84 Grand National hot start problems

[indianagn]

I am hoping someone can help me out. I have a stock 84 Grand National that I a purchased new. The car has 96,000 miles on it and has only been driven in the summer since 1988. My problem is that when the the outside temperature is 85 or higher, the car will not start when the engine is warm. After a cold start the car runs fine until you start to slow done/idle, then it runs rough like it is flooding. If you shut the engine off and let sit for 5 min or more, it will be 30 minutes before it can be restarted. During that time, if you crank the engine, it will only fire (generally only one or two cylinders just after you start to crank the engine) with the throttle in the full idle position. Trying full or part throttle will not get any firing.

I have replaced all of the vacuum lines, replaced the injectors and the throttle position sensor.

This happened to me a couple of nights ago. It was 90 out and I drove to town to get gas. The tank was reading 6 gallons. I noticed that when I removed the gas cap, there was a lot of pressure in the tank. Could this be related to the problem? Any suggestions would be greatly appreciated.

 

[3point8]

no hot start

I would suspect the ignition module. Its my understanding that the electronics within can be heat sensitive. If you take the coil pack off you might see the integrity of the potting material is compromised and let in moisture over the years causing internal corrosion. Its a relatively easy check.
HTH
Peter

 

[indianagn]

Thanks for the suggestion. I have not had a chance to check into it yet. I have been moving my daughter to college. I will check it out soon.

 

[GN84Turbo]

Sounds like leaky injectors even though u mentioned replacing them. get a fuel pressure guage hooked up to your fuel line (Postons has a cheap setup) and after shutting the car off, if the FP drops immediately, your injectors are most likely bad and are draining into the cylinders. If FP holds steady then check for other probs like spark.

I'd also do a compression check just to be safe. leaky water jackets can cause similar symptoms.

 

[indianagn]

I finally had some time to check out the car last night. I pulled the ignition module, and visually, there was no cracks in the potting material or moisture present. I then installed a fuel pressure gauge and ran the car. While at idle the gauge was showing 32 psig. When you hit the throttle the pressure increased to 39. After shutting the engine off. The pressure held and did not leak off. I only watched it for 2 to 3 minutes, but the pressure did not drop in that time.
The compression check did not show up anything either. I did not put it in the first post, but the car has less than 3,000 miles on an overhaul. New rings, mains, etc. The car had this problem before the overhaul too. I took it to my GM dealer to check it out, and it came back with a blown head gasket. He did not get to do the overhaul.

 

[FJM568]

I had a similar problem with mine...Mine would run fine until it warmed up, then the car would stall and wouldn't restart for at least 15 minutes...Then it would start up and run fine for a while and stall again...and so on...

The solution...

A bad crankshaft sensor...

edit...
BTW, if it's not the crank sensor, my second bet would be on the ignition module...But the crank sensor is the cheaper of the two...BTW, if you buy one, you will find the sensor is cheaper if you buy it with the mounting as opposed to without the bracket...

 

[GN84Turbo]

Yeah, I'd check the crank sensor then. Make sure there hasnt been any rubbing on the insides, or any obvious damage to it.

Be VERY careful installing it, make sure the harmonic balancer and the sensor are perfectly lined up before you try to start the car or you'll smash the sensor,
Every one has to be adjusted, they are not pre-adjusted and each one looks a little bit different when adjusted. I made the mistake of lining up my new sensor to look like the old one, slapped it on and cranked the motor, crank sensor shattered everyhere. good luck

Ohh i forgot to mention, a loose harmonic balancer or an imbalanced one will cause warm start problems, as i experienced this as well.

 

[Waco84GN]

no hot start

Hi Indianagn: Just a quick question. You mentioned
that you replaced your injectors. Did you replace
them with stock injectors, or upgrade to larger injectors? If a larger injector; did you change the chip also? Just a thought.

 

[indianagn]

I ordered the crank shaft sensor today and it should be in Thurs or Friday. I will try to get time to install it this weekend. Any tips on how to install and set it properly?
The injectors were replaced with stock injectors.