shadelifted

Hey, I hope all of you are doing better than I am. So I've had this Jeep for years and years and never had the money or time to take care of it really well. I'd fix major stuff that broke and learned a ton about working on cars along the way. About 3 years ago I had some time on my hands and decided I wanted to get serious and fix up my ole girl and get her running smoothly not just surviving.

I did an engine rebuild myself, cleaned out the engine bay, refreshed all the grounds, repainted the engine and bay, fixed some broken wires, replaced some worn components and put it all back together. I made some mistakes along the way (leaving the wire bundle that powers the brake pump off on accident, not plugging some of the wires to the starter back on the correct prongs, putting the distributor back in at 180 degree off, etc)

But she survived and was running better than ever for the most part. Problem was I couldn't drive her due to registration complications.

Fast forward a year and a half and I move across the country, get her registered, resolve some issues from sitting in the driveway too long (replacing the now rusted out coolant system and a leaky hose) and she's running great. I installed a manual switch for my electric fan since I couldn't figure out how to get it to turn on like it was supposed to.

It was running great minus one little issue: at 45 mph and above, it would buck and hesitate if I let off the gas slightly. I tried everything I could think of, read dozens and dozens of posts, replaced spark plugs and wires and the distributor cap, refreshed grounds multiple times but it wouldn't go away. It would shake pretty violently at 50-65mph if I wasn't accelerating and barely touched the gas.

Over the months it got worse and worse and now it's backfiring heavily, losing power when I try to accelerate, shaking violently whenever it gets between 2-3500 rpm and I'm worried I'm gonna damage something. So I finally have some time on my hands again to dive in, so I started troubleshooting and researching.

Eventually my research led me to believe it was the TPS. It had been changed in the past but never adjusted. I found Cruiser54s wonderful tips and tried to follow along but got a little confused at some parts, and eventually arrived at tip 8, adjusting the TPS.

When I test the resistance on the TPS (back probe B with red and black on battery) with the key off I get 0 ohms. With the key on same position I get 9 ohms.

When I test the voltage, key on, back probe B and A I get 4.64v. not terrible I think. 17% of that is 0.73v for the output. Back probe B and C and I get... 0.02v. If I adjust the TPS to max I get 0.34v. If I deflect the throttle to all the way open I get 2.02v output.

Unless I'm doing something wrong there, that to me says the TPS isn't outputting the right voltage.

So I replaced the TPS. The new TPS got the exact same voltages. The plug is a little damaged and the ground wire recesses a little at times. So I took the old TPS out and pulled the ground pin out, did the same with the harness side of the plug and plugged the two directly into each other to ensure good contact. No improvement.

I chased the brown and white ground wire, (and following the steps to repair the sensor ground followed the other brown and white wires) and found the duct tapped splice in the wire bundle.

Unlike the description in Cruiser54s post there were 5 wires all spliced into one (instead of 2 groups of 3 I think he said?)

Now I'm stumped and feeling like I got in way over my head... Is this second TPS also bad? Am I misunderstanding something here? I'm getting pretty desperate. I could really use some help.

Saudade

The TPS for an automatic has 2 wire bundles. One terminates in a 3 pin connector, the other in a 4 pin connector (still only has 3 wires). Your comment about "5 wires all spliced into one" is confusing. Did you have to unpin the connectors on your new TPS to plug in?

Here's a pic from my '88.

Oswalla

Do an ohms test from bundled wires to tps connector, if good wiggle wire bundle to make sure its solid connection.
Not uncommon to get bad aftermarket tps right out of the box. Ebay old stock is your only source for oem tps, atleast in my neck of the woods no dealer carries them anymore.

Personally I would be checking your fuel pressure as well for that backfire.

shadelifted

Sorry for the confusion. The ground wire (terminal B on the flat 3 prong connector) runs up the main wire bundle parallel to the valve cover towards the map sensor, then joins 5 other brown and white ground wires in the wire bundle on the fire wall just left of the map sensor in a splice that goes from 5 brown and white wires to one single one that I assume are all grounds. One of them comes from the map sensor, another comes from a sensor on the intake manifold.

shadelifted

I'm not sure i'm following which bundled wires you're referring to. Are you saying check continuity from ground of tps to ground of the engine harness side? Or one of the other pins? The pins on the square 3 pin bundle maybe?

Oswalla

If your reading about the tps ground in the wire loom, that I'M thinking of it is not that bundle. The connection is closer to the tps connectors. Mine was in the area of the loom by the injectors. Trying to recall from doing this many many years ago. As far as tps testing I cannot explain it better than Cruiser did in his tips.

Oswalla

"The ground wire (terminal B on the flat 3 prong connector)" Yeh from the B to wire connection you exposed. If thats what your trying to achieve.

shadelifted

The picture I replied with shows where the TPS ground wire leads to. i pulled the bundle apart and traced the wire until i got to that splice. from there it goes under the brake pump and I didn't want to follow further.

I followed Cruiser's tips for the adjustment, and like I said above I'm concerned that the output voltage is so low. the input is not great but acceptable at 4.64v but the output being 0.38v at max adjustment for pin C on the 3 prong flat terminal with throttle closed is not anywhere close to 17% of 4.64v. Not sure if that makes sense.

Oswalla

I just looked up what I think your refering to. TIP 6 ? If so scroll down to comments Cruiser explains where to check for ohms. And that set you have in your hands is what he is refering to. My 90 also has a connection like that in the loom by the injectors before it gets to that point you exposed. But if you got good connection from your exposed point to the ground terminal on both tps connectors you should be good to go.

shadelifted

Yeah that was what I was referring to. I get good ground to the loom and even at varying ground points around the engine bay. When the key is off i get 0 ohms on the DMM.

Is it possible that this TPS is bad fresh from the store? Both this one and my old one give me roughly the same, i get 4.64v in, and anywhere from 1.1 to 2.01v out on the squar side when measuring pin B (output) to D (ground). The highest i can adjust it to is 1.44v right now, or on the C (output) to B (ground) for the flat one i get 0.34v at max adjustment.

Oswalla

Yeh .7888 is what your needing and .38 is not even close. Id say you got a dud.

shadelifted

Thats so sad. I'll call the store and hopefully theyll let me return it for a replacement or something. Thank you for your help, I apologize if i'm being a little confusing, its been a long day and this is driving me up the wall at this point.

Oswalla

With readings that bad I am surprised the tranny is shifting properly. I always have shifting problems first when the tps goes bad..

shadelifted

It was hard to tell with how violently it was shaking, it shifts well at low speeds, but recently its been really random when it would shift. Sometimes it would do it fine other times it would wait forever before shifting, or just shift back and forth between the same gear several times before settling for the lower gear, or something like that. Plus the RPM would fluctuate pretty crazily at times. Jumping up and down 500-1000 rpm's. When it got to that point I got really nervous that by continuing to drive it I would damage the transmission or engine.

shadelifted

Got in contact with NAPA, will change out the part and test the new TPS tomorrow morning. Ill post an update with the results. Hopefully that part of the problem will be fixed at the very least -_-