Hey guys,,and girls too.
92 400E. New plugs, wires, rotors, coils,,all new vacume lines, tech 3 months,...dealer two weeks,...pressure at fuel rail 65lbs...hit the gas under load and the pressure is maintained or even jumps about 5 lbs...does not drop at all.
New maf but i did not do anything to tune it to the car. I read that it needs to be matched but Im not familiar with that. I thought it is plug and play. Slow acceleration and the engine runs perfectly...reaching cruising speed..perfect...only under acceleration either moderate or aggressive....aggressive is worse. Any ideas would be great.

Brian

I had something similar on my 300CE.

Crank position sensor.

__________________
Allen Kroliczek
Oak Grove Autosport | Oak Grove Autosport
01 G500, 82 300TD, quite a few more.....

Thanks Allen the crank sensor was replaced with the tune up. Anyone else in the brain trust have any idea. The independant doesnt know what else it might be.......the dealer doesn't know what else it might be.

My problem is the same but in the winter the problem does not exist only in the summer tried a new mass air sensor but no change fuel pressure is ok have not checkt the fuel volume becuse I don't now where I jump so the fuel pumps run with ignition on.
Fuel pumps are not old in my car the car is 1994 E320.

There is no code thinking of the coil but my first thought was mass air sensor since the problem seems to be temperature sensitive.

Have you checked the fuel injectors to see if they have the right spray pattern/atomization?
Other things to consider are the distribition pipe, diaphram pressure regulator.
Seems to me if it was anything electrical the check engine light should be on.

__________________
1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

I don't know how to check the injector spray pattern, I do know the car has just over 200K. I thought about the pressure regulator at the rail but Im reading stable pressure. The car has one new fuel pump and one older one but again stable pressure. There is a brand new MAF. I read on onethread about disconnecting th o2 sensor and driving but I dont understand that theory.
Thanks for the help.
Brian

come on steve...you have no idea?

Something in the enrichment circuit. On my '85 the warm-up regulator changes the control pressure when there is a drop in engine vacuum (ie. stepping on the gas). Not sure if your '92 is similar, just throwing it out there.

__________________
1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

These things are such nightmares. I have a 93. How's your gas mileage? Wiring harness replaced? May not make any sense, but it seems to me the wiring harness is pretty much the non-obvious suspect for mystery diagnoses; if it's orig, what you are doing is surgery on a person with no brain

There is always the possibility the ignition control unit or even a coil could be weak and unable to make enough heat to light the fire under load. As I'm sure you know the KV requirement doubles or triples during hard accel. Just a thought
Bill

If I was going to shotgun a car with that symptom the first thing I would do is both dist caps. I am surprised they have replaced about every other part but still haven't replaced both caps. You should at least inspect them both and scrape any crud off the electrodes.

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Usually if the cap is bad it has turned a shade of green internally. Didn't the post say the rotors had been changed? That would mean the brackets are up to date and the caps had been inspected.
Bill

Yes rotors, distributors, coils, vacume lines, spark plugs, one fuel pump. Now fuel pressure regulator as of 20 minutes ago, thank god i've got a lincoln as a spare,. It is perfect cold....ran perfect, turned it off. The heat accumulated,
restarted and ive got the same stumble at idle, almost sounds like a miss, smooths with a little throttle, stumbles under anything other than slow acceleration, then smooths out.

Im starting to think a KIA might not be a bad idea. I undestand the Sephia comes in black. By the way the harness was changed about 100k ago at Mercedes of Naples Florida. The dealership, not a local shop. Reminder it spent 3 weeks at the dealership here in Sarasota. They diagnosed one of the new coils was bad, replaced it...did the parking lot idle test I believe even though they said they drove it til it got hot. I drove it home and had the same problem more than 1000.00 dollars later. That was also after nearly one month and another 1k at the local mercedes aftermarket shop. Im considering taking up drinking to salve my soul.

Steve, im guessing this is too tough for you.

For what it's worth there is another option you might try. You stated that you have been having a factory dealership work with the problem without coming to an acceptable answer. The factory does have a team of technical specialists working for the respective zone offices, at least here in So Cal. They usually work with resolving technical issues in newer models but have been known to assist with diagnostic situations when requested. You could have a meeting with the service manager of the dealership you do business with and see what can be done to help resolve the issue at hand. You can also contact the zone service manager with Mercedes Benz for the area you are in to see if you could get help in resolving a technical issue in an MB product. I would be surprised if you didn't get some technical assistance through the dealership. The assistance discussed would only be available through the dealer though. Just another possibility.
Bill

Here is the next part of the puzzle, car has been at the shop about a month. So far everything suggested has been done. The computer still has a crank sensor code,,,,tech removed the MAF and cleaned the throttle body and now the car which never had an idle speed issue has a severely high idle which can not be reduced. Also I'm told that when carb cleaner is introduced near intake manifold passenger side of engine the rough performance stops. Any ideas?