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Thread: Spoofing the Motronic 1.3 (aka basic engine theory)

  1. #1
    Join Date
    Dec 2003
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    1,639

    Default Spoofing the Motronic 1.3 (aka basic engine theory)

    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
    Bellevue WA
    90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
    86 Porsche 951 - Track Toy

  2. #2
    Join Date
    Dec 2004
    Location
    Sydney, Australia
    Posts
    4,353

    Default

    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

    Join the Aussie
    540i LE yahoo forum

    08/88 535i e34 M30+miller MAF, 'stiens, tints & teeth!

  3. #3
    Join Date
    Jan 2004
    Location
    Fogtown
    Posts
    656

    Default

    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

  4. #4
    Join Date
    Mar 2004
    Posts
    404

    Default

    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
    .....Got to keep the loonies on the paath.

  5. #5
    Join Date
    Dec 2003
    Posts
    835

    Default

    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.
    erased due to slander

  6. #6
    Join Date
    Jan 2004
    Location
    indiana
    Posts
    115

    Default Martin is correct : spilt second has constant temp...

    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).
    JoeS
    _____________________________________________

  7. #7
    Join Date
    Dec 2003
    Posts
    1,639

    Default did you ever get a wideband joe?

    .. 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.

    Quote Originally Posted by 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).
    Bellevue WA
    90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
    86 Porsche 951 - Track Toy

  8. #8
    Join Date
    Dec 2003
    Posts
    1,639

    Default oh..you mean it shifts like an M3 now????

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

    Quote Originally Posted by 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.
    Bellevue WA
    90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
    86 Porsche 951 - Track Toy

  9. #9
    Join Date
    Jan 2004
    Posts
    4,148

    Default A little more info on the motronics 1.3, it may or may

    not help you some.
    Attached Images Attached Images    


  10. #10
    Join Date
    Jan 2004
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    4,148

    Default And some more

    .
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