Teaching a Caddy to speak Diesel

I asked this question over on that other board last spring but got no real input other then caustic remarks. Over the winter I hope to start project 40, a 6.2/6.5 turbo diesel and 4L80 in the Caddy. At this point I have a good idea of the mechanical side of the build and the physical installation logistics but what now remains is how to control the tranny.

The diesel build will incorporate a mechanical injection pump so there is no requirements for computer controls for the engine, but the tranny is another story. So far I have narrowed it down to two scenarios:

1. Keep the current ECM in the car and disconnect all the stuff I don't need but retain the HVAC functions, the digital dash etc. but piggyback a standalone tranny controller out of NA diesel van (before they went to the electronic pump but used the 4L80) and parallel the VSS input. Disable the CEL and allow the cars ECM to run in full default. I can give the tranny controller both TPS and a tach signal with off the shelf bits.

2. Some how dumb down the OBD1 ECM that is now in the car so that is no longer wants to have anything to do with the engine other then getting the aforementioned TPS and tach signals and let it only control the tranny, and of course all the ancillary stuff.

I would really prefer to use scenario 2 as everything in this car seems to want to talk to the ECM. Also it would mean I only have one harness to worry about patching into the system (the tranny stuff) plus it would allow me to easily re-program the tranny for VSS, lock-up, line pressure and shift points.

Would really appreciate some input here from anyone who has played around with programming, or anyone with an idea of how to get this tranny to shift properly while still having unimportant things like a speedometer, cruise control, AC, heat, brakes etc. Remember the only bad ideas are the ones left unspoken.

For those that are interested, I will be documenting this build as soon as I get started on the actual build up and can generate some pics. First time I have dug into one of these new electronic trannies. Last one I did was a 400, maybe 25 years ago. Should be interesting.

Bill

Bill, first let me say that I know nothing about this subject, but does the 4L80E have a mechanical counterpart like the 4L60E/700R4? If so, can you swap out the electrified parts for the mechanical ones and program out everything but ancillary functions in the OBDI?

Don't let electronically controlled transmissions scare you; they're really quite simple. As an illustration, I could setup a 4L60E to drag-race in a non-electronic car with two toggle switches and WOT switch on the throttle.

You didn't state what year it is - I assume a '94?

I'd say option B is just fine. I know of a B-body that's successfully running a 4L80E off the stock PCM simply by inverting one of the shift solenoids with a relay. JaySS will have more info on this, but I know the car is on the road and has some miles on it.

Secondly, I think the biggest concern for the PCM would be the loss of the opti signal feeding back to the PCM. But then again, if the motor can run independently of the computer, then if the computer won't just throw up its hands and quit with no opti input signal, it should control the transmission just fine.

FWIW, the PCM needs only TPS, coolant temp and VSS inputs to control the transmission. I'm just going off the top of my head here, but I don't see why it isn't doable.

Like I said, hopefully JaySS will see this and throw some quarters at it; they'd be worth more than my two cents.

Krzdimond wrote:

Bill, first let me say that I know nothing about this subject, but does the 4L80E have a mechanical counterpart like the 4L60E/700R4? If so, can you swap out the electrified parts for the mechanical ones and program out everything but ancillary functions in the OBDI?

Robert:

Really wish there was. Would make my job much easier. The 4L80 is based on the old 400 with an OD stuck on the back and a lock-up convertor. Was actually toying with the idea of using a 400 with a gear vendors but as this is a daily driver, not having the lock-up becomes an issue. They did use the 4L80 in the early years before electronic fuel controls but drove the tranny with a stand-alone controller. This is the one that is currently being sold by GM Performance (for $1,200 I might add) for specifically this kind of application.

Quote :

You didn't state what year it is - I assume a '94?

I'd say option B is just fine. I know of a B-body that's successfully running a 4L80E off the stock PCM simply by inverting one of the shift solenoids with a relay. JaySS will have more info on this, but I know the car is on the road and has some miles on it.

Secondly, I think the biggest concern for the PCM would be the loss of the opti signal feeding back to the PCM. But then again, if the motor can run independently of the computer, then if the computer won't just throw up its hands and quit with no opti input signal, it should control the transmission just fine.

FWIW, the PCM needs only TPS, coolant temp and VSS inputs to control the transmission. I'm just going off the top of my head here, but I don't see why it isn't doable.

Yes the Caddy is a 94. The issue here seems to be convincing the ECM not to go into full default (limp mode) with all of it's bits disconnected. A bunch of stuff just doesn't happen in limp mode like no-lock-up, no cruise etc. Either we have to convince it that things are supposed to be this way or find a way into the default tables to do some modifications. If need be I can even give it an Opti signal off the front of the crank using the cranksensor from an electronic 6.5. Can even give it things like a MAF, air temp etc. The job here is finding out what the ECM really needs to do what I want in such a way that it doesn't just give up and move into a retirement home. There is just too many dependancies built in that I'm not fully conversant with. Have no problem turning off the CEL if need be but that doesn't convince the ECM that it isn't in full default.

Thanks guys, keep it coming.

