upgrade to '7427 from '7060 - ready to pull the trigger

[Daveo91]

EDIT 5/3/21: revised attached spreadsheet to latest version with all edits discussed in this thread.
EDIT 11/7/21: revised attached spreadsheet to latest version - updates made to connections at terminals F12,F13,F15 on '7427 PCM


Well I'm finally ready to do this upgrade and have all the plans and materials (I think). I was held up for a long time by the 4L80e in my '91 Burb since I thought it used the Bosch style force motor with required cleaning cycle. Found the good news this week that it's actually the next gen Holley force motor in there so it seems like I should be OK to move forward with the swap. (It's actually a '93 Goodwrench replacement tranny) I have PCM, red/blue connectors, and BIN that should be a good starter for a vortec 383. Time to start the re-pinning project. I used the '91 and '94 G30 with 4L80e pinout diagrams in the two attached zip files to create the attached Excel pin mapping chart. If you go into the Excel it may be confusing at first glance. The 7427 pin addresses are in the middle columns and then you work outward from there to description, origin, wire color, and finally the 7060 addresses in the outer columns. I've double and triple checked what I can and am 99% sure I have everything correct on the 7427 side since there are multiple sources to use for validation. The 7060 pinout is harder to verify with fewer sources available. My plan is to verify wire color as I go along and if there's any disagreement I will have to trace it out and make sure origin is what I think it is.

Not asking anyone to do a detailed check, but if there is something glaring that I'm doing wrong ,or something missing, please point it out. And who knows, maybe this will help someone if there's anyone out there that needs to upgrade from a '91-'93 '7060 PCM.

Many thanks to Dave W for the help, pinout files, BIN, selling me the PCM and connectors, etc.

[1project2many]

You've got a nice chart with great notes for reference. I like it.

When doing an ecm swap I used to find muself checking and rechecking "from" and "to" columns. This was made more difficult depending on how much information was on the reference sheet. Here's a format I currently use as the instruction sheet for the actual swap. I start with the first pin of the old connector and move through each pin to the last. I deal with each wire as fully as possible when I get to it. I will make notes such as "remove from harness" or "repurpose for ..." The marks --> indicate that a terminal should be physically moved. I build it in Excel using three columns and large boxes so there is plenty of white space. I color alternating rows or use alternating fonts to help keep track of the line I'm on. I find this simple format to help me keep track of what's been done and I cross off each step as its completed.

7060 Notes 7427
A1 --> F6
A2 --> E8
A3 --> E9
A4 --> E11
A5 Not Used XX
A6 Remove from Harness XX
A7 --> E6
A8 Not Used XX
A9 Not Used XX
A10 Not Used XX
A11 --> E1
A12 --> E13
B1 Not Used XX

I became confused trying to follow your chart through the VSS pin changes. It appears that you are listing A10 as one of the 7060 TOSS pin locations while the posted image for the 91 FSM shows A10 as unpopulated. You also list B5 as the TOSS signal although the '91 service manual page you've included shows this to be for 4wd vehicles with B11 being used with 2wd. And pin B6, which appears in the manual to be TOSS ground, does not appear in your chart. Not saying you're wrong, just noting inconsistency.

[Daveo91]

You've got a nice chart with great notes for reference. I like it.

When doing the a swap I used to find muself checking and rechecking "from" and "to" columns. This was made more difficult depending on how much information was on the reference sheet. Here's a format I currently use as the instruction sheet for the actual swap. I start with the first pin of the old connector and move through each pin to the last. I deal with each wire as fully as possible when I get to it. I will make notes such as "remove from harness" or "repurpose for ..." The marks --> indicate that a terminal should be physically moved. I build it in Excel using three columns and large boxes so there is plenty of white space. I color alternating rows or use alternating fonts to help keep track of the line I'm on. I find this simple format to help me keep track of what's been done and I cross off each step as its completed.


I became confused trying to follow your chart through the VSS pin changes. It appears that you are listing A10 as one of the 7060 TOSS pin locations while the posted image for the 91 FSM shows A10 as unpopulated. You also list B5 as the TOSS signal although the '91 service manual page you've included shows this to be for 4wd vehicles with B11 being used with 2wd. And pin B6, which appears in the manual to be TOSS ground, does not appear in your chart. Not saying you're wrong, just noting inconsistency.

Awesome, thanks. Feel free to take the excel template if it's useful. And I like your idea of making the simpler chart in Excel for installation instructions. I think I'll do that and also have the more detailed chart on hand for reference.

Regarding the inconsistencies. Thanks for taking a look at these. On A10 for the 7060: I see what you're referencing on the FSM, but on sheet 4 of the 91 G30 wiring diagram it shows A10 connected to a terminal on the DRAC with a brown wire. Or am I not reading that diagram correctly?

On B5 and B6 for the 7060: you make some good points - I need to do some more research this weekend. I think I'll just have to study existing state on my truck before I tear into it. I do have 4wd - in fact the VSS connections are the most confusing part of this whole conversion. My truck has two sensors on the trans, plus one in the t-case. But I think the 4wd trucks that used 7427 just had one sensor in the trans? Will I just not end up using the sensor at the output end of the trans?

[1project2many]

Yes, the diagram shows A10 being used while the more generic pcm pinout shows it unpopulated. In some cases when this happens both pins are connected internally so it probably won't hurt to use an ohmmeter to check the connections. And yes, definitely confirm every wire location on the vehicle as you are making changes.

As the model years went by the TOSS was removed and a calculated TOSS value was created using VSS and gear ratios. For those calibrations it was imperative to know if the transfer case was in low range in order to scale TOSS correctly. You should use a calibration that matches the vehicle wiring. I am thinking that it would be best to stay with the '94 wiring.

[Daveo91]

Yes, the diagram shows A10 being used while the more generic pcm pinout shows it unpopulated. In some cases when this happens both pins are connected internally so it probably won't hurt to use an ohmmeter to check the connections. And yes, definitely confirm every wire location on the vehicle as you are making changes.

As the model years went by the TOSS was removed and a calculated TOSS value was created using VSS and gear ratios. For those calibrations it was imperative to know if the transfer case was in low range in order to scale TOSS correctly. You should use a calibration that matches the vehicle wiring. I am thinking that it would be best to stay with the '94 wiring.

OK, I've done a bunch more digging today - answered some questions but also created additional.

1. I think you're right on the 7060 A10 pin. Looking at the existing connector for the 7060: A10 is unpopulated but there is a brown wire at B11. So I think this should be mapped to F12 on the 7427. But is this correct since I have a 4wd and the service manual says it's for 2wd?

2. 7060, Pin B5. There is a light blue wire on existing B5 connector that I'm fairly certain goes to the rear sensor on the trans, along with the dark green/yellow wire at B6. (I will need to check with multimeter for continuity on esp. light blue wire - the color is faded and I'm not 100% sure it is the same wire that is on B5. If so does it seem correct that I have this mapped to F13 on the 7427?

3. 7060, Pin B6. There is a dark green/yellow wire at B6 that again I'm pretty sure goes to the rear sensor on the trans. So I agree this needs to be mapped to something on the 7427, but where. I have looked at all the available connections for the 7427 and it's not obvious where it should go? FSM lists B4 for 7427 as "Sensor Ground MAP, EGR, Transmission" Would it go here? (sorry if this is a dumb question)

4. A more general question. How does the 7427 know if the t-case is in 4-low? On the 7060, I presume it knows 4-low if it sees a difference between the output trans sensor and the t-case sensor. But on the later PCM, there was no rear trans sensor so I presume the 4-low input became a binary value, on or off? Where does that signal come from? Will I have to mimic it with my installation?

5. My t-case sensor has a purple/white wire and a green/black wire. I see that the purple/white goes directly to the DRAC, but is that where the green/black wire goes as well?

