1992 GMC Sonoma Stalls during acceleration

StacyT69 · 02-16-2010, 07:30 AM

I have a 1992 GMC sonoma and it idles fine, however after it gets up to normal operating temp it starts stalling and backfiring during acceleration. Once I let off the gas it goes back and idles fine.. I've changed the Spark plug/ wires and coil. This did not fix the problem.. I've also ruled out the Cat. Converter. Does anyone out there have a solution? Oh.. I also changed out the EGR valve about two months ago only because I got an error on my check engine light. Not because it was running rough. So the EGR valve is new. The truck ran fine after changing the valve for 2 to maybe 3 months but now I've got this problem.. I changed Fuel Pump and Fuel filter about a year ago. So both of them should be fine I guess.. I think it's got something to do with Firing because of the back firing it is doing during acceleration. I'm running out of options.. PLEASE HELP!!!!!!!!!!

old_master · 02-16-2010, 09:33 PM

What engine is in the vehicle? If you're not sure, post the 8th character in the VIN.

StacyT69 · 02-17-2010, 06:55 AM

Sorry, I forgot to add this didn't I. It has a 2.8L 4 cylinder.

old_master · 02-17-2010, 01:19 PM

Better post the 8th character in the VIN. 2.8L is a V6 and the 2.5L is a 4 cyl.

StacyT69 · 02-18-2010, 06:59 AM

Really.. No wonder I never could get the right parts!! Hee Hee

Sorry about that... I forgot to get the Vin number off my truck last night.. However I'm pretty sure it's a 2.5L 4 cylinder. Not sure why I posted a 2.8L.. I think it's because I was reading other people's forums and had 2.8 on my mind I guess.. Again Sorry about that..

old_master · 02-18-2010, 12:43 PM

No problem... it happens

Ok, 1992 GMC Sonoma with the 2.5L 4 cylinder engine.... (8th character in the VIN should be "A")

With the possibility of confusion involved:

What brand and part number are the spark plugs that you installed?
Do you have the tools to check fuel pressure?

StacyT69 · 02-18-2010, 06:11 PM

I don't have a gauge to check fuel pressure. However I just changed the plugs ( AC Delco R43TS6). Also replaced coil (Napa IC29SB) and Spark Plug Wires (Napa 3156-9041).

I'm now looking at the VIN # and it is an "A".

A guy I work with said that it could be the Temp Sensor.. Do you think that's possible? If so, then how does my temp gauge on the dash work. OR does it even work that way? One thing is for sure.. it only acts up when it's at normal operating temperature. Runs like a dream up until that point..

old_master · 02-18-2010, 07:02 PM

The parts you used are correct... gotta make sure

Have you replaced the distributor cap and rotor recently?

The temp sender is a possibility. There are 2 temperature sending units on your engine: One for the dash gauge and one for the computer. They are inexpensive and might be worth a try. Make sure you tell the parts store you need the sender for the computer, NOT the dash gauge. It's commonly called "ECT sensor". Most likely it's located near the thermostat, (next to where the upper radiator hose connects to the engine.) Here is a link to it, notice the style of electrical connector, the dash gauge sending unit has a different connector, and is located in the cylinder head. http://shop.advanceautoparts.com/web...S_575717680___

Post your results.

StacyT69 · 02-19-2010, 04:04 PM

No, I have not changed the distributor cap or rotor.. For sure, One of the things on my list. However I was looking for some advise before attempting that.. My distributor is hard to get to.. Which you probably already know that..

If it was the temp sensor, Why wouldn't I get an error code?? That's why I'm hesitating on the sensor.. However I'm going out tonight and atleast check the wiring and connections. I'll let you know if I find anything.. If you're sure that can possibly cause my problems.. I'll go ahead and change the sensor. Whole lot easier to get to than the distributor.. LOL

old_master · 02-19-2010, 04:27 PM

Each sensor has a range that it operates within. The ECM "watches" for a signal within that range. If a sensor supplies the ECM with a signal that is within range, the ECM will "believe" what it sees and not set a Diagnostic Trouble Code, (DTC). If a sensor is out of calibration, but still within range, the ECM will assume the data is correct and make adjustments to fuel mixture, EGR, ignition timing, etc based on the data it receives. In the case of an ECT sensor, it might be "telling" the ECM the coolant temperature is 30 degrees hotter or colder than it actually is, and the ECM is making adjustments accordingly. If you have an ohmmeter, and a thermometer, I can explain how to test the ECT for accuracy.