Bill

Wish I could give you some ideas. I know nothing about PCM/ECM programming other than I call someone to have it done.

Good luck on the project!!

You should get into contact with JaySS. He has connections to folks who know the details of a swap of this magnitude.

Sherlock:

Will do. No real hurry on this as its going to be at least March before I have to address the problem in earnest. Just though it would be a fun discussion and possibly another alternative not only for me, but anyone using these trannies behind an old school engine. Now their only options is the TCI module or the aforementioned GM box. This way, it can be done for the price of a used ECM/PCM from an LT1 car, the tranny harness and the programming software.

Bill

sherlock9c1 wrote:

Don't let electronically controlled transmissions scare you; they're really quite simple. As an illustration, I could setup a 4L60E to drag-race in a non-electronic car with two toggle switches and WOT switch on the throttle.

You didn't state what year it is - I assume a '94?

I'd say option B is just fine. I know of a B-body that's successfully running a 4L80E off the stock PCM simply by inverting one of the shift solenoids with a relay. JaySS will have more info on this, but I know the car is on the road and has some miles on it.

Sorry for the delay, I did see this earlier but I had to ask some questions before I could start to formulate an answer. Joel is right - although we tend to stick with what we know - the 4L80E option should be far more practical (easier - and cheaper, unless you know someone marking down $3000.00 GV units to a handful of change and some pocket lint) than a TH400/Gear Vendors unit, once the trepedation of dealing with the electricals is overcome.

Anyway, Option A or B will work. Or it was suggested that potentially there is an Option C - remove the factory PCM entirely. This one I wasn't sure would be doable. What I don't know is how much the D-body BCM relies on the PCM to function. A quick look at the '94 Fleetwood FSM was not conclusive.

One way to check would be to extract the ALDL pin (which should be the only com port available on the OBDI PCM for the BCM to intercept) from the PCM and take the car for a spin. This should be a quick way to determine how much the car depends on the PCM to operate properly and if it is practical to lose it and use the diesel based ECM alone. I guessing that it will be readily apparent that the PCM has to remain onboard.

Assuming that the the factory PCM is required, then yes, I am told all engine related flags can be switched off and a relay added to invert the shift solenoid B (IIRC) output from the PCM to properly operate the 4L80E.

sherlock9c1 wrote:

Secondly, I think the biggest concern for the PCM would be the loss of the opti signal feeding back to the PCM. But then again, if the motor can run independently of the computer, then if the computer won't just throw up its hands and quit with no opti input signal, it should control the transmission just fine.

FWIW, the PCM needs only TPS, coolant temp and VSS inputs to control the transmission. I'm just going off the top of my head here, but I don't see why it isn't doable.

The PCM will definitely need RPM & TPS. Joel mentioned coolant temp, but this doesn't seem to indicate the need for it -

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- for the transmission anyway, perhaps you were thinking of the transmission temp senders, or does the '8051 require it to select the proper shift table?

One issue will be replicating the opti specific signals. I believe that the low res signal is all that will be required, but if that isn't easily done, then it should be possible to feed in some generic crankshaft RPM signal - say 8X/rev - and scale it appropriately to adjust the shift points. It just means all of the programming software RPM values will multiplied by some factor to understand the true RPM they represent.

I think this is enough to get started.

- J

Jay:

Thats great. Exactly the kind of stuff I was looking for.

The reason I want to use the current ECM/PCM is primarily the ease of programming. Not really concerned with electronics per say nor do they scare me. It's just this car spends alot of time away from home and if something does go wonky on it, can you imagine the average garage wrench trying to figure out how to diagnose something like this? It is afterall a 15 year old car and things do go wrong. Just trying to make it as simple as possible without totally re-designing the car.

From what I can glean from the various manuals and web searches, all of the on-board computers talk to the ECM in way or another. What the ECM does with this information remains a question. Also this car has traction control that is controlled directly by the ECM talking to the ABS. Can live without it but as I prefer open diffs for day to day driving, the TC makes plowing through snow considerably easier. Sort of the best of two worlds.

I do know the speedo cluster gets its info from the ECM and certain functions of the HVAC need to talk to the ECM. Having fan control through the ECM would be nice as well. Non of the aftermarket controllers have worked out well for me. As far as the temp sender, I think Joel is right. Coolant temps direct the tranny controller to help warm up the engine (more revs in each gear and no lock-up). Once in closed loop though, everything is supposed to work as advertised. This is a no-brainer as I have a few places on the 6.5 to plug in a sender unit. I'm still a little confused as to the need for an opti signal. I can rig up an engine speed sensor (tach) fairly easily and if the FSM is right, the ECM gets rpm info from the distributor anyways, thus a simple tach circuit is all that is needed. Am I right?

Once again, thanks for the information. Have saved it in a word document to refer to. When the time comes to do the install, will have to get into the intricacies.

Bill

I guess I better exchange that programming cable...

Yeah, that was my concern - engine temperature affects how the PCM controls the transmission. Then again, fooling that is easy; figure out what resistance equals 190F and just solder that into the harness, and you're done.

Okay, I'm done. Back to the JaySS show.