Sorry, but here goes...
 

I have read the archives, which have helped but I am still confused. My 1990 300E cut off on me yesterday pulling onto the highway, a car going about 60mph had to jump into the other lane to avoid hitting me( I was pulling across the first lane of traffic to get to the second, It cut off in the first!:( ) The A/C was on and it stumbled. It seems that when I have the A/c on my problem is worse. As of late I am experiencing: low idle worse with A/C on, hesitation when starting off, and loss of power. But these syptoms are only sometimes....not always. I read in the archives that OVP with the single fuse is the bad one! Part # 201 540 38 45...Mine has the single fuse also, but is Part # 201 540 32 45. Is this likely the culprit?

Any help is greatly appreciated.

Also a correct algorithm for troubleshooting this kind of problem would be very helpful to me also!
You guys are the best!

It is a dangerous situation, so I hope one of the techs will confirm, but it sounds to me more like a cracked solder joint in your fuel pump relay. My next guess would be something to do with fuel pressure such as clogged injectors, fuel pressure regulator, accumulator, check valve(s), fuel pump(s), or gaskets. Hope you find the problem easily, Andrew Seidel.

Thanks Andrew,
I appreciate your reply. I am getting frustrated by all the possible causes. I hope I can find the problem soon without testing every part on the car.
Thanks again

I don't think OVP failure would cause total engine shutdown. Rough running and poor starting, yes. The give away with the OVP relay is the ABS light coming on.

I think you should follow 5banger's advice and go for the fuel pump relay

Welcome. If it is not the fuel pump relay, I would take it to an experienced tech at that point--with the fuel system, the cost of the parts to do fault isolation is more than their labour rate. I have some more hints if you decide to go down the road yourself. Cheers, Andrew Seidel.

My vote is for fuel pump relay!
 

If it was under acceleration, it could also be the ignition coil or a dirty fuel filter. Do a search under ignition coil or fuel pump relay.
Good luck!:cool:

Mick J & Brandon

A faulty OVP sure WILL cause the engine to stall!! It did it to me MANY times, that is one of the give-away symptoms.

OVP, vacum leak, EZL, crank sensor, filters, leaking cald start valve, bad fuel head and busted A/F sensor boot are likely culprits, along with the fuel pump relay.

Personally, I'd jump the OVP and drive it.



Joe

Thanks to all,
5banger- I definately would like to do as much on my own to learn and save money. But I am not afraid if at some point I need to take it to a tech..So how should I go about testing the fuel pump relay? Also, my popular mechanics CD says it is located near the battery..no more info given?
Thanks again,:)

My experience is with W201, so we need someone to chime in with the wiring diagrams for your model to tell us which pins to test and where the relay is. Likely, it is the largest box, other than the computer, near the OVP.

Empirically, you could run the car in idle and tap on the relay and see if the car stumbles. Actually, this is how I confirmed a bad OVP on my 2.6. Many simply remove their relay, open the case, and inspect and resoldered the connections. Usually, it is a hairline crack in a trace or metal corrosion on the ground lugs of the relays:

http://db.mercedes.cx/sec/200206/24/0056.html

Here is my guess at the approximate order to test/repace. It could use fine-tuning from other forum members:

1) OVP ($$)
2) fuel pump relay ($$)
3) run tankful of strong injector cleaner ($)
4) check valve(s)and fuel pump(s)($,$$)
5) fuel filter and accumulator ($,$$)
6) ElectroHydrualic Actuactor (if appl.) and its gasket ($$,$)
7) injectors and related rubber($$-$$$)
8) fuel pressure regulator ($$)
9) fuel distributor ($$$)
10) and then the list gets really long ($!)

Edit: If the problem is related to ignition components, you can wire an inductive sensor (I simply clipped one off a timing light) to an oscilliscope and clip the sensor around each spark plug wire. The oscilloscope image cross-references with diagrams in the MB repair manual that tell you what could be wrong. I used this to find 3 bad spark plug wire ends.

My experience is based on painful times with a 190E 2.3 and not much better time with my 2.6. I wish you much less pain, Andrew Seidel.

I vote:
1) Fuel Pump relay
2) Fuel Pump itself

Possible, but less likely:
3) Fuel Filter (probably would only bother under load)
4) Fuel pressure regulator


Low idle with AC may not be related to the cutout problem.

Thanks guys,
This helps alot

I took my car out for a test spin a little while ago. This is what I got: (today anyway)

without the a/c on almost normal only minimal hesitation on start-off.

With A/C on worse hesitation but it was Idleing ok at a stop!

Iam giong to go check out the fuel pump relay.......Wish me luck :rolleyes:
I'll keep you posted

Thanks again,
:)

your fuel pump relay is obviously working. You will not be able to test it for a failure that causes the car to stall unless it is doing such.

The hesitations are not caused by an intermittant fuel pump relay but they might be caused by the OVP relay. But even though an OVP can cause Davids car not to run it is not likely to cause a KE car to die under acceleration.

I take back my fuel pump relay/fuel pump suggestions if it is so easy to reproduce with the A/C on.
These would cause a less predictable intermittant (or total) failure.

I'll take a stab here and say it might be your voltage regulator. Two phillips screws hold it in on the bottom of your alternator.

If those brushes aren't making good contact, then this certainly will cause missing/stumbling that you're experiencing.

It happened to me for awhile -- my car would just conk out while idling, usually when hot -- then one day it quit altogether leaving me stranded on the fwy.

It's at least worth a look, and if it's worn but still functional it might be good "run insurance" to grab an extra for when it does fail.

Good luck!

~Paul

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'91 300E, 215K miles