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

I would keep in mind the O2 sensor because it might be starting to go. A buick I worked on would do something similar but this car would actually stall sometimes. I hooked up a snap on scan tool and mointored the O2 sensor and saw something wasnt normal, replaced it and the car was fixed.

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

The o2 sensors were services about 20,000 miles ago....So far the dealership as I said had it two weeks. Coil. Replaced the aftermarket one the independent just installed. The 2nd independent had it 1 week. Couldn't diagnose it. The first independent had it 4 weeks, replaced the crank sensor, temp sensor, both coils...see above..wires, rotors, cap but only one. The other one looks cracked to me though but Mercedes Benz of Sarasota did not identify the cracked second one so Im not sure it's an issue. I'm thinking that some of the motor heads here would have some input on the subject. (Steve). By the way the injectors seem to be fine, no spitting just the chugging loss of power under acceleration (worse when a/c is on until the speed is reached. Then its smooth as a kitten purr. Idles perfectly. One new fuel pump, the other one is original but the rail pressure seems fine ( I think. )

HELP

yea I know its a puzzle....anybody?

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