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Thread: Poor running after sitting, which then cures itself...

  1. #1
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    Poor running after sitting, which then cures itself...

    First post on here, and I'm puzzled by this one. '93 400E with nearly 200k miles on it now. Have had the car for about a year now, gradually going through maintenance items as time and budget allow, trying to learn and correct its faults and quirks. Here's the basics of it - let's say I've been using it as a daily for a week or so. It will be running fantastic - engine is butter smooth, barely know it's running at idle, no squeaks or rattles, shifts well, propels you forward on that never-ending wave of torque. It's wonderful.

    Let it sit for 48-72 hours - starts right up, idles great. But once you're doing like 40mph and you give it some gas, it bogs down. Gas pedal can be floored and it just sits there at like 1500rpm, ever so gradually climbing to 1600. Manually downshift it to 3rd, it improves, but there's still a bit of a shudder. After maybe 20 miles and/or 20 minutes, the problem is completely fixed. Back to its old self. You can actually feel it improving as the minutes tick away.


    Let it sit for say 5 days, and it still starts right up. But now it hunts at idle. It might stall at a red light. It will bog leaving an intersection, even if shifted into 3rd or even 2nd. 40mph to 60mph is glacial. This time it takes about 30 miles/minutes to fix itself. But it again returns to its old, wonderful self. If you literally drove it everyday, I don't think you'd know this problem even existed.


    I changed the auto trans filter and fluid right after I bought the car (about 8k ago) but that didn't make a noticeable difference. It has a very slight trans leak. A few drops over the course of a week.


    Just yesterday I drove it for the first time in a week as I was away, so I tried to pay extra attention. It stalled a couple of times. No power. Bog slow. I'm open to non-trans related issues, but yesterday it shuddered a bit when put in either R or D while stopped. Put it back in N and it goes back to super-smooth, though with some hunting. That suggests to me its trans-related, but I defer to the wisdom on this board.

    I can't imagine anything involving electronics or cables would behave like this. I will freely admit I really have no clue how autos work. I keep an eye on the fluid level, but if it was low, I don't see how it would fix itself. The only explanation I can conjure up is that somehow air is working its way into the trans due to the leak, and the longer it sits, the more air gets in. Once you start driving it, it will be terrible until it gradually self-purges the air and then all is well again. But that's just my half-baked theory, unimpeded by actual knowledge!

    I searched but didn't seem to find any posts with this exact issue. It does not seem to matter if its spent its week outside, or in a dry garage.

    Thoughts? The car is incredible when at 100%. I'd like to see if I can keep it at 100% more often. As it is, it forces me to drive it often, which I'll admit isn't really a bad thing.

    Thanks for any suggestions.

  2. #2
    E500 n00b nocfn's Avatar
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    Re: Poor running after sitting, which then cures itself...

    Sounds like an issue where you need to replace the insulators behind the distributor caps. Remove caps and the rotors to reveal the insulators. Replace them, then install rotor and caps. Search here for that so you can read it better. Be sure you have proper sized tools for the caps. The hex wrench must be perfect inside the bolt and the proper size.

    As for the transmission, where is the leak coming from? While it shouldn't leak per se, it is an old car and German at that so it isn't surprising. The dip stick tube seal front right is a leaker, and the OL protection switch on the front left. If the leak is around the pan area then I suspect you need to shore up the bolts in torque spec, and always in a crisscross pattern. This is the most common DIY leak point, but plenty of INDY folks use cheap gaskets and do not torque to spec, warping pan. Things settle after about a 2-3 temp cycle as well so going over the torque of pan bolts a few days or so after a removal is suggested.
    Last edited by nocfn; 2 Weeks Ago at 06:54 AM.
    1994 E500
    249/275 - 8F19 or 8F32 or 8320

    1991 560 SEC
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    2014 E350 Cab 799/264

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    .036 Hoonigan™
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    Re: Poor running after sitting, which then cures itself...

    If the engine is misfiring and running rough when the power loss / bog occurs, it is a good possibility the cause is the insulators behind the distributor caps as mentioned above. Details are in this thread.

