1990 GMC FS Jimmy/ Timing Q & Haynes manual

On the firewall, directly above the distributor, is a large plastic cover. It has two large plastic wingnuts that hold it on. Inside, you will find a relay and a terminal block. Somewhere in there, you will also find the tan (or tan/black) wire with an inline connector similar to what you find on the O2 sensor. Disconnect that and set timing to 0 for starters. You can bump it up a little from there if you've got a little wear on the timing chain. It will set a code when running, so clear it out when you are done.

I haven't gone out to the truck since your post, but if I had seen a cover like that at the time I was looking I would have inspected it. I see no cover what-so-ever anywhere. I have an OEM under-hood light on a 20 foot retractable cord where the manual says my cover should be. Thank you for you help.....

~KJ~

Ah, forgot. The 90 Jimmy is still on the old 87 body style. Look in the plastic sleeve over the brake booster or somewhere near the steering column where it exits the firewall near the bulkhead connector. It should be in the same place it is on the 87 pickup, if your book tells where. And it should be tan/black, IIRC.

HOT damn! Now were onto something. I don't remember seeing anything like that the last time I opened it up, but I wasn't looking for it. So I guess I got the wrong manual here don't I?

~KJ~

Unfortunately, you have one of those bastard year vehicles the Haynes and Chilton's books don't cover even as poorly as normal. 88 through 91 suburbans and FS blazers used a bastardized wiring harness more similar to the 87 model FI trucks than the 88 and later trucks. Getting good info on them is tough outside of the factory manuals. There is a wiring diagram for the fuel injection system in the book for the 81-87. I have the Haynes book for those years, and it really, really sucks. If you have ABS, the wiring for that unit is similar to the 88 and later trucks. As far as the FI system, though, it's very similar to the 87. One difference you might see is you probably have the later model terminal block on the firewall with 4 terminals on it. If your model has the terminal block with 2 studs on it, then the 87 wiring diagram should be a perfect match. Fortunately, the only major difference is the presence or not of an air pump (it has an air control solenoid on it). The VSS circuit and the cruise (no speedo cable) are from the later year vehicles just to keep things fun. I had a 90 4WD Blazer for a short time and I can give you a little help if you have anything else specific. Keep in mind that changes were made within model years during this period as GM ran out of parts or changed things to keep up with the new regs or features.

I knew I shouldn't have bothered to get a book! I find everything I need to know on here, just thought this might keep me from waiting....

~KJ~

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I've been talking to DOC off the NG and he and I can't find it still. It's not within that sleeve, unless it is in one of the shrink wrapped looms. I'm wondering if the "Typical 1988 through 1995 engine controls" page in my Haynes will apply? It says it's a PCM - I *think* my truck has an ECM? Basically what I am planning on is finding it at the PCM/ECM, cutting it and putting in a switch, labeling it & making things that much easier in the future.

~KJ~

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Don't get all Elliot on us. There is a four pin connector on the dist. It has blk/red, tan/blk, wht, and ppl/wht wires, in that order. That tan/blk (or whatever color it is on your truck) is the wire your looking for. Get the color there, then look around. I've heard rumors that they were sometimes up near the computer, under the glovebox. But AFAIK, my

90 350 Auto K5 had it near the steering column. It was taped along side of a bundle of loomed wire, but it was outside the loom. Might be tough to spot. Run your hand down the big bundle that comes out behind the left valve cover and follow it up to the bulkhead connector.

BTW, on that truck, the computer wire is pin D5.

Sorry, your real world exp wont help here. Thank you for the input.

~KJ~

,

In all honesty, I thought you would call me Elliot. But hear me out, I don't think my reasons are too exotic. I can see the tan wire on the Dizzy, Haynes did help me with that. But I can't find it anywhere that anyone suggests. I have attempted briefly to follow it in the loom (that looks non-OEM now...) without much success. IMHO if this switch runs directly to the ECM/PCM (is it a PCM or an ECM?) then I should be able to put a switch on it, clearly label it, then stick it way up under the dash w/ the xCM. Then checking the timing at tune up time will be easier, and I wont go tearing my nice 'neat' looms apart. If you would like, I have some pictures of the engine compartment that I sent to Doc. Thank you for the help thus far!

