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Thread: E500 won't pull past 4000rpm

  1. #1
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    E500 won't pull past 4000rpm

    My 1994 E500 has recently stopped pulling properly between 4000rpm and redline
    No misfire or stuttering, it just goes flat from 4000rpm; worse in the higher gears.
    I appear to be getting full throttle and car has recent (correct) spark plugs gapped at 1mm, air filters,fuel filter, rotor arms, caps, new upper loom and rebuilt lower loom, pcv hoses etc. The car ran fine after this work was carried out and still starts, idles and runs perfectly up to 4000rpm, hot or cold
    I haven't had a chance to get the codes read yet but my local tuner did put his afr probe in the tailpipe and it showed approx 14.5:1 across the board which I understand is correct for the facelift cars and matched what was seen during a dyno run a couple of years ago before the current issue arose.
    We also think we've ruled out the cats as an infrared temperature probe shows nothing unexpected on either bank, before and after the cats
    Any suggestions on where to look next?
    Last edited by B16 NYK; 06-17-2018 at 12:37 PM.

  2. #2
    Member rinconmann's Avatar
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    Re: E500 won't pull past 4000rpm

    Perhaps ECU? Engine control unit? Maybe, Old engine wire harness? If so buy used ECU from a member. I think I paid...well too much in Santa Barbara, CA 10 years ago. Anyways I recall similar issues when my 1st harness went out at about 100K. I replaced harness and ECU and all was well. If you don't have the right 32 pin code reader you need to go to a MB dealer or shop that has one for a PROPER CODE READ. Someone here can save you big time as they hoard parts...you know who you are!

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    Re: E500 won't pull past 4000rpm

    I would run the car and check fuel pressure, to make sure there are no issues with fuel delivery.

    Very likely that your catalytic converters are plugged, which suffocates the breathing of the engine. In the past when folks have complained of this type of symptom, more often than not it's been an overly restricted cat.

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  5. #4
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    Re: E500 won't pull past 4000rpm

    Do the cats rattle? How many miles are on them and are they OE? I’d be willing to gamble they’re toast, no matter what the sniff and temp tests show. But maybe that’s just me. Mine were toast and rattling with zero performance issues. I could also see it being a MAF.

    maw
    Last edited by maw1124; 06-16-2018 at 08:42 PM.

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    Re: E500 won't pull past 4000rpm

    You may want to hook a vacuum gauge up to one of the vacuum lines and see what happens when you drive it. If it goes to zero at any point it’s probably the cats. A good place to tap in is by the brake booster where one line feeds the three HVAC pods.

    https://www.500eboard.com/forums/sho...ll=1#post73065
    Jon D.
    1994 E420
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  9. #6
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    Re: E500 won't pull past 4000rpm

    You also get this symptom with the wrong type of ignition coils.

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  11. #7
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    Re: E500 won't pull past 4000rpm

    I didn't see this mentioned, but you also need to check all codes, clear all codes, run the car into the 4000rpm phantom limiter, and see if any codes have returned. Could be a failing starter lockout / neutral safety switch (NSS), or a mis-adjusted NSS if it won't rev beyond 4000rpm.

    If it DOES rev beyond 4000, but is very weak from 4000 to 6000rpm, then the plugged catalysts would be pretty high on the list to check. Zero codes (after clearing and driving again) would also point towards either catalysts, or a fuel supply issue. If the fuel pumps are old / original, it's not a bad idea to replace them with new Bosch as preventive maintenance anyway. I've only heard of one case where the tank strainer was restricting fuel supply, so while very rare, it's a remote possibility.

    Dave M.
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    Re: E500 won't pull past 4000rpm

    If there’s any kind of back-firing when trying to get it above 4000 RPM, for troubleshooting purposes, be careful. I think I damaged a head gasket by holding it in 2nd gear trying to do this. It has been running on Bar’s head gasket sealant since 2014.
    Jon D.
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    Re: E500 won't pull past 4000rpm

    Quote Originally Posted by gsxr View Post
    I didn't see this mentioned, but you also need to check all codes, clear all codes, run the car into the 4000rpm phantom limiter, and see if any codes have returned. Could be a failing starter lockout / neutral safety switch (NSS), or a mis-adjusted NSS if it won't rev beyond 4000rpm.

    If it DOES rev beyond 4000, but is very weak from 4000 to 6000rpm, then the plugged catalysts would be pretty high on the list to check. Zero codes (after clearing and driving again) would also point towards either catalysts, or a fuel supply issue. If the fuel pumps are old / original, it's not a bad idea to replace them with new Bosch as preventive maintenance anyway. I've only heard of one case where the tank strainer was restricting fuel supply, so while very rare, it's a remote possibility.

    Good catch, GSXR. I’d written NSS but deleted it because OP didn’t indicate a CEL. Maybe they don’t always throw a CEL, but my NSS did.

    maw

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    Re: E500 won't pull past 4000rpm

    Thanks chaps, some suggestions to follow up there
    Just to clarify, car has done 74000 miles and does pull past 4000rpm, just weakly so not likely to be NSS. No CEL either. No rattle from cats or signs of impact damage to the exhaust
    Re GSXR's suggestion of a possible fuel supply problem; wouldn't that cause the AFR to go lean at higher revs?
    Thanks again for your suggestions
    Nick

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    Re: E500 won't pull past 4000rpm

    Good detective work. How’s the MAF? And I’m gonna double down on GSXR, are the fuel pumps original? At 74k miles, I can’t think of what would be bad, other than what I’ve said. My cats and NSS were both bad in the 60k’s. A lot of these things (fuel pumps in particular) are more time than mileage dependent.

    Clear codes, see what comes back.

    GL,

    maw

  17. #12
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    Re: E500 won't pull past 4000rpm

    Quote Originally Posted by B16 NYK View Post
    Re GSXR's suggestion of a possible fuel supply problem; wouldn't that cause the AFR to go lean at higher revs?
    1994 models remain in closed loop at full throttle, and regardless the LH will fuel based on MAF readings even if it's ignoring the O2... so in theory, if there is a fuel shortage, it may still keep AFR's at normal levels. To check fuel delivery you'd need a gauge that can be monitored while driving at heavy throttle over 4000rpm to see if the power drops. I kinda doubt this is the problem, in the past when I've had dying fuel pump(s), it was very intermittent and not RPM-specific.

    Since your issue is high-RPM only, I'm still leaning towards plugged catalysts as high on the list. They may not rattle. Jon's test with the vacuum gauge is the easiest method, a more precise test involves getting an exhaust backpressure gauge that can be viewed while driving. That will tell you positively, and immediately, if the cats are plugged.


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  19. #13

    Re: E500 won't pull past 4000rpm

    B16 NYK,
    If there is any way you can temporarily delete the cats, then drive it and see if you have the same issues at high RPMs, that can eliminate the cat issue or confirm it?

  20. #14
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    Re: E500 won't pull past 4000rpm

    As I originally said:

    1) check fuel pressure live while driving

    2) replace catalytic converters due to plugging.

    Cheers,
    Gerry

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    Re: E500 won't pull past 4000rpm

    Jon D.
    1994 E420
    1995 E420

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