fuel problems - w126
 

'90 420sel, 175,000 miles, car has been FANATICALLY maintained with all services and problems corrected promptly. has been in the shop for 2 months and they can't figure out what it is. i have had a mercedes tech look at it - no idea. i am about to shove it into the ohio river.....

the problem: hot day, car had been used just prior. started up the car and heard a "whump" and from that point on it idled like crap - idles almost as if a motor mount had collapsed.

what has been done so far: checked for vacuum leaks, complete tune up including rotor and dist. cap, new fuel distributor ($$$$ - at the advise of the first mercedes tech who just knew that is what the problem was), new fuel pressure regulator ($$$ - the end had blown out evidently) , checked to make sure all cylinders were firing, checked to make sure all injectors were good and not clogged, checked EHA to make sure it was functioning properly.

still idles like crap and blows black smoke. runs o.k. when at speed.

the mechanic is going to try to have one more person (mercedes tech.) look at it on monday and then take it to the dealership. i frankly don't have much faith in the dealership - that is why i didn't take it there in the first place. i am afraid they are going to start it up and say, "well, looks like you need a new crate engine....." they do not like to work on anything pre '99.

Did they check the lambda control?

If this were my car, I would find somebody who can:

1. Verify camshaft timing and ignition timing, along with ensuring that a proper amount of non-ported engine vacuum is being produced.

2. Put a set of pressure gauges on the fuel system to verify proper pressure.

3. Check the on/off ratio at the x/11 connector.

What is the on/off ratio at the x/11 connector? Does the 560 have it?

The X/11 plug is on the drivers side inner fender, a round multi-pin plug with a cap that unscrews. You can measure the on/off ratio of the oxygen sensor and see if the fuel mixture is at the proper specs. To my knowledge, it's on all '80s/early '90s MB models.

Steve Brotherton wrote a great article about this, it's a great read.

http://www.peachparts.com/Wikka/EngineControls

#1 and 2 have been done
 

he checked timing even though new timing chain, guide rails, etc. were replaced last year. he also checked vacuum on fuel system. everything within normal limits.....

mine does not have the port on the driver's side fender. i checked with a neighbor who has an '89 560. she does not have the port either, but she does have a diagnostic connector on the passenger side which mine does not have for some reason.

Is this car C.I.S. or full electronic?

I'd guess a blown Warm up regulator caused by a back fire or maybe a converter that came apart.

Michael

I doubt it is the warm up regulator because the car was already at operating temperature or above.

It is C.I.S. - not electronic.

You may have something on the backfire theory though.
It was extremely warm that day - around 105 deg. F and the car had literally just been used around town so it was hotter than usual as well. I had filled up the day prior to this...... and I always use premium per instructions.

A 1990 model would have KE-Jetronic, which doesn't use a warmup regulator or a frequency valve like the older CIS systems. Fuel mixture is controlled by the EHA valve on the fuel distributer, that valve gets a electronic signal from the computer. The computer looks at the O2 sensor voltage, coolant temp, air temp, throttle opening, and barometric pressure.

You have to pull the trouble codes to find out what is going on with the fuel system, if that is the problem.

I have a list of code definitions, though it's too large to paste on this site. If you can get me the code(s), I can let you know what they mean. If you don't have the round diagnostic plug on the drivers side fender, you should have an eight pin plug shaped like a rectangle near the battery. Steve Brotherton's article goes into detail on how to read the codes.

problem pretty much solved
 

after all that hicack - turns out it was a combination of a bad fuel accumulator (which i have not replaced as of yet) and a rotten vacuum hose that connected to the tranny modulator of all things...... anyway, it is running but it still doesn't idle as it should and is hard to start - occasionally stumbles (hesitates?) when accelerating from a stand still.

question: would all of the above problems be a result of the bad fuel accumulator?

Accumulator? in one word..No.
The accumulator only holds the working pressure in the system until you go to start it,so the engine doesn't have to crank over and wait for the pump to build pressure.
These engines are Known for Clogging the intake ports. A dealer will have the equipment and know how to clear the ports which may be closed up enough to do what you describe.
The cheaper alternative is to seek out a Carboclean franchiser *and get them to run over your car with their machine.
In the mean time get the mechanic to Double check his work on the cam timing,it only takes a few minutes to remove the cam covers,turn the engine until the cam marks line up and read off the crank shaft timing mark to ensure it's all within spec.
*http://www.hilltopmechanics.com/carbonclean.html

If it happened just like that
its ;likely not carbon buildup
whch would increase with time gradually.

2 mo is a long time to not get it solved.

I have the darn hot/warm start issue w the 126
but the rest of the operation I am very happy with.

Check the stinkin relays
they can be tricky lil devils

Anyway
Just wanted to wish you good luck.

Wow, that douchebag really deserves a banning.

"Pro's" as in "prostitute your self" Ron? whats the matter,? No new names in the last few months? Site too boring? ....too many no nothing' posters and 'no experts' is your problem .':scream::laugh3::freak:

what kinda problem do you mean .. cuz i noticed when my car get warmed up and i shut it off and try to start it again it will crank over longer than usual and then fire up .. usually when it does that i let it crank for a second and if it doesnt fire up right away i switch my key off and then back on real quick and it will fire right up .. always fires up on a quick second switch of the key ..weird stuff and its been driving me crazy ..just dont know where to start to diagnose