What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

4l80e to NV4500 ECM Questions..

mckustomfab

mckustomfab

1/2 ton status
Joined
Jan 24, 2005
Posts
317
Reaction score
306
Location
Carrollton, Tx
Here is a ECM/PCM question.

I have a 1991 R/V 3500 (4x4 Conversion) currently I have the 2wd 4L80e still hooked up so the truck is mobile but it is starting to slip. I also have a NV4500 and NP205 that I have been collecting parts for. The NV4500 was originally going to be for my Cummins swap but the time frame on that has slipped some.

Now i said all of that to ask this...
If I swap out the 4l80e for the NV4500 what ecm/pcm problems will i have? I know the '91 4l80e ecm/pcm is different then the diesel or 700r ecm. I have spoken to a few TBI shops one told me it would drive but it would slip into limp mode and only go to around 1200rpms. I also have the parts to install the tone ring into the 205 tailhousing for the VSS. I started researching and after looking at some ECM pin out diagrams I think i have a few Options.

1) Get a "7747" ECM and and connectors and repin the harness while chasing all the circuits to make sure they are correct
2) Buy a aftermarket engine harness that is designed to work with the "7747" ECM and make the needed connections
3) Send out my ECM to be reflashed and then swap around the connectors that are needed to make the 5 speed work with the ECM.

I'm trying to do this without dumping a lot of cash into it because i am still holding out hope that in the near future it will be getting a Cummins. So if anyone can think of a option I missed, or if anyone has any incite on this project i am all ears!
 
Need to get the PCM #, and compare the pinouts/functions vs. the '7747. I'm not really sure what happens if a PCM sees nothing from the trans, I would expect it would severely limit performance.

As far as I see, ECM/PCM pinout is your only problem. All the functions/sensors are the same except trans. VSS 205 is a no brainer, but I'd question its use over the VSS 241. If you already have all the 205 required parts to install it then I suppose that's pretty much done as well, just a thought. I went VSS 205, going to the 241 now.Plus side is, you find a '7747 donor that is '90-91, it will have the right t-case if 4WD.

I don't know if those ECM/PCM connectors are the same, if they are, it's likely just a re-pinning of a few connectors to get it done.
 
I currently have ECM# 16147060 and everything i have seen says that the connectors for it are different from the 7747 and the pin out is different too. I have given thought to finding a 7747 and the connectors and just re pinning it but still not sure yet. Seems like that maybe the easiest and possibly cheapest route.

Also on the NP205 i have all the stuff to mate it to the NV4500 so all i need to do is modify the tail housing for the Speed sensor. I have given thought to just throwing the setup in and seeing what happens but the city is a real pain about "inoperable" vehicles.

I really cant think what the difference would be for the ECM, it would still be getting a VSS input but i would be doing the shifting not the pcm. Keep the ideas coming!
 
If connectors are different, then depinning/adding 7747 connectors may be possible, but ONLY if the terminal is the same. I have no clue if those two ECM's use the same terminals, but different connectors. An easy fix if so.

If you don't actually have the 205 tailhousing for VSS, I would reconsider it for the swap. I know my personal preference is speaking here, but other than bashing off the rocks, the 241 is a better case...better low range, rated for more torque, probably shifts easier, and is easier to move around because it's lighter. I suppose the slip yoke sucks, and it IS a $400 fix, but it's out there. Especially if you have a 205 with slip yoke already.

In any case, the reason to not just throw the 4500 in there is because the "logic" in the PCM is this: If there is a trans problem, to try and make sure the vehicle can still move, do not stress the trans more than necessary. No input from trans=serious problem. Limit the stress the motor puts on it. That would be done via reduction in engine performance, and while I've not done it, I would very much expect that you'd be sorely disappointed in how it ran afterwards. Not to mention a "false" check engine light that now won't be useful if something else goes wrong.

Finding the terminals used in both PCM/ECM's should be pretty easy to do, that would tell you if all you need is a 7747 and the connectors.
 
The terminals are what the wire is actually crimped to...to break it down into how you'd assemble an ECM connection, you'd strip the wire, crimp the proper terminal onto it, slide that terminal/wire into the proper connector (the plastic piece that mates to the ECM/PCM in this case, that holds all the wires) until it locks in place, then insert the terminal locks, which are often blue or gray colored, and have a bunch of fingers that somewhat resemble a comb.

Disassembly is normally pretty easy, just remove the terminal lock (jewelers flat tip screwdrivers normally work well) and then use a straightened paperclip to compress the locking tab on the terminal, and pull gently rearwards on the wire/terminal you are removing.
 
Ok, i follow now! I will have to do some checking, if i decide to go that route then when i get the connector I will see if i can get a short section of the wires too.

Does anyone see this being the most cost effective way? I spoke with a guy that does custom TBI harnesses and he told me about $150.00 and he could set up the ECM to work with the manual trans. Is that a decent price or should i start looking for the 7747 ECM and Connector?
 
I'll have to defer to EagleMark on this one for specifics.

I *assume* that the PROM (what is specific to a particular vehicle/drivetrain) could be easily modified (or swapped) for a manual trans application, since they were available at that point, even though the '7747 was the ECM used if manual trans, vs. yours which is an actual PCM. That would be the ideal solution, a PROM that was set up for your vehicle/engine, but calibrated for the manual transmission.

If you end up being able to swap connectors for that idea, you don't really need any of the wiring from the donor vehicle, just the actual plastic connectors and locks. But it's much easier to cut the wiring off and de-pin them at home. I always try to grab as much wire as I can, I often re-purpose old vehicle wiring (that is in good shape only of course) for other electrical projects, both automotive and other.
 
