Starting issues
Thread Starter
5th Gear
Joined: Jul 2010
Posts: 5
Likes: 0
From: Fort Valley Georgia
Starting issues
I recently posted about a lack of low end power and was greeted with many good suggestions. It turned out to be a very clogged air filter! obvious i know, but i just over looked it. Now my C4 is having trouble starting. The battery and alternator are both new and working (alternator puts out 13.9). When i go to crank it up it turns over but doesn't start. I have to pump the gas to get it to start and then rev it up to keep it running. Once its running, it idles fine. And if I crank it up while the engine is still warm it cranks right up. And sometimes there is white smoke at first. Any suggestions? It is a 1989 convertible C4 corvette.
Last edited by dcamax2; Jul 11, 2010 at 10:46 PM. Reason: Forgot to include year model.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
ALWAYS include the year C4 you want help on. All C4's were not made exactly alike!
When it won't start, that is when you start diagnosis to find out why. Engines require hot spark and spark at the right time, fuel and air and in the correct ratio and cylinder compression in order to start and run. Use a timing light while someone cranks to see if timing is correct. Bring a grounded wire next to an unplugged spark plug boot to see if you have a snappy at least 1/2" spark. Buy a noid light (available at parts stores) and test an injector on each bank during cranking to see if it pulses. Measure fuel pressure, it should be steady 35-42 psi and it should hold up for at least 30 minutes after the ign is turned off or you have leaky injector/s or a defective check valve in the fuel pressure regulator. Spray starter fluid into the MAF and see if the engine will start, if it does you have a fuel delivery problem. Last, measure cylinder compression.
When it won't start, that is when you start diagnosis to find out why. Engines require hot spark and spark at the right time, fuel and air and in the correct ratio and cylinder compression in order to start and run. Use a timing light while someone cranks to see if timing is correct. Bring a grounded wire next to an unplugged spark plug boot to see if you have a snappy at least 1/2" spark. Buy a noid light (available at parts stores) and test an injector on each bank during cranking to see if it pulses. Measure fuel pressure, it should be steady 35-42 psi and it should hold up for at least 30 minutes after the ign is turned off or you have leaky injector/s or a defective check valve in the fuel pressure regulator. Spray starter fluid into the MAF and see if the engine will start, if it does you have a fuel delivery problem. Last, measure cylinder compression.
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
A cold engine requires more fuel to start than a hot engine.
The 9th cold start injector was deleted starting in '89 so how is cold start enrichment done there?
Try the carb cleaner/starter fluid method when cold and see what happens. But I would rather remove the air duct and shoot it straight into the plenum than to the expesive and delicate MAF sensor. See what the fuel pressure is doing as suggested. A noid light will tell you if the injector harness is supplying voltage to the injector while cranking. An ohm test of each injector coil will tell you if any are out of spec or have a break (dead injector) in the windings; although if you had a dead injector you would have a consistent miss through out engine RPM.
BTW pumping the gas pedal on a TPI with motor off isn't adding fuel to the motor. It's only opening the throttle blade to allow more air during cranking.
My daily driver was doing the same thing you describe only when cold and would only barely start with pedal floored a WOT even though it was fuel injected. The problem turned out to be a vacuum hose I simply forgot to reconnect that goes to the intake duct.
The 9th cold start injector was deleted starting in '89 so how is cold start enrichment done there?
Try the carb cleaner/starter fluid method when cold and see what happens. But I would rather remove the air duct and shoot it straight into the plenum than to the expesive and delicate MAF sensor. See what the fuel pressure is doing as suggested. A noid light will tell you if the injector harness is supplying voltage to the injector while cranking. An ohm test of each injector coil will tell you if any are out of spec or have a break (dead injector) in the windings; although if you had a dead injector you would have a consistent miss through out engine RPM.
BTW pumping the gas pedal on a TPI with motor off isn't adding fuel to the motor. It's only opening the throttle blade to allow more air during cranking.
My daily driver was doing the same thing you describe only when cold and would only barely start with pedal floored a WOT even though it was fuel injected. The problem turned out to be a vacuum hose I simply forgot to reconnect that goes to the intake duct.
Last edited by 86PACER; Jul 11, 2010 at 11:13 PM.
Instructor
Joined: Aug 2009
Posts: 146
Likes: 0
From: Broadway Virginia
Check your fuel pressure when running and also after cycling the key on and then off. See if your pressure holds.
Suspect leaky injectors.
Mine had the same problem 6 -8 mo's ago.
Suspect leaky injectors.
Mine had the same problem 6 -8 mo's ago.
Last edited by walter schweigert; Jul 11, 2010 at 11:14 PM.
