89 300E HELP!!

[gransport66]

Hello all, i am here to ask for everyone's help. I am helping a friend with her 89 300E that very intermittently will die, with no warning just die. I haveyet to experience it but she describes it like this, when coming to a stop or corner, brakes applied, turn the corner and lt off the brake go for the gas and it's shut off. No stumble, jerk nothing just shut off. She has spent $2400+ trying to fix this concern, with a MB "expert" with 40 years experience. I am an Infiniti tech but this thing has me stumped. Thank for looking, Andrew

[sptt]

Has the tech replaced the OVP Relay yet? Fixes a lot of issues on this car with just shutting down. Also, the alternator has a voltage regulator that can easily be checked out and replaced from underneath the vehicle without removing the alternator. Doesn't sound like that's the issue but a good thing to check. Does the car idle and run perfect before it does this? What work has the 40 year MB tech done?

[big dog 2]

Yep, OVP relay........

[gransport66]

Sorry, I forgot some of the important info. The car starts easily right after it dies, and its always when coasting/braking. As for the parts already thrown at it, the crank position sensor, overload relay and fuel pump relay were replaced on the first visit. Then two fuel pumps were replaced along with two fuses. The third attempt was to put in a used EZL control unit. All new parts are said to be genuine M-B parts.
This is what I know, the "expert" has never driven the car to try and duplicate the concern even though she told him to keep it as long as needed to ensure its fixed. Also I've done a lot of internet searching and this sounds like a very common M-B issue, for all models, and for all of the posters who have had this type of coasting issue it was narrowed down to many of the items already replaced. Of the items that have cured others' cars the hall effect speed sensor seems like a logical next step.
Thanks for the replies, hope this you with what you all think I might test/check next. Andrew

[mak]

On the 103 engine this is seems to be a common age related wear tear problem and it is normally rectified by replacing /soldering the fuel pump relay FPR and the over voltage relay OPV.
Most likely the fuel relay is not good do connect directly at the pump or jump the pins and retest.
mak
300se

[dhjenkins]

The speed sensor shouldn't make the engine die. Jump the fuel pump relay as suggested and see if the problem persists.

[long-gone]

He mentioned above that the fuel pump relay and pump were already replaced.

There's a check valve at the fuel pump that can stick and may cause intermittent trouble, or perhaps the fuel pick-up is gunked-up/clogged.

My brother had a car once where the windage baffles in the fuel tank broke loose and no longer kept the fuel from sloshing back and forth. When his tank was below about a third or a quarter his car would sometimes sputter or stall when cornering or braking as the fuel pick-up would momentarily not be submerged.
Does this only happen when the tank is low? Just a thought.

[johnjzjz]

We found on one car that the brake booster one way valve ( check valve in the and at the booster to keep VAC from backing up into the intake again ) when the brakes were applyed and going slow, stayed open and caused a massive vacume loss just for a monent this caused a sudden stop in the engine -- have no idea if this is something you have but it did happen in my shop and we found it actually by accident -- jz

[gransport66]

Thanks guys, this is all good info. As for the Overload relay and fuel pump relay they are supposed to be new Mercedes parts. Back to the issue of it dieing the owner tells me it is very sudden without a hint of a warning, just exactly like someone reached over and turned the key. I have been driving the car for a day and a half now and have tried wiggleing the key to no avail. I will keep driving/checking on the car to see if anything comes up. Thanks again, Andrew

[r_p_ryan]

Could be the micro switch on the throttle lever. This tells the computer to go into idle mode when the gas pedal is released

[Cal Learner]

Originally Posted by gransport66

Thanks guys, this is all good info. As for the Overload relay and fuel pump relay they are supposed to be new Mercedes parts. Back to the issue of it dieing the owner tells me it is very sudden without a hint of a warning, just exactly like someone reached over and turned the key. I have been driving the car for a day and a half now and have tried wiggleing the key to no avail. I will keep driving/checking on the car to see if anything comes up. Thanks again, Andrew

That symptom sounds just like the engine speed sensor is faulty. I don't know if the '89 MY had a cam position sensor or still uses the TD signal sensor, but something is telling the ECU what the engine speed is, and that may be faulty. If the engine speed signal is lost for 1 second, the fuel pump relay shuts off the fuel pumps, and creates the very situation you're describing--like someone reached over and switched off the ignition.

[dhjenkins]

Is the key still in the on position when the car dies (long story)?

[dhjenkins]

A parts search shows a 'reference' sensor mounted at the flywheel.

Seems to be a Gen II thing, so not sure what it does...