Spoofing the Motronic 1.3 (aka basic engine theory)

[Jeff N.]

OK - after a break for a while, I'm back to trying to tune out my modified M30 motor. Serveral observations:

First, my engine performes better at low to mid throttole on the cold run cycle. I believe this is because of added low speed timing advance. (My wideband 02 suggests my mixture is OK) The theory that I'd like to validate is

- if the mixture is richer than stoich, you want to advance the ignition timing at low RPMs. Richer mixture needs more time to ignite thus the added advance.

Second, my engine looses noticable power on hot days (80 degrees F+). I am running a MAF and AIT sensor (Air Intake Sensor). I believe the MAF should account for the change in air density and not need the AIT. The AIT I believe is retarding my timing. The theory I'd like to validate is -

- if the air tempature rises, the amount air is less dense. You have to reduce the fuel pulse to maintain a constant mixture. Alternately, or concurrently (which is what I think the motronic does) you reduce the advance to mitigate the chance of ping/knock with a lean mixture.

I'm really starting to wonder if I should put a choke on the AIT sensor to force the car to see a constant air temp. I've run the AIT unplugged which generates a CE light. I suspect this condition causes the motronic to adopt a very conservative timing (retarded) timing position. Retarded timing = low power.

Also, I believe my car, due to the cam, benefits from low speed ignition advance that comes on during cold run. Advanced low speed timing = better power. I'm wondering if I should also consider choking the cold run sensor to a "cold" state to for the ECU advance the ignition. I can counter the rich mixture by adjusting my MAF signal.

Thoughts anyone?

Jeff

[genphreak]

Hmm I can't add much, but it's a real PITA that Motronic has no data logging port. Could there be some way to achieve this I wonder... it would make many things much more easy.

The factory system doesn't seem to collect enough inforrmation from the engine port... :) Nick

[Anton CH.]

OK - after a break for a while, I'm back to trying to tune out my modified M30 motor. Serveral observations:

First, my engine performes better at low to mid throttole on the cold run cycle. I believe this is because of added low speed timing advance. (My wideband 02 suggests my mixture is OK) The theory that I'd like to validate is

- if the mixture is richer than stoich, you want to advance the ignition timing at low RPMs. Richer mixture needs more time to ignite thus the added advance.

I always thought that denser mixture burns quicker. But double check that. 11.5 AFR being the quickest. Are you getting knock?

Second, my engine looses noticable power on hot days (80 degrees F+). I am running a MAF and AIT sensor (Air Intake Sensor). I believe the MAF should account for the change in air density and not need the AIT. The AIT I believe is retarding my timing. The theory I'd like to validate is -

- if the air tempature rises, the amount air is less dense. You have to reduce the fuel pulse to maintain a constant mixture. Alternately, or concurrently (which is what I think the motronic does) you reduce the advance to mitigate the chance of ping/knock with a lean mixture.

Did you modify the epprom code in M1.3? I know your are supposed to do so b/c the ecu uses IAT for air density calculation with AFM whereas MAF accounts for density by itself.

I'm really starting to wonder if I should put a choke on the AIT sensor to force the car to see a constant air temp. I've run the AIT unplugged which generates a CE light. I suspect this condition causes the motronic to adopt a very conservative timing (retarded) timing position. Retarded timing = low power.

Also, I believe my car, due to the cam, benefits from low speed ignition advance that comes on during cold run. Advanced low speed timing = better power. I'm wondering if I should also consider choking the cold run sensor to a "cold" state to for the ECU advance the ignition. I can counter the rich mixture by adjusting my MAF signal.

Thoughts anyone?

Jeff

[Bellicose Right Winger]

You can trick the AIT with a fixed resistor, but I think you'll have to trick the DME's coolant temp sensor also, since it adds fuel on a cold start. Hopefully it'll still start after you cancel all the cold start enrichment.

Paul Shovestul

[Martin in Bellevue]

Why not spend some time with yer kid for a change?

Not that it helps you much, but the split second boxes provide for a constant resistance signal for spoofing the IAT signal to 70F. I am still using the IAT from ProM.

Thread hijack:
I looked at the clutch stop on the m3 this morning. There was an extra nut in there, making full release impossible. It goes right into 1st & reverse now. It is much better. The pedal travel is wildly long now, like it should be.
Also, the supacharged m3 convertible didn't get anywhere near the 31mpg on the 770 mile roadtrip to CA, that the 535 got. Nowhere near that mileage, & I didn't have quite the high average speed that I got with the 5er due to traffic, construction zones, dodging drunks & wrecks while trying to get out of Hippieland at 2am on a Sunday morning. That thing is impressive blasting past traffic pockets on the highway.

[JoeS]

I thought it was 72 degrees, but who is counting. I , as well, notice better performance on cooler days , but it is not a huge difference. My problem is in the indiana winters on start up the car runs like **** until it is half way warm. (since it thinks it is 72 degrees).

[Jeff N.]

.. mine used to run like crap on cold mornings too. turned out the idle mixture was way too rich. when cold it was basically flooded. once warmed, between the cold run ending and the warm engine better able to take the fuel, it would run fine.

bet you're rich as all hell on that idle circuit.


I thought it was 72 degrees, but who is counting. I , as well, notice better performance on cooler days , but it is not a huge difference. My problem is in the indiana winters on start up the car runs like **** until it is half way warm. (since it thinks it is 72 degrees).

[Jeff N.]

...not like that rock crusher when I drove it??


Why not spend some time with yer kid for a change?

Not that it helps you much, but the split second boxes provide for a constant resistance signal for spoofing the IAT signal to 70F. I am still using the IAT from ProM.

Thread hijack:
I looked at the clutch stop on the m3 this morning. There was an extra nut in there, making full release impossible. It goes right into 1st & reverse now. It is much better. The pedal travel is wildly long now, like it should be.
Also, the supacharged m3 convertible didn't get anywhere near the 31mpg on the 770 mile roadtrip to CA, that the 535 got. Nowhere near that mileage, & I didn't have quite the high average speed that I got with the 5er due to traffic, construction zones, dodging drunks & wrecks while trying to get out of Hippieland at 2am on a Sunday morning. That thing is impressive blasting past traffic pockets on the highway.

[Bill R.]

not help you some.

[Bill R.]

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[Bill R.]

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[Jeff N.]

The other stuff I pretty much have figured out...curious the source of all this.

Thx Bill!

Jeff

[BillionPa]

bosch manual?

[zygoteer]

... Richer mixture needs more time to ignite thus the added advance.

True, the speed of the flame front (explosion) is slower.


... if the air temperature rises ... you reduce the advance to mitigate the chance of ping/knock with a lean mixture.

Yes, this is logical action that most ECU's take, but obviously in varying magnitude.


... I can counter the rich mixture by adjusting my MAF signal.

This will work, but only partially - not the complete answer.

[Jeff N.]

Concur that spoofing a cold run to get advance and then cutting back the airflow signal is a less than desireable hack.

Again, curcur adjustments are ECU dependent. Have any details on how the motronic adjusts?


True, the speed of the flame front (explosion) is slower.



Yes, this is logical action that most ECU's take, but obviously in varying magnitude.



This will work, but only partially - not the complete answer.