# GMC Sonoma (S-10) running bad, Advice needed



## clovis (May 13, 2002)

'95 GMC Sonoma, 4.3 six cylinder, Automatic.

165,000 miles, and I am the third owner. I believe the truck was wreck hard early in its life.

The truck has been running rough when it warms up. The service engine soon lights up when it starts running rough, and acts like it wants to die at low speeds, especially when you take your foot off the gas, and coasting to a stop. 

I took it to my mechanic, and he plugged in his hand-held scanner. It kept giving a 'LINK ERROR' message.

Wondering if it was a coincidence, I took the truck to AutoZone to see if it was throwing an codes.

His scanner kept saying "ERROR" at AutoZone.

Both scanners look very similiar in make and model.

Can I trouble shoot the system on my truck, to make sure that it is working properly when the scanner is plugged in?

Thank you in advance!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


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## idahodave (Jan 20, 2005)

Just an out and out guess..bad coolant temperature sensor causing rich mixture when warmed up.


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## Wis Bang (Feb 20, 2009)

The '95 was a strange year, It is still an OBD 1 computer but the ALDL data link is out under the hood instead of under the dash. The OBD 2 started in '96...that's why the OBD 2 code reader isn't working

My '93Jimmy 4.3 was just doing the same thing, again. The EGR valve, located above the water pump on the front of the lower intake manifold is a plunger type w/ the works hidden inside the manifold.

Go to advance auto [or a GM dealer] and pick up a pint can of 'SEAFOAM' a top end cleaner designed to remove the carbon buildup.

W/ the engine running, have someone hold the throttle open just a tad, and pull the brake booster vacuum hose loose from the booster between the master cylinder & the firewall & slowly pour the contenst of the whole can...slower than slow so it wont stall...and then shut the engine down for 5 - 10 min...

DO THIS OUTSIDE! be prepared for it to start hard & it will smoke, lots of smoke for a while as the seafoam & carbon burn off...

It should stop your CES lamp and you will notice an improvement in driveability...

All the first gen S-10/T-15 w/ 4.3L engines do this. Later units eliminated the EGR but you have the same engine as my 93...My ALDL is under the dash and a paper clip inserted into the two correct spots will make the CES lamp 'flash' the codes which are listed in my Haynes manual...another plug will flash the ABS trouble codes on the brake light too....

Check out www.S-series.org and the S10 forums, Google s-10, lots of tech tips including how to read the 95 codes...they call the 95's OBD 1.5.....


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## clovis (May 13, 2002)

Thank you for the info!!!!

The plug-in for the scanner is under the dash though. Are there 2 plugs? One under the dash, and another under the hood?

BTW, as you know, this is the round body S-10, and not the square body. '95 was the first year for the new body, right?

Again, thank you!!!!
Clove


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## Wis Bang (Feb 20, 2009)

clovis said:


> Thank you for the info!!!!
> 
> The plug-in for the scanner is under the dash though. Are there 2 plugs? One under the dash, and another under the hood?
> 
> ...


The pickup changed to the 2nd generation [rounder] body style in '93 and the Blazer/jimmy in '94. My 88 S-10 longbed was the squared off body and my 93 Jimmy is too. The major difference between the first and the early second generation is mostly cosmetic. The running gear evolved slowly. The frame and running gear stayed close to the same until after 96. For example 94-96 seats will bolt into the first gens. 97 seats are different & by 98 they had twin piston front brake calipers [and rear discs on the SUV] which can be upgraded to First Gens w/ the upper A arm from an old caprice...

The ALDL [Assembly line data link] was under the dash thru 94 and moved under the hood in 95 but the computer didn't change intil 96 when they upgraded form OBD {Onboard diagnositcs] one to OBD II as mandated by the EPA as they figured out that OBD I [from all the automakers] has a few flaws.

Since the original emissions testing was at idle, OBD I shut down some of the emission parameters above idle plus it had been 'hacked' so the feds demanded the update. Here in NJ the dyno emissions test is used on pre 96 vehicles while the OBD II are simply plugged in and checked for 'fault codes'...

Check out the S10 sites as it is possible to jump two points in your plug and flash the 2 digit codes on your CES lamp the same as the 86 - 94 but I don't know which points like I did w/ my 88 and still do w/ my 93...The EGR should flash a code 32

OBD I resets the computer [clears the fault codes] when you disconnect the battery while OBD II [four digit codes] has to be cleared w/ a scanner. 

