Joined: Mar 2005
Location: Mississauga, Ontario, Canada
95 3.8 manual 5 speed electrical problem
1995 Mustang 3.8 L V6 Manual 5 speed. Car starts, runs perfectly fine, no functional problem symptoms.
Interesting problem, apparently electrical, likely power/ground connection related. Suddenly while driving one evening, the speedometer stopped responding, then came back, (has operated normally ever since), Temp gauge became erratic, bouncing up and down, generally settling to a higher than normal reading, the speed of the Temp gauge excursions is such that it is impossible that the actual temperature could vary at that rate, physics being what it is... The temp sensor (on top of engine near thermostat) as well as the thermostat is new since this spring... wiring seems visibly intact to the sensor. After a day or so, the Service Engine light comes on. I do not have a code reader, but I expect it to be temp related.
Points of interest:
(1) increasing electrical load (turning on blower full, rear window defogger on) causes Temp gauge to move two letters higher, i.e. from A in NORMAL to hot line, back again when heavy load removed...
(2) turning ignition to start/crank position while running generally resets the Temp gauge to a more reasonable expected point, but this does not last, drift returns...
(3) when the ignition is switched off, the Temp gauge pegs clockwise to the 3 O'clock position (needle horizontal), a "feature" I do not recall seeing before.
I have rebuilt/tested the ignition switch, checked fuses in the engine compartment box, checked/cleaned battery terminals, ground connection from battery to engine, all fine. I have disconnected, disassembled/checked/reassembled the ECU, looks fine, no cold solder joints etc. I have removed/cleaned/tested/reassembled all instrument cluster connections, all OK.
I am in the process of measuring the actual engine temp during operation with an external sensor. This will tell me if engine temp is as it should be... (My assumption is that there is no physical temp problem)
Sadly, I have only a Haynes manual for this car. The electrical schematics are "generic" (generally useless, more block diagrams than schematics...) so I cannot trace wiring, the next logical step, in any efficient manner.
To anyone having any thoughts in this area, or any similar experience, your input would be appreciated. Also, anyone having elctrical wiring diagrams, Email scans/postings of these would be awesome...