My 1989 IROC with 305 TPI has a starting issue. When it is cold, it fires right up pretty much with the bump of the key. When it is hot, it just cranks and cranks and usually only fires on the second try after what seems like forever. Two days ago I replaced all eight fuel injectors and also the coolant temperature sensor. No Change with the problem. I'm stumped. What else can I check that would cause this hard starting issue?

 

Check the ignition module under the distributor cap. I had an identical problem two years ago. When it get's hot, it ***** the bed if it's on it's way out. Usually there is driveability problems as well when it gets that bad.

 

One thing I left out. When hot, if I press the accelerator all the way to the floor when trying to start it seems to help it start but not any quicker. It acts like it is flooded and smokes after it fires. It then runs fine afterwards.

 

I think when you hold the pedal to the floor during a start, it tells the computer not to inject any fuel. Sounds like you may have a flooded engine when warm. There should be more air than fuel on a warm engine. You may have a rich condition. Which is what you want on a cold start. But if those parameters remain unchanged for a warm start, there's going to be a problem. Sounds like maybe leaking injectors, but you said you changed those. What coolant temp sensor did you replace? I think there's two, one drives the gauge and one signals the ECM...I think. It's been a long time since I've delved into this system.

 

Coolant temp switch on front of the intake or Intake Air Temp might be bad.
I thought the same as Edge about the injectors leaking down giving yo a hot soak condition, but you changed those.

 

The coolant temperature sensor that I replaced is on the front of the intake. Not the sending unit in the left cylinder head. I replaced all eight injectors with brand-new Accel 21lb ones. There are not any leaks. When I say that I hold the accelerator pedal to the floor during starting, it just helps it to start. If I do not do this then sometimes it will not start at all. It acts just like a flooded condition on a carbureted engine. With the accelerator held down, more air is let in then it finally fires, a bunch of smoke comes out of the exhaust, probably from the excessive fuel burning off, it sounds rough then smooths out after a few seconds and everything is fine. I am wondering if the injectors are spraying the correct amount of fuel but for some reason, the plugs aren't firing? I know the ECM will prevent the injectors from operating under certain situations but is there a situation where the plugs will not fire? By the way, my plugs do look good.

 

Did you replace the fpr also? have you ohmed the injectors hot or cold?

 

BINGO. Tealman92 hit the nail on the head. My fuel pressure regulator was bad. The rubber diaphragm had a split which allowed fuel to leak into the intake manifold after shutting the engine off. The problem was identified by connecting a pressure gauge then watching it lose pressure and not maintain the normal 40 psi or so. Thanks to everyone. Another gremlin solved until the next one creeps up!

 

Glad you got it sorted out.