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My car hates 173 dme...

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    My car hates 173 dme...

    I had an 86 325es that had been converted to motronic 1.3. It had a markD chip and ran great. Then it started messing up. It would constantly stall like I kept shutting the key off then on then off and on and repeated it. Idle would surge. Narrowed it down that when I put the 153 dme in it ran perfectly fine...well as well as a 153 can run.
    So last month I did a shell swap. New shell was an 89 325i. Cool, the engine harness is finally correct to the body harness. Did the swap. Front end, rear end, all drivetrain and interior. The dash and all body wiring were still in the car unmolested. I decided to try out the chipped 173 again. Ran amazing for about a week and a half then the same previous issues occurred again. This time I knew I could check codes and pulled a 1264-ego heater. All the wiring is new as well as the o2 sensor. I checked fuse 9 after researching and it's fine and the relay is operational. I put a stock 173 in the car and same issues so I'm not thinking it's the chip. Could it just be something in the engine harness? It isn't the prettiest. I'm about out of ideas on where to check at this point. I'm currently running the 153 again with no issues. Are there any differences between the two dmes? Like does one read more efficiently and doesn't like what it is getting? I can get a video of how it runs with the 173.
    Note: battery was disconnected before doing any changes between any electronic parts.

    #2
    It's the engine harness. Never figured out why, but twice I have had cars come in the shop with the same exact issue. From memory, the TPS voltage in the harness was off. It should be 5v and I was getting 8v which would indicate a short somewhere.

    One car, I swapped the harness and it was fine, the other owner was OK with just keeping a 153.

    On a side note, there's not a whole lot of advantage to running a 173 over a 153 - unless you have a performance chip for one and not the other (chips are not compatible).
    john@m20guru.com
    Links:
    Transaction feedback: Here, here and here. Thanks :D

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      #3
      I have a markD chip in the 173. I thought it was the chip going bad so got a good stock 173 with the same result. The 153 isn't awful. But I do get a hiccup every couple of miles that's rather annoying. It'll flash the check engine light and misfire almost.
      I'll try to grab an engine harness. Any idea why it's fine with the 153 and not 173? Seems weird unites the 173 reads more efficiently and particular

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        #4
        Not entirely sure why one worked and the other didn't. The only diagnosis was the weird voltage on the TPS connector on the harness. Key on, engine off, two of the 3 pins should be 5v and I was getting 8v (IIRC). If you have a volt meter, probe the three TPS pins and see if you also have something weird going on. Perhaps the 153 is less sensitive to voltage on the TPS?

        I have read the stock chips and there's no advantage to use a 173, except the hardware is a little updated over the 153 (Motronic 1.1 vs 1.3).
        john@m20guru.com
        Links:
        Transaction feedback: Here, here and here. Thanks :D

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          #5
          I'll take some readings tomorrow. Are you also on camaro forums as well? Think I've seen you on there

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