pipe between the exhaust manifold and the intake manifold. Replace this switch first when you get this code. Next, check electrical connections at EGR valve solenoid and then the ECM. Check all vacuum lines for leaks especially around the EGR valve. Possible ECM failure.
33 Mass Air Flow Sensor Circuit (1985-1990) Inspect intake system for leaks, Inspect for vacuum leaks, Check MAF connector and wiring, Check MAF for open using digital Ohm meter. Possible ECM failure.
33 Manifold Absolute Pressure High (1984) Check vacuum hoses. Check wiring to sensor. Change sensor. Check connections at ECM.
34 Mass Air Flow Circuit (1985-1990) Clean the throttle body. Check MAF connections. Replace MAF relay. Replace MAF Sensor. Possible ECM failure.
34 Manifold Absolute Pressure Low (1984) Check Vacuum hoses associated with MAP sensor. Check wiring and connections, particularly at ECM. Replace the sensor. Possible ECM failure.
35 Idle Air Control Circuit (IAC) Check fuel pressure, injectors, leaking throttle body. Change the IAC valve.
36 Mass Air Flow Burn Off Circuit Check connections at MAF, MAF relay and MAF Burn off relay. Check resistance of MAF relay and MAF burnoff relay with digital Ohm meter. replace if less than 18 Ohms. Possible ECM failure.
41 Cylinder Select Error Circuit (1985-1991) Check wiring at ECM. Possible PROM failure, or incorrectly seated PROM. Reseat PROM. Possible ECM failure.
42 Electronic Spark Timing Circuit (EST) Check wiring at ignition module. Replace ignition module. Possible ECM failure.
43 Knock Sensor Circuit Check ECM wiring. Replace knock sensor
44 Lean Exhaust Present Check wiring.connectors at Oxygen sensor. Check fuel pressure. Replace Oxygen sensor.
45 Rich Exhaust Present Check evaporation charcoal canister for smell of fuel (which normally comes from filling fuel tank to full). check fuel pressure regulator. Possible leaking fuel injector or sticking/bad EGR valve. Possible bad Oxygen sensor.
46 VATS Anti Theft Circuit Fault With negative battery lead disconnected and using high pressure, non residue contact spray cleaner, spray into area where ignition key inserts followed by inserting and removing key several times. Check for open/short on harness from steering column VATS ignition key to ECM. Possible defective anti-theft module.
51 PROM/EEPROM Error Faulty or incorrect PROM in the ECM. Change PROM with correct version for automobile.
52 Oil Temperature Circuit (Low Temperature) Check connections at the oil temperature switch. If OK, replace switch.
53 System Charging Voltage High or Low If voltage is more than 17.1 or less than 10 volts, this code will be set.Check battery leads, alternator drive belt for tightness and have electrical shop check alternator output. Voltage with engine off should be 12 volts. Voltage with engine running should be 14-15 volts. Use digital volt meter for checks and measure at the battery terminals.
54 Fuel Pump Circuit (Low Voltage) Using digital Ohm meter, check fuel pump circuits for shorts or opens.
55 Engine Running Lean This code is set when there is not enough fuel when accelerating. A possible fuel pump failure or insufficient fuel pressure due to a fuel line restriction is indicated.
62 Oil Temperature Circuit (High Temperature) Check wiring associated with Oil temperature switch. Replace switch.
63 Oxygen Sensor Circuit (Open) Check wiring and connections to Oxygen sensor.
64 Oxygen Sensor Circuit (Lean Exhaust) Check wiring and connections from Oxygen sensor to ECM. Check ECM ground terminal and battery ground. Check fuel pressure and fuel pump. Replace Oxygen sensor if all of above OK.
65 Oxygen Sensor Circuit (Rich Exhaust) Check evaporative charcoal canister for fuel fumes. Replace if contaminated. Check oil for presence of fuel. Check fuel pressure regulator, fuel pump, check for leaking injectors, Check for stuck/defective EGR valve, Replace Oxygen sensor if all above OK.
66 Air Conditioner Pressure Limit Exceeded Check the sensor electrical terminal connections and possible short to ground or open circuit in the pressure senor circuit senor wiring. Replace the Air Conditioning Refrigerant sensor.
67 Air Conditioner Pressure Limit Exceeded Check the pressure sensor or air conditioning clutch ciruit for possible short to ground or open circuit pressure sensor circuit in the sensor wiring.Replace the Air Conditioning Refrigerant sensor.
68 Air Conditioner Relay Fault Check the air conditioning relay circuit and the relay for possible short to ground or open circuit.
69 Air Conditioner Clutch Fault Check the air conditioning clutch circuit and the relay for possible short to ground or open circuit.
72 Gear Selector Switch Fault (Start Lockout) Check the connections at the TCC solenoid and Park Neutral switch. Replace the ECM or repair the transmission as needed.
[Info taking form 1984 thur 1996 Haynes Repair Manual]