Is your CES lamp staying on of did it go off? Both systems stop flashing the CES lamp when the out of range parameter is corrected and you operated for a number of 'drive cycles', this is called a soft code. Hard codes [lamp never goes off] indicate more serious problems. The CES is simply the car telling you something wasn't right w/ some part of the emissions controls.

My 93 usually resets the lamp but still idles bad. The EGR [exhaust gas recirculation] valve is supposed to close under a certain speed and RPM. when a small chunk of carbon gets in the way it cannot close off the EGR flow resulting in a poor idle, even stalling when you let up on the throttle or de-clutch as you come to a stop.

Seafoam works and is under $10.00 a pint. They even sell galion cans too! 

If you do figure out how to jump the plug, the first code is always a 12, one flash followed shortly by two flashes. Each code flashes three times before the next code. a clear computer will just flash 12 over and over so after the 4th one you know the codes are clear...

I've seen 4.3L w/ over 300K, mine is pushing 180K. My 88 was a 2.8L v6 and it died at 196,293, I purchased a 'bolt in' HT 3.4L crate engine & sold the truck at 306K during 7 years and a year later it is still going. They are pretty tough little trucks...I picked up a part for work that weighed 1,800# from the supplier. First they loaded the 'bad' unit which was too expensive to repair and was apart so I had 3,600# in a longbed 1/2 ton S-10, back when it was still the 2.8 and only realized it as the longer grades put me down in 3rd gear.


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## clovis (May 13, 2002)

Wis Bang,

*Thank you!!!! Your posts have helped so much!!! While lots and lots of folks have helped over the years, your posts have been some of the BEST that I have ever recieved!!!! *

I did check out the website link you offered. That is a wonderful site!

The truck I have plugs in under the dash, to the far left when seated. It is not centered under the steering wheel like I expected. Is it possible that it has a second plug in under the hood?

The SES (service engine soon) light does go off, and only comes on when the truck is warm. The really rough idle has gone away, for the time being, but still idles bad.

If you shut the truck off, and restart it while it is still warm, the SES light comes on immediately when starting, and stays on. It doesn't do this when it is cold.

Your info was so good, as well as the s-series link, that I printed it off for my mechanic.

Again, thank you so much.

I think I will try the sea foam. Never seen it before, or used it, but it sounds like a probable solution.

Let me say this again: Thank you for your time and help!!!!!!!!


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## clovis (May 13, 2002)

I forgot to mention:

You may have just saved me $50 for a pair of seats out of a 97!!!! A local guy is parting out a 97 extended cab, and I was thinking about taking the seats. I would not known that they wouldn't fit until it is too late.

Clove


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## Wis Bang (Feb 20, 2009)

U R welcome. I was involved in the S-10 boards alot learning if I could put the crate engine in my pickup as it was approved for pre-86 non fuel injected units. 

I started that installation on Monday Sept 10,2001, took all week afterwork plus Sat & Sun...didn't get much work in on that Tuesday & drove home w/ the WTC smoke pillar in my rear window. Smelled the WTC all that week too. 

During the pre-swap research, I read about Seafoam for the first time.

Glad I could help your post turned me from a lurker to a member.


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## Wis Bang (Feb 20, 2009)

clovis said:


> I forgot to mention:
> 
> You may have just saved me $50 for a pair of seats out of a 97!!!! A local guy is parting out a 97 extended cab, and I was thinking about taking the seats. I would not known that they wouldn't fit until it is too late.
> 
> Clove


Seat swaps was another big topic. I replaced the worn out buckets in my 88 w/ the same charcoal tint from a 92 grand am, $26.00 for both @ Harry's U-pick it in Hazleton, PA after passing on a white leather set in a Sunbird 'cause they were white [could have dyed 'em] and a small rip in one...


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## clovis (May 13, 2002)

Just an update on this....maybe I am a little premature posting it:

A code 32 was thrown from jumping the two prongs. Mechanic pulled the EGR, and cleaned it. It was stuck open.

He also replaced the thermostat, which was also stuck open. You will probably think I am dumb, but I wondered why it took so long to get luke warm heat out of the truck! Nice hot heat now. 

