300E HESITATION FROM STOP!!
 

I have a 1988 300E that has developed a serious hesitation problem quite suddenly about a year ago. Wnenever the car comes to a complete standstill in traffic or at the lights it has no response when initially trying to accelerate away. It feels like it completely lacks power at this stage. If the accelerator is held down steadily (but not all the way) for about 5 secs the car just crawls away and feels rough, the transmission will then suddenly kick down and the car will accelerate away very fast and hard. Ihave a very good tech. who has changed plugs, leads, resistors and had the injectors checked. I am reluctant to change the injectors just on chance particularly since the car seems to go so well once it is up and running. The only unusual thing so far seems to be that every time my tech. has checked the car he has had to re-adjust the air mixture. For a very short time after this it seems to run very well but the problem re-appears. I have also noticed a few minor vacuum leaks around my aircon, fan and headlight adjuster. I would be grateful for any suggestions or feedback from anyone else who has experienced this problem. It has now gotten a bit dangerous when taking off from a standstill at an intersection as we do not know if the engine will suddenly die on me or not. Its so bad my wife prefers to drive our Ford Falcon. Please help!!!!!

[Edited by AusMB on 02-02-2001 at 06:50 PM]

I have replaced ignition coils along with the distributor cap and rotor for this.

The ignition coil will break down under pressure.

Re: 300E HESITATION FROM STOP!!
 

TRY DISCONECTING THE E.H.A. (ELECTRO-HYDRAULIC ACTUATOR) WITH THE CAR OFF, AFTER YOU'VE WARMED IT UP. PART OF THE FUNCTION OF THE EHA IS COLD START ENRICHMENT AND IT MAY NOT START IF YOU DO THIS COLD. IF THE PROBLEM IS RESOLVED IT'S PROBALY NOT THE FUEL/AIR SETTING NOR THE INJECTORS. (THE CAR WILL ALSO SEEM A LITTLE UNDERPOWERED DURING ALL ACCELERATIONS DUE TO THE LACK OF ACCELERATION ENRICHMENT.

THIS BRINGS YOU TO THE EHA, THE CONTROL COMPUTER, THE OVERVOLTAGE RELAY AND ANY NUMBER OF SENSOR THAT MAY BE AT FAULT. I'D SUGGEST A WIRING DIAGRAM AND START ELIMINATING PROBLEMS ONE AT A TIME; START WITH THE OVERVOLTAGE RELAY

INTRUDER

300E hesitation from dead start
 

This sounds VERY similar to my 300E's problem!

I disconnected the EHA. Cold start was horrible, but the
running performance was GREAT once the engine had some
temp/heat.

I next looked into sensors, and found (so far) a scratchy
Air Flow Sensor. The Overvoltage and Altitude Compensation
MAY have something to do with it.

If you don't want to spend the money for an M-B CD set, try
you library, and look for chapter 5 of "Fuel Injector &
Electronic Engine Controls" for 1988-90 (European cars,
Chilton P/N 8120.)

This is EXACTLY the problem I'm having with my 87 300E. Can you tell me if you've had any luck correcting this problem and what the repairs were? I'm taking my in this week to the shop and would like to have a heads up on what you may have discovered.
Thanks,
Nancy

I have a '91 300E that had the same problem plus it was running rich. I ended up replacing the fuel distributor and the O2 sensor. Bosch Fuel Injection & Engine Management Manuel was very helpful in troubleshooting the problems I had with my car.

Whadsel,
After replacing your fuel distributor and 02 censor,
did it fix the problem?
_________

Clauser1

yes it did and I've put about 2,000 miles on it since and no further problems also improved my fuel mileage.

Thank you
 

I appreciate the input on this problem. My mechanic was talking cylinder problems- now at least I can put my two cents in on the O2 sensor and the fuel distributor. Thanks again.
Nancy

Whadsel,
How difficult it is to replace the fuel distributor?
did you have to make any calibration or adjustment after
you change it?

