Making some progress, got my 4-low switch mounted on the t-case gate today. Looks like it's going to work. Operation smooth and positive, grounds out when t-case in 4-low, no interference with boot assembly when it's installed.
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I am about to do this swap myself on a '92 GMC C2500. I found some errors in your pull sheet...
B11 -> F13 should be F12
C1 -> E15 & F15 should be E15 (F15 only needed for 7.4L Linear EGR)
EDIT: Not sure where all your confusion with the VSSB is from... Find a VSSB with 9 pins and swap it for the DRAC in your 91 suburban. you'll need to add a dip switch so you can set for your tire size/gear ratio. I don't see ANY reason in wiring in another VSSB. For my conversion I will have to run a new wire from C11 on VSSB to F13 on PCM, that's it.
Last edited by tayto; 08-15-2021 at 10:32 AM.
The difficulty with the VSSB is because I have 4wd. 91-93 4wd used 3 sensors, two input/output in trans and VSS in t-case. 94 and later dropped the trans output and got a signal for 4-low from a switch on the lever. '91 suburban DRAC is integral with the cluster so rather than messing with that to keep my speedo working right, I decided to just run a VSSB from a '94 in parallel so I could get both signals needed for F12 and F13 from that. I split the signal at the t-case VSS connector and ran a second twisted pair from there to the the new DRAC. Speedo works right and vehicle speed shows correctly from the PCM so I think what I did is working.Originally Posted by tayto
But I agree, if you're just looking at the main tab in my pull sheet it does not show what I did for F12/F13. There's another tab that shows how I wired the VSSB. I will try to correct the sheet to make it more clear and post here.
Regarding the concerns on E15 and F15 - thanks for pointing that out. I was curious why it needed two ignition feeds there. I will eliminate F15, but just curious, could it cause any issues to have it connected? (I am grasping at straws here, but am still having intermittent Code 43, knock circuit errors)
I just removed an engine & dash wiring harness from a 1990 suburban about a month ago, the DRAC was under the radio IIRC
EDIT: it was 2wd btw
Last edited by tayto; 08-16-2021 at 07:36 PM.
Hmm, maybe it's under the radio, but I'm pretty sure it's built into the cluster. I have been in and out of the dash a number of times and have never seen a stand alone DRAC, but wasn't looking hard at that time. '91 3/4 ton 4wd suburban with 4L80e was a definite enigma.
i just bought a 91 suburban cluster on ebay to go with the harness I pulled. it got delivered yesterday, unless the integrated DRAC is behind the speedo face I doubt it's there.
The DRAC on a 91 suburban is around the area that the column bolts to the dash. You need to run a VSS wire from it to the 7427 to get a speed readout to the PCM. No idea why, but this was how I had to do mine to have the MPH readout in the datastream and get the 80E to shift correctly.
94 Blazer, Turbo'd 350 TBI - DD
1991 2500 Suburban Adventure truck - 4wd conversion, 4-link F/R, 582ci CNP Big Block with Terminator X EFI backed by a 6L90 and twin stick'd NP205 t-case
2012 Porsche Panamera Turbo - Date night car :)
1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac
Cool, thanks. I'll take a look next time I have the dash apart. Is it a white, translucent box like it is on the later trucks? I just don't remember seeing it last time I was in there. But it's kind of a moot point now since I'm running a parallel VSSB from a '94 that provides the speed signals to the PCM. Seems to be working OK.
Just got done this swap on the '92 GMC I've been working on. Swap went well, about 2.5 hours all in. Truck noticeably runs and idles better. Well worth upgrade not to mention a more complete hack with more tuning options. Haven't even done a custom chip yet, seems quite happy with BNKM I got from the wrecker. Only had to add 1 wire from the VSSB to the PCM. I had a partial harness from a 93+ GM truck from years ago, it had the wire I needed and pinned in to the VSSB and connector between VSSB and PCM. I have attatched my pull sheet for others.
Last edited by tayto; 08-29-2021 at 08:56 AM.
Cool, glad it went pretty well for you. Thanks for posting the pull sheet.
On my knock count issue (different post) I've replaced spark plugs with 41-993 Delco Iridium, and tightened up the loose manifold heat stove with steel dish scrubber (per your suggestion). I also found the dipstick tube was loose. Hopefully one or a combo of those will solve my maxed out knock counts. Haven't run it yet after doing those things - also in the middle of replacing the P/S pump. Hopefully done in the next day or two. I'll post on the other post after I do.
dave, i hooked up my laptop last night a d noticed my knock counts were in the 10,000 range at idle. I think the 7060 PCM uses the older TBI ecm knock sensor? I have a newer knock sensor with a black snout that I was going to swap when I do a coolant flush.
EDIT: i re-read your orher post, I will measure knock sensor Resistance when i get home. btw my SES isn't lite but It shows ERROR. next to code 43 in Tunerpro RT
Last edited by tayto; 08-30-2021 at 07:36 PM.
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