86 C4 starts, runs, rough idles and sometimes stalls



86 C4 starts, runs, rough idles and sometimes stalls

Postby monsolo2 » October 27th, 2014, 9:30 pm

Grumpy, I just bought a nearly flawless (interior & exterior) 1986 C4 coupe. When I drove it home from the dealership, I noticed a slightly rough idle but still good performance out of the engine. First thing my son and I did was replace the plugs, wires, distributor, and rotor... started her up and she purred like a kitten until it kicked down into low idle ~600rpm. The engine then lost rpm until it finally died.

I'm thinking the problem might be in the throttle body somewhere... I'm also going to check the full pressure as well in order to rule out a fuel problem. I'm just trying to zero in on a possible culprit as quickly as possible since I really want to drive it this weekend. Also, the "Service Engine Soon" light has come on a couple of times while driving today BUT I got no codes out of the computer when I jumpered the terminals this evening! It just keeps blinking "12" continuously...

Car only has 66k miles on it, by the way.

Thanks!

Derek
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Re: 86 C4 starts, runs, rough idles and sometimes stalls

Postby 87vette81big » October 28th, 2014, 9:43 am

Possible faulty ignition module.
Possible faulty HEI Distributor pickup coil.
Possibly faulty HEI ignition coil.
Possible Power source problem to Ignition and fuel injection.
Possible plugged fuel filter.
Possible faulty fuel pump.
Need to test all. Verfiy problem .
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Re: 86 C4 starts, runs, rough idles and sometimes stalls

Postby grumpyvette » October 28th, 2014, 9:53 am

it sure sounds like the throttle body or IAC is dirty and needs to be cleaned, and TPS sensor set,I'd also suggest replacing the fuel filter as they can cause issues when partly clogged, the links below should prove useful.
verify your fuel pressure is steady at about 38-40 psi and the fuel rail pressure stays that high for at least 5-7 minutes after the engines shut off.
this helped verified the fuel pump and regulator function and helps eliminate potential injector related issues.
as always you verify compression on all 8 cylinders ,verify the ignition,advance curve and spark,verify fuel pressure,stays consistently at near 38-40psi and that fuel delivery if maintained.
pull trouble codes and verify the fuel rail pressure and look for defective sensors, set the timing,get a set of NOID TEST LIGHTS, and verify the injector pulse at each location, and then youll have a realistic base to trouble shoot from


buy a CHEVY SHOP MANUAL FOR YOUR YEAR CORVETTE!
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
Image
http://www.harborfreight.com/5-in-1-dig ... 98674.html
put a fuel pressure gauge on the fuel rail on the shrader valve,

Image
a vacuum and fuel pressure gauge is useful
Image

reading the links and sub links will prove rather useful, now and even more so later


viewtopic.php?f=55&t=3145&p=8395&hilit=throttle+body+clean#p8395

viewtopic.php?f=48&t=10003&p=43220&hilit=test+alternator#p43220

viewtopic.php?f=32&t=168

viewtopic.php?f=32&t=10349&p=42530&hilit=relocating+sensor#p42530


viewtopic.php?f=32&t=10385&p=42943&hilit=start+sequence#p42943

viewtopic.php?f=80&t=1470&p=3304&hilit=corvette+fuel+filter#p3304

viewtopic.php?f=32&t=6011&p=18597&hilit=light+timing+degree#p18597

viewtopic.php?f=50&t=9453&p=34615&hilit=harbor+gauge#p34615

viewtopic.php?f=36&t=3105&p=8272#p8272

viewtopic.php?f=32&t=10675&p=46102&hilit=fuel+pressure+gauge#p46102

viewtopic.php?f=32&t=2697

viewtopic.php?f=32&t=596

viewtopic.php?f=80&t=728

viewtopic.php?f=32&t=1401&p=26962&hilit=corvette+fuel+filter#p26962
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: 86 C4 starts, runs, rough idles and sometimes stalls

Postby monsolo2 » October 29th, 2014, 7:15 am

Guys, thanks for the info! It's just good to have feedback simply becasue it gives me encouragement to jump in and problem solve. I'll check the fuel pressure first and then work my way to the throttle body and clean it and then check the TPS and other things.
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Re: 86 C4 starts, runs, rough idles and sometimes stalls

Postby grumpyvette » October 29th, 2014, 8:36 am

let us know what you find and if possible post a few clear pictures of the process, and car.
youll find a hour or so reading thru the links and sub links will provide a great wealth of related info and incite into related factors, or the function or testing of sensors, that you may not currently be thinking about, or things that you might not think that are related to your issue that PROBABLY ARE
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: 86 C4 starts, runs, rough idles and sometimes stalls

Postby monsolo2 » November 1st, 2014, 10:47 am

Will do! Since you've last posted, I've been doing a LOT of reading, here and on various other sites. I'm convinced it's the IAC so I'm changing it out today... chances are, it's also 28-years old. I'm also going to change out the coil as well... :geek:

When I'm done, the fuel pressure will get checked. I'll let you know how all of this goes... :mrgreen:
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Re: 86 C4 starts, runs, rough idles and sometimes stalls

Postby monsolo2 » November 1st, 2014, 11:19 pm

Ok... after MUCH struggle and cursing of GM engineers, I managed to get the IAC replaced and set according to procedure. The biggest question out of all of this? Where can I find replacement plastic connectors??? The connectors on this car are so old that they are extremely brittle and I broke two while just trying to lift up the retainer to pull them off! In fact, one of the connectors that broke is the MAF sensor connector... I think that's why the ECM is now throwing a code 34 and 42! The other connector is the IAC...

Argggggg! :x
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Re: 86 C4 starts, runs, rough idles and sometimes stalls

Postby grumpyvette » November 2nd, 2014, 9:01 am

the search feature, is always an option here, on this site, but to save time , look at the sub links in these threads, to find sources for replacement electrical connectors, and NAPA can frequently ORDER replacement connectors for repairs at about 3- 5 times the cost youll find them at else ware, but at times getting the part the next day beats waiting a week so the price may be justified. if its a connector thats likely to break frequently buy extras, and have them handy

viewtopic.php?f=36&t=3105&p=8272&hilit=connectors+pigtails#p8272

viewtopic.php?f=32&t=168&p=41767&hilit=connectors+pigtails#p41767
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: 86 C4 starts, runs, rough idles and sometimes stalls

Postby monsolo2 » November 2nd, 2014, 9:45 am

Thanks, Grumpy... I'm ordering new connectors today. I'm also going to reconnect the two connectors and figure out a way to keep them secured temporarily. I'm also going to remove the negative battery cable and clear the ECM and then drive her around and see how she performs.

More to come... :ugeek:
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Re: 86 C4 starts, runs, rough idles and sometimes stalls

Postby philly » November 8th, 2014, 10:08 am

zip strips seem to get the job done for me when i need a fast fix while waiting for replacement parts
-phil

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