96 blazer stalls when hot

On your Blazier the fuel pump relay is behind glove box.

On your Blazier the fuel pump relay is behind glove box.

Can I test the fuel pump relay itself, or is it easier to test the fuel pump. I'm assuming in order to really know whats going on, this test would need to be done when the car fails on a hot day.

the other question is, this could still be related to the ICM getting hot. If it isn't sending adequate spark, or no spark at all, the computer will not allow the fuel pump to generate the pressure. However, it should still build pressure when the key is turned on and not sparking.

Hmmmm, this is fun, I feel like I'm the mechanic sherlock holmes following the clues to solve a mystery. I think he would have solved it by now though. :lol:

Can I test the fuel pump relay itself, or is it easier to test the fuel pump. I'm assuming in order to really know whats going on, this test would need to be done when the car fails on a hot day.

the other question is, this could still be related to the ICM getting hot. If it isn't sending adequate spark, or no spark at all, the computer will not allow the fuel pump to generate the pressure. However, it should still build pressure when the key is turned on and not sparking.

Hmmmm, this is fun, I feel like I'm the mechanic sherlock holmes following the clues to solve a mystery. I think he would have solved it by now though. :lol:
Sherloc
You are doing good so far on picking up the clues.

Yes key on the vcm/computer signals the fuel pump relay to turn on 2 second prime up.
That works if relay is good and has power/ground and computer primeup signal to it to it.

Yes best to test when pump quites.
Check for 12volt power to pump should be a gray wire.
Some even have a singal wire fuel pump test lead under hood.

I always tap a lead wire into it some place between relay and pump.
And run the lead inside and hook up a bulb test light to it and drive until it quits.
If bulb goes out you have loist power to pump.
I check for voltage with a test light or volt /ohm meter
If it stays on and no pump running move onto fuel pump.


Back in the good old days on the good old cars we could listen to a car drive in repair shop and know what the problem is.

Now days we have to spend a hr. or more hooking up test equipment and test driving and going threw the shop repair program to get a clue to what is going on.

If we are luckie hooking up a good scanner will point us in the right direction.
But scanners do not tell all.

No two cars very seldom are the same or have the same problem.
We have to solve mysteries on each on.
Good Luck

ICM heat sink

I got an old scrap heat sink from something. I trimmed it to the same size as the original. Using the original holes as a template I drilled matching holes in the scrap heat sink. Using new long bolts and nuts I assembled ICM/silver paste/stock heat sink facing out/silver paste/scrap heat sink facing out the other way/U bracket.

Using a piece of aluminum sheet, I made a "serif" U bracket that matched the coil mount bracket and mounted the assembly on the old bracket. The silver paste is used to thermally connect a CPU or chip to a heat sink.

Reconnect.

Car has not failed since.

Awesome and thanks for the reply, I still think I will do this mod because that bracket gets hot. You couldn't take any pictures of your set up could you? I'm assuming you still haven't had any issues.

Still working great. Eight days no failures so far.
You need two people for these two tests, too.
When you turn on the ignition key, find out which relay is for the fuel pump. I have a gang of them together in back of the glove box. I moved them all around (they are the same) and nothing changes. I cleaned all these contacts when I pulled the dash. Same with the three relays under the hood.
When your car fails, pull the #1 plug and see if you get spark. Be careful, it's a hair raising experience.
I would guess fuel pump though from your video.
I think there is a fuel pump test terminal somewhere, but I don't remember where right now.

It's been cool here for four days. Took a 100 mile trip with no problems.

I ended up spending my easter changing a fuel pump in the truck. What an experience. Was quite the ordeal. I did purchase and replace the fuel pump relay. At 10.00 it was worth the purchase just in case. Anywho, After I replaced the relay I was purposefully driving it around on Saturday running out as much gas as I could. Temperature was about 74. I never got a running failure, but anywhere I went, If i turned the vehicle off, the fuel pump would not reengage when I tried to restart. It would have to sit a bit before restarting and running fine. Fuel level was very low. I know mine is not ICM related as I took my old ICM and plugged it in and got no start and fuel pump would not engage.

