2003 GTP, random no-start condition
 

2003 Pontiac GTP, 187,000 miles. Completely stock
I need some help diagnosing a no-start condition that I have been experiencing for months now. The engine cranks but won't start.
About 300 miles ago, the no-start issue was more severe, the engine would not start even when sitting for a day. I replaced the MAF sensor and the engine started right up, but then a few hours later, when I attempted to start the engine, it just cranked.
Then the aftermarket fuel pump that the previous owner had installed was suspect to me. I replace with a new pump and tried starting the engine and it wouldn't start. But after trying a few times, it finally did start.
Then I cleaned the air filter. Sometimes the engine would start sometimes not.
Recently, it seems the engine starts every time when cold. But after I have driven 15-20 miles, it will not start. But if I let it sit for 20 minutes and keep trying to start, it will eventually start.
When the engine does start, it runs well. The idle is strong, no stalling, no check engine light is on. Car has power.
Also, I noticed after driving 15 miles or more that the factory boost gauge on the DIC will start showing boost even when the engine is idling. Also, the engine idle becomes rough when this happens and acts like it wants to stall. If I turn it off and try to restart, it will not. But after 20 minutes and 10 attempts to start up, it eventually will.
I replaced the MAP sensor with a new sensor, and I still get the boost showing on the gauge, but again, only after driving 15 miles or more.

What should I try next?

Crank position sensor. They are known to go bad on the 3800s.

One way to tell is as you are cranking(and wont start), Is it showing any RPMs or none? If none, then its the crank sensor. It should be showing a few hundred RPMs as the motor turns over.

I assume this is SC'd? Wonder if this year has the ceramic resistor in the fuel pump circuit?

Basically, when it won't start, check for spark, fuel pressure, and injector pulse....

I tried starting up the car yesterday (after it sat outside in 25° temps all day) and the engine started right away. I went for a short trip, but total mileage was only 11 miles. I did not shut off the engine until I got back home for fear that it will not start up again.

During the drive, I kept my eyes on the boost gauge and I did not see any boost register (except a few times when I had to press further on the accelerator)
Well, when I arrived back at the house, I shut off the engine, and then tried to restart right way. The engine restarted right away.

I will try driving a longer distance tomorrow and if the engine will not restart, I will take notice of the tach as I turn the key.

This 2003 model I am having problems with has the L67 engine.

I checked various resources for replacement AC Delco fuel pumps for the L67 engine, and the model numbers were the same from 2001 through 2003.
The fuel pump that I installed was from a 2001 model GTP. That pump worked fine in that supercharged GP.

I will check the ICM, coil pack, plugs and wires again. It is evident that these are working fine because when the engine is running, it preforms well. Also, the engine starts when it has cooled off completely.

I will have to get a shop with a fuel pressure gauge to test the fuel pressure, but with the fuel pump I installed, I don't believe that the fuel pressure is low.

I have checked the injectors to see if there is any visible abnormalities , and they look fine to me. With that mileage, they can be suspect. Not sure about the "injector pulse" though.

Most recently, the engine will not start after driving it 20 miles or more in 1 trip. And during the drive, I notice that boost is showing on the boost gauge even at idle.

Have a can of carb cleaner handy......when it won't start, spray some carb cleaner into the intake.....if it almost starts, or starts and runs only until the carb cleaner is used up, then you know you have a fuel delivery problem.....

I can't remember when they stopped using the ceramic resistor in the fuel circuit of SC'd engines,,,,basically this created a two speed fuel pump.....if the ceramic cracked,under certain temp conditions, you would have an open circuit.....there was a recall to install a new resistor and move it from the fender well to the firewall in the engine compartment.....

https://www.gmforum.com/attachments/...resistorgp.jpg

This resistor problem is pretty common and easy to eliminate. You can bend it just to check or you can leave it this way. It wont hurt anything if left that way.

This GTP is a 2003 model. Would it have the fuel pump resistor bypass?

Someone with access to GM wiring diagrams would have to track this down for you.......

Forgetting the possible resistor issue, havbe you done the basics when it won't start?

Check for spark, fuel pressure, and injector pulse?

Need a spark tester....

F/P gage....

noid light.......