~KJ~

No, just warned of possible Elliot like behavior. It wasn't personal, or nuttin...

They probably wrapped it up with the other stuff when they rewrapped.

It's ECM. Sounds like a plan to me. If I were to do it myself, I'd do it in the cab where the splice isn't exposed to the weather. The wire makes a sort of loop to give just a little slack when you pull the computer, but you aren't going to get enough slack to put a connector in there at a convenient location without adding wire, too.

Anyway, Doc's got you straight. Later.

Start accepting that you don't know everything. I can't tell you how much I've learnt here and I still haven't even grazed the surface. I was (am?) cocky when I first came on here - I accepted that my limited knowledge wasn't going to impress anyone and decided to sit back, wait, and learn.

~KJ~

There are many, many fields of automotive work where I don't know the answers. I usually let the guys that do this for a living handle those. But there are a few areas I am well versed in, and can sometimes explain it in a matter that those are not so used to doing this stuff can understand. There's a lesson there you should learn.

I repeatedly gave you some simple one and two step tests, asked you to perform them, and post back results. You didn't listen, and always went for oddball solutions. This doesn't just apply to me, but also to people with credentials longer than your arm on this group. And all we want to do is help.

At the beginning of the Isolating... thread, you claimed:

"Yea my degrees are in electrical engineering. More pertinent to this activity is that I also have a 2 year AAS-EET degree in electrical technology. "

Yet you show nearly complete ignorance of electrical systems, especially troubleshooting. I'm an EE, too, with a lot of continuing education in the mechanical engineering field. I've also been to classes from Kubota and other engine manufacturers and now do instrumentation work, among a myriad of other things. It's obvious to me you have no skills whatsoever in the electrical field other than basic electricity. Troubleshooting the way you do speaks volumes. If you want specifics, I'll list them, but the O scope you were thinking about buying speaks for itself (1). You've made too many statements on this group that haven't the faintest glimmer of correctness to them, and still continue to give advice on things you have absolutely no idea about.

If you want to get along here, learn to listen. If you don't have a clue what you're talking about, don't give advise. You don't have to answer every post. Read this stuff and apply it. If you know better then don't bother asking, or at least say "Thanks" and move on to the next post.

(1) you'd considered buying a 40 to 60 dollar scope on ebay. Those one channel jobs are absolutely useless. Anyone that has seen a scope and used one knows that 2 channels is the minimum for doing any level of troubleshooting, and even the cheapest Tenma 2 channel units run 300.

You still haven't looked behind the PS kick panel like I suggested have you?

Doc

the PCM or Powertrain Control Module.. wasn't used until the 4L60E (i.e. 1993).... was just a plain old ECM before that.

-Bret

i think it is just below the brake booster inside the conduit. tan w/ a black trace is the right color. -Pete

1990 GMC FS Jimmy/ Timing Q & Haynes manual Group: alt.autos.4x4.chevy-trucks Date: Wed, Apr 7, 2004, 12:42am (EDT+4) From: snipped-for-privacy@yahoo.com (KJ) 1990 GMC Jimmy Full Sized SLE 350CUI TBI TH700R4 NP241 I would like to check the timing/advance the timing. Am planning on attaching a vacuum gauge and adjusting it forward until the highest/steadiest vacuum is achieved. However I cannot find the 'tan' wire for the spark advance. Haynes says it is under the "relay protective cover" or some shit like that on the fire wall. I see two pig tails on the dizzy, both have two wires. Can't easily follow any of those wires, and none of them are tan anyways from what I can see. The Haynes manual I got is for; Chevrolet & GMC Pick-ups 1988 thru 1998 All Models 1990 and 2000 C/K Classic 2WD and 4WD All Gasoline engines Includes Suburban (1992 thru 1999) Full-size Blazer & Jimmy (1992 thru 1994), Tahoe & Yukon (1995 thru 1999) I know the 1992 through 1994 Jimmy/Blazer is NOTHING like mine, but I felt it would fall under the 1988 through 1998 selection since it is basically a K10 with a cap. Think I should try to find a better match, or is the best there is from Haynes? ~KJ~