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1 QUESTION AWAY FROM DRIVING 700

posted by  TurboWagon91 on  Fri Jun 8 17:02 CST 2007
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last visit: Tue Mar 12 09:22 CST 2013
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Hiya fellow Brickers. I have a 91 745T, which I purchased not running from a local used car dealer. I have been through the car thouroughly, and am at the point where the car will start, but won't go over about 400 RPM. My car is equiped with the Bosch LH-2.4 Fuel system & the Bosch EZ-116K Ignition. Here's my question. While testing wiring, voltages, etc., I have found that the Yellow wire, which goes from term.# 25 at the fuel ECU, to term.#8 at the ignition ECU, has 0 voltage with the key on, engine running or not. Does this indicate a bad ECU, or does this voltage (load signal) originate at the AMM? Since the engine starts & runs, but acts like greatly retarded timing, I believe this load signal will allow the Ignition ECU to provide spark advance to run the engine. The car has 136000 miles on it, 44 lb. fuel pressure at the rail, has spark, complete major tune-up, including fuel filter, 145 lb compression per hole, all new vacuum hoses, new power stage, throttle sensor, coolant sensor, and more. Any advice or suggestions would be GREATLY appreciated.
Thanks in advance.
Ken








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    1 QUESTION AWAY FROM DRIVING 700

    posted by  someone claiming to be Barry De Hatchette on  Sat Jun 9 01:48 CST 2007 [RELATED]

    "I have found that the Yellow wire, which goes from term.# 25 at the fuel ECU, to term.#8 at the ignition ECU, has 0 voltage with the key on, engine running or not. Does this indicate a bad ECU, or does this voltage (load signal) originate at the AMM?"

    No, that "load signal" originates in the ECU, "twice per rev in the part load range". It's a variable voltage and seems to be a "test" to let the EZK know that the LH is doing just fine. If the EZK doesn't see it as expected, it will set a 1-4-4 code and the check engine light.

    Seems like you haven't made it to the "part load range" yet, which I assume is based on something like 2000 rpm. But that's just a guess. At any rate, I'd say that 0.0V is normal in your case.

    Have you tried the OBD I diagnostic exercisers in Mode 3? That's all I can think of right now.








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    1 QUESTION AWAY FROM DRIVING 700

    posted by  someone claiming to be George on  Fri Jun 8 18:54 CST 2007 [RELATED]

    Here is an easy test for the AMM:

    With the ignition OFF, unplug the AMM from the wiring harness. Then, start the car. It will idle rough, but if the AMM is indeed faulty, you should be able to run the engine up to about 2500 rpm or so. This is "limp home mode" - when the ECU does not see a signal from the AMM it defaults to a preset mixture that allows the engine to run just well enough to "limp" to a garage or back home.

    When the AMM failed in my 240 (LH 2.2), it would just barely idle and the car did not respond to the throttle being opened.







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