2003 Blazer: Mechanic Can't figure it out
 

I am a mail carrier. This truck 2wd will start and run up and down unpaved roads for 4.5 hours. THEN starts to shut off. I speed up and slow down all day. I have owned nothing but Blazers doing this job. But I can't figure it out. I am in Florida and it is rainy season. So when it gets damp it will not shut off. It seems like it isn't getting fuel, but it is. I think the fuel pump is having issues. My parts guy says there is a motor on an air (?) something that opens and closes when i press the gas. the mechanic is looking for a code. Codes are misfire and catalytic? I need some direction. I changed the cap and rotor recently then it became loose and was tightened. I need an answer PLEASE.

Do you have a fuel pressure gauge on it when it quits running? Catalytic converter rattling?

Could the tank vent valve not be opening, causing it to suck a vacuum in the tank? Have you tried taking off the gas cap when it starts messing up?

So it shuts down or it wont shut down?

Only in the rain?

What are the specific codes (ex P0300)?

George

Two things that come to my mind are:


Failing fuel tank vent as mentioned, which will cause vapor lock (suction in the gas tank) that the fuel pump cannot override, will will starve the engine of fuel and cause the same issue. Pop the gas cap next time if happens, if you get a "woosh" of air, try to start the truck afterwards. If it starts and runs fine again for a little while, I'd start looking in that direction.


Failing ignition control module that's mounted to the same bracket as the coil. I've seen countless of these fail as they heat up. Will work fine for sometimes 10-15 minutes, sometimes 1 or 2 hours, and then the truck will loose power and die and will not start back up again until it sits and cools down for 15-20 minutes. Replacing that is a simple 2-bolt swap, but they can be costly unless you try to get a used one from a junk yard.


The gas tank vent test is free though, I would start there. If that happens, you can get by for now by simply not putting the gas cap on all the way so it will allow air to slowly seem into the filler neck, but that's not a long term good idea because it will also allow moister and dust to be sucked into the gas tank which will cause all sorts of other issues...


If all else fails, have your fuel pressure tested as also mentioned. The S series is unfortunately notorious for fuel pump issues, any many times the pump will work fine for a while until it warms up and then just stop working...