I think I ended up with about a gallon or less of fuel left by the time I got home. Replaced the fuel pump Sunday. I didn't get to drive it much today, temperature was 94. I did drive it for about 15 miles in traffic. No running failure. When I did get back to the driveway, I turned it off and it did restart, but it hesitated on the restart, 3 cranks or so. Not the usual instant fire I get. We'll see tomorrow. It's supposed to be over 80 again and I will be driving to work. I ended up breaking the hose barb off of the vent on the back of the tank when I lowered it. So a new one was purchased. We can add to the long list of parts purchased trying to fix this thing. Fuel tank vent, fuel pump, fuel feed, return and vent lines replaced, and a new fuel pump relay. Oh yeah, and I bought a new gas cap too just in case. Sucks to be spending all this money on these parts. I was planning a complete overhaul of the interior, guess that will have to wait a little longer. And, I still have a leakdown issue so next weekend it looks like I'll be replacing the spider assembly with the new injectors.

ok, no failures and it restarted in 94 degree weather after driving over 20 miles in traffic that took me about an hour. I would have normally got a running failure or at the very least, the vehicle would not have restarted until I let it sit. I'm calling this fixed for the moment. However, I want to put out there for everyone to consider that this may be caused simply by a clogged, old charcoal canister filter or bad gas tank vent. As previously mentioned, I busted the hose barb off of the gas tank vent which ended up needing replacement. What are the chances that on a hot day, fuel vapors are at a max, and with either the charcoal canister clogged, or the gas tank vent not operating properly caused a sort of vapor lock in the tank? Any thoughts? I know I could possibly test this, but that would entail me taking taking the tank down at least twice more and I'm not willing to do it. :nono:

ok, no failures and it restarted in 94 degree weather after driving over 20 miles in traffic that took me about an hour. I would have normally got a running failure or at the very least, the vehicle would not have restarted until I let it sit. I'm calling this fixed for the moment. However, I want to put out there for everyone to consider that this may be caused simply by a clogged, old charcoal canister filter or bad gas tank vent. As previously mentioned, I busted the hose barb off of the gas tank vent which ended up needing replacement. What are the chances that on a hot day, fuel vapors are at a max, and with either the charcoal canister clogged, or the gas tank vent not operating properly caused a sort of vapor lock in the tank? Any thoughts? I know I could possibly test this, but that would entail me taking taking the tank down at least twice more and I'm not willing to do it. :nono:

With high pressure fuel pumps you do not have vapor locks.
Even in the old days when they had low pressure pumps there was very seldom any real vapor locks.
Most were weak fuel pumps and overheated engines and weak secondary ignitions.

I have only had one real vaper lock job in my 50 years working on cars that you might say was a vapor lock and fixed it with a good tune up.
But the old wood cloths pins sure got used up back them.
I have say as many as 12-15 cloths pins hanging on the fuel line on them old good cars.:lol2:
Ps
On the old modle T gas tank in front of windshield if you could not drive up the hill just turn around and back up it.
That put then tank higjer and gave it more fuel and fuel pessure.
If they had high pressure pumps back then it would have justed jumpped the hills.:lol2::iceslolan

Are you still going to change the spider?

As for me, still perfectly nice and cool outside. Waiting for the hot.

Roger that MT, I did fail to mention the fuel pump I got had an updated wiring harness I had to splice in. Apparently the old version would vibrate loose ever so slighlty and cause possibly arcing, burning of the contacts and over heating. Another possible cause. Definitely not a good thing to have arcing on the fuel tank me thinks.

Yes, I'm still going to replace the spider. I still have a leak down issue and I'm thinking that is causing a little bit of a hard start when it's warmed up, otherwise, It starts right up on the first crank. Looks like I'll be doing that next weekend.

still no failures. I replaced the injector assembly today and she's purring like a lioness.

Here's a video (http://www.youtube.com/watch?v=eHKQipPhpoY). I know it's a little dark but you can hear her purr. Drives very nice. Nice acceleration and nice smooth idle. And starts up every time with a bump of the key. Solved for now.

Great!!!

Regarding the stalling problem...I had a similar experience with my '97 Blazer, 4.3L 2-door. It started back in 2007 when I was working/traveling in southern VA where it got pretty hot during the summer. On a very hot day on a long trip driving on the interstate I could feel the engine starting to cut out on me, but I managed to get to my destination ok. However when I got into town the Blazer stalled out. It would re-start, then run about 20 seconds then quit, and it took me four or five tries to go 1/2 mile to the nearest gas station. I thought there was water in the fuel so I added some dry-gas, and put a few gallons of fresh gas in the tank also. I was able to drive away and didn't re-experience the problem that day. But a few weeks later on another very hot day the engine stalled again when in town, but I again managed to get to a gas station and I added some fresh gas and was able to start and drive away. I began concluding that my fuel pump was going bad and the addition of fresh gas (stored underground where it is cool) cooled the pump off enough to temporarily correct the problem. For a while when I drove around I would keep my tank around 1/2 full and get fresh gas every 100 miles for longer trips, and park in the shade when possible. On the evening before some long trips I would put a two-gallon can of gas in the refrigerator, then the next day put the can in the rear under ice, all for insurance in case I stalled out along the highway. I never had a problem again with it stalling out when I took these precautions, but I got tired of babying this fuel pump so I changed it in 2008. I didn't have a problem with it the rest of that year that I recall, although I can't be sure I encountered the same hot conditions again that year. Then I quit working in VA and returned to PA where my home is. Here it doesn't get that hot in the summer, and I never had another problem with it stalling out, although I didn't drive it a whole lot since the time I was working away from home.