mass air flow sensors and air filters

http://www.youtube.com/watch?v=CXuO5OmKPyY

http://www.youtube.com/watch?v=sSuL58YE ... ure=relmfu

http://www.knfilters.com/MAF/massair.htm

http://www.knfilters.com/MAF/2MAFSensorVideo.htm

http://www.knfilters.com/MAF/3MAFSensorVideo.htm

http://www.knfilters.com/MAF/4MAFSensorVideo.htm



http://www.corvettephotographs.com/c4vettes/maf.htm
Image

"Most of the C4 Corvettes used a MAF (Mass Air Flow) sensor to determine how much air is being pulled into the intake manifold. The exceptions are the 1984 Corvette that used a speed density system--a sort of predictive method of measurement---and the 1990 through 1993 C4 models which were also speed density based. In 1994, Corvette went back to the MAF based system but used the speed density approach as a back up. (1989 Bosch MAF installation shown at right).

A Mass Air Flow sensor has an extremely fine wire inside its bore. The 1985 through 1989 C4 engines used a Bosch MAF sensor that heated the wire to 100 C. The 1994 and later C4 models used a AC/Delco MAF that heated the wire to 200 C. The amount of current required to reach the temperature is measured in each case. (Note: the LT-5 engine used in the ZR-1 used a speed density system and continued to use that system in 1994 and 1995 since the engines had already been made prior to the last two years of production. The ZR-1 therefore has no MAF even after Corvette went back to the MAF based system).

Theory of Operation

As the air travels past the heated wire enroute to the intake manifold, it will cool the wire and additional current is added to again heat the wire to the design temperature. Since the amount of air moving past the sensor is directly related to the amount of cooling experienced by the heated wire, a feedback condition is established whereby the exact amount of moving air is directly related to the amount of current passing through the wire and the intake air is therefore precisely measured.

Once the amount of air is known, the computer controlling the engine can add or subtract fuel as required to maintain the magic 14.7:1 air-fuel mixture resulting in the cleanest burn possible from an emissions (pollution) standpoint.

It does this by varying the "on time" of the fuel injectors. The injectors are pulsed on and off and the width of the pulse is lengthened or shortened as required. When you first start a typical engine, the pulse width is around 4 milliseconds but as soon as the engine "catches" the pulse width is shortened to about 2.2 milliseconds for idle. During operation, the measured air flow through the MAF will cause the computer to increase or decrease the pulse width as explained above.

MAF Operating Conditions

The Bosch MAF is more complex than the AC/Delco version. Both measure the air flow but the Bosch MAF has a circuit called the 'burn-off circuit' that cycles on for about 2 seconds when you shut the engine down. This circuit heats the wire to a high enough temperature to burn off any residue that may have collected on the wire during operation. If you are in a quiet area, you can hear the relays click on and then off on a 1985-1989 C4 as the burn-off cycle occurs.

There are two relays involved with the Bosch MAF: A power relay that passes current to the MAF wire during normal operation and the burn-off relay that provides the current for the cleaning cycle. Both are located on the firewall in the engine compartment, just behind the battery on the drivers side. Bad MAF power and burn-off relays can cause hard starting problems and should be changed periodically as preventative measure and any time you experience hard starting conditions.

The AC/Delco MAF has a power relay but no burn-off relay. For this reason, you should pay even closer attention to the condition of your air filter on a later model C4 than normal since a contaminated wire in a AC/Delco MAF is going to stay contaminated for the most part and cause false signals to be passed to the computer.

Also, the Bosch MAF outputs its information as a analog signal to the computer but the AC/Delco sends its signal as a digital component of varying frequency. For this reason, you cannot measure it's operation directly.

A scan tool is generally the best way to troubleshoot engine problems and with the 1994 and later Corvette, it is virtually mandatory. (An oscilloscope will also work on the AC/Delco MAF but a regular test meter will not).

MAF Problems

Faulty MAF sensors will normally light the check engine light on the drivers information center if the problem is constant and store a trouble code. If intermittent, a trouble code will still be stored as long as the battery is not disconnected.

Normally, the problem is a poor connection at the sensor and wiggling the wires, unplugging and reinserting the connector will often cure the problem.