The truck started and ran great, until it warmed up. The truck started idling rough and the SES light cam on.

Back to square one. I bet it is the EGR valve.

Going to see if we get any codes, and try the Seafoam.

Again, I cannot thank you enough for your help, thoughts and time!!!!!!!

Clove


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## agmantoo (May 23, 2003)

disable the egr valve and see if it doesn't start to run OK with it disconnected. Disabling is one of two ways, either unplugging the electrical connection or plugging a vacuum line. I cannot remember which is on that age 4.3 This will hurt nothing !


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## clovis (May 13, 2002)

I will try that too.

Thanks, Agmantoo.

Clove


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## Wis Bang (Feb 20, 2009)

Mine does that and shows code 32 & the seafoam cleared it right up...


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## clovis (May 13, 2002)

The mom and pop auto repair shop that I patronize also has a 95 S-10. They tell me that they have had problems with the EGR valve in their truck too. He said that they take it out once a year to clean it. 

He even offered to clean my EGR if I removed it, and brought it in, all for free. How is that for a great parts store?

I bought the Seafoam, and instead of using the whole bottle in the throttle body, I opted for 1/3 in the TB, 1/3 in the crank case, and 1/3 in the gas tank.

We checked the code again before adding the Seafoam, and it threw a 32 again.

It did smoke out the tail pipe when poured in the TB!!! And lots of smoke when I refired it after waiting.

My mechanic (who happens to be a close friend) had pulled the EGR, which was stuck open. He cleaned it the best he could, reinstalled it, and the truck ran perfect. Perfect, that is until I drove it home, and experienced the same rough idle and it wanting to die.

I had a SCARY experience today, when the truck wanted to die, and did die when I pulled onto the highway. It did not want to restart, several times, after several stops.

I got it out on a country road, and pushed the gas pretty hard, and the truck ran great after that! The seafoam seems to have helped even more.

Time will tell if the problem is fixed, and if the Seafoam worked.

The oil needs to be changed. How long should I leave the Seafoam in the crankcase? Is a few days enough?

Again, thanks!!!!!!!!


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## Wis Bang (Feb 20, 2009)

not too long. Change the filter!


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## fixer1958 (Dec 12, 2005)

They make an aftermarket EGR gasket that has a screen in it to keep the carbon chunks from hanging in the ports.


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## Ross (May 9, 2002)

Great site Wis Bang I know where my break time today is going to be!!


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## clovis (May 13, 2002)

Thanks again guys!

Day 2 update...the truck seems to be running better that it ever has. Seems like it is using less gas too. Of course, it could be my imagination, I doubt it. It just idles so smoothly, and runs great when driving. 

I know this will sound crazy, but it seems that the automatic tranny shifts so much better. (Go ahead and laugh) It really does seem to shift better, when it should, and shifts smoother. It seems like that the tranny was slow to shift into second and third, maybe by a few seconds before the treatment. Am I loony?

I know it has been just 2 days.

Clove


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## Wis Bang (Feb 20, 2009)

The EGR was stuck open and the truck was trying to run even w/ the excess exhaust present whent he EGR failed to close. Celar al that up and it would feel like it shifts & runs better!


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## clovis (May 13, 2002)

Just an update: The truck is still running great! 

I still swear that it shifts better and smoother...might be just an idea in my head, but it sure seems better.

Thanks again everyone!!!!!!!!


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## Wis Bang (Feb 20, 2009)

clovis said:


> Just an update: The truck is still running great!
> 
> I still swear that it shifts better and smoother...might be just an idea in my head, but it sure seems better.
> 
> Thanks again everyone!!!!!!!!


The transmission should have electronic controls instead of a 'TV' cable [throttle value] cable mechanically telling the trans what the engine is doing. Since the 'puter was struggling to keep the engine running w/ all that recirculated exhaust, the trans wasn't operating the way it should. Once the computer operated within the correct parameters the trans would shift smoother too, it's not your imagination, it probably wasn't 100% when you bought it.

Always glad to see a happy s-10 owner!


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## Wis Bang (Feb 20, 2009)

Ross said:


> Great site Wis Bang I know where my break time today is going to be!!


It is one of the best sites for S-10/T-15 trucks & Utes.

Another is s-104x4extremist.org, guys doing solid front axle conversions to eliminate the Independent front suspension for better 4x4 perfomance...


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