MS41.1 Tuning for E30 M52/OBD2 swap + troubleshooting

[mjweimer]

My OBD2/MS41.1 M52 swap is not quite behaving properly and after a bunch of troubleshooting I'm leaning towards an issue with the DME. I have a 328ijunkie /Markert Motorwerks swap tune currently but with their shop expansion and name change I don't think they are still in the swap tuning game.

Who is the current go-to for a proper tune for MS41.1/M52 swap (S52 cams/M50 intake/SAP delete/etc)? I have zero experience tuning/programming so looking for a patient/knowledgeable person to help program a spare DME and/or help diagnose my issue.

Cheers.


Edit for clarity:

Z3 2.8 swap into my '90 325iS, got the car running but experienced some strange behavior that turned out to be a bad cam position sensor. Replaced that (along with the crank sensor for good measure) and am now left with a 1900-2k RPM cold start idle that settles down to around 1000 RPM eventually but throttle inputs are abrupt and snapping the throttle has massive rev hang.

Throttle cable is not holding the throttle open at idle and cruise cable is not holding the TB open at idle

TPS is new and shows a clean voltage sweep across the throttle open/close = .68V at idle

Throttle body is a new OBD1 piece and has not been altered

ICV is new but was also swapped with a known good spare to check function, both buzz with key on and react the same otherwise

All vacuum lines, ICV +CCV hoses, CCV, etc. were replaced when the engine was built

Smoke test of the engine shows zero leaks

Coolant temperature and intake air temperature readings look correct via INPA


In my search for info, I have found many different threads with similar issues but not many have a firm conclusion...one high idle thread stated they ended up swapping their DME to fix the issue but they also swapped the MAF. My car seems to run well...just not quite right. With no vacuum leaks and the throttle closed, it seems as if the DME is commanding the ICV open further than it should (along with whatever timing/fueling changes that occur) with the resultant high idle.

Open to suggestions for next steps. I have INPA but no other diagnostic software at the moment.

[jsta1109]

You could always do it yourself. It really isn't overly complicated and relatively inexpensive to do. You can have a look here for some help https://sites.google.com/site/openms41/. There is also more information on the RomRaider forums.

Tuning for the cams and intake can be done on the road with a wideband and some patience, open loop target an AFR around 13~, closed loop adjust fuel to your trims and you'll be close. You can also get ignition timing pretty close with the inbuilt knock control as well.

[mjweimer]

You could always do it yourself. It really isn't overly complicated and relatively inexpensive to do. You can have a look here for some help https://sites.google.com/site/openms41/. There is also more information on the RomRaider forums.

Tuning for the cams and intake can be done on the road with a wideband and some patience, open loop target an AFR around 13~, closed loop adjust fuel to your trims and you'll be close. You can also get ignition timing pretty close with the inbuilt knock control as well.

Thanks for the links, I have been over on the RomRaider site reading and learning a lot. I'm sure it's not too hard once you get into the details but its way outside of my normal skill set.

[Northern]

What kind of problems are you having? It's not hard to pop open your ECU and look for corrosion.
I think the biggest problem with the ECU is that it lived in an E36 engine bay for most of its life and it's not unlikely that it's seen some water at some point.

[mjweimer]

The car has developed a condition where it goes immediately to 1900rpm upon start-up and sits there for a couple of minutes before it then drops down to 1000rpm. Any throttle on/off results in serious rev-surge (not the typical M52 rev-hang).

Car was running fine prior to being dropped off for paint work and then at some point while at the shop it started acting up. My next course of action is to reset adaptions in INPA and see if that does anything. I don't know why it would but it something else to check off on my list.


The ecu is thankfully nice and clean, I did a thorough check when I removed it from the car and no sign of issues. It was in a Z3 so the DME box tends to stay more dry than the E36 mess.

[Northern]

^ mine does something similar too - It will rev to 1900 on cold start and stay there. If I blip the throttle a bit, it will rev appropriately, and drop down to wherever it is supposed to be for warmup idle target.
If I reset adaptations, it goes away for a while and I have no idea why.

I've thought that this issue could have something to do with either running m3 software or an M50 throttle body (I see TPS adaptations, so maybe the TPS "D" piece is in a different position, I've never checked.)

[amcp]

S52 swapped with M50 manifold/tb same thing happens to me when cold. I'll give it some throttle and it will drop in idle a bit.

[mjweimer]

This is all really interesting. On Sunday, I reset the adaptions using INPA and the start-up/idle is back to normal. I can't drive it much at the moment due to its state of (dis)assembly and all of the salt/snow out on the roads.

What is the TPS "D" you are referring to...the base "idle" stop set point? Unfortunately I pitched my stock M52 throttle body so I cannot compare the two.

[Northern]

This is all really interesting. On Sunday, I reset the adaptions using INPA and the start-up/idle is back to normal. I can't drive it much at the moment due to its state of (dis)assembly and all of the salt/snow out on the roads.

What is the TPS "D" you are referring to...the base "idle" stop set point? Unfortunately I pitched my stock M52 throttle body so I cannot compare the two.

Yes, the shaft that the TPS sits on, I'm wondering if the alignment is the same, or if one is like 10degrees off. I seem to get 12.8-15 degrees of TPS adaptation after the car drives for a while.
I only found three screenshots with TPS adapts in them, but this one is the smallest. (I have no idea what is normal either).

[Northern]

Just so it's clear, TPS AD is the field I mean.

Just found one from Oct 2020 at 13.05% as well, after I switched to 41.3

[mjweimer]

That is a really interesting observation. It sure would be good to know if a normal M52 has the same adaption range.

What software is this where you can look at the adaption values? I am very unfamiliar with digging into this side of things.

[Northern]

I'm doing that with RomRaider Logger, "Learning Table Values" under the Tools menu.

To get that working:
You need an OBD2 port in the car, or a "bmw 20 pin to obd2 adapter". The OBD2 port is just a K-line wire from pin 88 on the ECU,+12V, and GND. If you can find an OBD2 port from a junkyard car, you're practically halfway there.
INPA K+DCAN cable (the $15 ones from ebay/amazon work great, but sometimes they show up dead)

All the software (Romraider/Romraider logger, Java updates, FTDI drivers for the cable, definitions for the logger to talk to the ECU, etc) can be done with Shake's MS41 ECU Portal here:

https://sites.google.com/site/openms41/tuning

Once you have that done, you should also be able to datalog or view live data from just about anything the ECU sees as well.