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91 S10 computer help

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Old 11-14-2010, 01:40 PM   #1
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91 S10 computer help

I have a 1991 S10 2.5L 5speed manual 2wd truck. No A/C or Cruise control. It runs like crap. The idle goes up and down and not in a predictable pattern. I've used my SunPro sensor tester on every sensor I could get to. The O2, manifold air temp, manifold air pressure, tps and water temp sensors all tested good or were replaced, the water temp was replaced. I had to put a new fuel pump in the fuel tank. I also put a new fuel filter, new plugs, wires,cap and rotor and still not idling well. Have to keep a gear lower and rpms up to keep it from chuggin on the road. Been this way since I bought it. The computer would not send codes for the check engine light that's on when running. I unhooked the battery, removed the computer and the prom then reinstalled everything and still doesn't send the codes. The service number on the computer that came in the truck is 01227165. A got a pair of computers from a guy with a bunch of S10 parts, but he wasn't sure what engine/trans combo's they came from. They both have service number 1228062 on them. The numbers under the bar codes are different however. I put one of the 1228062's in my truck and got it to start and run. I used my gm code reader to test the running modes of the truck and watched the check engine light flash steady 2 beats per second, meaning O2 sensor wasn't sending a signal yet, then started flashing slow with different speeds. Meaning 02 sensor was working and truck was fluctuating between running right, running lean and running rich and over and over again. I shut the truck off, pulled the jumper out and started the engine again. It idled high, although didn't go up and down like before. The check engine light was on. I shut it off and put the jumper back in then turned the key to run. The check engine flashed codes 12 and 43. Which my book shows as "Electronic spark timing (EST) circuit - low voltage detected OR Electronic spark control (ESC) circuit problems. Just wondering if any of these ECM's are correct for my truck and what do I check next?
Old 11-14-2010, 01:42 PM   #2
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Re: 91 S10 computer help

Forgot to mention I already replaced the EGR valve with a new unit.
Old 11-14-2010, 05:48 PM   #3
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Re: 91 S10 computer help

What brand of fuel pump and EGR did you install?

Were these ECM's supposed to be for the old duke?
Old 11-14-2010, 05:53 PM   #4
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Re: 91 S10 computer help

This may help...

http://www.exatorq.com/ludis_obd1/c3xref.html

Looks like it is a V6 ECM

1228062

Application:1988-93 truck 2.8 V6 TBI “R” LL2
1988-91 truck 4.3 V6 TBI “Z” LB4 w/ AT (“S” & “T” body)
1989 truck 2.8 V6 TBI “R” LL2 (Isuzu)
1990-91 truck 2.8 V6 TBI “R” LL2 (Isuzu)MEMPAK IDs:…CALPAK IDs:…Program ID:78 ($4E)Pgm ID Addr:$D004Scan ID Addr:$????:$????EPROM type:2732EPROM offset:$D000

Last edited by lesterl; 11-14-2010 at 05:55 PM.
Old 11-14-2010, 06:10 PM   #5
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Re: 91 S10 computer help

full 12 volts to the FP? check at tank and make sure!

try another FP relay sometimes they die too

remove and clean the IAC and the hole in the TB unit of all carbon crap

this controls idle speed variably very important

replace any ignition parts over a year old especially if you can see wear or carbon powder on any

this is like the second time ive heard of a 91 with a 2.5L thats really odd must have been an early 91 thing?

AFAIK 2.5L was last in '90

hmm

well good luck
Old 11-14-2010, 06:14 PM   #6
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Re: 91 S10 computer help

1993 was last year for 2.5l

1991 was last year for E code 2.5l, 1991-1993 were A code motors (few extra HP.) IIRC.
Old 11-14-2010, 06:42 PM   #7
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Re: 91 S10 computer help

