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Thread: 1994 E500E - Unresolved Misfiring [Pulled Codes]

  1. #1
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    1994 E500E - Unresolved Misfiring [Pulled Codes]

    Hello all! Longtime lurker, first time poster.

    I have a 94' e500 with 110k miles on the clock that could use your help. It has an updated upper wiring harness, original lower harness.

    Over the past month or so I've been experiencing an issue with an engine misfire while driving. The vehicle would be at cruise (say 45mph) at light throttle to maintain speed and the engine would suddenly feel lean for just a moment and then return to normal. Over the course of a month this issue manifested into a more prominent but momentary "blip" in power, and now to a rather severe lurch while at partial throttle. Heavy or WOT the car pulls fine. So I don't it's a fuel starvation issue.

    I started with the usual suspects: caps, rotors, plug wires, and plugs. I installed new bosch caps & rotors, and F8dc4's. The insulators are original but in fine condition. The wires had already been replaced by the PO with Bremi wires. All appear and feel new, though in typing this I just realized I haven't actually checked their resistances. No improvement with the issue after the above changes.

    Next I suspected the ETA. It's original to the car (93' production date), so I replaced it with a shelved unit that I picked up from a junkyard a year or so ago. It's an old unit as well, but since I had it on the shelf I figured I'd try it out. Once installed and calibrated, I test drove the car. No change in run quality (though it does rev' a bit higher on startup which is neat). I replaced the throttle body boot and the the PCV hoses during the change too.

    So next I did what I should have done from the start and pulled the codes. This was new for me, as I've only ever used the DM module LED blinker. This time I tried out the HFMscan software/ adapter to pull the codes across all the modules. Two codes were stored: 004; and 010. I've paste'd the readout below:

    004, Post
    4 Voltage at air mass sensor with hot wire.
    Voltage too large/small or ground cable at air mass sensor
    open circuit. (The fault may be ignored on vehicles up to 07/91)
    Verify voltage at air mass sensor with hot wire.
    While IGNITION=ON = 1,0-1,2 V - ENGINE=IDELING = 1,3-1,7 V.
    Verify also the ground cable for sensor. (While IGNITION=OFF < 6 Ohm)
    __________________________________________________ ___________
    010, Post
    10 Idle speed recognition from electronic accelerator pedal faulty.
    Control unit has short circuit.
    Verify idle speed recognition signal voltage from EA pedal actuator.
    While IGNITION=ON, and accelerator in idling position < 4,8 V
    While IGNITION=ON, and accelerator in full throttle position > 5,5 V
    On vehicles up to 7/91 fault may be displayed although no fault exists.


    Looks like a fault with the MAF sensor, and what I believe is the momentary switch above the pedal? I think I saw another post on here about an issue with that. I'm new with HFMscan, but I'm pretty sure it pulls fault codes from all modules right? Not just the diag module.

    Before I throw more parts at my problems, what do you guys think?

    I did try driving around with the MAF unplugged. But I experienced the same issue.

    Open to all thoughts and criticisms lol. Thanks!
    1995 E320 - 1988 300CE - 1993 400E - 1987 300D - 1987 300D - 1984 500SEC - 1985 500SEC - 1986 190E 2.3-16V EFI - 1987 300TD - 1994 E500E

  2. #2
    .036 Hoonigan™
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    Re: 1994 E500E - Unresolved Misfiring [Pulled Codes]

    Quote Originally Posted by CRodgers View Post
    So next I did what I should have done from the start and pulled the codes. This was new for me, as I've only ever used the DM module LED blinker. This time I tried out the HFMscan software/ adapter to pull the codes across all the modules. Two codes were stored: 004; and 010. I've paste'd the readout below:
    Minor clarification... HFM Scan for LH will only pull codes from the LH module. AFAIK, it can not pull codes from all 6 powertrain modules. You need a hand-held blinker box, or MB-specific digital scanner (Star/SDS), to check the other modules. More info in the "sticky" posts in the DeCoding forum at this link.

    Anyway, code #4 does make the MAF appear to be suspect. However, first clear that code and see if it comes back. It could be a phantom code from aeons ago. And the fact that driving with the MAF unplugged doesn't change anything, makes me thing the MAF could be a red herring.

    Code 10 may be related to your ETA replacement. The throttle linkage is very, very picky about being set up just right.

    Total wild guessing here, but the one time I encountered something similar to what you describe, it ended up being a vacuum leak due to a deteriorated rubber hose elbow. I'd start by chasing down every vacuum tube under the hood (there are only a half-dozen total) and verifying everything is intact and holding vacuum. A smoke machine might speed up the process if you have one.

    Dave M.
    1997 E420 (Bugeyes)
    1994 E420 (Blondie)
    1994 E500 (Q-ship)
    1992 500E (Mach 5)
    1987 300D (Sportline Stage 2)
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