vette will crank,start, die

[rlg]

Hello from Okla.

I have had many Vettes over the years most of the 63-79. And have done several restorations.

This is my second C4.

Here is what happened.

The previous owner cut the pre cats off, bad job.
I replaced the entire system, removed all cats. I also removed the guts to the air pump. as we were finishing up my son pushed the Air tube against the starter, when I hooked up the battery it smoked pretty bad.Moved the tube ,the car started ok. The next weekend I supported the tube out of the way.

Started the car drove it for about 15 minutes then it started to idle badly.

Now it will crank ,start but won't idle on it's own. I can keep the car running at 1000rpm or more but when I let off of the pedal it dies.

Replaced the ecm unit.

Still does it

The radio also stopped working and the oil pressure gauge jumps around when you turn on the key.

No check engine light , All fuses ok.


I have all of the manuals but don't see this problem.

I read a post here this morning that talked about the 8th injector.



Recently tuned up And ran well (little miss at idle) before I changed the exhaust.

I know how to retrieve the codes but was wondering if anybody knew the short version of what happened.


Any ideas??

Thanks

Bob

 

[vetteoz]

Now it will crank ,start but won't idle on it's own. I can keep the car running at 1000rpm or more but when I let off of the pedal it dies.anybody knew the short version of what happened.Any ideas??

I'll take a punt and say IAC valve seeing that you can keep it running off idle.
The IAC valve controls the idle air flow like the idle screws on a carb.
It has no feed back to the ECM so there are no codes.
Faulty IAC
Blocked IAC passages in TB.
Or broken / bad wiring to IAC valve.
Will need to reset valve as per FSM after removal

talked about the 8th injector.

9th (cold start ) injector not used on your model and only used in cold starts; plays no part in idle.

 

[rlg]

Thanks Vetteoz

I bought one yesterday but couldn't get a wrench on the old one to remove it.

Do I need to remove the throttle body?

I didn't see anything about that in the FSM.

I might have missed it.

I am going to replace the oil sending unit as it is erratic and it seems that it plays a part in fuel delivery..

Fuel pressure is at 42 lbs

I have one bad injector.(3rd one from the front ,drivers side.)

I also checked the ccm and no codes there either.

Thanks

 

[G Winter]

Are you sure you only have one bad injector. On my 90 once I had injector failure , the rest just follow close behind the first.
If it seems to be loading up with fuel at idle pull the vacuum line off the fuel pressure reg to check for gas in it. If gas in that line you have a bad diaphragm.

Glenn

 

[rlg]

Glenn

I check the resistance and all came in at 16.4 except the one in ? and it was 3.5.

My biggest problem is I can't get it to idle on it's own. it catches and imediatly dies unless I use the accelerator to keep it at 1000 rpm or higher.

I have several parts I am trying today(Oil sending unit,IAC,and Ignition mod.)

I took back the ECM I got and picked up another one.

I will check the regulator.

Thanks

Bob

 

[vetteoz]

I bought one yesterday but couldn't get a wrench on the old one to remove it.
Do I need to remove the throttle body?

I would suggest removing TB and giving it a good clean anyway especially the IAC passages

I am going to replace the oil sending unit as it is erratic and it seems that it plays a part in fuel delivery..

Two seperate components;
one the sender unit for the pressure gauge and the other the pressure SWITCH that runs the fuel pump.

My '90 had 2 seperate units , a 1 wire for the gauge sender and a 2 wire for the pump;
some '90 owners have reported having the '89 style unit that combines the two in the single (3 wire ) housing shown.

 

[rlg]

Vetteoz,

What is strange is my vette has the 3 prong housing but with just one prong and wire.

I had to go to GM to get it.

The parts guy said that there might be another switch with 3 prongs down by the oil filter for the fuel shut off.

Thanks for the picture , if you have one of the fuel cut off it would help.

Thanks


Bob

 

[vetteoz]

my vette has the 3 prong housing but with just one prong and wire.

Same style as my '90.There should also be a 2 wire pressure switch for the pump.

The 3 pin above the oil filter is listed as
AC Delco # 10096136 CHARGE MON & TEMP GA, 3 BLADE TERMINAL,

http://198.208.187.182/internet/Veh...Engine+VIN+=+8++++++&productline=20&part=5704
On earlier L98's this was oil temp sensor only.

 

[rlg]

Thanks for all the info.

The problem turned out to be the IAC. Replaced it , installed new oil gauge switch. She fired up immediatly, idled well and the oil gauge didn't remind me The late great James Brown. This is a great site.

Thanks to all

Bob

 

[vetteoz]

The problem turned out to be the IAC.

Sometimes I even impress myself
Did you reset idle?
I don't believe the TPS is adjustable in your model but the IAC is the same as in the article
Corvette Action Center Knowledgebase :: 1985 - 1991: Technical Article: How to Adjust your Early C4 TPS and Idle Speed

 

[rlg]

Vetteoz
It worked great,

If you ever need a windshield for your car, let me know. The company I work for has locations there.

one of our techs just returned from 3 months there to help with your busy season.

Thanks again

Bob