Last edited:
I got more work done on my Crewcab so i'm starting to think about this more and more.

I'm going to bump this up with another question, any idea how bad it would be to try and piece my chassis harness together with a 7747 ecm and engine harness? Keeping in mind I am still a newb on efi and wiring.
 
It *probably* will be very close if not exact, but I'd want to verify the firewall pinouts between both combinations. Mistakes in wiring are probably the #1 cause of issues in swaps like these.

IIRC the TBI harness is pretty well separate of the rest of the vehicle wiring. Couple of wires/plugs here and there that need connected for power, that's all I can think of.
 
They aren't really complex, if you can find the factory ones.

The ECM pinouts are pretty easy to find, might have them over at diy-efi.org by ECM #. Factory wiring diagrams are harder to find online, I can't think of any sites off the top of my head, which is too bad.
 
I have downloaded a few of the factory service manuals. I just have to sit down and start tracing them out and comparing them. Also here is a link to where someone scanned and uploaded A LOT of 73-91 factory service manuals. Link
 
Update and a new question.

So i picked up a '89 7.4l Tbi BBC with engine harness and ecm. So now im looking at how much different the body harnesses are between the ECM and PCM.

I know the easy way would be to keep my harness and install a BBC PROM in my PCM. I may explore this to get the truck moving and running but I really want to use the harness and ECM I picked up with the engine so i can install my NV4500 and transfer case.

I have been comparing the body harnesses between the ECM and PCM and they look the same for the most part. A question I have is, for now my main concern should be the power supply to the ecm side, correct?
 
Power supply is usually the only thing that is "integrated" with the vehicle harness...everything else (sensors) usually just run back to the ECM/PCM, but power is going to go through some fused source(s) of some sort, and since some are constant, some ignition only, the wires come from different spots.

IMO the best solution to add EFI to a vehicle, if you aren't using a completely stock setup that requires no splicing/sodlering, is to get a fuse/relay center (most cars newer than about 1990 use one underhood) and use the stock fuse panel accessory terminals to switch the relays on the center necessary for key on power, and also to cleanly (and safely, since you can fuse the feed with the panel) distribute battery 12V for things that need constant power.

It also makes adding additional electrical components easier/cleaner, since it will give you a lot more fused taps, closer to the battery.

I'd wager a guess that improper battery supply (ignition vs. constant) is the #1 problem people experience when modifying EFI to fit a vehicle. It's not hard, you just have to understand the harness before digging in, then double check everything before you finalize it.
 
I will sort through the ecm /pcm pin outs and see if they get the power, constant and switched, from the same places. Seeing as I have both complete oem harnesses I would like to use them. The fuse/relay center is not a bad idea, I will have to dig around the salvage yard when I get back. I know it's asking for a lot but I would be over joyed if the ecm harness from the big block would work in place of my pcm harness without to much hassle. Guess we will see... :dunno:
 
Seen this thread? http://www.gearhead-efi.com/Fuel-Injection/showthread.php?317-16147060-PCM-Information-85 Didn't proof this one, but another re: this PCM http://www.gearhead-efi.com/Fuel-Injection/showthread.php?807-16147060-85-Superceeded-to-D8

Normally using just the PCM number in google you will find all sorts of info out, was looknig for a connector picture...this looks like a '7747, no? http://img.auctiva.com/imgdata/7/3/0/7/6/0/webimg/351344913_tp.jpg Appears to be similar connector to all the similar year ECM's from what I can tell, but pretty tough to be certain from that distance.

I ended up doing a separate panel for the EFI on mine initially, then later realizing that if I were to have done a relay/fuse center, I could have run the electric fans, electric rear view mirror, etc off of one component, vs. running wires and junction blocks all over the place.
 
I ended up doing a separate panel for the EFI on mine initially, then later realizing that if I were to have done a relay/fuse center, I could have run the electric fans, electric rear view mirror, etc off of one component, vs. running wires and junction blocks all over the place.
Click to expand...

Do you have any links for info on installing a fuse/relay center? I have done some searching and have not found very much. I may have to give this some serious thought. Thanks for all your help.
 
Boy, tiny photo, but if you are not quite sure of what they look like even: http://thumbs4.ebaystatic.com/d/l225/m/mxqJSgyCm2mxvijF9L5mJPA.jpg

Wiring isn't really difficult, this link shows some pinouts and diagrams https://www.google.com/search?q=und...&q=underhood+relay+fuse+center+-ebay&imgdii=_

Wiring diagrams tend to look worse than in person, completely understand. All they tend to be, when torn down, are strips of contacts that fuses and relays connect to, that gets power from the battery, and switched via relay if necessary. On the ones I deal with, you could run say, a row of 5 fuses off of one relay, then another row with battery 12V, etc. There are various sizes if you just google "underhood fuse relay center" you will see them.

I'd caution against trying to go "simple". Some of the panels are massive, so way overkill, but I'd probably want about double the number of fuses I know I need today, for later additions, and/or rewiring.

I tend to stick with GM stuff simply because that's what I know, and Delphi components are pretty easy and cheap to get. I've gotten to the point I don't care for splices anymore, if possible I buy the correct terminals (and wire if necessary) and crimp new instead. Terminals (and crimpers) are quite cheap for the real common GM stuff that you are likely to find in the wrecking yards.
 
You must log in or register to reply here.

Latest Posts

Top Bottom