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Why does my Blazer stall in hot weather only?

(1998 Chevrolet Blazer)
in Show Low, AZ on July 02, 2010
I have a 98 Blazer that has plagued me for months on end. I installed a new fuel pump, dist cap, rotor, wires, plugs, crank sensor, coil, ignition module, swapped the MAP, cleaned the MAF, new filters, checked just about everything and on hot sunny days especially when stuck in traffic, it stalls and won't restart until it cools.

I can drive it all night,and on cool days and it will run like a top!!!

I have not replaced the 02's yet, nor the crank sensor. I did break off the coolant temp sensor and JB welded it back on and the gauge reads fine. When it stalls it acts like it's too lean and starves out.

I have gotten a few P0171's and another lean condition on the 02's, but I'm ready to rip off the hood so it will let the heat out of the hood compartment!!! PLS Help!
Displaying 3 answers & 7 comments
Popular Answer
on July 10, 2010
Same model year Blazer, mines a 4 DR 2WD.

I am experiencing the same issues. I replaced bank one O2 sensors one and two, Ignition wiring, plugs, fuel filter, and flushed the hell out of my cooling system. You may want to take a look at the front two O2's. I had a check engine light the first time I stalled, it read low voltage on them (lean mix of course) but they were really fouled because of the bad mixture that they was hitting them. (one was bulging a bit)

It almost seems to me that the heat kills the relays but if that were the case the horn and everything else relay dependent would fail as well. Like you said, I just want to rip the effin hood off of it.

I am going to take the tank down tomorrow and look at the wiring harness. My theory to this is if the connectors are corroded at all they will put extra resistance on the relay and it will stick. This probably occurs more in the HOT weather because electrical components (relays / wires) are more susceptible to failure. I have heard from many people that the wiring harness on these models are notorious for problems.

Another theory that I may look into if the harness is in decent shape is to have the VCM read on a full diagnostic and reset. I often wonder after getting those lean codes and such if things are actually reset properly with other engine management. Disconnecting the negative battery terminal may clear the light, but what is the VCM REALLY doing?

I will post again tomorrow with my find.
on July 10, 2010
Well thanks for your input. Mine ended up throwing a rod due to revving it trying to clear it out and keep it running. 'Engine seemed healthy and only 120k on it. 'Didn't burn any oil, good oil pressure and all. So it's endoed. I've decided I'll never buy another computer controlled vehicle again. I'm now looking for an older model 4x4.

I can't tell you how much I regret letting my old 1983 S15 go. I drove it hard everyday for 8 years and I liked it better all the way around. It was carbureted and didn't have any computer controls at all. I rewired and modified every weak link on the thing and it took me places PPL said I couldn't go and then some. I had better mileage as well.

I took my 98 to the performance garage where they do all diagnostics and they were stumped too. They said I did everything they could think of to do. I don't think I want to spend the money replacing the engine as the sensors, the ECU, and other stuff prevent it from running right - if at all. I may as well buy a new one for the expense of replacing all that stuff. So I opt to rebuild an older one.

I wish you luck!!!
on August 06, 2010
Ok, so here's what I've determined.

I have done a thorough scan, no codes. I followed the wiring all the way to the VCM and found no shorts.

I ran the hell out of the Blazer on a hot day, took a fuel gauge with me. When the car shut off it read 30 psi, 30 below spec. THIS told me that the pump was failing..

I replaced the pump, come to find out that it was a Carter that didn't look to be more than 3 years old at best. While I was working on it I took a GOOD look at what GM had used to deliver the fuel to the rail... SHIT tubing!

Look at the tubes that run from the pump to the line itself... that hard nylon line, it isn't that pliable. GM, however, made damn near a 90 degree half loop with those things to make them work to connect the pump to the line.

THEORY: NOW, if a clogged fuel filter will overwork a fuel pump to the point of overheating and failing then eventually dying who is to say that those hoses can't be a culprit too? Those things brand new are like really dense drinking straws; pliable to a degree but after a certain amount of bend they "crimp" shut almost... fluid can still get through but not at consistent flow.

POINT: Those hoses are bent to fit the line and the pump together, I believe that when they get warm from constant flow (especially in the summer when the gas tank is warm and the recirculating gas is warm) that they begin to bend from the heat and eventually crimp tight (almost like a lock.) At first, you'll notice a little hesitation when it's hot.. eventually they will take a toll on a new pump and it will begin to fail... it's getting overworked.


I replaced the pump, filter, and the harness. I drove yesterday in the 95 degree heat for 250 miles. After about 90 (where I was failing) I did notice a bit of hesitation in acceleration.. not a starvation for fuel but a notable delay. I didn't have my gauge with me but I'd almost wager that the pressure dropped at least 5 - 7 psi.

I am going to replace the send and return hoses (from pump to line) with something more pliable temporarily. I will post back with my conclusion... I firmly believe that these things are killing pumps.. they are not made to flex as much as they have been forced to do.



I tested fuel pressure after the install, before the new hoses. The pressure dropped 5 psi while it was hot outside.

I now have a steady, nominal fuel flow, at ALL temperatures, at all times.
on October 27, 2010
Well im not sure if your fuel pump was the problem. It might of been bad. Who knows. But what i do know weather doesn't effect P.S.I. the pump puts out. Also you're not supposed to check the P.S.I when you shut off your vehicle because some cars will drop the line pressure to 0 after shutting down. run the engine and check pressure. Now what it sounds like to me is that You have an idle problem. Clean the throttle body, clean the idle port inside the throttle body. Run the engine until normal operating tempreture 195-210 degree then check the idle with a scan tool. should be between 700-900 rpm. I would take it to 800 rpm. Note: check your IAC valve. Make sure its not rusted over or siezed.
on October 27, 2010
Hot weather CAN affect the output of a fuel pumps pressure if the pump is vulnerable to overheating due to lack of lubricity. After running a pump on low gas several times it begins to wear at the pumps electrical components.

It was IN FACT the pump. I ran tests through ALL scenarios to check the validity of the problem. Before driving in 90 degree heat the pressure was where it belonged, after a short drive it was lower, then finally it was 30 psi. As the pump cooled down the pressure went up. I checked the pressure at ignition on only to see if the pump was BUILDING PRESSURE in the fuel system at all. This IS procedure. One has to also shut the engine off to run leak down tests etc.

Since the pump was replaced in the mid summer, never had the problem again.
on October 27, 2010
That was me, by the way.
on December 20, 2010
OOOhhhhh....was it really you?!
on December 20, 2010
Yes! Gotta love smug replies when there is proof on the table..
on February 27, 2013
so i have 2001 blazer 4dr 4x4 has had everything done from fuel pump, sending unit, cap, rotors, plugs wires, spiders. when we first got this vehicle it didn't run. it runs now but when it gets up to 180 degrees it starts to run like garbage. we have had it checked out by 2 different mechanics. one said clean both converters. we did that. all sensors are changed. there is a stero system in this vehicle and an alarm system. we can not figure out what is wrong. another mechanic said the wiring, some one else said the main computer. could you figure this out.
on June 09, 2014
pull the battery tray under it there is a black box with a 75 amp fuse clean the fuse ends that bolt on then check the frame and body grounds ad more if you need to but run them direct to the battery rust will kill electrical connections and i did change my cam sensor but i would wager on electrical issues. ok this did not help it is the bcm or the pass lock i have tried everything and i am gonna replace it with a ford f150 gm built this to fail you cuase they think we will buy a new car from them well i choose ford or dodge.
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