Last week I went back to VA, spent a few days there, and on the way home in PA guess what happened... my Blazer stalled out, right on the turnpike! It was in the 90's that day and it was being driven pretty hard. Anyway, I was able to restart it after letting it sit for about half an hour, and I drove to the next exit where I was able to fill up with fresh gas. I drove the rest of the way, 90 miles, without any trouble.

This is a long story but I got to thinking about the fuel pump... I think the pump itself is ok, but the failure may be that small dc motor driving the pump. I wonder if it is getting hot and failing. I tried e-mailing the
Carter company (manufacturers of the fuel pump) about the possibility of the overheating of that motor causing it to temporarily fail, but I have not heard back from them yet. If quality control is an issue with them it could be "luck of the draw" in aquiring a decent fuel pump, no matter where you buy it. I bought mine from NAPA, and it was over $400, and I assumed spending a lot of money would get me a good fuel pump. So I don't know for sure.

After the turnpike incident...The next day after I got home from my trip I popped the hood and took a close look at the engine. I noticed that the fuel lines go over top of the motor to a mounting bracket, and down the back of the motor, and -where I could feel- are fastened somewhere on the block or valve cover (it is impossible to see directly because there is very little space between the firewall and rear of the engine). I started the engine and ran it about five minutes and could feel those fuel lines get warm. I think the fuel is picking up heat in this area and of course whatever fuel isn't being used by the engine is returned to the tank. And I would bet it is being dropped into the tank in the vicinity of the fuel pump where it is immediately picked back up by the pump. I suspect the excessive heat can cause the fuel to lose viscosity enough when pumping to cause a problem with fuel pressure, but in my case I didn't experience it as sputtering or conking out when going up a steep grade. When it
ran, it ran fine. I believe instead the pump's motor just overheated and died, temporarily, until it cooled down enough to function normally. I never had a "Service Engine Soon" indicator lamp come on which I have come to believe makes it a fuel problem, as there are few if any sensors on the fuel lines (other than, perhaps, tank pressure).

I attenpted to solve this problem by re-routing the fuel lines away from going down the rear of the engine to along the firewall and above the brake master cylinder, then down the inner fender to the frame and along the top of the frame to a point near the fuel filter. It really wasn't that difficult. I cut both lines just before the mounting bracket, bent them, then ran hose -the pressure line right to the filter and the return line at nearly the same location. I insulated them with some rubberized pipe insulation. I noticed, when I reached behind the the motor to feel the fuel lines, that my return line was badly corroded anyway so I was glad to do something about this problem. I left the vapor line as-is. I spent about $75, most of it going toward the pressure line hose.

I have driven the Blazer enough to test it out to make sure there were no leaks, and after an hour driving I checked the temperature of the return line and it was warm but not much more than the frame. It wasn't even 80 degrees outside so not a real hot day. I happened to check the old steel lines which were still hanging in place and they were hot to the touch. I wish I would have checked them more thoroughly before I re-routed the lines, maybe they would have been a little cooler with fuel in them. But I am sure I made an improvement so far. I added a thin piece of aluminum sheeting as a deflector between the exhaust pipe and the new lines, as there was a lot of radiant heat yet from the exhaust pipe reaching the insulation-covered hoses.

It may take a year or more for me to know if this will solve the problem, as I have no plans to drive down south for a while to give it a good test. Maybe someone else will give this a try.

When I put my scantool on it recorded an inlet air temp of 185 degrees during an 80 degree day. So I looked at the clearance on the airbox snoot and saw that the intake snoot was 1/2 an inch from the back of the headlight wall. No clearance. I removed the rubber snoot and the temp dropped to 100 degrees and stayed below 120 until I stopped for the night. It was too close to the wall to allow any airflow to the engine.

I think this is related and you're on to something.