TPS ?????

Alright I have a 1988 4.0 and tried to fix this problem by doing this...

Replaced...tps (3 times in last couple of months), new O2 sensor upstream, cleaned the idle air control motor as well as the throttle body, replaced the map sensor and tomorrow the plugs, plug wires, cap and rotor and fan clutch will be new.

Now the latter of the list im not sure will make a change just time for new parts in those areas.

I cannot for the life of me figure out why my Jeep is running so crappy. With my tps plugged in and I tap the gas it hesitates and dies. If I hold the brake and barley hold the gas it dies and the gas mileage dies to about 6 mpg while driving. It also revs to about 4 g's while sitting still. Now heres the crazy part of this equation...I unplug the tps and all the power comes back and i can barley touch gas (as if moving up in a fast food line) and it dont die and believe it or not my mpg's go back up to about 15 and this is with 4:56's and 35's. Now what I have noticed in the past couple of weeks while driving with the tps unplugged it has started a little hiccup so to speak while driving at a constant speed, and then started acting like it is loading up and starts kinda backfiring thru the throttle body and exhaust but only for a couple of seconds the smoothes out again as I accelerate. Now all these syptoms I figured were pointing to the tps being bad but as I mention Ive changed it 3 times in the last couple of months. What can be causing this problem?

Im scratching my head as to why my check engine light isnt coming on (although may be burned out) and how the computer even knows when to shift gears with no tps reading...is there a super default mode? :banghead:

Ok, DON'T CHANGE THE TPS AGAIN!

TEST it, adjust it, but only replace it if can't be adjusted within specs.

Auto or manual? You need to check the reference voltage to the TPS, and if an automatic the output voltage needs to be 83 percent of the reference voltage. If a manual transmission, then output voltage needs to be 17 percent of reference voltage.

Test and adjust, then post up your numbers.

Good luck.

On a RENIX XJ, the CEL is driven by a timer that only counts miles, then destroys itself, turning on the CEL. Your 1988 is a RENIX and does not live by the same CEL rules as the later models.

Have you tested your TPS? To do this, you need to monitor the output to the TCU with an analog voltmeter. Watch the sweep of the needle as you depress the skinny pedal. The voltage change should be smooth with no glitches. The TPS adjustment is critical on a RENIX. Get a digital voltmeter and follow the procedure in your FSM.

When the TPS in my '90 4.0 M/T went bad she'd start and idle very high (2K rpm+). At first I could feather the throttle and make it go down but after a while it refused to do so. Every time I tested the TPS it was good but replacing it with a JY one finally solved it.

Sorry its and automatic and all 3 tps sensors were spot on with voltage readings.

.8 volts at closed, smooth reading as moving to wot, and about 4.2 volts at wot.
This is why I cant understand where the bad signal is coming from.
I will also trace the ground wire from the tps to ecm connector to ensure a good ground tomorrow.

Thx for all feedback I know this has been asked a thousand different times but the symptoms im having just dont make sense!

Ok, and if you measure the reference voltage on the 4 wire connector with the key ON what is the reading between "D" (ground) and "A" (positive)? That is your reference voltage.

Now, with the 4 wire connector installed back on the TPS, key ON throttle plate closed, back-probe "B" and "D"--that value is the output voltage and needs to be 83 percent of the reference voltage--if reference voltage is 5.0 volts, then output is supposed to be 4.15 volts.

joe_peters said:

Ok, and if you measure the reference voltage on the 4 wire connector with the key ON what is the reading between "D" (ground) and "A" (positive)? That is your reference voltage.

Now, with the 4 wire connector installed back on the TPS, key ON throttle plate closed, back-probe "B" and "D"--that value is the output voltage and needs to be 83 percent of the reference voltage--if reference voltage is 5.0 volts, then output is supposed to be 4.15 volts.

Click to expand...

That's how to adjust a TPS. Accept no substitutes. Ever refresh all your grounds in the engine compartment? Clean the C101 connector?