I'm banging my head here over a vref hihgh voltage problem on my 1990 GT....I'm running an EPEC and have two spare 89-93 EEC's here and no matter which one I hook up, I get a reading of 12+ volts from the vref 26 pin (instead of the normal 5v) after turning the key forward....what could it be? When using the epec, I get the 5 volts, key off...then turn the key forward and I get 12+v....on the A9L, I get nothing, key off...turn the key forward and I get 12+v....At first I thought this was the signal return wire but I think I've further traced it to the #26 vref...Even if I unplug all the sensors, I still get this 12+ from vref....with all sensors plugged in, the datalogger shows 100% TPS, -40f ACT, -40f ECT, and so on.....This problem has been around this car since the last owner had it and I thought it might be easy to fix....the car was originally an AOD car that was swapped to a t5....I checked all the clutch switches and nuetral safety as well as plugs on the tranny....nothing....I just worked many hours fabricating a turbo setup for this car and I would very much like to get these sensors to producing proper feedback so I can drive this thing....what could this be? TIA
VREF voltage too high
- Thread starter 93TY#0475
- Start date
When measuring Vref, always use the black/white wire on the TPS, BARO, ACT, ECT or other sensor for ground.
Disconnect the battery positive cable and then disconnect the computer. Measure the resistance between the orange/white wire (Vref) and the red wire on any injector or actuator. Make sure that you are not touching the probe tips when you make your measurements. If you are, then your measurements will be inaccurate. You should see an open circuit or resistance more than 1 Megohms.
Next measure the resistance between the orange/white wire (Vref) and the battery positive cable. You should see an open circuit or resistance more than 1 Megohms.
Reinstall the computer connector to make the next test, but leave the battery positive cable disconnected.
Measure the resistance between the black/white wire and battery ground. You should see less than 1 ohm. Check the same black /white wire on the TPS and MAP sensor. More than 1 ohm there and the wire is probably broken in the harness between the engine and the computer. The 10 pin connectors pass the black/white wire back to the computer, and can cause problems.
If any of these tests fail, you have wiring problems.
Disconnect the battery positive cable and then disconnect the computer. Measure the resistance between the orange/white wire (Vref) and the red wire on any injector or actuator. Make sure that you are not touching the probe tips when you make your measurements. If you are, then your measurements will be inaccurate. You should see an open circuit or resistance more than 1 Megohms.
Next measure the resistance between the orange/white wire (Vref) and the battery positive cable. You should see an open circuit or resistance more than 1 Megohms.
Reinstall the computer connector to make the next test, but leave the battery positive cable disconnected.
Measure the resistance between the black/white wire and battery ground. You should see less than 1 ohm. Check the same black /white wire on the TPS and MAP sensor. More than 1 ohm there and the wire is probably broken in the harness between the engine and the computer. The 10 pin connectors pass the black/white wire back to the computer, and can cause problems.
If any of these tests fail, you have wiring problems.
pro50
Member
hey, question for you. im having the same problem. im curious to see if your car will start or not.i cannot get my fuel pump to turn on or the injectors to fire and im seeing 12v at the vref wire. let me know what you find, maybe we can help each other solve our problems. thanks
Mine starts easily when cold then floods out while cranking with a hot engine...I think I've found my problem, but not 100 percent sure....o2 sensor harness....there's a dead end wire (pin30) in my 8pin socket by the MAF...someone at another forum pointned that out as a possibility....the male part of that plug has 8 wires going in and the female portion has only 7.....I think I need to check another stang like mine to see what mods I need to do to my o2 harness then take it from there.....
pro50, did you convert from auto to T-5 or vice versa? if so, here's a link to a similar problem as mine...
pro50, did you convert from auto to T-5 or vice versa? if so, here's a link to a similar problem as mine...
Fixed it!!! My o2 sensor harness was in fact for an AOD car....I took apart the 8pin connector, swapped pins and the car runs awesome now (with another ecm)....having the wrong o2 harness will fry any ecm you connect to it, from what I understand... I guess you learn something new everyday....
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