Hi there I have 1991 s10 blazer. I have been having some problems once it reaches about 90 degrees outside she only runs for about 20 minutes and then the engine revs up and down and then she stalls out. Ive replaced the spark plugs, ignition module, fuel pump and fuel filter and oil filter. I am kind of stumped right now. someone told me it sounds like vapor lock but i was only aware of that happening on the older models with carbs. not really sure what to do. any suggestions? thanks

 

also i did change the thermostat twice now

 

this is probably a dumb question since you would have mentioned it but is the engine popping any codes? does the temp gauge read out of the ordinary when this happens?

 

I'v checked for codes but have got a whole lotta nothin and the temp gage stays static at about 210 which is normal. had some problems in the past with the heads and head gaskets but those were resolved the only "weird" thing that happens like i said it starts reving and the oil pressure gauge goes nuts it just starts bouncing all over the place

 

Can you give a few details about your truck, like fuel system. Will it start again after it stalls? Those temp gauges can get out of tolerance, mine was reading high and popping a SES light, but the problem was in the wiring not the engine temp. Sounds like it's either temp related or time. If it's time related it might have something to do with which loop mode your truck is in. When you first start your truck it runs in open loop mode. After it's warmed up it runs on closed loop mode and things like the O2 sensor report to the computer to control fuel mixture. If it's temp related and you are overheating because of a bad temp reading seems you would notice the engine boiling over. When it happens can you see water returning to the coolant reservoir?

 

I believe from what ive read anyway its TBI but i dont know for sure im new to this site. it starts again after it stalls but if i dont let it sit for about 15 minutes itll just stall again in less than a minute so pretty much after it stalls i just have to sit and wait. like i said the temp gauge seems to be reading normal and ive replaced the thermostat a couple times just to be sure. when it does stall and i open the hood there isnt any liquids boiling over or anything like that or that i notice anyway but it does seem to act funny like this only when its hot outside which is what led me to changing the thermostat and the other guy i was talking to to believe it was vapor lock. i also read something about maybe the fuel pressure regulator could be bad but again i dont know. how big of a deal is it to replace the O2 sensor?

 

it's most certainly TBI, the CPI engine didn't see light until the 92 model year. if you're curious with GM vehicles from the 90s including yours, look at the VIN number. the 8th position is the engine. the 4.3 liter TBI is a Z.

so how does the car stall on you? does it just drop off immediately? does it stumble for a bit? when you're trying to start it back up, does it crank ok? does it smell flooded?

the thermostat plays an important role in coolant system regulation but doesn't report temperatures which i think is what cidium is getting at. it has two sensors for that. one is right on the engine block on the top near the thermostat housing, that reports to the computer. the other is on the passenger side on bottom, that reports to the gauge, and is called a temp "switch".
this was just FYI, i'm not sure your problem is related to this but want to contribute what i know since i've had to read into similar issues myself lately. this doesn't sound like open loop or limp home mode to me, though. i also doubt it's vapor lock as yours is a TBI engine: it's highly unlikely but possible i guess.

 

well i will be driving and itll start to act like its not getting enough gas. if i take my foot off it dies right away but if i butterfly the peddle it buys me a couple minutes to pull over out of everyones way and just turn her off. also when i am playing with the throttle right before it dies itll kinda like die and then come back on. when i try to start it back up itll crank ok and if i havent let it sit itll start run for maybe 15-20 seconds and then die again. it doesnt smell flooded

 

That sounds very similar to the problem I had last summer with my '92 GMC 3/4 ton van. I was driving up to Canada and if I gave it too much gas it would try to stall on me. The problem was a bad coolant temperature sensor (the one in the intake manifold by the thermostat). Next time you have that problem in the heat I would try and read the resistance of the CTS and see if it matches the correct value at the given temperature.

 

turns out it was nothing more than the fuel pump ****ting out along with the distributor cap damn thing had melted on the bottom