Clean your MAF sensor wire. Use the special MAF sensor cleaner, like the CRC brand stuff here: https://www.crcindustries.com/products/mass-air-flow-sensor-cleaner-11-wt-oz-05110.html

Also check/inspect the connector for the MAF sensor and the wires to that. You might need to use some electrical contact cleaner on the harness connections.


If you have an OBD-II reader (scan tool or app that can read live data), check your intake air temperature data as well. I've seen a bad IAT sensor (reading extremely cold, like -200°F or something crazy) cause that issue. If that's the case, it will run better with the IAT sensor disconnected.

 

^^^along with cleaning the maf...don't touch the wire....just spray it.... It's fragile.

 

Ok, so I cleaned the MAF sensor and replaced the IAT. No joy. But I did get rid of my error codes, so progress. It seems to start faltering when the engine temp hits about 194. Once it drops below that, it starts again and runs normal. Could this be a temp sensor that is malfunctioning or something like that? Not sure where to look at this point.

 

I'm wondering if it could be the ICM? Any way to test it?

 

Temperature 194°F? Is that a number you're getting from OBD-II live data stream? If that's where that reading is coming from, then the sensor is working properly. If you're getting that from a "point and shoot" IR thermometer, then you really should check the data stream before loading up the parts cannon. Watch for wacky numbers on temperatures (very cold, like way below zero).

Without a scan tool/scan app to watch live data, you can try disconnecting sensors one at a time, seeing if it improves the way it runs, then reconnect.

Don't assume that the sensor you disconnect that makes it run better is actually bad, though. Sometimes disconnecting a certain sensor makes it make assumptions for several sensors or switch to open loop mode.

 

Yes, that reading is live from my ODB-II scanner. 194F. Not seeing anything on my scanner that raises any red flags though. Intake air is just above ambient as well.

 

You could check the coil and/or the ICM. What I usually do as a "test" is run it until it's misfiring or shutting down, then super-cool it using a liquid. I use the cans of "air" for cleaning your computer keyboard. Flip the can upside down and a very cold liquid will squirt out. Hit the coil and/or ICM with that. That will quickly cook things down. Try starting again. if that cures it, whatever you cooled is bad and going flakey/going out when hot.


BTW, how did the vacuum leak search go?

Also, what are your short term and long term fuel trims running for each bank?

 

Found a vacuum leak on the intake gasket, so had that replaced. I'll have to check the trims. Don't remember what they were off hand. I read about using a cold, wet cloth on the ICM. Think I'll try that since I don't have any compressed air handy.

 

A very cold wet towel might work. But what I was suggesting would be better.

It's not compressed air. I'm talking about something like this: https://www.crcindustries.com/produ...ies.com/products/duster-8482-moisture-free-dust-lint-remover-8-wt-oz-05185.html

You can get that or something like it at office supply stores, or at Walmart in the electronics area.

It's a liquid chemical that evaporates well below room temperature and is gas when it comes out. If you turn the can upside down, the liquid (probably tetrafluoroethane) squirts out and evaporates below 0°F at atmospheric pressure, and it cools to the boiling point of that liquid when you spray it on something. Don't get the liquid on your skin, it will cause instant frostbite. The cans generally warn of danger, death and destruction if you turn them upside down.

 

Well, this time I started it and put the cold rag around the ICM. I got a new code for the cam sensor. Not sure if it a true reading, or something related to the rough running. I have to go out so I will stop at staples and see if they have any.

 

Here is a screen grab of the fuel trims. I went ahead and replaced the CAM sensor since I had a spare one. When the engine died, I sprayed the ICM, then restarted the truck. It ran for a few moments before dying again. Leads me to believe it is in fact the ICM that is bad. No CEL codes at all.

 

This is really starting to piss me off! Replaced the ECM and it is still stalling at running temp! I've attached a screen grab of my sensors right when it was dying. WTF else could possibly be causing this? Oh, and the P0300 is back.

 

This is really gonna piss ya off then,....ready?

I came across a similar problem before on a Silverado when I was at the dealership as a technician...truck had been everywhere,and had all kinds of parts thrown at it before I got it..I played with it for hours..longer then I’d like to admit tbh.


Ended up being “ground D”,the ground attached to the thermostat housing. Some clown put a big ol not OE gasket on the housing.. When the truck got hot it would lose ground to the fuel pump relay which you guessed it,..was grounded at the thermostat housing on that model.

