1988 GT electrical

[vmatuza]

I own a 1988 GT. Up until recently, it ran perfect. We did a basic tune-up on it, plugs, wires, distributor cap, rotor. (we changed from Split Fire Plugs to Motorcrafts)
Over the past couple of weeks, the car lost power, now it is hard to turn over, backfiring through the manifold, and dies out after a couple minutes of idling.
We used an OBD on it, but can't find the common thread in the 3 codes we got.
Coolant temp sensor voltage low or grounded
Air charge temp or vane air temp sensor too low
Throttle position sensor voltage too low.
We've rechecked the wires so many times I lost count, set the timing to +12 TDC, what is causing all of this???

 

[RacEoHolic330]

Well, you should check your tps voltage with a volt meter by putting the positive on the green wire and the negative on the black. If it's not close to .98 loosen the 2 screws holding it on and adjust it until it's right. You may have other problems as well, but that might help a little.

 

[HISSIN50]

In general, I also like to look for commonalities (common VREF wire, ground, a bulkhead or 10 pin connector, etc).

Good luck.

 

[vmatuza]

88 Mustang GT-electrical

Sorry for not getting back to you sooner. Yesterday was non-stop rain and we have no garage, so that was a day wasted.
Someone suggested it was clogged cats, but they only have about 50K on them. The car was never driven much until recently, I gave it to my son. It has always been driven gently,(with playtime when necessary, I mean hey, it IS a mustang) It has 119K on it, many of those miles used on loooooooooong trips.
My son bought an amp/speaker box about 3 weeks ago, and installed it, changed out the original stereo, and installed (sigh) ground effects lighting. I had him disconnect all of this since the car died, but it didn't help the problem. The amp was hot wired right to the battery with a breaker/fuse within the wire. The ground effects were also connected directly to the battery. The stereo went into the original wiring but never worked right. Bad signal, poor volume, etc, but the cd player always worked okay.
Is there anything within that info that could've caused the current problems? As I said, the car ran fine, no problems until recently. The hard start came after changing the sparkplugs, the rest after installing the amp.

Thanks for your help, I will look into your answers as soon as I get home from work today.
:SNSign:

 

[jrichker]

Your 3 codes suggest a problem with VREF, the 5 volt referenece voltage provided to the
sensors by the computer. Per Hissin50's recommendations, start looking for wiring problems.

Diagram courtesy of Tmoss & Stang&2birds

View attachment 442500
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif