Long term fuel trim is affecting my WOT map fueling OBD1

[dragon850]

1993 BMW 850ci M70 V12 stock ECUS.
Running 11psi SC rotrex kit with 24lb injectors and 4bar(58psi) FPRs.
Problem I am having is when I get my WOT afr tuned just right at 12.5 after driving around for a while the whole WOT table goes screwy, up and down like a roller coaster, as low as 10.2 and as high as 13.2 in some spots, having a hard time locking it down by compensating. Really hate this lack of control, actually considering taking OEM ECUs out using them for target practice and wiring in something like Tec3r to control the engine but don't want to loose EML throttles. Any suggestions?

[Def]

Tec3R - ugh... what a wretched standalone to use now. It's beyond outdated now.


I think an AEM Infinity 710 can run a V12 with batch fire injection

[NOTORIOUS VR]

Tec3R - ugh... what a wretched standalone to use now. It's beyond outdated now.


I think an AEM Infinity 710 can run a V12 with batch fire injection

^^^ what he said... TEC3 lol... please don't.

An Emtron would be the ticket here for a V12 IMO.

If the WOT table is getting screwy after some time of driving it's because the ECU is probably trimming during cruise, which to me means you didn't setup something right in the tune (what are you using to tune anyway?) or you didn't do anything and expect it to work with the SC as is? When you go WOT it's applying the LTFT to the WOT table and then you have your issue.

[Def]

Looks like a MS3 Pro Ultimate (they seriously need to rethink their branding...) can do a V12 sequentially - that'd be a pretty sweet setup if you've got the cam sensors to trigger things sequentially. The stock sensor wheels might just do batch fire with a crank wheel.

[dragon850]

Thank's for the input guys, I mentioned Tec3R cause I have it sitting on the shelve brand new...yeah I know it's outdated
Another issue is EML electronic throttles, the only system I know that is compatible with EML and V12 is MoTEC ...at $4500.

[dragon850]

^^^ what he said... TEC3 lol... please don't.

An Emtron would be the ticket here for a V12 IMO.

If the WOT table is getting screwy after some time of driving it's because the ECU is probably trimming during cruise, which to me means you didn't setup something right in the tune (what are you using to tune anyway?) or you didn't do anything and expect it to work with the SC as is? When you go WOT it's applying the LTFT to the WOT table and then you have your issue.

I think you hit it right on the head, motronic seems to be applying LTFT on low/mid/high part throttle maps and messing with WOT.
I am using TunerPro RT but have only touched the WOT map. The original SC tune I am using was made by a BMW tuner in Netherlands on the dyno, however it was tuned using 8psi supercharger and 24lb injectors. My set up is at 11psi, I am using same 24lb injectors however I was maxing them out at higher RPM so I upgraded to 4BAR FPRs from stock 3bar effectively raising my fuel pressure to 58psi, I believe this took my injectors up to 27lb.
The low/mid/part throttle maps were not compensated for these changes.
I have a dyno tuning session scheduled with an experienced OBD1 Honda tuner ( not one OBD1 BMW tuner in SF Bay Area) hope he can tune out the fuel trim. I have an INPA set up that he can use to look at the STFT and LTFT and adjust accordingly.
I hope I am on the right path.... any suggestions welcome.

[vwmikel]

By changing the fuel pressure you really have changed everything. I can't say I've dealt with your specific motronic system, but typically there is a base map and then a series of modifiers for various conditions. The best way is obviously to use a braked dyno to limit RPM and sweep through the map to get the AFR correct. Things like AFR change under boost can be done in the modifiers so it isn't trying to fight the request vs actual and you only see that dip under heavier loads.

[NOTORIOUS VR]

I think you hit it right on the head, motronic seems to be applying LTFT on low/mid/high part throttle maps and messing with WOT.
I am using TunerPro RT but have only touched the WOT map. The original SC tune I am using was made by a BMW tuner in Netherlands on the dyno, however it was tuned using 8psi supercharger and 24lb injectors. My set up is at 11psi, I am using same 24lb injectors however I was maxing them out at higher RPM so I upgraded to 4BAR FPRs from stock 3bar effectively raising my fuel pressure to 58psi, I believe this took my injectors up to 27lb.
The low/mid/part throttle maps were not compensated for these changes.
I have a dyno tuning session scheduled with an experienced OBD1 Honda tuner ( not one OBD1 BMW tuner in SF Bay Area) hope he can tune out the fuel trim. I have an INPA set up that he can use to look at the STFT and LTFT and adjust accordingly.
I hope I am on the right path.... any suggestions welcome.

If you changed the base fuel pressure, that's probably the start of your issues.

I don't know how that Motronic ECU deals with injector calibration, but if there is an injector constant and dead time tables you will need to adjust that all first before anything else to keep the fuel trims happy. Unfortunately I don't know what logging capabilities you have on that ECU, if you have none at all I would suggest you just give up now because it will be a nightmare to do any sort of calibration without being able to see how the ECU is reacting to the changes (especially fuel trims!).

Best you can do at this point is make best guesses and try to remain at lambda 1 at all times until the WOT map is active as that is most likely what the ECU will want to be at during closed loop operation, that will probably minimize the fuel trim issue and get you where you want to be for now.

[dragon850]

If you changed the base fuel pressure, that's probably the start of your issues.

I don't know how that Motronic ECU deals with injector calibration, but if there is an injector constant and dead time tables you will need to adjust that all first before anything else to keep the fuel trims happy. Unfortunately I don't know what logging capabilities you have on that ECU, if you have none at all I would suggest you just give up now because it will be a nightmare to do any sort of calibration without being able to see how the ECU is reacting to the changes (especially fuel trims!).

Best you can do at this point is make best guesses and try to remain at lambda 1 at all times until the WOT map is active as that is most likely what the ECU will want to be at during closed loop operation, that will probably minimize the fuel trim issue and get you where you want to be for now.

Fuel pressure itself is not monitored on an M70, I basically just raised my injector output from 24lb to 27lb which made motronic trim fuel in closed loop.
Unfortunately the XDF file for the M70 is not very advanced, all I have to play with is timing, ignition and low/mid/high part throttle maps. I do have an INPA set up that shows STFT and LTFT values, so the plan is to keep the car in closed loop through the RPM ranges and adjust the maps accordingly while monitoring STFT/LTFT on INPA, then RE tune the WOT. (basically same thing you suggest is to remain at lambda 1 throughout RPM).

[dragon850]

On another subject, let's say I do go for a MoTEC engine management(or some other standalone), how would that play with the rest of the car systems? Will the OEM speedometer cluster work the same for example? What do I loose by going with standalone?

[vwmikel]

Have you considered just using a rising rate fuel pressure regulator? Normally, I think they suck, but what you've done seems like a relatively small change. It should improve your LTFT and give you the extra pressure under boost.

[NOTORIOUS VR]

On another subject, let's say I do go for a MoTEC engine management(or some other standalone), how would that play with the rest of the car systems? Will the OEM speedometer cluster work the same for example? What do I loose by going with standalone?

I doubt anything on the 840/50 is CAN based, so everything should work just fine with an aftermarket ECU. Should be pretty easy to tell if you have schematics available.

Have you considered just using a rising rate fuel pressure regulator? Normally, I think they suck, but what you've done seems like a relatively small change. It should improve your LTFT and give you the extra pressure under boost.

Normally I don't agree, but it could be worth a shot for a band aid with the tune already done from Europe and back with the injectors it calls for.

[dragon850]

Have you considered just using a rising rate fuel pressure regulator? Normally, I think they suck, but what you've done seems like a relatively small change. It should improve your LTFT and give you the extra pressure under boost.

I thought about this, so go back to 3 bar rail FPRS and add a rising rate fpr for when the car goes into boost? Hmmm, well that might be something I will have to do if I the fuel trim cannot be tuned out.

[dragon850]

I doubt anything on the 840/50 is CAN based, so everything should work just fine with an aftermarket ECU. Should be pretty easy to tell if you have schematics available.




Normally I don't agree, but it could be worth a shot for a band aid with the tune already done from Europe and back with the injectors it calls for.

Here are the E31 schematics: http://www.armchair.mb.ca/~dave/BMW/e31/e31_91.pdf

Really this got me thinking, I could connect 1 rising pressure regulator through the Y adapters from two fuel lines going into two rails. Is there a recommended one?

[dragon850]

Since I would want my WOT AFR at around 12 I assume would then have to re tune my WOT map based on the connected FMU?