I bought the EGR valve and fuel pump from Napa. It is an "A" code engine. I was doing some searching online myself on the computers I have and from what I've found so far the 1227165 unit that was in the truck when I bought it for a 1986 TPI 5.0L V8 engine. Not sure if that research is correct. I'm not a computer expert but would think a computer for a V8 wouldn't work well in a 4 cylinder. The research I've found on the 1228062 computers I got today to try look like for a 1989-1990 4.3L V6. Can Computers be used with different cylinder engines if the removable eprom/prom are switched? Or are the ECM and Eprom/proms mated to each other. Also this past week I've been having trouble getting it to start when cold. Been having to spray a little gas into the top of the TBI to get it started. When warmed up I can shut it off and restart but it won't start cold. I put a new fuel filter this past week since this problem started. While I had the fuel filter off, I turned the key on just to see if any fuel would shoot out of the fuel and none did. The pump did run it's normal cycle when the key was turned on. I'm getting close to breaking point with this engine, lol. Does anyone know if an Oldsmobile 4.3L V6 diesel engine from a front wheel drive car will bolt in place of the 2.5L A-code gaser? lol
Old 11-14-2010, 08:11 PM   #8
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Re: 91 S10 computer help

I know u dont wanna put anymore money into this thing but go buy another computer. Thats wat I will do or search craiglist.
Old 11-14-2010, 08:34 PM   #9
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Re: 91 S10 computer help

If you arent getting gas, a new ECM wont help.

That being said, I think you stumbled upon one of your issues fuel delivery....

If the pump isnt running, check for the ground on top of the frame rail behind the drivers rear tire, sometimes it can corrode or break. For that matter check and make shure you get 12v back to the pump.

As a side note, the pump will only recieve power when you first turn the key to run for 4 seconds it will run to prime. The pump will run again when the engine fires (or the oil pressure comes up.)
Old 11-14-2010, 08:49 PM   #10
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Re: 91 S10 computer help

I looked up that part #1227165 at work and it is the right computer for ur trk it actually fits a lot of vehicles like camaros,cavaliers and even postal vehicles. Just letting u know
Old 11-14-2010, 09:01 PM   #11
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Re: 91 S10 computer help

It's too dark to do anything more tonight. I'll remove the IAC tomorrow and clean that. It's about the last thing I haven't cleaned. To make things clear. When I turn the key to the run position but don't "start" it, I do hear the electric pump in the gas tank whirring for about 4 seconds then it shuts off. If I turn the key back to off then wait a few seconds and turn back to "run" the pump whirs again for about 4 seconds then shuts off. So the pump is running. I'll try to test if I'm getting 12volts to the pump tomorrow. After than I'll see if I can figure out a way to test the fuel pressure. Don't see a shrader valve on any of the fuel lines. Anyone know if the 1228062 ECU's are compatible with my 91 A-code 2.5L 2wd, 5 speed truck? On a side note, why will it run after squirting some gas into the TBI to get it started but won't start on it's own? Is there something that forces the injector to spray gas at start up that is separate from spraying gas while running?
Old 11-14-2010, 09:10 PM   #12
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Re: 91 S10 computer help

It is probably a fuel pressure thing.

Check post 4 on the other ECM....
Old 11-14-2010, 10:21 PM   #13
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Re: 91 S10 computer help

check the 1228062# and it shows to fit 88-93 v6 only no 4 cyl.
Old 11-17-2010, 09:26 AM   #14
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Re: 91 S10 computer help UPDATE