[Daveo91]

Well I have the answer to at least question 4 now. This thread (http://www.gearhead-efi.com/Fuel-Injection/showthread.php?2826-7427-Rev-limiter-4L80E-question&) helped a lot, especially 3rd page. Pin F8 on '7427 is the 4-low signal - if it get's grounded out, then PCM knows it's in 4wd. The reason I missed this when I was doing my mapping is I was looking at FSM and wiring diagrams for a G30, i.e. no 4wd options.

So it seems like I just need to figure out a way to ground out F8 when t-case is in 4-low. Might have to get creative as I don't think my t-case or lever has any electrical trigger for when it's in 4-low. No additional lights come on and PCM knows by looking at differential between rear trans sensor and t-case sensor. maybe I can devise a momentary on switch that goes to ground when the lever is moved to 4-low? Go to junkyard and look for the switch on a '94 or '95 with a t-case lever? I'm not sure I'll have any luck finding a ready-made solution since I'm sure my case of upgrading a squarebody to a 7427 is pretty rare.

Still need to figure out answers to the other questions. I'm pretty sure I'm OK on #1 and #2, number 3 is the one I'm most concerned about. Not sure where to map 7060's B6 on the 7427.

[Daveo91]

I've redone my Excel for the '7060 to '7427 conversion. I added a sheet that starts with pin A1 from the '7060 with description, wire color and mapped pin on the 7427. Should be easier to use during the actual re-pinning procedure as @1Project2Many recommends.

The questions I still have regarding this conversion have been consolidated down to those associated with the 4wd speed sensor differences between the '91-'93 7060 and the '94-'95 '7427.

7060 has five pins associated with speed sensors: B5 and B6 from rear (output) trans sensor, B9 and B10 from front (input) trans sensor, and B11 from DRAC which comes from sensor on output of T-case.

7427 also has five pins for speed sensors, but some differences: F2 and F3 from input trans sensor (map to 7060 B9 and B10), F8 is a 4-low signal from the t-case lever (grounds when in 4-low), F12 is trans output speed that comes from DRAC, and F13 is called vehicle speed signal but also appears to come from DRAC.

- Trans input speed sensor connections are easy. Direct match between old and new PCM. Wire colors are even the same.
- 4-low signal at F8 is also easy. To figure out at least. I have to add a switch at the T-case lever that will ground that signal when lever is moved to 4-low. I have a plan that I think will work.
- It's the connections at F12 and F13 where I get fuzzy. At F12 I currently have it mapped to 7060 B11, but I'm not sure that's correct? I did it that way since they are both brown wires that come from C13 terminal on the DRAC.
- My main question though is F13. on 7427 this is a dark blue wire that also comes from the DRAC (Pin C11), but on the 7060, there's only one wire that comes from DRAC. I could map 7060 B5 (trans output) here, but not sure?

Why does the 7427 need two signals from the DRAC? In reading, it seems like one is 40 pulses per rev, the other is 2000 pulses per mile? Can I get both signals from my '91 DRAC? Or do I even need the second signal? (I did go to pick-n-pull and bought DRAC from a 1/2 ton '94 4x4 Burb. But then I'd have to reprogram that to get my speedo correct?)

One more question: does anyone know where the DRAC is on a '91 squarebody suburban? I'm not seeing it mounted by the PCM and I recently had the gauge cluster out for something else and I don't remember seeing it in there, but I wasn't looking for it. Maybe behind the radio?

[brian617]

Some years of 4l80 4x4 had three speed sensors, input, output, and vss on t-case and some only two, input and vss on t-case. The 4x4 ground input is used on the two speed sensor trucks for couple of reasons one being that it wont set gear ratio error codes for output shaft speed in 4x4 low.

91 suburban has DRAC integrated into cluster if i remember correctly.

[Daveo91]

Some years of 4l80 4x4 had three speed sensors, input, output, and vss on t-case and some only two, input and vss on t-case. The 4x4 ground input is used on the two speed sensor trucks for couple of reasons one being that it wont set gear ratio error codes for output shaft speed in 4x4 low.

91 suburban has DRAC integrated into cluster if i remember correctly.

