# back to square 1 with S10



## Freyadog

Still having problems. Thumpers S10 will no idle.

Take alternator off and she purrs like a kitten. Put the alternator back on and she quits idling and stops.

take alternator off and purrs like a kitten. Put brand new alternator on and she quits idling and stops.

any ideas would be appreciated.


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## Fossil

I have had a couple of S10 trucks in times past and I know from weird experiences that their wiring is very 'iffy' in spots. It sounds like the charging circuit is going to ground somewhere which should never happen, obviously. If this is a V6 I would start checking around the wiring in the engine compartment and look for melted spots or abrasion somewhere. I inherited one of the trucks that had been worked on with side cutters and wire nuts. The thinking was apparently if it didn't work just cut all the wires and cap them off....The horn circuit was a nightmare. Good luck, but it will take some hunting and poking, probably.


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## LincTex

Clean the "Idle air control" solenoid plunger. It'll idle fine after that.


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## Tirediron

If cleaning the Idle air motor doesn't solve this problem, clean all of the cab to engine grounds to bright metal, replace and seal with paint, if it is TBI , unhook the battery ground cable for 2 minutes to clear the computer.


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## Thumper

more info on Freyadog's and mine S10 it is a 1998,2.5l, tbi, manual trans, two wheel drive. Have replaced every sensor or relay that the book has in it and still no dice.


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## SouthCentralUS

Every time I have a vehicle problem I can find the instructions on Youtube.


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## Thumper

Oh ya! have done all the ground.

Have looked on youtube


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## Tirediron

We had a 2.8 v6 s truck that had idle issues, I ended up having to knock the plug out of the throttle butterfly closed position screw and turn the screw in a bit then the idle air motor could keep it running.


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## readytogo

Remove only the negative cable from the battery and connect a 12 volt test light between the negative battery terminal and the negative cable. The light should be off or very dim. If you open a door, the light will brighten up showing a significant draw from the interior lamps. Close the door and it should go very dim or off - if it stays bright, it indicates a draw on the battery. Remove the fuses one at a time until you locate the circuit that is drawing. Also check all the wiring around the ignition system.


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## LincTex

Tirediron said:


> We had a 2.8 v6 s truck that had idle issues, I ended up having to knock the plug out of the throttle butterfly closed position screw and turn the screw in a bit then the idle air motor could keep it running.


Just an FYI - but you can't do that on a Ford because it raises the TPS voltage above 1.0 volts at idle (supposed to be .94 - 1.0 at idle) or the computer isn't happy.

On those, I just cut away a portion of the gasket "between the holes" under the IAC to allow some air to bypass. It works every time!

On motors with big cams, I drill a small hole in the throttle plate. It's the same effect as turning the screw... but doesn't jack around the TPS voltages.

Freya/Thump - make sure the throttle bore around the plate is very clean.


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## fteter

I'm writing this under the assumption that you've checked your compression and it's all good.

Take a look at your plugs. Do they all have a light coat of black soot? If so, I'd guess your fuel is running too rich at idle. Like due to your CPU driving too many pulses per msec, which would cause your fuel to run rich. That would tie into why it runs better without the alternator then with it.

A few tests to check on the validity of my guess (and, it's just a guess, as I'm not looking at the engine). Disconnect the power leads to one of the injectors and see how it idles with the alternator on. Is it better than when the injector is connected?

The bad news here is the fix: replace the engine performance computer (the CPU). The start program is torqued. That's a pricey fix, so check a few other things before going that route.

A fairly common issue in the S10 is too little air blowing over the Mass Atmospheric Pressure (MAP) sensor on the older models or the Mass Flow (MAF) sensor on the newer models. Causes this type of behavior. So step 1 would be to check your air intake. Make sure everything is clear.

Another issue, just as common in the S10, is a sticking EGR valve. If it's stuck partially open, it will dump exhaust fumes into the idle air flow. Not good. So step 2 is to check this by opening the vacuum source and watching the valve while you start the engine. If the valve opens, it's time to replace the EGR.

Note that either of these latter two issues could send signals to the CPU that would result in messing up the programming, which could lead to the clue of soot on your plugs. Ties directly into your problem if you have the soot coating. So, if either of these two issues, occur, be sure to reset the CPU after making the fix. Disconnecting both battery cables for about 15 minutes should do that (the poor man's reset).

How do I know all this? I'm no mechanic by any stretch of the imagination. But I own a 1988 Chevy S-10. Learned all this from my local dealership mechanic...the hard way 

Hope this helps!


