DavidNC

(97lt1) I discovered, what I think is, a .01v short between something in the #9 fuse gauges circuit and the pcm grd (paybe all grds). My 5v ref's have been off, so in searching for the problem I removed the PCM and tested all power abd grd connections, ti find out that the two pcm grds were reading .01v. I removed fuses until the reading read 0v, which was the #9 fuse gauges circuit. If the pcm is in, the sensor grds read .01v, unless the pcm batt fuse is removed.

I need help with ideas of how to further isolate this issue. Any good drawings of the #9 fuse gauges circuit?

The guys on the z28 forum helped me get this far,so I want to thank them.

The car won't even run anymore, but for the last 12K miles I have been getting progressively wores performance and idle characteristics until the car became undrivable.

1stz28

I would check the resistance on the GND circuits in question (wherever you measured the .01V to Bat GND) and between the two circuits you suspect are shorted together. If the GND circuits are supposed to go directly to ground (DC continuity) and you are measuring voltage then there is some resistance of some kind in the circuit. Even if something (.01V) is shorted to ground you should still measure 0V at ground. Could actually be an open or a partial open on the ground circuits in question and they are trying to ground through another circuit...like the guage circuit you mentioned. I could be totally off base but just trying to throw out some ideas.

DavidNC

I traced the wires all day today across then engine bay and into the dash. Intersting, I followed one of the ground leads across the firewall and to the MAF. It passed through a splice with other grounds. 0v at the MAF end. I followed one of the new grounds back to the passenger side and through the firewall to a 4 pin connector. Disconnected this connector and the .01v reading went to 0. I measured the end of the connector removed and got 7.6 v. Very strange. I'm now trying to follow the grd lead behind the dash area.

DavidNC

You'll love this. Pin 5 of my obd11 connector reads about 7 v. This is supposed to be a signal grd. Doesn't that mean ot shoud read 0 v?

1stz28

It is sounding more and more to me like there is a ground problem and not a short circuit. Schematics would be very helpful but without them you should be able to measure the resistance on some of these ground circuits to look for opens. Have you checked the condition of the chassis grounds for corosion/breaks/etc? Are the splices you mentioned factory or backyard mechanic style with twisted wires and electrical tape etc which would indicate some less than professional work being done in the past and also a good place to start looking for breaks etc. Keep in mind I am not an expert on auto electrical systems...just trying to throw out ideas.