TPS 5 volt supply

My 1988 XJ 4.0 has an idle problem, bucking, and has no power. I was testing my tps, with the connector unplugged, i check the voltage at connector A and B and only got 2.39v. The ground was bad so I put a new one. Now i got 2.70v. How am I suppose to get the 5volt ???

The voltage for the sensors comes from a voltage regulator in the ECU. I know it is a pain, but drop the computer and backprobe the connector and check if you have 5v or not. You could either have a bad ECU or a bad sensor. IIRC the 5v goes to the TPS, the MAP, and the Air Charge Temp Sensor. As an alternative, you might hook up a meter to any one of the sensors and one by one disco the other sensors. If the voltage jumps back to normal, you know which sensor is the problem.

or search for "Renix sensor diagnostics", find the link to LUNGHD's website or any one of the other bazillion TPS posts and properly test it as well as the other sensors.

Got 2.70volt at the TPS
Got 5volt at the Map
And where is the Air Charge Temp Sensor ???

Americanpower said:

Got 2.70volt at the TPS
Got 5volt at the Map
And where is the Air Charge Temp Sensor ???

Click to expand...

Screws into the top of the intake - I believe it's aft of the throttle body (but don't hold me to that at the moment.) It will be in the main plenum, however, and not one of the runners - and it should be fairly close to the throttle body.

Good news, if you have 5v at one of the sensors, it is not the ECU, but a wiring problem. Check all your connectors back to the ECU.

I can't remember when they did away with connector C101. It was located just above the brake booster. It is notorious for flaky contacts.

Just made a second test.
TPS 2.69v
MAP 4.86v

Given the age of the system involved, it's unlikely your reference 5VDC signal is still going to be a solid 5.0VDC. However, it should be close enough (and +4.86VDC is not too shabby.)

The problem with supplying an external fixed/regulated 5.00VDC signal is that you then either have to feed it into the reference circuit of the ECU or you have to then adjust all of your sensor signals accordingly - you're better off leaving the +5VDCREF alone and figuring out why your TPS isn't getting full reference voltage, then readjusting relative to current reference voltage.

I still have 2.70v at the TPS with a direct ground but the engine seems to has stopped bucking.
The new ground solve the problem but, I don't know why.

Americanpower said:

I still have 2.70v at the TPS with a direct ground but the engine seems to has stopped bucking.
The new ground solve the problem but, I don't know why.

Click to expand...

Try checking it with the plug connected. The 5 volt supply almost has to be regulated and/or a feedback system. It may need the connection to produce anywhere near the right reference voltage.
I ran my TPS wires over the top of the TB rubber intake, cut the wires a quarter of an inch lengthwise through the insulation with an exacto knife, right on top of the rubber. Makes a TPS test like a five minute operation. Back pinning the connector, besides taking three hands, is often really unreliable.
I actually cut the slits on both sides of the TPS connector, I once had the connector, right at the TPS, cause a radical voltage drop (high resistance). Somebody sprayed it with (what smelled like) WD40.
A bad MAP (or the MAP vacuum line) will sure enough make it stumble and buck, it will also drive like your towing a dump truck. Pull the MAP plug and see if there is a noticeable difference. Pull the MAP vacuum line and see if there is a noticable difference.