Get a test light,hook it to positive,test all the grounds to the block...then crank the truck,and let it get hot..now recheck them all again. I JUST installed a 4.3 in a S10 a few weeks ago,and iirc there’s one on the back of the head,one on the block on the bottom passenger side,and one near the alternator which is probably ground D on a S10.

Just a shot since the truck isn’t in front of me...but it was such a bazaar vehicle it stuck with me all these years. I effin’ hate when these clowns say check your grounds..but in this case..check your grounds...eff that damn truck!

 

Might as well. Nothing else has worked.

 

@BravadaX. The '96 doesn't have a ground at the thermostat .There are 2 wires IIRC on the back of the passenger head. Just for fun, I put a big ole braided wire ground strap from the alternator bracket to the frame.

 

Well, you keep tossing parts at it. What have you done to diagnose?

Am I understanding that it quits and won't restart?

If that's the case, there are two "first steps" for diagnostics.

Check if it's a fuel issue by spraying starting fluid in the intake tube and trying to start it. If it runs for a few seconds on ether and then dies when the ether runs out, you most likely have a fuel issue.

Pull a spark plug (#1 is good) and put it on a solid metal grounded part of the engine. Crank the thing and see if you've got good spark at the exposed plug. You don't even have to pull a spark plug out if you have a spare, just take the #1 wire off the plug and put it on a spare spark plug and watch for spark while a friend cranks it.

 

Oh it will start back up, it just won't run right. At least not until it cools down. You can hear some popping as it shakes and falters. Almost like it is either flooding, or running out of gas. Sometimes it wills tart right back up, rev up for a few seconds then run right for a few minutes before it starts coughing and cutting out. But cold, runs like a dream. I knew the engine had issues when I bought it, and I have fixed several of them. Some of it was simply tune up related (i.e.plugs, wires, cap, rotor). Some things I had spares of (coil, cam sensor).


All in all I have only put about $200 into this thing. I am so close to having it fixed it's frustrating. The only things I can even come up with that might be the culprit are the crank sensor and the spider assembly. Whatever it is is definitely under the hood. If I leave the hood open while running it takes longer for whatever it is to flake out vs. when the hood is closed. This morning it ran for nearly half an hour before flaking out, but it was also 63 degrees.

 

OK. If it runs correctly on ether (starting fluid), but dies after the fluid is burned up, it's a fuel issue. I'd suspect the spider at that point.

If it doesn't start or run any better with starting fluid, then you're looking for an ignition issue. Same test with the spare spark plug with the #1 wire attached. Set it up on the AC compressor bracket. Crank it and see if you've got a regular, strong spark there. If it's intermittent, you've got an ignition problem.

The crank sensor could definitely be a problem. When it starts sputtering, does the RPM shown on your scan tool drop to zero intermittently? Or does it drop much lower than the actual engine speed? That's a sign the crank position sensor is dropping out. The RPM signal (and spark) is based on the crank position sensor. If it cuts out and you'r coasting in gear, engine spinning, but the OBD-II RPMS show zero (and the tach might drop to zero as well), you've lost igntion. It could be the crank position sensor.
I'd test the sensor by the manual rather than just summarily replacing it. But I would have tested/observed the other parts before replacing them, too. YMMV

 

Also, when replacing the crankshaft position sensor, you have to be very careful with it to get it shimmed where the clearance from the sensor to the reluctor wheel (behind the cover) is correct. Too close and it hits, and the reluctor wheel will cut/wear the end off the sensor. Too far and it won't operate correctly.

Also, when you replace the crankshaft position sensor, you have to do a relearn procedure, often referred to as a "CASE relearn," using a Tech-II or a fairly advanced scan tool.

 

Also, when you replace the crankshaft position sensor, you have to do a relearn procedure, often referred to as a "CASE relearn," using a Tech-II or a fairly advanced scan tool.

That's what I thought also. When I installed my new engine, it ran perfect...no codes. I took it to the dealer for the relearn...said it didn't apply to my '96. I had the cam retard checked..."0"

 

We had a cool morning here so I fired it up and watched my ODB scanner. Attached is the sensor readings that were pretty much stable for twenty minutes. When it started to die, the RPM's did not go to zero until the engine completely stalled. It's almost as if a timer was on this thing. Twenty minutes, then stall. I thought maybe it was the intake temperature, but it never went over 76 degrees. I guess I can rule out the crank sensor.

