ZZ4 started running like crap



ZZ4 started running like crap

Postby grumpyvette » January 14th, 2015, 1:51 pm

XQIZT wrote:I'm still tracking down a poor running situation with the 85 (ZZ4 motor installed, but still the stock TPI intake and runners).

Here are the symptoms:

Decent idle although its not rock steady. It's not hunting, but it just doesn't hold steady. I'll see RPMs randomly anywhere from 740 to 870 sitting at a stop light, but it is not rhythmic hunting.

There is a noticeable shake at idle and under load on acceleration (both from leaving a stop and when increasing speed from one cruising speed to another). This shake is rhythmic and increases with speed. It feels like a tire out of balance (although its not that).

Poor power. The car just feels sluggish.

Poor fuel economy and exhaust odor...although no black smoke from tailpipes.

Sounds like light backfiring in the exhaust. Not loud snaps and bangs (like plug wires on wrong cylinder). These are more like gentle thumps/bumps (whooOOmp, whooomp). Happens mostly at cruise at lower RPMs, but not at idle.

I still have the original digi-dash and I've noticed that at cruising speed, the tach will randomly jump from 1800 to 2700, fluctuate around and then settle back down. Its random and the motor is not increasing it's RPMs and my foot is steady on the gas. Not sure if this could be a tell tale of some other problem, but it started doing this BEFORE I had any drivability issues.

viewtopic.php?f=70&t=5372&p=18557#p18557
Here's what I've done:

Checked timing with a digital timing light. Dead on 10*BDC with proper wire disconnected from distributor. (SES did activate, so I know the SES works)
New PVC valve.
New air filter.
Confirmed plug wire routing.
TPS set at .54v.
Cleaned MAF with appropriate cleaner and confirmed burn off per FSM.
New spark plugs. R43TS Delcos gapped at .40.
New adjustable fuel pressure regulator. Set of 45PSI at idle.
New fuel pump, sock and fuel filter. Pressure holds when it is keyed on and allowed to sit (not running).
EGR system completely removed.
Tested for leaks with an unlit torch. No noticeable changes in RPMs anywhere.
Wires, cap, rotor, coil, ign module are less than 1 year old.
New battery.
Alternator tested and passed, per Autozone. I had them run it twice to confirm.
Cleaned throttle body.
Injectors ohm tested and passed.
Chip was recently programmed by TPIS to eliminate Code 32 for deleted EGR. Car ran fine for a year with no problems with this chip in it.

I've gone through the "symptoms" sections of the FSM and ran as many tests as I could. I'll be getting a compression gauge for further tests.

I'll be removing the valve covers and checking for anything suspicious there as well.

I have been autocrossing, but not a lot...less than 10 events in the last 1.5 years.

What else? I am trying my best to identify the problem through tests and not just throw parts at it and hope for the best.


IF that new engine was running decent then it was changed,or originally installed, in the car, obviously something has CHANGED or got worn, or failed, ignition modules and sensors FAIL, electrical connections corrode ,some times they will continue to work PARTIALLY ,youll need to test and find out what adjustment or component is wearing or failed or what came loose or was improperly installed, Id also do a compression/leak down test on all cylinders, and verify the cam lobe lift with a dial indicator, ID pull trouble codes and check for exhaust back pressure, verify alternator voltage,don,t assume the timing is correct until you verify BOTH TDC on the damper and timing tab are correct, damper outer rings come loose! AND VERIFY THE IGNITION ADVANCE CURVE. be aware that if your oil pressure drops the fuel pump shuts off , fuel filters get clogged pumps wear, sensors fail,and the MAF SENSOR COULD BE DEFECTIVE, WITHOUT IT THROWING A TROUBLE CODE.
LOOK FOR LOOSE OR CORRODED ELECTRICAL WIRING CONNECTORS, in THE WIRING HARNESS, and VERIFY YOUR FIRING ORDER, YEAH I KNOW YOUR SURE ITS CORRECT, CHECK IT CAREFULLY AGAIN, YOUR NOID TEST LIGHT AND MULTI- METER CAN SAVE YOU A GREAT DEAL OF PROBLEMS AND SCRATCHING YOUR HEAD IF YOU TEST BASIC ELECTRICAL CONNECTIONS< RESISTANCE AND VOLTAGE, CHECK YOUR SENSORS AND GROUNDS, A SHOP MANUALS MANDATORY, HEAT SENSORS AND IGNITION MODULES AND OIL PRESSURE SENSORS HAVE A LONG TRACK RECORD OF FAILING OR PARTIALLY AND INTERMITTENTLY NOT FUNCTIONING
and use an infrared them gun to check all the exhaust port temps are similar, and check each sensor.
New parts can be defective right out of NEW packaging, don,t assume new parts can,t be defective or were installed correctly..VERIFY TEST!,, KEEP IN MIND KNOCK SENSORS ARE NOT RANDOMLY INTERCHANGEABLE THEY ARE APPLICATION SPECIFIC


ONCE YOU PLOT THE IGNITION ADVANCE CURVE IT WILL,OR SHOULD LOOK SIMILAR TO THIS

Image
btw the engine SHAKE, or vibration could be a defective or loose damper or flexplate or miss matched components [/b]

http://www.diagnosticnews.com/engine-kn ... rs-part-1/

http://www.diagnosticnews.com/engine-kn ... rs-part-2/


Measured Value
Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
Engine Oil Temperature Sensor. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.
Oil Pressure Sender/Switch. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.
Outside Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
In Car Temp Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
MAF (Mass Air Flow) Sensor. .4 Volts @ idle, 5 Volts @ Full Throttle.
Oxygen (O2) Sensor. .1 Volt Lean Mixture, .9 Volt Rich Mixture.
TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.

