OVP vs FPR ( signs and symptoms) w124 300E
 

OVP (Over voltage protection)
can restart ?
surges before stall mostly on deceleration?
engine can run(rough) w/o relay plugged?


FPR (fuel pump relay)
No restart?
stall anytime any rpm?
No relay, no run?
If bypassed, will start.
can still hear Fuel Pump preload on ignition on and still have a bad relay?

Am I correct in assuming these symtoms for these components? Please add or change as necessary.

OK I've had both so feel qualified to post!

FPR - Only ever heard of it failing to start. Doesn't usually cause cut-out once on the move. Not sure why..
No relay no run, correct
Bypassed will start, yes.
If you hear the fuel pump run when you switch the ignition on, it is fine (on that occasion). Other times you turn ignition on and fuel pump doesn't run. This is the usual intermittent faulty FPR.

OVP - can run without, yes (cold starting sucks, ASD and ABS lights will probably light)
I've run my 2.5-16 without OVP briefly, it doesn't run that badly. Perhaps when cold, or if the weather was really bad it might be worse. But when engine is warmed it seems to run pretty much as normal.

Just my experiences in 5 years of ownership!

thanks
 

for verifying these. My other revalation, my 1990 300E has the FPR on MAS computer. SO, my next question is to verify if the fuel pumps are working.

upon switching key to "ON" position and hearing the primary fuel pump "preload" the line, would the secondary pump have current going to it as well? Reason I ask is because if it does, all I need to do is check voltage supply to the 2ndary pump and if it's present, the pump should be humming, vibrating or atleast doing something to tell me it's working as well, correct? If not, then I need to remove it and check it manually on the bench.

It is safe to assume that FPR is working because main pump "preloads" on ON position. And there is only ons FPR that operates both pumps?

when i lost our ovp on the 89 CE, it would briefly start and then stall...wouldn't run.

abs light came on....i think the CEL as well..

fortunately i had a spare in the shop...

i have learned over the years reading these posts that you keep a spare ovp, fuel pump relay and klima relay as well as a voltage regulator in a pouch in the shop or the trunk in your car....

cheap insurance.