A faulty MAF will normally cause a no start or difficult start condition and although you can eventually get the car into the "limp-home" mode in most cases, you need to attend to the problem ASAP.

AC/Delco sensors can become intermittent or give false readings if the wires become contaminated as explained above.

The MAF is a critical part of the emission control system and as such will cause the computer to react to problems very quickly, setting trouble codes and reducing performance in ways that cannot be ignored for long.

MAF Mods

The Bosch MAF is often modified by removing the two screens that are present in the front and rear of the cylinder. Removing these screens significantly increases the air flow through them and this results in more horsepower. Removing the screens is an old trick from the Corvette Challenge days in 1988 and 1989. It does work but is illegal in many states so be advised not to do anything that will get you arrested for a pollution violation.

The AC/Delco MAF is not readily modified. It is what it is but since it is a larger diameter than the Bosch, it responds well to changing the air filter to a free flowing type such as the K&N filter."

Image
http://www.mamotorworks.com/corvette-c4 ... 6-893.html
http://content.mamotorworks.com/pdf/601096.pdf
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: maf burn off relay info

Postby grumpyvette » November 30th, 2012, 7:38 pm

MAF Circuitry Operation Summarized - ECM Codes 33, 34 and 36

http://www.micro-tech-auto.com/maf.html

http://forums.corvetteforum.com/c4-tech ... units.html



READ THE LINK

http://www.corvettebuyers.com/c4vettes/maf.htm
Image
Image

I have attached an Image of the MAF cicuitry to include the ECM inputs/outputs the MAF Sensor and both the Burn Off relay and the Control Relay.
I did this because it seems that perhaps my request for assistance is not clear.
This may get long winded so bear with me please. I think this info might be useful to others having the same problem. Recurring Code 36.
Basically my question is how long should the burn off period be? 2 seconds, 10 seconds, 30 seconds or whatever it is.
Before I get started let me mention something. The general convention in schematics is to show relays in there static state (no power applied, which is the case with this schematic)
OK here goes. As you can see from the schematic Power is applied to A and D of the MAF Burn Off Relay and C of the MAF Power Relay. When the car is started the MAF Burn Off relay does nothing. This is the normal state of this relay when the engine is running. The coil has not been energized and the switch is open. Also notice that the 12 VDC is also applied to A of the MAF Power relay. As your engine turns during starting the oil pressure builds and closes the oil pressure switch which applies 12 V to D of the MAF Power Relay which energizes the relay causing the switch to toggle to A and 12 V is then applied to E which serves as the power source for the MAF sensor. All pretty simple so far. I have checked all of these functions and they work as they should.
Ok now for the part relating to my question. I am going to make a couple of assumptions here so bear with me.
Assume your engine is warmed and has been running for at least 5 or 10 minutes. You shut the engine off. The oil pressure drops which de-energizes the MAF power Relay then shortly after that occurs the ECM asserts the Ground at F of the MAF Burn Off relay which engergizes the relay, closing the switch which then applies 12 V to E of the Burn Off relay which is also the Burn Off Signal or D of the MAF Sensor. At the same time the 12 V is also applied to C of the MAF Power relay and since it is de-engergized, due to lack of oil pressure (engine off), the 12 V is routed from C to E of the MAF Power Relay and to E of the MAF Sensor itself to supply power to the sensor. Now here is the part that most folks seem to have a problem with. I think everyone assumes that since the engine is off the MAF and the ECM are no longer active. This can't be the case. I have to assume since there is no signal to the ECM from the MAF Burn Off relay itself that the ECM has enough smarts to read/sample the MAF Signal, C of the MAF Sensor during the Burn Off period. After all don't forget the ECM is the guy that asserted the signal to begin with. I have to also assume that the ECM has enough smarts to know that when 12 V is applied to the Burn Off Signal D that is should produce a certain output on the MAF Signal to the ECM. This is the only way the ECM can know which code to set. In my case it is setting a 36. So this brings me to my question or questions I should say. The Service Manual covers Codes 33 and 34 very well and tells you exactly why the fault was set but it is vague at best about a code of 36. Basically a code 33 indicates the ECM has seen a HIGH air flow input , greater than 2.2 Volts of MAF Signal, just after the engine was started and 34 indicates the ECM has detected a LOW air flow signal, low voltage at MAF Signal input to the ECM just after the engine. Now since my ECM is not setting either a 33 or 34 and the same input is used to decide whether or not to set the 36 I have to assume the ECM is ok.
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: maf burn off relay info

Postby grumpyvette » November 2nd, 2013, 10:05 am

I found these bits of info
tequilaboy wrote:Here's a plot to illustrate the pw limitation for constant flow of 255 gm/sec assuming a stoich AFR of 14.73:1. This will give you an idea of the excess air that can be supported via PE tuning alone with a pegged MAF at mid-high rpm. Pegging at low-mid rpm is unlikely, but could be a concern for a very large displacement or turbo car.