Went to a salvage yard yesterday and bought a computer from what they called a running truck. $50. They told me it came from a 4 cylinder 5 speed truck and was compatible with a 1991 S10 A code engine. They told me this while looking at their computer screen. This is a salvage yard that does not let people pick their own parts. They say it's insurance related. Also they don't give any kind of warranty whatsoever. The computer looked the same as mine with a couple exceptions. First it was painted black. Mine is not painted and made of aluminum. Second, there were no stickers or tags anywhere on the computer. Mine has a couple stickers/tags with service numbers, bar codes and some other numbers. Now with my computer the truck starts and runs but idles all over the place. With a V6 computer I tried last week it would start and run but idles up and down, though not as much with the original computer and the idle seemed a bit higher. Now, with the recent computer the truck will pop once when I start it then nothing except a strong gas smell from the engine. I tried starting it a couple times. The first time it popped then never popped again. I noticed the exhaust manifold was wet and smelled of gas so I pulled the plugs. They were wet. I unpluged the coil to cap wire and turned the engine over with the plugs out and it was like a garden hose spraying out of the rear most cylinder. They all blew gas out but the rear cylinder had the most by far. So I cleaned the plugs, gapped them to 45-50, they were at 60, and let the truck sit overnight. This morning I put the plugs back in, re connected the coil to cap wire and tried to start it. Again, one pop, then nothing. Would just turn over and again a strong gas smell. I'm getting the feeling I'm just throwing crap on the wall and hoping something will stick.
Old 11-17-2010, 08:53 PM   #15
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Re: 91 S10 computer help

The Black ECM is a reman.

Sounds like the injector driver in the ECM could be shorted?

Pull the air cleaner off and have someone crank the engine while you watch the spray pattern from the injector with a good flashlight.

BTW dont buy parts at a salvage yard to try to troubleshoot with....... you could get screwed.....
Old 02-07-2012, 07:11 PM   #16
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Re: 91 S10 computer help

Just curiouse if he OP ever figured out his problem.... lol
Hate resurrecting a posting that's over a year old but his problems sound like mine.
I need to test my fuel pressure as while replacing parts chasing this elusive idle problem
i bought a new fuel filter then discovered that previouse owner deleted it!!! which leads me to believe fuel pressure was low and wouldn't run with a filter in place, quick bandaid so he didn't have to replace fuel pump.
lol, side note...... Lester, I will be checking fuel pump ground first and then it's voltage, Thanks for that good sound advice
Old 02-07-2012, 09:25 PM   #17
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Re: 91 S10 computer help

Check the injector filter. Without a fuel filter, I'd bet money that little ring of screen is packed solid with crud.
Old 02-07-2012, 11:03 PM   #18
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Re: 91 S10 computer help

Quote: Originally Posted by Blkwdw86
Check the injector filter. Without a fuel filter, I'd bet money that little ring of screen is packed solid with crud.
Ok, will check that, didn't know that there was such a thing. I never really messed with fuel injection much so my knowledge is a little limited when it comes to this, now with that being said....... where's the injector filter? I can see the injector atop the throttle body but not sure where the screen would be, will I need to remove injector or is the screen where the fuel line meets the TB?
Thx
Old 02-07-2012, 11:44 PM   #19
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Re: 91 S10 computer help

Could get a TBI kit, it will come with gaskets and the screen and such.
Old 02-08-2012, 08:24 AM   #20
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Re: 91 S10 computer help

IIRC, the injector filter sits in the cover on top of the injector and is a last line of defense against debris entering the injector through the fuel flow from the pressure regulator.

I'm with Lester on that one, teardown, cleaning, and rebuilding the TBI is never a bad thing. That the truck went so long without a fuel filter (!!!), I'd call it necessary.
Old 02-08-2012, 11:22 AM   #21
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Re: 91 S10 computer help

I took apart the fuel pressure regulator to see what it looked like, just to see if any debris was in it but it turned up spotless, nothing on the inside or rubber diaphram.
Would places like advance auto or NAPA sell these kits? or is it a dealer item? I'll check advance autos web site when I get the chance
Old 02-08-2012, 09:31 PM   #22
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Re: 91 S10 computer help

last tbi kit I bought was from advance for a 4.3l ran $21.....
Old 02-09-2012, 10:10 PM   #23
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Re: 91 S10 computer help

Quick question, I removed the injector's retainer to pull the injector but it seems to be stuck, something else hold this in or do they get hung up often? I didn't pry HARD as I didn't want to break anything but I pulled it hard enough to where it should have came out.
Old 02-09-2012, 11:07 PM   #24
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Re: 91 S10 computer help

Ya have to pry up pretty hard, a large flat bit and a fulcrum work wonders.
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