    If the engine is smooth when the power loss / bog occurs, I'm willing to bet it's your fuel pumps. I had this exact problem and was only able to pinpoint the cause by connecting a fuel pressure gauge I could watch while driving. When the power dropped, the fuel pressure also dropped waaaay below min spec. A pair of new Bosch pumps cured the problem permanently. Details are in this post.

    A third possibility is your NSS/gear-position switch on the transmission. If this is sending the wrong signal to the computers, it may reduce power or limit RPM. This will trigger a code on the E-GAS module (or, T/LLR module if your 400E does not have ASR). The transmission internals, and the slight fluid leak, have absolutely nothing to do with your power loss problem.

    BTW - welcome to the forum!

    Dave M.
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  5. #4
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    Re: Poor running after sitting, which then cures itself...

    Thanks for the suggestions, I had been reading up on the cap insulators so I will investigate those first. I was actually going to hook up a FP gauge yesterday until I discovered it was not where I was, so i will have to try that later. Can't figure out why the pumps would only work poorly after sitting though - maybe they somehow get clogged up when it sits?

    The tranny leak seems like it's from the pan. It's definitely at the rear of the tran, just hard to see if its coming from up higher first without a lift (which I don't have). I put a new gasket on and torqued it when I replaced the filter, but I might not have done the crisscross pattern. Honestly don't remember since it's been a year.

  6. #5
    E500 n00b nocfn's Avatar
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    Re: Poor running after sitting, which then cures itself...

    Big E - update your profile so that we can see where you are geographically. From what you said, my bets are the lower pan and gasket. Also the MB trans level is either full or not. So do not exceed the mark on the stick, never even a 1/4 pint more can be a problem. I suspect starting at one corner torque to spec then opposite corner and clockwise with a small torque wrench will eliminate your leaks unless you really botched the pan....

    If you have no records of those insulators being changed, Id spend on those first. Cheap too is the fuel pressure regulator and its a 3 second swap out. But, new insulators and a 20 mile drive at operating temperature should cure your sickness.
    Last edited by nocfn; 2 Weeks Ago at 11:25 AM. Reason: punctuation
    1994 E500
    249/275 - 8F19 or 8F32 or 8320

    1991 560 SEC
    199/268
    2014 E350 Cab 799/264

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    .036 Hoonigan™
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    Re: Poor running after sitting, which then cures itself...

    Quote Originally Posted by Big E View Post
    Thanks for the suggestions, I had been reading up on the cap insulators so I will investigate those first. I was actually going to hook up a FP gauge yesterday until I discovered it was not where I was, so i will have to try that later. Can't figure out why the pumps would only work poorly after sitting though - maybe they somehow get clogged up when it sits?
    If the pumps are 20+ years old, they are due for replacement. They wear out and can work intermittently. If you read the links I posted above, mine would start to act up after 10-20 minutes of driving.


    Quote Originally Posted by Big E View Post
    The tranny leak seems like it's from the pan. It's definitely at the rear of the tran, just hard to see if its coming from up higher first without a lift (which I don't have). I put a new gasket on and torqued it when I replaced the filter, but I might not have done the crisscross pattern. Honestly don't remember since it's been a year.
    The trans leak is almost never, ever, ever from the pan. It's almost always from something above the pan, running down to the pan gasket/edge, and then running around the edge of the gasket so it LOOKS like the pan is leaking. Your case may be different, but it would be a ~0.01% chance.


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  9. #7
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    Re: Poor running after sitting, which then cures itself...

    I have zero records with this car, so everything is an adventure. I do know, however, that it had one owner for its first 17 years and it was serviced at an MB dealer in 2010. Based on its condition at 198k miles, I have to think it was very well cared for until 2012ish when the original owner sold it. Since then, it's not had a ton of miles, but went through a few owners. It sat at the lot I bought it from (oddly, a tiny, used-car lot in rural VA with mostly pickups and US stuff for under $5k) for at least 6 months before I bought it. I used the poor running behavior to beat them down on price more. Then on the 2-hour long drive home, it drove perfectly!

    Thanks for the info, I will do some more reading and investigate.

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