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## AdmiralD7S

fteter said:


> How do I know all this? I'm no mechanic by any stretch of the imagination. But I own a 1988 Chevy S-10. Learned all this from my local dealership mechanic...the hard way ]
> 
> Oh thank God! I do pretty well with vehicles, but when I was reading this post, I thought "I'm a flipping idiot compared to this guy! He's a mechanical clairvoyant!" Sorry to hear you learned it the hard way, but also glad to hear I'm not as far behind the curve as I thought I was for a minute there


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## fteter

AdmiralD7S said:


> fteter said:
> 
> 
> 
> How do I know all this? I'm no mechanic by any stretch of the imagination. But I own a 1988 Chevy S-10. Learned all this from my local dealership mechanic...the hard way ]
> 
> Oh thank God! I do pretty well with vehicles, but when I was reading this post, I thought "I'm a flipping idiot compared to this guy! He's a mechanical clairvoyant!" Sorry to hear you learned it the hard way, but also glad to hear I'm not as far behind the curve as I thought I was for a minute there
> 
> 
> 
> Way too funny AdmiralD7S. Just way too dang funny!
Click to expand...


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## LincTex

.
LOL....

I would have "redneckified" this thing a long time ago by adding a toggle switch circuit so I can kill the alternator at stoplights, LOL!


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## Tweto

I have a 98 Sonoma (same as an S-10) with 220,000 miles on the 4.3 that developed a leaky intake gasket. There's a possibility that when the alternator is on that the weight presses down on one side of the intake enough to raise the adjacent side to leak air causing a ruff idle or no idle. When its running above idle the vacuum is enough to pull the intake down a seal it.

My S-15 ran ruff and leaked antifreeze at idle but ran great above idle and didn't leak antifreeze.

Just a though since you may have tried every other possibility.


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## Grimm

LincTex said:


> .
> LOL....
> 
> I would have "redneckified" this thing a long time ago by adding a toggle switch circuit so I can kill the alternator at stoplights, LOL!


LOL!

I would have done something like this too! I had my Ghia rigged with all kinds of buttons and switches when parts could not be found to fix a problem.


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## hashbrown

I would buy a one wire alternator and forget it.


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## Tirediron

the alternator is not really the problem here, more the symptom provider, something is causing the idle circuit to act up when the alternator brings the voltage up or the alternator is causing too much load for the idle circuit to keep the engine running, again causing a symptom, not a problem that you should see. 
I think that this is leaning toward ECU problems, since the limp home should keep the engine running with almost max idle air motor gap.


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## LincTex

definitely more troubleshooting methods need to be employed...

Put the alternator back on. Connect the plugs, but leave the belt off. What does it do?

Put the alternator back on. Disconnect the plugs, but leave the belt ON. What does it do?


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## Freyadog

Thanks all for input. Thumper is working 7 days a week and most days 12 hours. He is taking off this Saturday and Sunday. 

He says to let everone know that he will be in here and brainstorm these ideas this weekend with ya'll.

Thanks
Freyadog


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## Thumper

OK to lit everyone know what I have done so far : Have replaced fuel pump and strainer, CPU, injector ( there is only 1 Model 700 TBI), fuel filter, fuel pressure regulator, fuel pump relay,plugs, wires (8MM), cap, rotor button, Ignition module, MAP sensor (X2), MAT (manifold air temperature) sensor,engine coolant temp sensor, EGR valve solenoid (checked to make sure EGR valve was good), throttle position sensor (X2), idle air control valve (IAC),oil pressure sensor, alternator, have checked all wires for bear spots, checked PVC valve, new battery cables. Now this is everything that I can think of right know. Know remember this is a 2.5L 4 cylinder. Haven't had a chance to try some of the wiring trouble shooting yet but will as ASAP.


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## Tirediron

the pickup coil in the distributor in the TBI V6 and V8 engines were troublesome, it shouldn't cause the problem you described, but you have changed almost every other component in the system.


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## Justaguy987

I really liked the S-10's I have had, but never had any problems like you are having. Reading through this, I noticed what appears to be an inconsistently, but it may or may not matter or change anything. Several times it has been said that it is the 2.5L 4 cylinder and one place says it is a 1998. But my years working in auto parts and a quick check confirmed that the last year the 2.5 was used in an S-10 was 1993, after that, they went to a 2.2L 4 cylinder. I'm not sure if changing the year or engine size would give anyone any better ideas, but thought I would point this out.


