2001 Chevy Blazer Engine cuts out on very hot days

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?