Image

For this condition (pegged MAF for all rpms), AFR targets below (richer than) the dark blue line (or richer than the yellow line below 3800 rpm intersection point) will not result in any additional enrichment, since the pw will be internally limited.

The medium blue line represents the richest AFR target that you can achieve by tuning the PE vs coolant temp and PE vs rpm tables. This is approx. 5.89:1.

Note: This plot alone doesn't tell the whole story, the pw limitation can also come into play below approx. 4,000 rpm if the MAF flow should exceed the dark blue line of death. This plot is based on a fixed 12.8 target AFR. Richer or leaner targets will skew the resulting curve.

Image

Note: This post is intended to give 86-89 MAF users an idea of what can be achieved via traditional PE tuning methods only. These limitations can be overcome with MAF upgrades and/or special tuning. This does not reflect an overall limitation of a MAF based system.


Lemme wrote:Found this equation on how pulse width (pw) is calculated for an efi controlled engine. May be able to relate it to the c4 ecms calcs

http://en.wikipedia.org/wiki/Fuel_injection#Sample_pulsewidth_calculations

pw ms = (air lb/min)/(rpm*strokes per rev*afr*fuel lb/min)*1000*60

Example at idle for 350 ci

air lb/min = 1.03 (approx 8 g/s)
rpm = 700
strokes per rev = 2
afr = 14.73
fuel lb/min = 0.37(22 lb /hr injectors)

Substituting in values gives pw ms = 8.4 ms [COLOR="Red"]Actual bpw from datalog = 2.23ms[/COLOR]


Example at 5000 rpm for 350 ci

air lb/min = 28.42 (approx 215 g/s)
rpm = 5000
strokes per rev = 2
afr = 14.64
fuel lb/min = 0.37(22 lb /hr injectors)

Substituting in values gives pw ms = 32 ms [COLOR="Red"]Actual bpw from datalog = 10.23ms[/COLOR]

Interesting that this formula seems to be giving pulse widths 3 times that of my 87! Does the batch fire system fire more than once per cycle?
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: maf burn off relay info

Postby 87vette81big » November 2nd, 2013, 2:32 pm

Lemme is my bud Steve Grumpy.
We know each other well.

He never was taught Injector Offset Values.
Injector flows still after current cutoff in measured milliseconds time.
He got jerked around bad on CFC4 after I was kicked off like Rich.

Steve continued to use Bosch3's Blew his AFR195 engine in his black 87vert.
I ditched the Bosch 3's & installed 24# per hour Trickflow injectors.

Dave Dahlgren taught me EFI fundemental tuning.

He got bastardized on CFC4 also.
But I fought nightly for Dave too.

Dave is right.......

BR
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Re: maf burn off relay info

Postby grumpyvette » November 2nd, 2013, 3:41 pm

Id say one of the most common mistakes I see is guys make when trying to build a 500 hp plus TPI based corvette engine,is those who scrimp , ignore the math, and don,t bother to think thru ther engines requirements,and think the stock injectors will work, resulting in a engine running lean in the upper rpms when the stock injectors max out who then come around with that CLUELESS look, and say something brilliant like "well it idled and ran darn nice until the first time I really stuck my foot to the floor and held it there!"

if thats your plan, buy the 42 lb injectors, or what ever size the calculator suggests plus a bit larger just as a hedge for safety, before you burn up some rings etc. a properly tuned MPFI engine will have the pulse duration, of the injectors match the sensors suggested air flow rates,and it can only do that up to the point the injectors operating at about 80%-85% of its flow capacity on the upper end of the flow rates , but can easily drop flow down to only a 30% duration if thats required, yes youll find guys that say they installed 30lb or 36 lb injectors and it ran like crap1 youll also find they don,t know how to tune injection themselves after asking more detailed questions


RELATED INFO
viewtopic.php?f=55&t=1200&p=31258&hilit=calculate+injector#p31258

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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: maf burn off relay info

Postby 87vette81big » November 2nd, 2013, 4:17 pm

Your correct Grumpy.
But there is more......
Issue is the stock ECM Eprom Algorithms are set for Stock injector flow characteristics.
More than just mean flow that most see or understand.

