300E MAS fuel pump relay or crank position sensor - PeachParts Mercedes-Benz Forum

Guyton Buzz · #1 08-08-2012, 09:05 AM

When my car cuts off by itself (just dies), I hear the fuel pump buzz for a second or two before it also stops. Would this indicate that MAS (fuel pump relay) is OK - and problem is elsewhere, like crank position sensor? Have replaced OVP module. Have inspected and reseated MAS, no corrosion, solder joints inside do not look cold or corroded.

Have 1993 300TE, 300K miles, cutting off. I had felt a few hickups, and believed it might be noisy fuel pump on the way out. Replaced pump with one from salvage yard, and new fuel filter, big end toward back of car. This is a one pump system. Ran great for a whole day, like 4 hours of continuous in town traffic and milk runs. Next day, died on side of interstate, just sputtered and cut off. Had driven maybe 40 miles at that point. Would crank back up, and run a short time, sometimes 20 - 30 seconds or more. Limped to off ramp, then wrecker back to the house.

13.35 volts at battery. Banged on OVP and MAS relay when at idle, no change. Would not stay at idle once warmed up, just stumble and shut down. Less noticeable at 2000 rpm, if gas pedal held down, but still hickups once in a while.

Replaced OVP (old one had corrosion on base contacts). No change.

Going to pickup an MAS (has fuel pump relay in it). New fuel pump on the way from Rock Auto.

Any other ideas, other than to stop flying low with the partz vultrurez in the junk yard? My thanks in advance.

wbain5280 · #2 08-08-2012, 08:52 PM

To start, resolder the fuel pump relay large pins. Then look at the fuel pump connections and make sure they are tight. Then check the crank position sensor.

meltedpanda · #3 08-09-2012, 11:19 AM

my experience with bad CPS is that it will not run - at all, rare to have them come and go in functionality