StacyT69 · 02-21-2010, 10:47 AM

Good News.... I think I may have found the problem.. Atleast it was a problem.. Not sure if it's the culprit behind my stalling problems or not.. I'll let you be the judge of that..

I went out and located the Temp sensor via your instructions. It was alittle hard to get to, however I unpugged the sensor and pulled the plug up to where I could get a good look at it.. There is two wires going into plug and I noticed that the wire insulation was missing from the plug about 1 inch back. Basically just bare wire was showing.. I first thought that something had melted but it looks like it was just basically dry rotted. I believe that the bare wires were touching each other causing the computer to get a false reading. I got some electrical tape and taped it up real good. I then took my voltmeter ( with the ignition switch "ON") I checked the voltage at the plug. I'm getting 5.02 VDC. So I figured aleast the wires were not broke.. I plugged it back to the sensor and so far the stalling is gone.. I drove it around for about 1.5 hours yesterday and it ran like a dream.. I really can't believe that fixed it.. How can something so simple cause such a big headache.. Do you believe that fixed my problem or is it just a fluke? The reason I say that is because the problem really came and went until about a week or two ago.. Then it seemed to happen ever time it got up to normal operating temp.. Does that make sense? When I first noticed the truck stalling and backfiring during acceleration it only happened about once or twice a week.. Then on my way to work one morning it started stalling/backfiring and then it cut off.. it would not start back up. I got a buddy to pick me up that morning and we left it until we got off work that afternoon.. I thought I was going to have to tow it home. However when we tried to start the truck that afternoon, it started and ran all the way home.. Atleast until it got back up to operating temp. Then it started stalling and backfiring as I pulled into my driveway..Since then it did it ever time it got up to temp until I fixed the plug yesterday.. Is it fixed or is that just false hope????

old_master · 02-21-2010, 11:21 AM

That could very well be the problem, good work! The ECM sends a reference voltage of 5VDC to the sensor through one of the wires. Depending on the resistance through the sensor, a signal is sent back to the ECM on the other wire. The ECM calculates engine temperature and makes adjustments to fuel mixture, ignition timing, EGR, etc. Years ago cars had a choke, when the engine was cold, it choked off the air supply to the engine and it ran with a richer mixture. As the engine warmed up, the choke would slowly open allowing more air into the engine providing a leaner mixture. The ECT sensor acts in much the same way, resistance through the sensor slowly decreases as the coolant warms up. The ECM then adjusts accordingly. If a choke stays on too long, or not long enough, the engine will not run properly, same holds true with the ECT sensor, but now there's electronics thrown into the mix which can instantaneously operate erratically.

You can check the calibration of the ECT very easily: With the engine at operating temperature, (195F degrees) unplug the ECT sensor and measure the resistance between the two terminals of the sensor. It should be approximately 240 ohms. At 70F it should be approximately 470 ohms.

StacyT69 · 02-22-2010, 10:08 AM

So far so good.. Still no stalling or backfiring..That must have fixed it because it would have acted up by now knowing the history.. I want to thank you for your help. Not sure it would have made sense without you.. I'm just glad I didn't replace a whole lot of parts just to find those wires touching.. Basically what I did change was just tune up parts and it probably needed those anyway..
Just gonna warn you now.. If I ever have problems again, I'm going to look you up..
Thanks again for your time!!!!!

old_master · 02-22-2010, 03:47 PM

Glad to hear that you fixed it! This is a perfect example of why gathering the symptoms and data, along with a good visual inspection is so important... It saves a ton of money in the long run. Knowing how something works is vital when it comes to figuring out why it doesn't work. Glad I could help.

bmiller184 · 12-05-2011, 02:15 AM

I have a 1991 S10 2.5L I have replaced Ignition Control Module, Ignition Coil, Rotor, Distributor Cap, Plug Wires, Plugs, Map Sensor, O2 Sensor, Fuel Filter, Fuel Pressure Regulator, and Fuel Pump. It is starting to run better but it is hard to start and once it does start it seems to idle ok but when I go to accelerate it cuts out and dies. Any Suggestions?

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