86 c3500 check engine light no ecu?

[fishingdave]

I have an 86 3500 5.7 dually and the check engine light is on but truck has no computer that i can find or plug. The truck is a type m heavy duty. How can i figure out whats wrong? Also i would love tp remove all the air pump crap has anyone done this and is it worth it?

Thanks

 

[1987 GMC Jimmy]

It sounds to me like the cluster may have been swapped in from a later vehicle. The only pre-'87 square that would have had a SES light would be a half ton CA model with Computer Command Control. I don't own a carbureted square body, but I'd assume the location of the SES light is where the Choke Light would have been on an earlier model. You can test this by unplugging your choke and seeing if the light goes out. Is it still running the stock Quadrajet?

On the air injection stuff, go ahead and remove it. It'd make some room under the hood and probably make a few extra ponies. You just have to remove the pump, the diverter valve, the vacuum lines associated with it, and plug where they thread into the manifolds with the right size pipe plugs.

 

[fishingdave]

My check engine light is on top center of the instrument console. I believe its wired to the emmission control relay box .the choke light does work and thats located with the speedo. My choke light only turns when the key is in accessory shut right off when running. Is that normal? Im new to this truck so not sure whats normal or not

 

[1987 GMC Jimmy]

Top center in the bezel and not right on the cluster with the other lights? The only clusters that had lights there were diesel clusters as far as I know. It sounds like you have a cluster from a diesel or your truck was originally a diesel. You can check the eighth character in the VIN to see. 6.2's had the letter C or J as the engine code. Anything other than that would have been gas. Still, I'm not sure why all that's lighting up since you have a 350 in there now with no computer controlling anything. Maybe @CSFJ would have an idea.

 

[GTME94]

I believe the check engine light is tied into the air pump system. Mine has a check engine light (no bulb anymore) and all the air pump hardware removed. We removed it all when I bought the truck (the engine was bad when bought, I have no idea if it made any difference)

 

[CSFJ]

Could you post a couple of pics of your instrument cluster? Maybe that would help narrow down what we're dealing with.

I just went out and got some pics of the cluster lights lit up.

First from an '87 Silverado with the tbi 350.

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[CSFJ]

These are from an '84 d30 with the 6.2 j engine

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[CSFJ]

If you have service engine lights in the position where the "wait" and "water in fuel" lights are on a diesel, I haven't seen a truck optioned that way before. The only light in the gauges of my diesel cluster that ever comes on is for the parking brake. I had to check to see what the others even were.

 

[fishingdave]

Its the same as the d30 instead of saying wait it says check engine

 

[CSFJ]

hmm. might be time to decode the vin, to see what we can about it's original build.

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[fishingdave]

Its 1986 type m heavy duty 350. Gwc is 9-10k This is a dually dump truck. 1gdhc34m2gj

 

[CSFJ]

The c&c models are outside of my experience. Hopefully one of the others will chime in soon. There must be some sort of control somewhere to command that light on. I've never run across one of the ccc carbed trucks. Not sure what the control box would look like, or its physical size. I know the computer for the tbi was pretty obvious when I pulled it, but you would have already found it if it resembled that.

 

[1987 GMC Jimmy]

The CCC ECM is the same size and appearance as the TBI one so it should have been pretty obvious if it had that. I don't know why that would be on a truck of that GVW and being a non-CA truck to boot.

 

[CSFJ]

If the CEL is in the spot they usually use for the glow plug lights, I'm wondering what warning lights are in the bottom of the gauges.

 

[chengny]

My check engine light is on top center of the instrument console. I believe its wired to the emmission control relay box .the choke light does work and thats located with the speedo. My choke light only turns when the key is in accessory shut right off when running. Is that normal? Im new to this truck so not sure whats normal or not

1. That is correct operation for the CHOKE warning light. It is extinguished when the engine oil pressure reaches about 10 psi - so consider it as a low oil pressure "idiot light".

2. Your truck was equipped with a Heavy Duty Federal Emissions package. Which consisted of a very rudimentary ECM,

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that had two input connections (engine speed from the tach terminal on the distributor and a temp sensor on the air cleaner). It only controlled two diverter valves. There were two air pumps, a decel valve and associated plumbing.

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There was also an EFE system and a nearly indestructible dual stainless steel exhaust (with no cats) - a beautiful setup.

3. As far as the cluster arrangement - I don't know whether you will be able to read my chicken scratches below - but they say:

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Under the speedometer: 4WD (L) & Choke (R)
Under the Gas gauge: It says Seat Belt/ Parking Brake (L & R)

As you are aware, the CEL warning was inserted into the center hole above the cluster and was not wired through the printed circuit - it (along with the 4WD light) had segregated power and ground connections.