What is this??

[87Hi-v15HND]

Haven’t been able to find much about this but I seen some one call it the advance timing circuit. I’m trying to get my engine timing set and do not know if this plug has any relevance to do so.

Can someone kind of walk me through the correct way to set the timing?

I know on the older Sbc’s you’re suppose to plug the vacuum advance port for initial timing I believe but I am unsure of the computer controlled advance timing..

Or maybe I don’t know what I’m talking about at all. I’m no mechanic, just a do it your selfer...

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[Honky Kong jr]

@1987 GMC Jimmy will know or @chengny

 

[1987 GMC Jimmy]

Hatzie mentioned this in your other post. It’s a 12V test lead for the fuel pump. You apply voltage there to test it directly. There’s a pin on the ALDL to do the same thing.

 

[Honky Kong jr]

Hatzie mentioned this in your other post. It’s a 12V test lead for the fuel pump. You apply voltage there to test it directly. There’s a pin on the ALDL to do the same thing.

I keep forgetting about @hatzie damn it.

 

[87Hi-v15HND]

Hatzie mentioned this in your other post. It’s a 12V test lead for the fuel pump. You apply voltage there to test it directly. There’s a pin on the ALDL to do the same thing.

Ok got it thanks! I must have misread that.

So I thought that had something to do with the computerized advance timing... is there a plug I’m suppose to unplug when I’m setting the initial timing?

 

[78C10BigTen]

Ok got it thanks! I must have misread that.

So I thought that had something to do with the computerized advance timing... is there a plug I’m suppose to unplug when I’m setting the initial timing?

I believe thats inside the truck up under the glove box side. If im thinking correctly. I may be thinking of the newer style.

 

[yevgenievich]

Initial timing is a single lead plug tannish wire under the brake booster

 

[87Hi-v15HND]

Initial timing is a single lead plug tannish wire under the brake booster

This one?

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[yevgenievich]

This one?

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Looks like it. Check engine light will light up when it's unplugged and timing should be steady around 0-4 at idle

 

[87Hi-v15HND]

Looks like it. Check engine light will light up when it's unplugged and timing should be steady around 0-4 at idle

Alright I’ll see what it does, thanks!

 

[hatzie]

Hatzie mentioned this in your other post. It’s a 12V test lead for the fuel pump. You apply voltage there to test it directly. There’s a pin on the ALDL to do the same thing.

Only some light truck ALDL ports have the fuel pump test terminal. It's the lower left corner terminal "G". If G is populated then it's a fuel pump test terminal on the light trucks. I believe it's only populated on the 88-98 T400 CK chassis. Some of the fuel injection Fieros, F-Bodies, Corvettes, and others had the fuel pump ALDL "G" test terminal as well. The RV chassis got the flying test lead instead.

Since the Metripack 280 ALDL port isn't a fully standardized piece of hardware like J1962 more than a few of the pinouts differ from year to year and even across GM divisions and models within divisions. Since the Acronym stands for Assembly Line Data Link it Probably had a bunch to do with which assembly plant built your particular rig. @Keith Seymore could comment on this with a bit more accuracy since he worked at GM.

A was always Ground and B was data enable and G was the fuel pump test when used.

Two different non-standard baud rates of TTL level serial data could be found on various pins depending on year, nameplate, division etc... 160 on C, D, & E or 8192 on M. Adapter plugs existed to convert data pins for the Tech 1 & Tech 1A (1981-1994) and 1991-1994 ALDL on the Tech 2. For ALDL you're better off with a Tech 1A.

 

[1987 GMC Jimmy]

Only some light truck ALDL ports have the fuel pump test terminal. It's the lower left corner terminal "G". If G is populated then it's a fuel pump test terminal on the light trucks. I believe it's only populated on the 88-98 T400 CK chassis. Some of the fuel injection Fieros, F-Bodies, Corvettes, and others had the fuel pump ALDL "G" test terminal as well. The RV chassis got the flying test lead instead.

Since the Metripack 280 ALDL port isn't a fully standardized piece of hardware like J1962 more than a few of the pinouts differ from year to year and even across GM divisions and models within divisions. Since the Acronym stands for Assembly Line Data Link it Probably had a bunch to do with which assembly plant built your particular rig. @Keith Seymore could comment on this with a bit more accuracy since he worked at GM.

A was always Ground and B was data enable and G was the fuel pump test when used.

Two different non-standard baud rates of TTL level serial data could be found on various pins depending on year, nameplate, division etc... 160 on C, D, & E or 8192 on M. Adapter plugs existed to convert data pins for the Tech 1 & Tech 1A (1981-1994) and 1991-1994 ALDL on the Tech 2. For ALDL you're better off with a Tech 1A.

Just checked my ALDL. I could have sworn I had a Pin G, but it was empty. I do have the test lead under the hood, though. Thanks for clearing that up.