OVP relay, don't leave home without - a spare
 

New to me '91 300SL. I was under the impression that a faiing OVP relay would lead to no or poor starting and running, but I have not heard of one failing while driving. Last week, my car started quickly and was running well - initially. I noticed some hesitation after a mile or two. Stopped to drop some stuff off, left it idling for a few minutes. It barely ran when I got back in.

Acted like it was out of gas (but gauge said 1/4 tank) so I limped into a gas station barely as it shut down. Put a couple of gallons in - motor would spin but no start and some random backfire.

About the only thing I could do beside get a tow truck was to uber to my house and pull a known good relay out of my W124. Ubered back, put it in, car fired right up and has been running even better since.

I now consider an OVP a mandatory spare when driving a Benz of that era.

Thanks for the great advice.

PS, I should add that this is the 3rd M104 engined car that has had issues with the OVP that I have been associated with. Pretty good record - 3 for 3.

It sounds like the OVP did the job it was designed for - protect electrical components from voltage spikes.

Those little relays are given a hurculane amount of work protecting the ECU and later the abs and other electrical goodies.

My 380sl had a bad relay which resulted in the system defaulting to mechanical only fuel injection which is nothing more than boring old higher fuel economy.

They should always be replaced as a matter of preventative maintenance.