Battery offset tables present too.
Must readjust accordingly.
Program yourself.

STEVES BAD ADVICE CAME RIGHT FROM FIC Injector. JOHN B.

Brian R.
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Re: maf burn off relay info

Postby 87vette81big » November 2nd, 2013, 4:52 pm

If You Run an old school Holley 4- bbl, you bypass all maybes, what iffs, FIC crap, lieing forum tuners,
.
Make more HP & TORQUE TOO.

Why I had the BO LAWS 1085 CFM PRO FLOW MADE FOR MY 410.
Worth every penny Grumpy.
Showed off to Dave after I had it made.
Read the build sheet sent.
He smiled & approved 100%.

BR
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MAF & code 34

Postby bytor » May 8th, 2014, 10:55 am

Hey Grumpy, got my first check engine light on my 87 Corvette. It’s a 34, low MAF flow. Intend to follow the service manual check procedure below, check the MAF relays and re-verify base idle. I cleaned the throttle body and replaced the IAC about a month ago and the car has been running great until yesterday. With you experience with C4’s are there any other things I need to check?

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Re: MAF & code 34

Postby grumpyvette » May 8th, 2014, 11:17 am

the threads linked below may help, but its more than likely a bad temp sensor or the TPS OR IAC is out of adjustment. so the first thing Id suggest is to adjust the TPS and IAC per the linked info and check for loose connections and vacuum leaks, and loose plenum and intake runner gaskets
34 Mass Air Flow Circuit (1985-1990) Clean the throttle body. Check MAF connections. Replace MAF relay. Replace MAF Sensor. Possible ECM failure.
34 Manifold Absolute Pressure Low (1984) Check Vacuum hoses associated with MAP sensor. Check wiring and connections, particularly at ECM. Replace the sensor. Possible ECM failure.

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MAF SENSORS AND RELAYS ARE FREQUENT SOURCE OF INTERMEDIATE OR HARD TO ISOLATE RUN ISSUES ON EARLIER TPI CORVETTES SO CHECK THEIR FUNCTION


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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: MAF & code 34

Postby 87vette81big » May 8th, 2014, 12:32 pm

If you have access to a Digital Oscillosope or a Snap On Vantage, measure the MAF Signal Output Bytor.
They are getting hard to find working 1986-87 MAF C4.
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Re: MAF & code 34

Postby bytor » May 8th, 2014, 1:56 pm

87vette81big wrote:If you have access to a Digital Oscillosope or a Snap On Vantage, measure the MAF Signal Output Bytor.
They are getting hard to find working 1986-87 MAF C4.


Good idea. I don't have a modern storage scope, I need one. My ole trusty Tektronix 561A oscilloscope is getting long in the tooth. Plus, weighing in at 30LB it's not very portable. I'll resort to it after some initial MAF test.

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Re: MAF & code 34

Postby 87vette81big » May 8th, 2014, 2:04 pm

Its more than sufficient your Textronics TTL Oscilloscope.
Lab scope Nice still.
Set it on the drivers tire with hood up.
Make parked garage tests with engine running.
Oscilliscope testing MAF Most accurate.
Just 20K HZ max frequency output.
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Re: MAF & code 34

Postby bytor » May 11th, 2014, 10:00 am

Code 34 update. During my research on this I found that the MAF sensor seems to be sensitive to the power and burn off relays. Since they are both the same part#, I switched them around and guess what, I got a code 36. One must be flaky. I pulled both relays and bench tested them, they tested fine under 1 ohm. I'm going to replace both and see if that corrects the problem.

On a different note, my fuel rail/regulator makes a strange sound when I key-on (not start) and the pump primes. I have not isolated the exact source of the sound yet. It's done it since I had the car. I found a kinked return hose at the tank and fixed that but still have this sound. It's kinda a hiss/click sound. Is it normal? I have normal fuel pressure.
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Re: MAF & code 34

Postby 87vette81big » May 11th, 2014, 12:03 pm

It hisses on my 87 Vert too Bytor.
I am using a 1990 ZR1 Stick dual fuel pump.
Both pumps on always with key on engine running.

The GM MAF Relays don't last long.
Not Pure Platinum Contacts alloyed with Rhodium.
Or Silver Contacts.
They are just copper pucks. Burn easy.
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Re: MAF & code 34

Postby bytor » May 11th, 2014, 12:41 pm

87vette81big wrote:It hisses on my 87 Vert too Bytor.



Thanks for the feedback 87vette81big, I wasn't sure on that sound. The car is running great now, we will see if the MAF codes stay away..
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