Anyone seen this problem before?

**Noil** · 05-26-2007, 05:56 AM

I have a 1993 Z28 that appears to have some serious problems. It is running so rough it is not drivable anymore. When the car is in park and idling the speedometer is bouncing from 0-20 mph. I have a diacom setup but it pretty much refuses to connect to the PCM. When it does I can read off dozens of error codes that don't make a lot of sense. When I took it in for service I was told the PCM was bad. I installed a new PCM but the problem is the same if not worse now.

I am hoping someone else has seen this problem before and can point me in the right direction of what to fix. I'd think this was some sort of electrical issue since the gauges are all over the place. The issue started with a check engine light coming on, and the temp gauge showing the car was overheating, then it would suddenly drop right back to normal range for no reason(faulty readings in my opinion). When the diacom is working, it also sees these bizarre readings(i.e. at idle the speed is jumping around).

Thanks for any ideas on what to look at. I don't think it matters, but the car is Vortech supercharged, and until this check engine and the now unusable car issue I had done all the work on it myself. It only went in for licensed service bause of new state laws here and it needing a full inspection at the time.

**toirn** · 05-26-2007, 07:13 PM

I'd suggest looking over your wiring harness real good.

Can't give anything more specific. Multiple guages moveing around in bizarre ways sounds like possibly some wires are shorting together.

Anywhere the wires may come into contact with metal (bulkhead passthrough, if the gromet deteriorated), or anything hot (headers) would be particulary susceptible to allowing multiple wires to cross together.

Closest thing I came to that involved a field mouse taking up residence behind my pcm. Chewed through about 15 wires before he was done.

If nothing obvious jumps out, then it becomes a very tedious job.

Also make sure your battery is in good shape and the engine/body grounds are connected properly. A faulty ground circuit would affect just about everything.