Need Assist w/Motronic 1.3 Conversion & Limp Mode

[mooseheadm5]

D.
Sorry about the thread hijack. Back on topic, I'm not sure what setup you have going right now, but if you could post or point to a post with more info on your current setup it may be possible to check the wiring diagrams to see what might be wrong. I will tell you that the transmission gear indicator board from a non-EH cluster can cause issues with an EH trans, but I don't know what year all your bits are from.

[wkohler]

Both an '87 and '88 535is with the 4hp-22eh were swapped to Motronic 1.3 using E32/34 harnesses and the 179 ECU with stock chips. The clusters weren't changed. Upon the installation of the harnesses, faults occurred with the transmissions, causing the limp mode happiness. The '87 can be driven without limp mode, but Darin can fill you in on what happens.

The '88 is constantly in limp mode, which isn't horrible with a S3.91, but it isn't correct, particularly since that car hauled ass before. The installer found a way to turn the light off, but it's still in limp mode and the tranny is still perpetually in 3rd gear.

Basically, nothing other than what was necessary to complete the 1.3 swap was changed, and the '88 functioned "perfectly" prior to the swap.

The person who could actually tell you everything he did is somewhere in the abyss.

I would almost say Darin is handling this rather well. His entire timeline has been destroyed by this issue.

[mooseheadm5]

hmm. Might have to think on that one a little bit.

[MLastovo]

D.
Sorry about the thread hijack. Back on topic, I'm not sure what setup you have going right now, but if you could post or point to a post with more info on your current setup it may be possible to check the wiring diagrams to see what might be wrong. I will tell you that the transmission gear indicator board from a non-EH cluster can cause issues with an EH trans, but I don't know what year all your bits are from.

Reasonable request.

The car is a 4/87 e28 with a ‘late’ e24 tranny and the original e28 trans ECU. Prior to the harness swap the trans worked great (except for reverse detailed in a bit) but the indicators on the dash could be manipulated via the selector lever i.e. they were not really perfectly lined up with the actual gear that was selected. I could put the car in drive and gently move the lever forwards and the neutral light would illuminate while staying in drive. In addition, upon selecting reverse from either park or drive the trans would engage with vigor. So much so that I am confident that in a very short time the diff mount will fail with spectacular effect.

Now, the car has an ‘early’ e32 harness with the same, original e28 trans ECU and most of the operation/symptoms have changed. Now it is stuck in ‘Limp Mode’ but it still slams into reverse. (I have no reason to believe the reverse issue has anything to do with the 1.3 conversion and it is simply based on logic and no specific knowledge.) At the same I can make the newly illuminated trans warning light go on and off by moving the selector as described above.

From cursory poking around today I think the best option is to swap the trans ECU with one specifically out of an e24. After that the options get more intense and, well, shitty.

And before anyone gets cute and suggests that they have the fix and it involves an additional pedal they are not part of the solution. A manual tranny is a work-around and not a solution.

Thanks,
D.

[MLastovo]

Just wondering what type of connections you've done to the tranny computer. Have you supplied it power to pin 35? Are you using the original TPS or the round plugged B35 TPS? I have no idea if they're electrically equivalent but they may be since both provide a variable signal.

Ya see that is where the effort gets a little fuzzy. I didn't do the work and the party who did has, um, fallen off the planet from the best I and other knowledgeable board members can tell.

r/
D.

[demetk]

Just wondering what type of connections you've done to the tranny computer. Have you supplied it power to pin 35? Are you using the original TPS or the round plugged B35 TPS? I have no idea if they're electrically equivalent but they may be since both provide a variable signal.

Ya see that is where the effort gets a little fuzzy. I didn't do the work and the party who did has, um, fallen off the planet from the best I and other knowledgeable board members can tell.

r/
D.

Ok I get what you all were saying now about this mystery person. So he did the work.

Anyway, to me the only electrical items that need attention are like I described above. I would imagine you can easily verify power to pin 35. Originally that power came from the original main relay via the original harness. Now that that has changed, I would imagine that a power takeoff from the new main relay is needed.

[mooseheadm5]

The original mismatch between selector position and gear may have been a cable adjustment out of alignment with the range switch, so I might dismiss that as being related. I will see if I know anyone with a late e24 TCU but I would follow demetk's advice on checking the power to the unit. It could be that as he suggests there is some small wiring difference between the two harnesses that is the cause of the problem. I don't believe that the TCU is the issue. it may be different simply because it is tuned for different shift points for the B35 and not for any reason that can cause your problem.
Are you handy with a multimeter?

[pldlnr]

Hey Darin,

I would be willing to bet that the issue, as others have stated, is due to the new harness not providing the necessary information to the TCU. The TCU requires several signals from the ECU and other places.

First, like demetk mentioned, you need voltage (12v) from the main relay at TCU pin 35. From the ECU, the TCU requires a signal for fuel rate and engine speed. The TCU needs to send the ECU shift input and full load signals. The TCU also needs the signal from the TPS.

