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Thread: E34 535i ECU - Transmission signals?

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    E34 535i ECU - Transmission signals?

    Gentlemen,

    I'm thinking of going Megasquirt and trying to determine whether my auto transmission's computer will still work if I do. Does anyone know what signals are shared between the E34 535i auto (4HP22 transmission) and the ECU? In other words, what inputs does the trans need from the ECU to work?

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    Why not tune the stock ecu?

    Quote Originally Posted by E34DIYer View Post
    Gentlemen,

    I'm thinking of going Megasquirt and trying to determine whether my auto transmission's computer will still work if I do. Does anyone know what signals are shared between the E34 535i auto (4HP22 transmission) and the ECU? In other words, what inputs does the trans need from the ECU to work?

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    Because you can't... Only options are the Miller W.A.R. chip or standalone.

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    Quote Originally Posted by E34DIYer View Post
    Because you can't... Only options are the Miller W.A.R. chip or standalone.
    I guess it depends on what boost you want to run. I'm running 8 psi with my stock 179.
    demet

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    But are you tuning the chip or just using a RRFPR and/or tweaking the AFM?

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    Just a RRFPR and a Hobbs pressure switch to ground the WOT signal at 4 psi. Some do a O2 sensor cutoff at boost but that throws the check engine light on. Blew a couple of headgaskets until I found a problem injector but I would imagine that would happen even with megasquirt since individual cylinders are not monitored by a single wideband. The car works well now. My wife drives it as the winter beater now that her e28 is in the garage. By some strange reason, which I have yet to figure out, her commute times have been cut in half. I think I need to be worried.

    I forgot to add that I adjusted the AFM to give me the best stoich running for passing CT emissions and I just left it there. This is how I adjusted it: http://www.bimmerboard.com/members/d...justment_d.pdf

    cheers
    Last edited by demetk; 02-05-2013 at 10:01 PM.
    demet

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    Nice. Back to my issue... I'm starting to think that I'm stuck with the W.A.R. chip until I can convert to manual transmission. There appear to be several circuits that communicate between the transmission and engine, so deleting the stock ECU on my auto trans car doesn't seem to be an option.

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    I see pin 51 & 54 as outputs from the dme to the tranny control unit. It doesn't tell me what outputs they are so I guess you need reference a 179 pin diagram. I'd be interested if you can find one.
    demet

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    Where'd you see the DME pinout? Bentley manual? I'm trying to find a copy of the Electronic Troubleshooting Manual for my 1990 535i, but I'm coming up empty.

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    http://wedophones.com/BMWManualsLead.htm

    I also see pin 3 -> pin 21. looks like the dme grounds the fuel pump relay pin 85. The tranny module maybe gets a ground from here.
    demet

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    According to my Bentley, pin 3 is fuel pump relay control and pin 21 is vacant.

    EDIT: It looks like pin #32 may be the only output related to the transmission control computer. Everything else could be engine inhibit for limp-home mode, which would be ignored in Megasquirt. If that's all it is, then maybe I'm not dead in the water after all.
    Last edited by E34DIYer; 02-05-2013 at 11:03 PM.

  12. #12
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    the 179 ecu can be tuned for boost. thats what Im doing in my turbo conversion

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    It looks like most of the communication between the two are inputs to motronic (you can ignore them then). Pin 32 is the fuel consumption signal, which can be emulated. This means, that your fuel economy gauge would work too.

    The only problem I see is keeping the TPS for the auto computer. Maybe you could just tap the signal line for megasquirt? I believe Its the black one on the white molex connector (8 or 10 pins?) in the ecu compartment.

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    Ah, the man himself weighs in. If I clip Pin 32, will that just disable fuel consumption calculation, or will it actually break the trans computer? I saw where this can be emulated using a Seattle Circuit emulator. Is there perhaps a cheaper option (<$90)?

    Regading the TPS - I thought the TPS wiring split, and the appropriate wiring went directly to the trans comp. Is that not the case?

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    If you clip the pin, you would get no kva signal from the ECU. This means no MPG calculation on the cluster and presumably a non functional transmission. It probably uses it as a load indicator.

    There are other ways to make the kva signal, but if you are not a programmer, $90 is a bargain.

    The problem with the TPS, is that there is only one of them. The Motronic setup was a switch to ground (not a variable tps) and is unsuitable for megasquirt. This happens to be housed inside the auto TPS, but the pins that go to the 55-pin are not from the variable TPS portion. The wires from the variable TPS, though running through the same loom, end up at that 8 or 10 pin molex connector.

