We have 89/90 'G' that keeps cutting out. It can go for weeks and runs like a dream, and then has phases were it is constantly cutting out at any speed, high or low. Just before cutting out it sounds like the fuel pump
speeds up.

Have today replaced the fuel pump relay, but it hasn't made a scrap of difference. Can anyway give any advice as we are running on one vehicle at moment, but partner going away next week for 12 weeks so we desparately need the merc running.

Regards

Why do I get drawn to these kinds of threads?? Hmmmm. Anyway I don't have that car but that symptom is very curious. On my car I don't even think I can hear the fuel pump. What exactly is the sound you hear? I hate guessing but perhaps it could be the OVP. In any case I would suggest doing some searching. Here is a recent thread I found about the OVP on your car. Hopefully someone else has something more insightful to add. 190E cold start problem

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

Do you have the 4 or 6 clyinder?

1. check all fueses
2. Check all vacuum lines
3. Check fuel pumps-remove them from the car and test them on a spare car battery by taking the 2 leads to the battery terminals
4. check all fuses hoses by fuel pump(s)
5. I would then check all electrical components in the cis-e system by following the procedures on the 201 service disc.
6. Check the wiring harness and make sure you are getting juice from the ecu to the all the devices.

Other things to check are your sensors.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Here is an interesting thread:

300E intermittent stalling

I searched on "OVP" and "buzzing"

It is a different car but similar symptoms. You might verify the voltage when the car is running just to make sure the voltage regulator is OK. At some point you may have to just try to find a decent mechanic. (hard to do). The ones that understand electrical systems are few and far between unfortunately it seems.

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I will pass all your information on to partner, who is home tomorrow for a few days - will let you know what happens

thanks

most of the time the ovp doesnt solve the problem, sometimes it does but most of the time its something else.

__________________
1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)