I have a 91 corvette with the L98 motor, 70k on it. Just installed Bosch platinum 4 plugs, MSD cap and roter, MSD wires, K&N, and a new PCV valve. It was running great. I could turn the key without touching the gas and it would roar to life. All of a suuden, it won't start easy at all. I have to hold my foot down on the throttle when I start it to get it to stay running at all. I am not a mechanic, but a guess may be the fuel pump relay?, Fuel system? A sensor of some kind? Please help me if you can, I am lost on this one. Thanks.


[Modified by gr8n10city, 2:35 PM 2/25/2004]

 

Check all your sensor connections and injector connections.
Maybe one of them has come loose :smash:
How long after tuneup till problem ?
:cheers:


[Modified by AGENT 86, 6:41 AM 2/25/2004]

 

In my experience, dump those Bosh plats in the garbage. I had single plats in the car once, thinking I was doing it a favor...it was one of the single changes I ever made on a car that I could FEEL the LOSS of punch! Go back and re-trace ALL of your changes and make sure something simple like two wires were not inadvertently switched, the coil hookups are exactly how they should be, and that ALL of the connectors are firmly snapped on all terminals and plugs. It can't be anything major.

 

It has been about 3 days since the tuneip. Perfect until last night.

 

My first guess would be something is not hooked up right, but check to see if youre getting fuel and spark to each cylinder. It could be a relay, yes.

I would guess a MAF problem, but you dont have MAF in 91.

 

Is it when the car is cold? Hot? All the time? Do you have to put your foot ALL the way down on the gas? That puts it into a flood clear mode and shuts the injectors off until it sees a certain RPM.

 

It has spark because I can get it to start by pumping the gas. I have to keep on the throttle or it dies. It seems like it would have to be in the fuel system, somewhere. I will install a new fuel filter this evening since I have no idea when it was changed last by the previous owner. I figure that in the troubleshooting sequence that I should go with basics. I checked all the fuses which were good. If the fuel filter doesn't do it I may have to figure out a way to get it to Autozone so they can check the OBDI diagnostics. Man, this sucks because the car was running great. I did check all the connectors too. The fuel pump could be going south???????? I hate being in the dark on a computerized car. Any thoughts would be much appreciated.

 

Answer the questions I asked. :)

 

First you should answer Scorps questions.

Short of that, what I am seeing is a motor that needs air to keep it idling. That would direct me to checking the Idle air control valve/solenoid.

On your computer controlled engine your foot is connected to the air flow control, the computer then determines fuel needed. pressing your foot on the gas pedal does not force in more fuel (directly as a choke or pump in a carbeueueurator), in fact, with fuel injection, holding open the throttle would increase demand on the fuel system and create even more of a
problem for a weak/clogged system.

A clogged fuel filter on FI car will generally cause it to stall or be powerless on acceleration, as you press the pedal. Air flow increases, fuel supply does not.

 

Ok Scorp, here are your answers:

Is it when the car is cold? Hot? All the time?
A: All the time
Do you have to put your foot ALL the way down on the gas?
A: No


[Modified by gr8n10city, 11:26 PM 2/25/2004]


[Modified by gr8n10city, 11:35 PM 2/25/2004]

 

Thanks Ski, That's why I am asking you experts. What you said makes sense to me

On your computer controlled engine your foot is connected to the air flow control, the computer then determines fuel needed. pressing your foot on the gas pedal does not force in more fuel (directly as a choke or pump in a carbeueueurator), in fact, with fuel injection, holding open the throttle would increase demand on the fuel system and create even more of a
problem for a weak/clogged system.

A clogged fuel filter on FI car will generally cause it to stall or be powerless on acceleration, as you press the pedal. Air flow increases, fuel supply does not.

 

Where is the Idle air control valve/solenoid? OK My bad, I just found it.


[Modified by gr8n10city, 11:49 PM 2/25/2004]

 

There is no check engine light, but I bought a code scanner and tried it anyway and got the compulsory 12 code that you get even when all is well. I cant figure this out. I went back and checked all the plug wire connections at the engine and cap. Nothing. I am completely stymied.

 

The older systems aren't all that great at detecting anything less than a hard failure. Many times it's just the circuitry that is monitored, not the actual function of the device. That is to say that the ECM can see the reference voltage and the feedback and therefore assumes everything is OK.

You may need to pull the IAC and do some cleaning. Clean the passages mostly and wipe off the pintle, no need to get crazy trying to clean the IAC, passages are most important.

Can your scanner read the sensors parameters in the ECM? If so, what are the IAC counts and what does your Engine Coolant Temp sensor read?

When you reinstall it, check the tech tips area for resetting the IAC and minimum idle

Another thing to check is the Engine Coolant temp sensor. If unplugged or an open circuit, the ECM will dump too much fuel thinking it's -30 degrees, hence you would need to open the throttle plate to add air. This can cause hard starting and foul the plugs. Also drowning the cylinders with way too much fuel for the amount of air that can pass through what are probably somewhat restricted idle air passages.

Just trying to give you some ideas before you start throwing parts at it :cheers:

 

I did almost the exact same thing with my 85 and I experienced the same problem as you. I took the Boschs out and got a refund. and put in stock plugs. helped a bit. but it still starts harder. maybe its the MSD gear. I wouldnt think so but sure seems like it.

To answer Scorps question my problem is only when cold. after warm up it starts immediately.


[Modified by Southern Comfort, 6:42 PM 2/25/2004]

 

This is just a guess... if the fuel pressure is right and you have checked everything as the others have instructed you... then check the cat (s)... When they plug up, everything gets real weird... no power, hard start, etc...
Good Luck...
Ted

 

Check fuel pressure I vote for something keeping fuel pressure low, pump, filter, etc.

 

:lurk:

 

Follow up on problem. It was the idle air control valve. You guys that said air were on the money. Bad thing is I could not get a code for it. Fixed and running well. Thanks

 

Happy to help, glad it worked out. About the code, see my previous post. OBDI is not very good, we have had cars that stumble, spit, misfire and everything else without codes.

It's all the same in the end though fuel, air, spark, compression... :cheers: