1999 Tahoe will crank but not start when it is 85 degrees or hotter outside.

[Mike593]

I had replaced the mass airflow sensor and the crankshaft positioning sensor on the Tahoe. Everything ran fine for about 15 minutes. I shut off vehicle and went back to move it out of the way and it would not start. Security light was on. I did the troubleshooting and found that the Passlock security module had shorted out. I replaced it and it started right up. Moved the vehicle outside for the day. Went out to move it back in later that afternoon and it would crank but not start. Security light is not on. I pulled the security module again to make sure it had not shorted out again. It was fine. The next morning I tried it and it started fine. It has been doing this all week. It will start when it is cool and not start when it gets above 85 degrees outside. It is not throwing any codes. Any help would be appreciated. Thanks.

 

[exp500]

Test the ICM. Spark test Dist and coil when no start. Report findibgs here.

 

[suterusu]

Test the ICM. Spark test Dist and coil when no start. Report findibgs here.

Forgot first step: post in correct forum for 1999 model year vehicle.

 

[Mike593]

Forgot first step: post in correct forum for 1999 model year vehicle.

Thanks, I posted it in the correct forum now. I have already changed the plugs, wires, distributor cap and rotor as well. Sorry I posted it in wrong year forum. Didn't even notice until you told me.

 

[Eman85]

When it doesn't start did you check for spark? Do you have a fuel pressure gauge? Did you hear the pump cycle? Not "throwing" codes, does this mean you have a scan tool or code reader? Do you have a scan tool?

 

[David Kriss]

I know that this is a long shot but it takes minutes and cost nothing to check. Check the ignition and fuel pump fuses. Use a meter when the engine won't start. I had a problem years ago with my AC. It would work until it was about 80 degrees. Above that the AC wouldn't work. The fuse that protected the compressor had a break. I couldn't see it when I looked at the fuse. I had to use a meter to find it. The two halves would make contact when below 80 degrees. Above 80 degrees, the pieces would separate and not make contact. Good luck.

 

[Newport Beach Vince]

I know that this is a long shot but it takes minutes and cost nothing to check. Check the ignition and fuel pump fuses. Use a meter when the engine won't start. I had a problem years ago with my AC. It would work until it was about 80 degrees. Above that the AC wouldn't work. The fuse that protected the compressor had a break. I couldn't see it when I looked at the fuse. I had to use a meter to find it. The two halves would make contact when below 80 degrees. Above 80 degrees, the pieces would separate and not make contact. Good luck.

I had this same issue in another vehicle as well. Thought it was the fuel pump and replaced it. Still had the problem. Long story short, heat was causing expansion in the fuse which had probably failed at some point but had not completely separated. I used a meter and just by wiggling the terminals on the fuse was able to find the culprit.