1992 Mercedes Benz 560sel POWER LOSS-METERS FLUCTUATION

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Does this happen at random or is this a constant condition? Also what scenario surrounds this? Does this occur when the engine is hot or cold? Does it occur on the freeway or at low speeds? Have you noticed any other issues such as poor fuel mileage, lack of power, any warning lights on? First I would recommend going through your vacuum lines on the motor and checking for any split or broken lines as vacuum issues on this vehicle can create strange conditions. The thing that concerns me is that both gauges are zeroing out together correct? Are the pegging out and then falling to zero? Since both receive signals from different sensors which then both route through the MFI engine control unit you may be looking at a possible failed ECU. Give me a little more detail as to the above conditions surrounding the stall and I can give you more of a certain idea as to what may be causing this.

First of all Its A 1992 500 SEL.
It happens on the Freeway at speeds of 70-80 MPH and when it does there is a complete loss of power, stiff excelarator pedal and I have to excelarate and release in order to change gears.
Once I stop, the engine revs up down and the rpm and oil pressure meters are all over the place as if there's a problem with the throttle actuator but both the actuator and the air sensor are new.
Could there be a voltage problem if the battery under load varies between 13.5 and 14.9 volts.

Thanks,
Jeff

This really sounds like a throttle actuator issue. How new is the part and is it an OEM or aftermarket part. I believe VDO makes the OEM version. As for the voltage as long as it's not rapidly fluctuating this is a good range. Tell me when the vehicle is reving is it bucking, surging...?

The throttle and air mass sensor are geniune Mercedes Parts which replaced a rebuilt throttle actuator within the last couple of weeks. Its does have a tendency to surge a little.
I have heard coments about computers re-learn in certains situations, is this a fact?

Jeff

I have seen computers glitch and erase the actual values of components which will cause issues. It definately is a possiblity with the engine management computer. These can be programed to a point with the proper MB equipment, however usually if you are experiencing these things frequently it is probably an issue with the hardware more than the software. I hate pointing to a control unit without positive data just because they are so pricey. Given the circumstances though this may be the case. I will continue to dig and make a few calls. Let me see what else I can find.

Thank you very much and I appreciate your efford.
Will wait you reply.

Jeff

Well I have spoken to a few friends with MB and all seem to conclude that without hooking the vehicle up to a meter and getting real time data from the engine as far as fuel pressure and signal from the throttle actuator as well as other electrical inputs it will be hard to determine what exactly is going on. But I did want to mention a few things we discussed. Another posible route may be an intermittent issue with either th cam or crank sensors. Both of these will normally cause stalls and complete shut down. I also wanted to know does the vehicle ever stall out outside of the high speed condition you described? Does it ever stall out or act like this at low speeds?

Thanks for your information and no it does not stall or shut down at high or low speeds, just the loss of power, meters fluctuation and engine revs up and down.

Jeff