Hey, 90mbenz

I have tried the above method. The problem is there doesn't seem to be anyone anywhere around that knows anything about this cars system, and I don't really know what I need to ask an independant shop in regards to their test equip. One guy told me that there was no way to check anything on this car.
I have been to the dealer in Augusta, and tried to talk to them but they wouldn't let me talk to a technician directly. Their idea was "just leave it and we'll take care of it". Well, I don't like how that all sounded.

Regards

I kid you not... when I had my 300SEL (same year by the way as yours)... when I changed from Speedway gas to Shell, my problem went away. I tried Speedway again... and sure enough it stalled in the same manner as you are describing. After going back to Shell... no problems. I also had the fuel filter changed in the same time.

Just thought I would share this as I did have this problem in the past

OVP relay, fuel pump relay, and fuel pumps, in that order.

A flaky OVP will cause all sorts of trouble, but intermittant stalling while driving that gets worse is either a bad fuel pump relay or a bad fuel pump. Relay is $60, replace it, don't mess about.

OVP will usually also cause instrument problems like a bouncing tach, flashing SRS lamp, etc. Replace that too, it's dead.

You should check the current draw on the fuel pumps (there are two) and replace if too high -- don't know the spec off hand, but I believe it's been posted. Usually a bad fuel pump just gives up the ghost and you are completely dead, though.

Last, clean the idle control valve and replace the two rubber hoses on it -- they get old and leak. This causes stalls on deceleration ONLY as the idle valve won't open back up fast enough as you slow down. Much worse on hard stops than gentle ones.

Had the same problems on the TE, cured by a new fuel pump relay.

Much cheaper than getting hit.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

It MAY be a faulty ignition switch. It sounds, from your description, like the fuel pump is dying--which could be the OVP relay, fuel pump relay, the ignition switch input to the fuel pump relay, OR the fuel pump itself. If I remember correctly, there is also a RPM limiting relay in the circuit. The key symptom is that it will 'restart'. An ignition related fault would not heal like that but would stay dead.

I presume you have changed the fuel filter.

I feel your pain. My car is same year and engine as yours and does the exact same thing. I too consider myself a good mechanic and this has me stumped. My wife refuses to drive this car because of this. Changed plugs, rotor, distributor cap, fuel filter, cleaned idle control valve, new hoses leading to idle control valve, pulled all relays and cleaned and put dielectric grease on, all to no avail. Please let me know if you find the solution. I love the ride of this car but it does make my blood pressure go up when it cuts off in heavy traffic. I don't want to die of road rage from the driver behind me when it won't start.

BMJR, I must've missed the fact that you had tried to get it diagnosed 'properly'. By bad.

There is an option that has not been mentioned yet. I've had a couple of cars with CIS injection, which is what you have in your car as well. They were Porsches, but essentially the same setup. One of them developed a problem that would let it start okay, but it could not rev properly at all. It got flakier and I tried everything to diagnose. That car did not have a computer, however. Part of the factory procedures run you through every component of fuel injection, and if everything checks out, the recommendation is to replace the fuel distributor. It is the toughest component to test and is the most expensive. I'm guessing a rebuild for our 300 SEL would run somewhere between $300 and $500 for the part. It can be successfully rebuilt if you are reasonably mechanically experienced (even though everyone warns you not to) for just a few dollars. It solved my problem. If you haven't already done so, spend about $18 and buy the Bosch Fuel Injection book which is stocked at the larger bookstores. It has detailed information and procedures.

Hope that helps.

Snibble,
I have read about the brand of fuel before and I have tried that, even though it's hard for me to believe that brand X will cause such a problem over brand Y premium gas. I tried shell but it made no difference. I usually buy premium at the local En-mark because they have 7 cent off per gallon on Tuesdays.
It's drawing 7.2 amps. I'll have to read up on that.
I'm pretty sure that I replaced the relay early on, but not the OVP. There seemed to be some confusion about which relay worked the fuel pump. I may need to take another look at that to be sure.
I cleaned the idle control valve, but it didn't appear to be dirty. I couldn't figure out exactly how it works, so I don't know what about it needed to be clean. I also replaced both of the hoses.
Yes I changed the filter and cut the old one open just to see if it had trash in it. It didn't.
If I ever find the problem I will definetely let you know and post my findings here.
I know what you mean. It's really bad when your dead in the road with someone behind you standing on the horn. What's really bad is when it does it at night. If it would quit while at highway speed (it's rare for it to do that) it wouldn't be so bad because you could put it in neutral and coast to a convienient place side of the road out of everyones way.
I have always thought that the CIS could be the problem but I know zip about it. I might have to get a book on it, if for nothing else but to learn how it works.

Thanks,
BMJR

Dude my wife has been driving the same way, always looking for a safe place to die. For two weeks my car was at the shop. They used the 88 SEL for an errand car for the whole time and it ran great. They gave it back and the thing dies - Dead. The tach goes to 0 immediately, all power stays on to the dashboard lights. The car will turn over but not start, until a while later, then it will run fine - for about 10 miles.
I took it to another shop ( after I replaced the OVP and the fuel pump relay - which made no difference). He found that there was a loose connection in one of the plugs for one of the relays. He tightened up the plugs for that relay and told me to sell the car. He says that most of the electrical connections on this car are very similar and that they get old and loose. That is his solution.
I am now looking for a newer Mercedes with different connectors.
Anyone looking for a parts car?

Good Luck - Scott

I won't pretend to have read every work of this thread.

Did you change OVP and fuel pump relay?

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"