Thanks,
__________

Clauser

300E Hesitation
 

I'm waiting for warmer weather & vacation to work on
mine. But I am still considering the EHA, and the
Air Flow Meter (the whole unit under the distributor.)
When I made a long curved spray nozzle, and connected
this to a can of Gumout, and sprayed it up under the
distributor, by holding down the air flow round vane,
the engine performed wonderfully for about a week!
I have heard there are some sliding pins in there, that
can get sticky, or the Air flow position sensor, that
I may have affected with the Gumout. I have checked
the throttle stops/microswitch, all OK. So, I will
look at the Distributor, and associated soon. With
the EHA disconnected, like I said in a prior post,
cold start is trashy, but warm running and fuel mileage
are 100% improved!!! So I feel it is electronic in
nature. (PS: I also get a CHECK ENGINE, NOT during
rough running, but after a hard run, stop, then after
the second start (like after I stop on the way home from
work.)

BnObob,
I had the same problem with the check engine light, and the MB mechanic told me this problem is usually the the O2 sensor. Hope this helps.

Hesitation
 

I had similar symptoms on my 1990 300CE:
the problems I fixed were teh following:
1.Vacuum leaks -replaced most of the vacuum lines and new rubber tees.
2. New Plugs, spark wires, distributor cap/rotor.
3. New (rebuit) fuel distributor as the plunger was leaking fuel. If you take off the air cleaner, and then depress on the sensor plate all the way, check and see if it is wet inside.
4. Replaced all the fuses and cleaned all teh contacts.
Car runs great.
Good Luck

Fuel distributor
 

I hear those fuel distrubutors are REALLY expensive.

I changed my injectors, cap, rotor, O2 sensor, and have wires, fuel pump and fuel sending unit on the way, got my fingers crossed.

This car is going to be for sale in NJ if anyone is interested, 130K miles, absolutely mint '89 300E, Grey/grey, many extras
Sam196370@yahoo.com if interested

Problem Fixed !!!!!!
 

A *great* MB mechanic and $500 resolved the problem. The computer wouldn't produce codes, though the CHECK ENGINE was coming on, and the power loss occured just after a hard deceleration.

Turns out the OVP relay malfunctioned during the
deceleration, and the engine idle wasn't being done properly. Also after turning off, then on the engine, the CHECK ENGINE came on for a minute.

Though the computer couldnt send out codes, it knew that the O2 sensor was bad (crudded up w/ 60K miles on it...definitely time to replace.) So, with OVP and O2 replaced, and Lambda adjusted, alles is gut ins MB-auto Deutschland!

:D

Hey guys:

I fixed a very similar problem on my mother's 88 300E by replacing every rubber vacuum line I could find, and replacing the rubber hoses from the fuel distributor to the idle valve and idle valve to intake manifold.

All the rubber parts were either rock hard or melting, and all appeared to leak. The hoses on the idle valve were very hard and loose -- this will affect idle mixture considerably, depending on whether they were leaking or not.

A tune up (plugs, wires, rotor, cap) and a long trip and it runs beautifully!

Peter

Just got back from my HONEST mechanic who usually takes care of my Honda accord, and does also work on my 300E. I had the oxygen sensor changed at 167,000 km by a SHADY Mercedes mechanic who claims to replace all parts by original Mercedes parts and today at 244,000 km have replaced the oxygen sensor again, and to my surprise the oxygen sensor taken out by my Honda mechanic is a FORD oxygen sensor which I paid 165.00 for. I would not have minded if this was told to me, and that he assured me that the part had the same qualities, and of course save me a few dollars. Now I know where a few rotten and stinky apples can ruin the reputation of other honest hard working mechanics. Just wanted to get this off my chest, because I feel cheated. If anyone wants to know the name of the shop I dealt with (IN LAVAL,CANADA). send me your E-MAIL and I will forward it to you. I might have been fished in, but I hope no one else gets hooked by this guy......WOW that felt good.

Checking the OVP relay
 

After my 300E's repair (O2 and OVP), the mech gave me the OVP to play with. Checking is easy. Look at the schematic on the side. Check the diode paths with an ohmmeter (low resistance forwards; backwards they are high ohms). Next check relay for *open* (roughly infinity ohms.) When I tore my old one open, and played 12V on the relay coil, the ohms through the relay contacts went from zero, to infinity, then zero to 1.5 megs (!!!), then zero then infinity. It is this 1.5 megs that caused the electronics problems. Relays sometimes get what I call whiskers across contacts (crud, microscopic metal, dirt, etc...) And no way to open/clean/reassemble this charmer! Just replace.