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Low output voltage on tps.

Tested continuity between D7 and the chassis and the voltmeter chimed fine, no breaks. I have been cleaning all the connections under the hood and noticed a stray connector. It is just one black wire. Looks like a ground wire or something. Will post a picture in a second.
3f4e7a83.jpg


Any idea what that is?
 
On my 90, that wire's not plugged into anything. Oddly enough I just came in from stripping the ECU and harness from my 89 parts XJ and recognized that connector. On the 89, it was plugged in but I don't know to what since some other parts of the harness have been stripped out. The kicker is that I opened up the harness and traced the wire from the plug you photographed, and it's black wires, one running to the TCU and one running to the ECU. I could trace it to the ECU pin if you need me to.
 
Curiosity was killing me so I opened up the harness further to find that the wire you found disconnected just goes over to the dipstick stud ground and to the TCU. The TCU harness has been cut but I could possibly jury rig it back to gether for tracing purposes. What's stopping you from reaching up under the passenger side dash, unplugging the TCU harness, pulling it down, tightening the connectors with a small pick, cleaning with contact cleaner and plugging it back in. I just did this, minus the connector tightening, in 10 minutes on my wife's 88 cherokee. My offer still stands, and I will check where the wire goes to the TCU connector if you want me to.

Did you know that sometimes the factory wire terminations on the eyelets at the dipstick tube stud were crimped over the insulation and made poor contact? Might check that out, too.
 
Okay, there are only 2 black wires running to the TCU. D7 and C5. I'm not a good enough forensic automotive sleuth to tell you which of the two cut black wires in my harness went to which. I tried with no success. It appears that the ground from the dipstick tube stud and disconnected connector in your Jeep go to either D7 or C5 at the TCU harness. You'll have to test them at your end. Just for giggles you could ground that disconnected connector to a known good ground and see what readings you get at the TPS.That would tell you if the dipstick tube ground was faulty or not.
 
See that gray plug in the photo? A black wire goes into B there. But, in my harness, that wire isn't connected to anything nor is the other balck wire in the TCU harness. I don't know if that's intentional or not. But it would be easy for you to do some exploratory surgery if you open up the harness where the ground wires go into it from the dipstick tube. It's all close to that junction.
 
Thanks for doing all this digging for me. I tried to disconnect dipsitck grounds and checked d7 for continuity and the voltmeter sill made a chime like. So I don't know:-/
 
Rushin said:
Thanks for doing all this digging for me. I tried to disconnect dipsitck grounds and checked d7 for continuity and the voltmeter sill made a chime like. So I don't know:-/
Click to expand...

Try grounding that disconnected connector, that seems to have no home, to the negative side of the battery . What do you get?
 
Ok, did more testing. I plugged the red needle on voltmeter to d1(tps power A on tps plug) and black to D3 (the ground for tps) and got 3.9 volts, same as when I do test A and D on tps. Then I plugged red to D1 on tcu and black to D7(power ground) on tcu a gt 4.6v. So what's going on? I really think tcu ia bad, becuase by testing right at tcu I eliminate ground issue with tps wiring and testing power between power ground and tps power I eliminate issue with tcu grounding. Am I right or wrong?
 
based on those numbers, it does sound like the resistance to ground is inside the TCU. Go back to the TPS and verify that the input voltage is 4.6V if you ground the DVOM to a known engine ground instead of using the TCU ground circuit.

P.S. continuity (beeping DVOM) doesn't necessarily mean that there is no measurable resistance in the wires, but in this case, I don't think that is your problem. Just a thought for the future.
 
Shorty said:
based on those numbers, it does sound like the resistance to ground is inside the TCU. Go back to the TPS and verify that the input voltage is 4.6V if you ground the DVOM to a known engine ground instead of using the TCU ground circuit.

P.S. continuity (beeping DVOM) doesn't necessarily mean that there is no measurable resistance in the wires, but in this case, I don't think that is your problem. Just a thought for the future.
Click to expand...

I am not so good with electrical stuff. I am ok with mechanical issue but ohms and volts really confuse me. I know the theory but still get confused, because i dont know whats acceptable resistance and how to properly measure it.

I did go back to TPS plug A and grounded DV neg needle to the head and voltage goes to 4.6, when i plug black needle to D on TPS plug it goes down to 3.9.

I feel like TCU is bad.

Anyone got one for sale?
 
Got 4 TCUs. Two of them fit and two did not. However, same shit. Only get 3.9 volts. I am about to flip on this thing!

I really need some help here.
 
thanks cruiser, i appreciate your help. I just did a load test with a volt meter: I put the positive lead of the volt meter onto the battery positive and negative lead onto the negative terminal on the battery. I get 11.6 volts. This is my reference voltage. Then I took the negative lead and stuck it into the ground point on the TPS plug. I get 10.6v. same when i put the negative lead to the TCU connector where TPS ground goes.

I tested other sensors the same way and got no voltage drop.

Any ideas?
 
Shorty said:
have you considered running an auxiliary ground from the TPS and then setting it using the 4.6V input? It's worth a shot.
Click to expand...

so cutting onto the tps ground wire? I kind of did this. I just put a an extra wire into the plug where the tps plugs to the tps harness. What i got was a good 4.6v but when i moved the tps arm there was no change the voltage just staid at 4.6v. I took the car for a short (very short drive) and it was stuck in first gear.
 
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