Sensor Locations

Sensor


Location
Engine Coolant Temperature Sensor. Front of engine, below Throttle Body.
Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter.
Oil Pressure Sender/Switch. Top, left hand rear of engine.
Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel.
MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear.
Outside Temperature Sensor. Right side of engine, top right corner of radiator.
In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid.
MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body.
Oxygen (O2) Sensor. Left side of engine, in exhaust pipe.
TPS (Throttle Position Sensor). Right side of throttle body at the front.

Image
Image
Image
you always need a base line to start from, on a TPI corvette.
a logical step by step approach and keeping accurate notes helps.
youll NEED a multi meter, a shop manual and a timing light and fuel pressure gauge at a minimum,
set and verify your ignition timing, pull trouble codes,set your tps and iac,, then check for vacuum leaks on the lines and intake,then get out your multi meter and verify all the sensors, chances are good
its a defective heat sensor or defective o2 sensor,
a logical step by step approach will lead you to the problem, youll be amazed at what youll learn reading links. use of a shop manual and multi meter can be very helpful
Image

http://www.harborfreight.com/5-in-1-dig ... 98674.html
put a fuel pressure gauge on the fuel rail on the shrader valve,
viewtopic.php?f=32&t=10688&p=46303&hilit=shop+manual#p46303
viewtopic.php?f=32&t=1401
Image
a vacuum and fuel pressure gauge is useful
Image
viewtopic.php?f=80&t=728&p=43477&hilit=camaro+sensors#p43477

viewtopic.php?f=55&t=1475&p=43635&hilit=trouble+codes#p43635

viewtopic.php?f=87&t=332&p=14266&hilit=leakdown+test#p14266

viewtopic.php?f=52&t=90&p=494&hilit=cam+degree+tools#p494

viewtopic.php?f=56&t=495

viewtopic.php?f=55&t=1475

viewtopic.php?f=50&t=902&p=44187&hilit=gear+puller#p44187

viewtopic.php?f=55&t=1241

viewtopic.php?f=32&t=10624&p=45703#p45703

viewtopic.php?f=70&t=4683
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: ZZ4 started running like crap

Postby philly » January 14th, 2015, 11:57 pm

if you determine all your external sensors are working properly, even your maf, then its time to find out what cylinder exactly is giving you the problem.

i would use grumpys temp gun trick to isolate the problem cylinder as it is likely only one that is giving you a slight misfire/ stumble... once youre there you can break it down by system

just because parts are new or were recently replaced doesnt mean they are good... if the shake/exhaust pop/ smell all came to be at the same time, chances are its the same thing causing all three... worst case scenario you may have a valve seating issue of some sort (either burnt bent or only partially functioning) but more frequently problems like these under load are caused by some sort of ignition failure. check you plug gap and check your wire resistance, then check your cap and rotor for a carbon trace and corrosion, and finally coil for proper operation (the manufacturer of all those parts will have parameters for resistance of wires and for signal and output voltage of coil, etc... use their specs not some generic ones) if all of that falls within spec check your knock sensor and see if its not just trying to throw your timing out the window all the time.

if the ignition and the inputs and sensors that it relies on are all good, move on to fuel, use a gauge in the test port to check that the pressure is where it should be and disconnect the vacuum signal to the regulator to see if its adjusting pressure as it should.... NOTE: if theres moisture inside that vacuum signal tube then youre diaphragm has a leak, and regardless of the pressure tests you really need to replace it, as its often impractical to see the fuel pressure while under load. while youre at the test port, perform a fuel pressure leak down test, if you dont have and cannot borrow a set of noid lights, its not hard to make your own and ensure that your injectors (which you say tested good) are all receiving signal input from the computer. that should about cover your bases on fuel.

pop the valve cover and see if the valves are all operating properly, both that the cam,lifter and rod are acting on the rocker, and that the rocker is imparting that action on the valve. if you have dual valve springs take the time to check that the inner spring hasnt broken and stayed mostly in place, check these carefully. if you really dont want to take the motor apart, i would suggest figuring out a way to measure valve lift of a good cylinder on one cycle and then of youre condemned cylinder in an attempt to find a lifter or cam lobe failure of some sort, maybe even a bent pushrod.

good luck and i hope its something simple like a crap ignition wire
-phil

There's never enough money to build it right, but there's always enough to build it twice!
philly

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