I’ve been tracing a dip in power at high revs (4,000+) in my ’87 560SEC (non-cat version).

After being told by several experts that the problem was the fuel distributor, I decided to do a little probing myself. I suspected a fuel mixture problem.

I found that if I simply disconnected the EHA the dip in power disappeared and the car ran fairly well. Thus I concluded, in the first instance, that the problem is closer to the CIS unit than the Fuel Distributor.

After inspecting the PCBs in the CIS unit and checking all the semiconductors and finding them OK, I turned my attention to the peripherals that pug into the CIS. I found that the wiper of the altitude sensor is open circuit though the two other leads show a resistance of 4k.

I can’t for the life of me find the altitude sensor. It is not where several manuals claim it to be. Being right-hand-drive, the unit has probably been shifted somewhere clever, but I can not find it. It is certainly nowhere in the passenger side footwell area.

As there is no prospect of altitude driving, I thought the easiest fix would be to just replace the altitude sensor with fixed resistors – can anyone measure the sea level reading (resistance) for an altitude sensor? The resistance between 1 & 2; 1&3 and 2&3 on the socket of the unit itself is all I need.

Upon testing the current at the EHA unit I found the key on to be 68.8mA (Specified 75); idle warm +3.2 (zero +/- 3); but steady revs -8 (+4~6) which means it is going lean instead of rich at higher revs.

Thanks for any help,
Robert