Here are the wiring diagrams for the whole system on a 1988 535i.

http://www.armchair.mb.ca/~dave/BMW/e28/e28_88.pdf

I also found the test procedures for the system. You can go step by step and figure out which signals you have and if the voltages are in the correct range. I think if you go through these tests, you should be able to isolate a missing or inappropriate signal voltage. If you have a volt meter, these pages tell you where and what to test.

[MLastovo]

Hey Darin,

I would be willing to bet that the issue, as others have stated, is due to the new harness not providing the necessary information to the TCU. The TCU requires several signals from the ECU and other places.

First, like demetk mentioned, you need voltage (12v) from the main relay at TCU pin 35. From the ECU, the TCU requires a signal for fuel rate and engine speed. The TCU needs to send the ECU shift input and full load signals. The TCU also needs the signal from the TPS.

Here are the wiring diagrams for the whole system on a 1988 535i.

http://www.armchair.mb.ca/~dave/BMW/e28/e28_88.pdf

I also found the test procedures for the system. You can go step by step and figure out which signals you have and if the voltages are in the correct range. I think if you go through these tests, you should be able to isolate a missing or inappropriate signal voltage. If you have a volt meter, these pages tell you where and what to test.

This is great help, THANKS!

Thanks also to the other contributors. I'll step through this and with any luck find the disconnect.

r/
Darin

[nnarth212]

Next round of bloody mary's on me... paypal?

good work, D.

[Ricky535]

Would a TCU from an 88-89 e32 work? They're readily plunderable in the yard.

[wkohler]

I figure there has to be a reason they are different between E34/32 and E24. Of course, I'm just thinking out of my ass on this.

[mooseheadm5]

D.
Sorry about the thread hijack. Back on topic, I'm not sure what setup you have going right now, but if you could post or point to a post with more info on your current setup it may be possible to check the wiring diagrams to see what might be wrong. I will tell you that the transmission gear indicator board from a non-EH cluster can cause issues with an EH trans, but I don't know what year all your bits are from.

Reasonable request.

The car is a 4/87 e28 with a ‘late’ e24 tranny and the original e28 trans ECU. Prior to the harness swap the trans worked great (except for reverse detailed in a bit) but the indicators on the dash could be manipulated via the selector lever i.e. they were not really perfectly lined up with the actual gear that was selected. I could put the car in drive and gently move the lever forwards and the neutral light would illuminate while staying in drive. In addition, upon selecting reverse from either park or drive the trans would engage with vigor. So much so that I am confident that in a very short time the diff mount will fail with spectacular effect.

Now, the car has an ‘early’ e32 harness with the same, original e28 trans ECU and most of the operation/symptoms have changed. Now it is stuck in ‘Limp Mode’ but it still slams into reverse. (I have no reason to believe the reverse issue has anything to do with the 1.3 conversion and it is simply based on logic and no specific knowledge.) At the same I can make the newly illuminated trans warning light go on and off by moving the selector as described above.

From cursory poking around today I think the best option is to swap the trans ECU with one specifically out of an e24. After that the options get more intense and, well, shitty.

And before anyone gets cute and suggests that they have the fix and it involves an additional pedal they are not part of the solution. A manual tranny is a work-around and not a solution.

Thanks,
D.

I have looked into it a little and have some ideas as to what may be missing that the TCU needs. I have found this info so far (cut from another one of my posts):

The TCU needs a rheostat throttle input (this comes separately from the TPS and not through the ECU,) a kickdown switch input (from the switch under the accelerator pedal), fuel rate input, and engine speed input (both from the ECU.)
In addition, the ECU gets its WOT signal from the transmission (not the TPS) but if you are running 1.3 that would not matter, though you may need to run dual TPS rheostats to make it work correctly. The 1.0 ECU also gets a shift signal, which may ease off the timing or otherwise cut power to allow a more smooth shift.

Note the bit in bold. I need to download a 1.3 diagram to figure out where the disconnects are, but I am starting to think it might have to do with a lack of TPS signal or engine speed signal. I'm still on it and will continue to unravel it because I am curious.

[wkohler]

Paul - How would the logistics work on running dual TPS rheostats? Where would the second one go?

[mooseheadm5]

Paul - How would the logistics work on running dual TPS rheostats? Where would the second one go?

You'd have to stack them and mod one to move the other. It'd be stupid looking. I'd think if the correct harness was used it wouldn't be necessary but I still need to look over the 1.3 stuff to see what signals go where.

[vintagemotorsportsofMD]

I just did this conversion, if anyone needs help PM me with specifics and I will be glad to help. It took hours and hours poking through all the diagrams and ETK to get my setup to work perfectly. You do need to use the round plug TPS in the conversion, you also need a viable e28 auto engine harness to cut open and take the entire shielded TPS switch wire out of and spice into the round 1.3 auto TPS connector. You also need to supply the TCU with 5v. The vain air meter ref voltage output is perfect to snag the 5v needed there, as the 1.3 motronic does not have a 5v output for the TCU or "AEGS" I believe they started calling it. As I said, if anyone has any specific questions feel free to PM me. I don't have a time to make a nice neat post at this point, but I will add a photobucket page of pics when I can remember to bring my camera home...