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    So to run my auto trans, I need to figure out how to defeat both the fuel/load signal, and the TPS inputs... Getting out of my depth here.

    Ryan, any tips on wiring the fuel signal emulator from Seattle? Any recommendations on which wires to tee into?
    Last edited by E34DIYer; 02-06-2013 at 06:27 PM. Reason: Automerged Doublepost

  17. #17
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    This is all possible, but it may be easier if you just tap into the existing harness, and leave the stock one in place to keep the tranny happy. This is known to work. Just clip and tap the injector wires and ignition lead. The rest can probably just be tapped and shared.

    This would also be much cheaper. Ms2 kits are only a few hundred I think. A used harness is cheap if you need to revert to stock.

    Actually, a micro squirt will run an m30 just fine and would be cheaper AND is water tight AND preassembled... Need I go on?
    Last edited by Goathumper; 02-07-2013 at 01:47 AM. Reason: Automerged Doublepost

  18. #18
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    My plan is to go to a Microsquirt-based Plug and Play as sold by whodwho, retaining my stock wiring harness, stock TPS, and so on.

    Here's my build thread with comments: http://forums.bimmerforums.com/forum...1924243&page=2

    Here's the MS PnP I am considering buying: http://forums.bimmerforums.com/forum...92&postcount=8

    I am trying to wrap my brain around anything that may break when I pull out the stock ECU. Matt Cramer at DIYAutotune thinks that the only essential output from the stock ECU to the trans is pin #32, which is fuel consumption data. Along with feeding data for MPG/distance-to-empty calculation on the OBC, we think that it might possibly send commands to the trans computer.

    I may temporarily cut the wire to pin 32 this weekend, just to see what happens when the transmission computer loses that particular signal.
    Last edited by E34DIYer; 02-07-2013 at 08:18 AM.

  19. #19
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    Bump - revisiting this. And I did cut pin 32 at the trans computer, with the result of knocking the transmission into limp-home mode.
    E30 325iC turbo convertible project in progress (updated 12/23/15):
    Car fully tuned on completely rebuilt M20 w/forged internals, MLS head gasket
    Suspension, brakes, exhaust fully installed
    New carpet, custom reupholstered seats installed, door panels painted to match
    Custom center console gauge panel installed
    Plastic bumper conversion complete, MTech2 front spoiler installed
    Rear bumper conversion in progress
    Build thread: http://forums.bimmerforums.com/forum...on-engine-swap

  20. #20
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    Update: I (well, Andrew) scoped the signals today. Here's what we found: Transmission fuel load signal matches the pulse pattern of the injectors. Only difference is that the transmission fuel load signal appears to be a 12V baseline that grounds to 0V for every pulse. It's sort of a binary On/Off signal, where "Off" = an injector pulse.
    E30 325iC turbo convertible project in progress (updated 12/23/15):
    Car fully tuned on completely rebuilt M20 w/forged internals, MLS head gasket
    Suspension, brakes, exhaust fully installed
    New carpet, custom reupholstered seats installed, door panels painted to match
    Custom center console gauge panel installed
    Plastic bumper conversion complete, MTech2 front spoiler installed
    Rear bumper conversion in progress
    Build thread: http://forums.bimmerforums.com/forum...on-engine-swap

  21. #21
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    Another update. Got a custom built MSPNP box installed in my car. Cranks fine, idles, and revs just fine. Keith (whodwho) wired it to send pulses to pin 32 to emulate the fuel load signal. Only problem is that my injectors are larger than stock and the signal isn't being scaled, so the pulses are way out of range of what the transmission computer expects. Hoping to get my hands on a fuel signal emulator so I can scale the signal.
    E30 325iC turbo convertible project in progress (updated 12/23/15):
    Car fully tuned on completely rebuilt M20 w/forged internals, MLS head gasket
    Suspension, brakes, exhaust fully installed
    New carpet, custom reupholstered seats installed, door panels painted to match
    Custom center console gauge panel installed
    Plastic bumper conversion complete, MTech2 front spoiler installed
    Rear bumper conversion in progress
    Build thread: http://forums.bimmerforums.com/forum...on-engine-swap

  22. #22
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    E34DIYer Did you ever have any luck with the auto?

    I’ve put a DIYAuto MSPNP in my 1989 635csi.
    M30 engine runs great. But the 4hp22eh auto is in limp mode. Trying to figure out what to do next?

    Without buying an expensive compushift standalone for the auto.

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