Mechanics

CHEVY ENGINE CUTS OUT ON VERY HOT DAYS

2001 Chevrolet Blazer

Engine Performance problem
2001 Chevy Blazer 6 cyl Four Wheel Drive Automatic 201000 miles

This problem started up about 2 years ago, it is hard to troubleshoot because it only happens when the outside temperature is in the upper 90's and the car has been driving for a while.

After vehicle has been running for about 20 minutes in very hot weather, the engine will start to cutout for a split second, catch again, then cutout again.

The engine does not die completely, but simply quits for a second. As soon as it happens I take my foot off the gas and start coasting (its usually on the highway), and after coasting for about 20 seconds, it seems to behave for a few moments, then starts misbehaving again. The longer I keep doing this routine on the highway, the more it cuts out (and the longer it stays cutout) until I finally have to pull over.

The engine does not die completely unless I keep pushing it and try to force it to keep going, then it will finally die.

I can pull off at an exit and it's fine at lower speeds - no rough idling, no problems at all. On the occasion that it does die completely, I can restart it no problem - sometimes while still coasting on the highway, I can restart (in neutral of course).

When it first happened, I suspected that the fuel pump was seizing up momentarily due to the high outside temperature and heat radiating off the highway heating up the gas in the tank. I thought that this might mean the fuel pump was not being cooled well enough. So yesterday the temp hit 98 degrees, it started up it's misbehaving so I got off an exit and filled the tank up with gas - thinking that if my theory was correct, the cooler gas from the pump would cool the fuel pump down and I would be able to drive for a while longer. But, no, after a mile, it started acting up again, so that theory might be totally wrong.


So now I am wondering if it is under-hood temperature that may be causing this. I've tried turning the AC off so the engine will run cooler, and I THINK it helps, although I have not been able to do this enough to prove it.


Here is a list what I have observed:

Outside air temp has to be in the upper 90's for the problem to start exhibiting itself.

I've been driving for at least 30 minutes at the start of the day so the engine is plenty hot by then.

It is a definite cutout - I'll watch the tachometer and it will do an immediate dip down near idle rpms, like someone turned a switch and shut everything down. The car will stumble and then catch right away at first, but taking longer to catch as I let this go on.

No problems idling or going slow in-town driving.




A question comes to mind since I'm not as familiar with fuel injection as carburetors with a bowl - if the pump decided to just stop pumping for a split second, could that cause an immediate cutout of the engine, or would it just start to get sluggish before finally quitting? Trying to figure out if it is fuel related or something else.
.

Interestingly, this morning it took a long time to start - and that never happens. It has always started up immediately. Not sure if this is related or not.


Any opinion as to where to start looking?
Avatar
Bscott1234
August 5, 2010.



Hi, I am thinking a couple of things here, oh first, yes if the pump cuts for a second it will seem to shut off/dip in rpm. Ok. 1: the fuel pump relay, could be getting hot and then cause an intermittent open circuit. So I would start with that, once it quickly cools, the circuit is complete again, as time goes on, the relay will get weaker and more fragile and may not be able to go back to a closed circuit, until a couple of tries, hence the problem you had in the morning. Two, crank position sensor, classic symptoms of a bad crank sensor. Also if you can mimic the same situation where the car will not start on the first try, dont try to continue to start it, you can then check for fuel and spark to see which one is missing. Another thing is that fuel pump could be acting up like you may have suspected. I know this is a lot of stuff to be dealing with, but unfortunately these are all suspect. Look into these few possibilities and let me know what happens.
Joe.
Keep me posted

Joe, thanks for the reply - I'll try replacing the fuel pump relay first since it's easy and cheap!

Couple more questions to better understand: Does the fuel pump work harder when the car is at highway speeds, or does it pump constantly? Trying to figure out why it does not seem to act up at slow or idle speed.

If the pump just keeps pumping the same all the time, is there something at the engine intake that might sense pressure, and if the pressure drops below a certain value, will immediately shutoff until pressure is back up? Wondering if that could cause the sudden quick loss of power.

You mentioned the crank sensor - is this something a repair shop can see when they check codes from the car computer?

Thanks,

Bob.

Tiny
Bscott1234
Aug 7, 2010.
Its a little complicated. The pump works pretty much the same. The fuel pressure regulator, takes care of keeping the fuel at the correct pressure. If the pump or the relay or the regulator is bad then you will have these problems

The pump will allways be on but it will. Only pump when need be

Bscott1234 - Would love to know how it turned out. My Blazer just started doing the same thing. And today it ranged from 93 to 100 degrees outside. The engine cut-out on me three times today. Pulled off to the side. Started right up and on my way I went. This is so weird - and I have no idea what the deal is. Any help is definitely appreciated. Thanks!

Tiny
Rapturecause
Jul 5, 2012.
Rapturecause: Check the fuel pressure when the problem occurs. Don't allow the engine to cool off at all. You should be able to borrow a fuel pressure tester from Autozone/Pepe Boys/Advanced, etc. Let us know what the pressure is when it's hot. Also, just to be sure, check it when it's cold.

Rivermikerat
Jul 25, 2012.