Hi everyone!


I have a problem with my 1991 Firebird V6 3.1, maybe someone know whats wrong with it. A couple of months ago the car didnt want to start after I had driven it, if I started it up right away it would start without problem but if i left it for 20-30 mins it would just crank, sometimes I could get it to start by cranking for like 5-10 sec and pushing the gas pedel and keep giving gas ones the engin started so it wouldnt stall.


I suspected that the car was getting too much gasoline and maybe the injectors were leaking into the engine so I tried adding some injector cleaner to the gas, and at the end of that tank the problem disappeared.
Only to return a month later, slightly worse, now I cant turn off the engine for a minute without getting the no start condition.


Hoping that it had something to do with the injectors i bought new ones and installed, it didnt help. I have also replaced the coolant temp sensor and checked for vacuum leaks, didnt find any.




The car always starts without problem when i haven´t used it, and it runs very good.


Any ideas?


/Tobias

 

Get a fuel pressure gauge and measure fuel pressure when running and then turn off. Let sit for a couple minutes so it will exhibit the problem. While trying to start the car what does your fuel pressure read now? Have you tried pouring a little gas down the throttle body to see if it will start? Check your fuel pressure regulator for a bad diaphragm. Unplug the vacuum hose to the regulator and see if there are any signs of gas. Check these things and let us know what you find. HTH!

 

Thanks for you reply! Hopfully I will get ahold of a pressure gauge this week, i will test the pressure and check regulator and come back.


/Tobias

 

Might be Heat soak on your starter, or the starter solenoid is getting worn out.

 

i would also check the ignition control module

 

It does sound like it could be fuel leaking into the intake from either the regulator or injectors. Does the car start normally if you leave it for several hours? I'm with bigal55 that you should start by looking for fuel leaking from the pressure regulator. Then using the pressure gauge to watch, not only for what the pressure does the next time you try to start the car, but also for how quickly it drops off after you shut the engine down.

It's difficult to do without the right tools, but if I see pressure drop to zero after shut down, the next step is to determine where the pressure is going. It could be leaking from the regulator or injector(s), or it could be leaking back through the check valve in the pump, or another part in the tank, like the damper or a hose. To pinpoint the pressure loss, I will isolate parts of the system one at a time. Using a valve or pinch off pliers, I will shut off the line from the pump right as the engine is shut down to see if the pressure then holds. If it does, I know the leak is in the tank. If it still drops, the leak is at the engine, either regulator or injector(s).

The symptom improved temporarily from an injector cleaning chemical. That's a sign that injectors may be the culprit. Unfortunately, while I myself do use a Motorvac injector cleaner for maintenance and to help with minor fuel related problems on customers' vehicles, there is really no way to properly service injectors or verify injector health without removing them from the engine. Once out, they can be taken to an injector service shop and cleaned and tested on an injector bench. That way you know which ones are good and which ones aren't. The injector shop can replace the ones that are bad and you get back a flow matched set.

If this were a heat soaked starter, the engine would not crank at all, or crank very slow when heat soaked. That doesn't sound like your symptom.

If the engine starts okay once it cools down, that could mean one of two things. Over time, fuel leaking into the intake will evaporate and have less effect on engine start. So, this would fit with the leaking injector scenario. Or, if this were an ICM heat failure, cooling down will allow the ICM to operate again. Be sure that when the engine doesn't start, you have good spark. I like to use KV tester and the GM HEI should produce 40KV. Another test is to use a screwdriver inserted into the plug boot and hold it 1/2 inch from a good engine ground while a helper cranks the engine. The spark should jump that 1/2 gap easily with a loud blue snapping arc.

 

Thanks for all the suggestions!


I did try the pressure gauge today, I was in a bit of a hurry but i really wanted
to test it out.
First i primed the fuel pump, got 44 psi, left it for like 2minutes and it didnt dropp.
Then I started the car and it was steady at 40 psi, reved the engine a bit, and
the pressure raised and dropped back to 40 psi. Then I pulled the vacuum hose
from the fuel pressure regulator and got 48 psi. Put the hose back and turned of
the engine and then had it had 44 psi, left it for 5 min and it was still at 44 psi.
Then I tried to start the car again, it did not start, just cranking.


Im no expert, but to me this looks lika a working fuel system....??


Is it possible that an overheating ICM can cause this, wouldn't the car stall
while running.


As I said, I'm no expert, I appreciate all the suggestions.


Guess I should check for spark next.


Thanks guys!


/Tobias

 

Next is to check for spark once it wont start.

 

yes it can. the are connectors are easily corroded as well. mine was and would cause intermittent no start/spark conditions. im almost willing to bet thats what it is. make sure to use copious amount of dielectric great when installing the new one.

when the icm is out there will be no spark. keep in mind you can also ohm the icm out, there are posts out there with what they should ohm out to. but even if it ohms out correctly it does not mean its still not bad.

 

OK, fuel problem eliminated. Now as ASE doc said, you need to check for spark during your no start condition. It does sound as if heat is affecting some component of the ignition system and the ICM is the "usual" culprit. Either have it tested or try a replacement and check the ignition coil and pick-up coil for shorts to ground when the no start condition exists just as a precaution. GL!

 

Be sure to KV test the ignition, when testing for spark, while the engine is in the no start condition. I say to KV test because, as you say, the engine isn't stalling, it simply won't restart after it's shut down. KV requirement at idle is very low, plus with the engine running you are providing the ignition system with 14 volts from the alternator. When cranking, voltage to the ignition is down below 10 volts. This will reduce spark KV capacity and can prevent spark output all together in a marginal system. A KV test, using either a KV tester set at 40KV, or using a screwdriver held 1/2" away from a good engine ground, like the intake plenum on the 3.1, will test the ignition's actual ability to support KV. Because an ignition can fire across a spark plug gap with the plug laid on an engine ground, doesn't mean it can produce sufficient KV to start an engine.

Once you have verified weak or no spark, while the engine is still hot, pull the dist cap, disconnect the pick up coil from the inside of the ICM and ohm test it. It should read between 500 and 1500 ohms. Also make sure there is no continuity to ground from the coil. Just as the ICM can suffer heat related failure, so can the pick up coil. Also check terminal contact for any sign of poor connection. Poor contact is not as likely to be part of a heat related failure but just be sure that everything is clean and tight.