Thank you - that makes sense that the DRAC is integrated into the cluster. I remember a bumped out section on the back which is probably where it is.

I understand the 3 sensors (7060, 91-93) vs the 2 (7427, 94-95). My question is how to make the 7427 play with the sensors, wiring and DRAC from 91-93 setup. Essentially, I have ONE brown wire coming from DRAC with a speed signal on it, I'm now reasonably confident that goes to F13 on the 7427. (my wiring diagrams in previous posts had it going to F12) But now I need to know if F12 needs to have a signal on it or if I can leave it blank.

Have since read and reread the 7747 to 7427 conversion thread (http://www.gearhead-efi.com/Fuel-Injection/showthread.php?173-1227747-to-16197427-Conversion-PCM-Swap-with-Wiring-Pinout-Directions!&highlight=16197427). tons of good info in there. I know that:

F12 is looking for transmission output speed, needing 40 PPR.
F13 is looking for VSS, needing 2000 PPM.

Do I need both or will supplying the VSS that comes from the DRAC to F13 be sufficient for 4L80e? If I do need the 2K PPM on F12, how do I get it? would my '91 vintage DRAC that's built in to the cluster be able to supply that? Or can I take it directly from the rear trans OSS?

Thanks for the help

[Daveo91]

After a lot more research I think I have a plan going forward. I have a VSSB/DRAC from a '94 suburban that I will wire in parallel to the original DRAC. New DRAC will provide both inputs to the PCM (pins F12 and F13) and will probably eventually provide the output for cruise when I get that working. Original DRAC will just provide output for speedo. Using the info and calculator on the DRAC page on TBIchips.com, it looks like I will need to move two jumpers around based on my tire size and gearing.

I will have to splice in a new twisted pair for the two wires from the T-case VSS to feed the new VSSB. Any suggestions where/how I should do the splice? Wiring will be as follows for pins C7-C15 on the VSSB:

C7: VSS Input, lt grn/blk (twisted pair with C12, from t-case VSS)
C8: engine ground, blk/wht
C9: 12v power, hot in RUN, brn
C10: ABS (won't use), wht
C11: VSS Output to F13 on 7427, dk blu
C12: VSS Input, ppl wht (twisted pair with C7, from t-case VSS)
C13: VSS/Trans Output to F12 on 7427, brn
C14: Cruise control (won't use initially), red/wht
C15: Speedo input (won't use), lt blu/wht

I revised the original post by deleting the excel attachment and replacing it with my latest version that has all edits and the added sheet for new VSSB wiring.

[brian617]

I recently did a 0411 standalone swap in a 95 c2500 6.5 diesel with 4l80e. I stole my output shaft speed (VSS) from the DRAC plug by depinning the connectors and soldering my new twisted pair on top of the pin crimps, sort of piggy backing them and re-pinning. I left the DRAC functional for the speedo and ABS.

[Daveo91]

I recently did a 0411 standalone swap in a 95 c2500 6.5 diesel with 4l80e. I stole my output shaft speed (VSS) from the DRAC plug by depinning the connectors and soldering my new twisted pair on top of the pin crimps, sort of piggy backing them and re-pinning. I left the DRAC functional for the speedo and ABS.

Perfect, thanks. I think I'll do this too. I got the connector at the t-case apart and I think I should be able to poke the new wires through the weatherproof stoppers and then solder the ends to the existing crimps. And I also found, in the engine harness from a '90 4x4 burb I had years ago, a twisted pair of green and purple wires that I'm sure were the wires from the t-case VSS in that rig. The existing VSS wires meet up with the main harness on the driver side of transmission; I think I will run the new twisted pair up the pass side to keep the two pairs well away from each other.

Thanks for the advice!

[Daveo91]

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.

16735

16736

[tayto]

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.

[Daveo91]

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.

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.

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)

[tayto]

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

[Daveo91]

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

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.

[tayto]

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.

[1BadAction]

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.

[Daveo91]

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.

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.

[tayto]

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.

[Daveo91]

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.

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.

[tayto]

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