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## Thumper

OOOPPSS!!!!! it is a 1989 2.5L S10 got the numbers backwards. sorry about that. 


thumper


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## Fossil

This is reaching but you might want to check anyway. I worked on one of these some years back with TBI and the complaint was no fuel. The guy had bought a pump and all but I could hear the pump running. I found that the two wires going to the spray motor in the TBI unit had been pinched by the air filter as I remember and were rubbed raw and shorting out. I wonder if perhaps you are experiencing a similar thing on and off? Worth a check as it is easy to deal with. Good luck.


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## LincTex

I'd like to see the results of this:



LincTex said:


> definitely more troubleshooting methods need to be employed...
> Put the alternator back on. Connect the plugs, but leave the belt off. What does it do?
> Put the alternator back on. Disconnect the plugs, but leave the belt ON. What does it do?


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## Thumper

LincTex said:


> I'd like to see the results of this:


It purrs like a kitten ether way


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## Thumper

Fossil said:


> This is reaching but you might want to check anyway. I worked on one of these some years back with TBI and the complaint was no fuel. The guy had bought a pump and all but I could hear the pump running. I found that the two wires going to the spray motor in the TBI unit had been pinched by the air filter as I remember and were rubbed raw and shorting out. I wonder if perhaps you are experiencing a similar thing on and off? Worth a check as it is easy to deal with. Good luck.


Have already checked wires for the injector. 
They are good


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## labotomi

Carefully remove the truck from the gas cap. Install a new truck onto that gas cap. 

Problem solved...


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## Tirediron

Ok without the alternator hooked up (either way) it starts and idles well ?

I would suggest you swap in a different battery to see if that makes a difference, also make sure that the big wire from the battery to the alternator is actually carrying current and not sending the power all through the sensor wire, which would show the ECU higher than acceptable voltage.


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## LincTex

Tirediron said:


> ....also make sure that the big wire from the battery to the alternator is actually carrying current ....


I have used a set of jumper cables to diagnose bad alternator wiring.

This happened *all the time* in auto parts sales... 
People would buy an alternator, then come in all pissed because it still isn't charging. I'd jump from the "big lug" on the alternator directly to the + on the battery and it would charge like a dream. Sent the customer away politely telling them we sell parts.... not fix the crappy wiring on their old P.O.S. car they keep cobbling together.


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## Tirediron

New Holland 1049 stackliners are famous for charging problems after their first alternator replacement, they were wired for the base 37 amp alternator, which few parts stores stock so they got 60+ amp replacements, often at customer request because the lights would dim if it got left idling with the lights on, the result was overheated connections that would only work intermittently or would show continuity with a test light but won't hold a load.

Hi jack complete, take us somewhere tropical, with good dark rum


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## Thumper

OK got it to run with alternator hooked up if MAP is unplugged will have to check out MAP wiring.


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## Tirediron

Ok that is weird, the map sensor shouldn't be part of the circuit until the O 2 sensor gets to temp and the system goes to closed loop. (unless my memory is as bad as it sometimes seems)


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## LastOutlaw

linctex said:


> old p.o.s. Car


*Hey! I have cars that resemble that remark!*


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## labotomi

Tirediron said:


> Ok that is weird, the map sensor shouldn't be part of the circuit until the O 2 sensor gets to temp and the system goes to closed loop. (unless my memory is as bad as it sometimes seems)


Perhaps it's in the electrical circuit but the signal isn't utilized by the PI loop until the O2 sensor is at temp.


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## LincTex

labotomi said:


> Perhaps it's in the electrical circuit but the signal isn't utilized by the PI loop until the O2 sensor is at temp.


I suppose its possible the MAP sensor is internally shorted?

Doesn't seem likely, though... sounds like a bad ECU


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## labotomi

LincTex said:


> I suppose its possible the MAP sensor is internally shorted?
> 
> Doesn't seem likely, though... sounds like a bad ECU


I'm not very familiar with automotive control systems but with industrial it's extremely rare to not have sensors powered and active at all times. The signals they generate may be disregarded based on other conditions but would be available regardless.

I don't see a purpose for doing it in this application either.


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## LincTex

labotomi said:


> I'm not very familiar with automotive control systems but with industrial it's extremely rare to not have sensors powered and active at all times. The signals they generate may be disregarded based on other conditions but would be available regardless.


I don't know GM, but Ford sometimes uses "sensor base" on several separate busses. If you have a direct short (because some goobers shouldn't work on their own cars) on one buss, it will only take out that specific buss, but there are enough signal parameters being received from other busses to keep the processor up to date, and the car running.

I know modern cars use alternator load feedback to the ECU to adjust idle speed - More electrical load = more idle air control opening signal. Same with power steering pressure and A/C clutch engagement. If GM added sensor base from the MAP sensor to the same buss as alternator load sensing, any bad sensor on that buss would cause a fail.


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