 

Does it run on starter fluid after it stalls? Have you tried that?

No offense, but you haven't even take the first diagnostic steps to determine whether you have a fuel issue or a spark issue. You're throwing stuff at it hoping for a result when you have no idea what's really wrong with it. Trusting blind luck isn't a good diagnostic strategy.


Also, a really good idea if you have the capability to log sensor readings is to log your readings to a file until it stalls. Then look for something that changes/flakes out when the thing dies.

 

Also, when you replace the crankshaft position sensor, you have to do a relearn procedure, often referred to as a "CASE relearn," using a Tech-II or a fairly advanced scan tool.


how do you do a case relearn? what does the truck need to relearn?

• https://www.s10forum.com/forum/f137/96-s10-4-3-shuts-down-when-hot-850915/#

 

nevermind, found it.


To perform the relearn, proceed as follows:

Connect a scan tool to make sure there are no trouble codes stored in the computer’s memory. If there is any power train trouble code other than P1336 (Crankshaft Position Variation not learned), the computer will disable the relearn function until the problem that aused the code has been eliminated. Also, make sure that the engine coolant (check it when the engine is cold) and oil levels are at an acceptable level.

1. Set the parking brake and block the drive wheels. Make sure that the hood is closed.
2. Start the engine and make sure that the engine coolant temperature is at least 158 degrees F. (70 degrees C.)
3. Turn the engine off for at least 10 seconds.
4. Select the crankshaft position variation learn procedure (CASE Learn)on your scan tool.
5. Make sure that the transmission is in Park. Start the engine.
6. Apply the brakes and hold the pedal firmly.
7. Follow the scan tool instructions.

Remember: That you are going to increase the engine speed to approximately 3000 RPM, 4000 RPM, or 5150 RPM. That’s the variation learn fuel cutoff RPM (depending upon the engine), and that it’s important to release the throttle when the engine RPM starts to decrease as a result of the fuel cutoff going into effect. Failure to do such will result in over revving of the engine, causing possible engine damage.

8. Once the engine has returned to idle, check the status of Diagnostic trouble code P1336. If the scan tool indicates that the CASE has been learned, the relearn procedure is now complete. If CASE has not been learned, check for the presence of other power train codes. If any exist, correct the problem, then repeat this procedure.

 

Ok, so over the weekend I got some ether and tried that. No change. Starts the same as it does when not using ether. I am assuming this rules out fuel system. So now what? Where do I go from here? I know it has to be electronics related. Would the temp sensor cause this?



I should also note that I kept my fuel pressure gauge on while I was testing and it never fell below 60PSI.

 

OK. If it doesn't start or runs bad on ether, and it also doesn't start or runs bad without ether, then you've got an ignition issue not a fuel issue.

Do you have a spare spark plug? can you set it on the AC bracket and connect the #1 plug wire to it? Check it when cold to see what a strong (enough to run) spark looks like. Then when it dies and won't start or run properly, check again with the spare plug attached to the #1 plug wire and check for weak spark.

I think you're going to find a bad coil, bad ignition module or bad crank position sensor. You also might find bad wiring in associated with any of those components. That's where I'd be concentrating now.

 

I went out just a bit ago and let it run until it died, watching my ODB scanner. I noticed the timing advance was dipping as low as -15 and then bouncing to -25. It normally stayed around -19 to -20. Once the truck died, I cranked it and saw that there was no RPM's showing until it started, albeit for only a few coughing seconds. So, I am thinking one of two things. Crank sensor or distributor.

 

I went out just a bit ago and let it run until it died, watching my ODB scanner. I noticed the timing advance was dipping as low as -15 and then bouncing to -25. It normally stayed around -19 to -20. Once the truck died, I cranked it and saw that there was no RPM's showing until it started, albeit for only a few coughing seconds. So, I am thinking one of two things. Crank sensor or distributor.

Crank sensor for sure.

Check for broken wiring first. Maybe clean the connector. If the cover is crunch or mushy, consider replacing the timing cover, too.

Check this post https://www.s10forum.com/forum/f107/overheated-and-wont-start-850995/#post12195575 for more information on changing the crankshaft position sensor. There's a clearance issue, and you will need shim(s) to get it installed correctly.