Trying to find an old thread where troubleshooting the TPS wiring was discussed but can't locate it, maybe it was, excuse me, another forum even? Seems like it might have been a post by jmartin maybe?

My TPS started acting up a couple years ago. Voltage was weird. Tried the pot but never got that to work. Finally broke down and dropped some bones on a new NAPA. Then the truck sat for over a year with a blown head gasket. After getting it running again the same thing started happening after a couple hundred miles. Even though the voltage "seemed" to be OK, the thing was coming apart inside. NAPA replaced it and it worked fine for a few days.

Thinking all was good I headed out for Columbus and Indy for the TDR Dodge Rally (Excellent factory tour, even got to see the D001, the 1984 W350 CTD prototype but thats another thread...) After 150 miles or so I started to notice that it would drop out of OD when I took my foot off the pedal. Not good at interstate speeds. Limped into Columbus and adjusted the TPS. I lost OD so I adjusted it some the other way and it came back but only for awhile. Made the 1 hour trip to Indy OK for the NHDDR but on the way home (3+ hours) it started acting funky again. I stopped and adjusted several times to no avail. Even after adjusting the throttle cable correctly it still drops in & out around 45-50mph and downshifts to 3rd when you let off the go pedal but only intermitantly, not all the time - thats whats got me thinking it may be in the wiring - or something else???

Long post just to try and find an old thread, sorry...

 

Are you adjusting it with a meter? Is the voltage steady or jumping around?

 

I didn't have the meter with me on the 500 mile trip so I was adjusting by feel. When I got home to look up the throttle cable gap I thought for sure that was my problem since there was none but after setting it using a 3/16" bit it made no difference.

I'm fixing to go check the voltage now with the meter and reset the gap too. Just finding it hard to get motivated after all that frustration. Up side is I averaged 17.7 mpg on the way home even with all that hunting around and no OD for the last 44 miles...

 

This is way I have adjusted before with some luck.

The injection pump throttle lever must be in the low idle position and the throttle lever must reach breakover when the throttle is wide open, turn the ignition key to the ON position,
connect the negative lead of the voltmeter to a good ground (1991 1/2-93 models may use DRB II),
insert the positive lead of the voltmeter to the center (output) wire of the TPS electrical connector (leave connector attached to TPS),
with the throttle lever contacting the low idle screw, the TPS output voltage should be 1 volt ± 0.05 volt,
adjust the closed throttle TPS setting, if required, by gently rotating the nylon adapter until the correct voltage is obtained
open the throttle lever to the wide open position
the TPS output voltage should increase a minimum of 2.25 volts from the closed throttle position voltage.
if TPS required adjustment, disconnect the battery negative cable for 2 minutes to reset adaptive memory, then reconnect the battery

 

The tv cable adjustment will not affect the od shift at all. The tps voltage must be fluctuating that could be caused by a bad tps or a bad voltage supply. There should be 5 volts coming to the tps and the tps modifies the voltage output to determine throttle position. Make sure the voltage does not jump around when you move the throttle.

 

Thats what I just did, except I haven't disconnected the battery yet - thats a new one on me. Maybe thats what is screwing things up? I'll take a test drive as soon as I get some more pastures mowed.

I cycled the TPS and get a smooth voltage from 1.1 to 4.8. We'll see what she does now.

Thanks guys.

 

What does the voltage do if you hold it at about where you would be at crusing speed and let off like you do when you are saying it drops out of od? Also the wide open throttle voltage seems high the spec says 2.25 volts higher than it is at idle.

 

Thats exactly what I was thinking.

The 4.8v or whatever it was (I didn't write it down therfore it don't stick in my mind) seemed high.

I'm not sure where the throttle would be when I'm cruising (~1,900 rpm @ 70mph or so), I've never gotten out to check .

 

Yea but it is probably half throttle roughly to do 70 so check it out around there and let it up and see what th voltage does. You need to try and simulate the problem to see what is causing it.

 

Do a resistance check on the white wire with the orange strip that runs from the VSS to pin 47 on the ecm. That is the speed reference wire that both the overdrive and cruise control uses through the ecm. If it has a high resistance, then the ecm is not seeing the correct speed.

 

Onemopar nut - I'll give that a try and see.

Cougar, I'll try that as well. To check resistance I set the tester on ohm and put a probe at both ends right? Cruise worked fine BTW.

 

The PCM supplies 5V to the TPS. Ground also returns to the PCM.

the output range is supposed to be 1v to 3.5v.

Don't forget that there are 3 potentially dirty connectors (9 connections in all) between the TPS and the PCM.

Like Cougar said, a clean VSS signal is also needed.

 

I drove her today after adjusting with the multimeter and she did fine. Will have to put a few more miles on it before I declare it licked. May try tracking down those 9 connections and cleaning/sealing just for peace of mind. I'll recheck that upper reading too.

Thanks guys.

 

3 on the TPS, 3 on the PCM, and 3 in the 10 pin connector under the intake manifold near the firewall.

 

Odd, did fine Tuesday. yesterday afternoon I noticed a few delayed shifts and then the drop from 4-3 when I take my foot off the pedal.

Rechecked voltage and rest is 1.2v while full throttle is 4.4v. Smooth tansition up & down though.

Still need to check those middle connections yet.