Where's the OVP in a '92 300TE 4matic? - PeachParts Mercedes-Benz Forum

Fintail Fan · #1 01-06-2005, 04:38 PM

My 300TE's curious tendency to stall at slow speeds and in the middle of intersections after starting from a stop, has now grown to include failing to re-start, (engine turns over, but just won't catch), even when it's been purposefully turned off, such as doing errands on a Saturday afternoon when the engine is still somewhat warm, or cold. In the times when it stalls while driving and the engine is hot, it may take @ 2-3 tries to get it started, (one or two light changes, which is not only embarrassing, but dangerous), but when doing errands, and the engine is warm or cold, it may take minutes or hours before it will restart. As I write, it has been two hours and it still won't catch.

I'd like to diagnose and repair this myself with the help of this forum, as I can't continue much longer with the car in this unreliable condition. If I can't fix it myself, I will have no choice but to take it to the dealer for who knows how much $$ to repair, which I would certainly like to avoid if possible.

All my searches have pointed me to the OVP as a likely culprit, (yes, I know it is blamed for everything), but since the car doesn't suffer a rough idle, hesitation, or any other symptioms which would indicate a possible fuel delivery problem, I pinning my hopes on this as the cure. Please correct me though if you think or know differently though.

If anyone has a photo, link, or can simply explain to me where to find the OVP in my car, what it looks like, whether it has a fuse, and if so what type, where it's located, etc., I will be especially grateful. Thanks.

1962 MB 220SEb Sedan 196,450 mi.
1992 MB 300TE 4Matic Wagon 147,000 mi.
1995 Subaru Legacy Wagon 125,300 mi.

G-Benz · #2 01-06-2005, 04:47 PM

I would surmise that it's located behind a black plastic shroud just behind the battery. It is a white rectangular unit with a clear top containing one (or two 10-amp AN-type fuse(s).

A single anodized 7mm bolt holds it down at the base. Remove the bolt and pull out vertically.

Your symptoms sound more serious than an OVP issue though. Does your fuel pump make a hissing (vs. buzzing) sound when the engine is running? Listen for it behind your passenger rear tire. Frequent stalling like yours sounds like your fuel pump is on its way out.

Fintail Fan · #3 01-06-2005, 08:22 PM

Now that you mention it, I think I have heard that sound - a hissing noise toward the back of the car. I never gave it much thought before, thinking it was just some blow-off from the air suspension or something. Maybe that's it. It's been doing it for a while, though I can't say if it pre-dated the stalling/hard starting or not. If it is a faulty fuel punp though, wouldn't there be some hesitation while driving? I have none. When it finally starts, I'll be sure to listen more closely for the sound. Is the fuel pump replacement a DIY job for someone of average ability, (I recently changed the serpentine belt and water pump, but sent the car out for a blown head gasket repair). I think from reading here that my car has two fuel pumps. How will I know which one is faulty, or should I just replace both to be safe if this is what the problem is? Thanks for the suggested diagnosis though, and the info on the OVP relay.

G-Benz · #4 01-07-2005, 10:27 AM

The hissing means everything is working fine as far as fuel pumps...and yes there are two.

Usually, when the hissing turns to "buzzing", then that is usually a clue that one of them is going to die soon...though there are some that claim theirs buzz and there are no ill effects.

My ML had a bad fuel pump, and symptoms ranged from hard starts (cold or hot) to just quitting while on the highway. Didn't hesitate, but when it finally died, I was stranded on a lonely two-lane over a holiday weekend!

The pumps are accessible by removing four bolts holding a plastic cover that protects the fuel pump system. I replaced a hose on my W124 in that area, but your only real issue is being able to crimp your inlet hose to prevent taking a gasoline shower while working! Disconnect the battery too to be on the safe side!

The OVP is around $80 and I would try that first. I'm not a fan of throwing parts at a problem, but I don't mind ruling out the cheap ones if i can.