Wiring for 86 diesel in 85 gas truck?

[Wincks2]

My 85 truck has an 86 6.2 diesel in it. Wiring is a mess. Some doesn't follow the 85 shop manual I have. Some wires are cut and hang in the air.

The 85 shop manual was in two large books plus 19 larger pages regarding wiring.

1. Anyone know whether there were relevant changes between the 85 6.2 and the 86 6.2? I have the 85 shop manual.

2. The page showing an Electronic Control Module is labelled "1985 C LD CALIF - 3 C SYSTEM - V8 AUTO - CC-TC 1-2-300" Is it relevant to my vehicle? Another covers similar ground except, I think, for a K truck, which I think means 4 wheel drive and mine is a 2 wheel drive.

3. I have two pages labelled, "FEDERAL DIESEL ENGINE RPO LH6 & LL4 & NA5/NA6" and "CALIFORNIA DIESEL ENGINE RPO LH6 & NB2". The former doesn't show an ECM. The latter does. I'm in Canada. Would I use the former?

4. Would I be correct in thinking I don't need the diagrams titled, "Electronic Spark Control' because the diesel doesn't use spark plugs?

[lindstromjd]

Originally Posted by Wincks2

My 85 truck has an 86 6.2 diesel in it. Wiring is a mess. Some doesn't follow the 85 shop manual I have. Some wires are cut and hang in the air.

The 85 shop manual was in two large books plus 19 larger pages regarding wiring.

1. Anyone know whether there were relevant changes between the 85 6.2 and the 86 6.2? I have the 85 shop manual.

2. The page showing an Electronic Control Module is labelled "1985 C LD CALIF - 3 C SYSTEM - V8 AUTO - CC-TC 1-2-300" Is it relevant to my vehicle? Another covers similar ground except, I think, for a K truck, which I think means 4 wheel drive and mine is a 2 wheel drive.

3. I have two pages labelled, "FEDERAL DIESEL ENGINE RPO LH6 & LL4 & NA5/NA6" and "CALIFORNIA DIESEL ENGINE RPO LH6 & NB2". The former doesn't show an ECM. The latter does. I'm in Canada. Would I use the former?

4. Would I be correct in thinking I don't need the diagrams titled, "Electronic Spark Control' because the diesel doesn't use spark plugs?

Sounds to me like your entire shop manual is for a gasser engine. 6.2's never had any sort of electronic controls on them; not even the newer ones. The 6.5's did, but those are slightly different animals. The only electronics I know of on newer 6.2's are for the 4l80e that some of the 1-tons came with. So...

1. There aren't any huge differences in how to wire a 6.2 of any year. Main thing you need is the hot wire to the injection pump on the front of the engine behind the timing cover, and the alternator wires, and the glow plugs. If you have manual glow plugs, you can eliminate a lot of extra wiring from the sensors in the backs of the heads that deal with automatic plugs and "after plugging" once the engine is running. Anything extra will be for sensors or accessories.

2. ECM has nothing to do with your 6.2; that would all be for a TBI v8.

3. I don't know what those would be for, but I would assume you'd use the one that doesn't show an ECM.

4. Yes. You are correct; you can ignore them.

What all else are you trying to figure out as far as wiring?

[Wincks2]

OK lindstromjd, thanks.

Re: 2. and 4.: OK.

Re: 1. and "What all else are you trying to figure out as far as wiring?"

The truck currently has manual glow plugs and a manually operated fan behind the radiator. The truck seems to be running pretty well now. Towed a camper trailer over 400 kilometers this weekend.

But because I don't know what sensors are connected I don't know whether it is running well. For example, the oil pressure meter and fuel meter are not working. I'm not sure what other ones are not working that don't have meters or lights in the cab.

So, I've been going through the truck mapping and labeling all of the wires to figure out what is present and working and what isn't.

I've been through about 80 wires so far:



Looks like about 50 wires left to go through.

Problem is I'm not sure which diagrams I should be matching my wiring to.

I thought the thing to do would be to test, add or fix the wiring, sensors, lights, etc. that would have been present if the truck was a 6.2 when it was new. Like the lights for Water in Fuel, Low Coolant, Glow Plugs and whatever other ones that are not as noticeably absent as the ones that are connected to lights on the dash board (throttle position switch? Cold Advance & Fast Idle Temp Switch? Low Coolant Switching Module?

Does anyone ever try to make these conversions the same as original 6.2 trucks?



Re: 3: Looks like some earlier research showed the LH6 means Engine Diesel 8cyl. 6.2L, NA5 means federal emissions code and NA6 means High Altitude. Don't have any note on LL4. For the other one my notes show the NB2 meaning Emission System California Tier O. I guessed the ECM is some sort of electronic controle module. There are at least two ECMs on the "California" diagram. One has the number 12020754 beside it and connects to circuits 440, (Fee, Battery - Fused), 439 (Feed Ign. Sw. "On & Crank"), 538 (this circuit is omitted from my circuit listing sheet), 902 (omitted from my circuit listing sheet), 435 (Electronic Control Module to Exhaust Gas Recirculation Solenoid), 422 (ECM to TCM Solenoid), 150 (Ground Circuit - Direct), 452 (Low Level Ground). The other has number 12020753 beside it and connects to circuits 416 (ECM 5V Reference Voltage), 488 (omitted from my circuit listing sheet), 437 (ECM to Vehicle Speed Sensor), 121 (Tachometer on Coil), 451 (Diagnostic Enabled), 417 (ECM to Throttle Position Sensor Signal), and 432 (ECM to Map Sig). I also guessed they were some kind of anti-pollution device.

I think my shop manual is the official one from GMC. It is the two on the left and the large papers shown and has an entire chapter on the Diesel engine

[lindstromjd]

If you don't have automatic glow plugs, I don't think your cold temp fast idle will work. IIRC from reading up on the wiring when I did my conversion, the cold temp fast idle gets its power from the glow plug controller. The fast idle for accessories might work if you have A/C, but I don't know how it's supposed to be wired up. I haven't gotten that far into my conversion to make everything like that work.

[Wincks2]

Looking at my diagram I can't tell whether the Cold Advance & Fast Idle Temp Switch gets power from the Glow Plug Relay & Controller - because I don't know how to read my diagram.

It is on circuits 39 and 936. Neither of those come directly out of the Glow Plug Relay & Controller, but they may indirectly. Once I understand what everything on my diagram means I will know.