After 360,000 or so miles on the bullet-proof-4.0L, had to swap it out for a reman. Third day introducing it back onto the road; about five miles out from the shop, got the first "bucking!" and CHECK ENGINE code; right back to the shop; onto the diagnostic; apparently a TPS P0121 code; mechanic (who's worked on my XJs through the years and did this heart transplant) checked the TPS connection, reset the computer, patted me on the head with a "sometimes it takes a little while for things to get settled in" and sent me on my way . . . as he headed out for his weekend. Within not too many miles, other buckings and CHECK ENGINE light back on.

Stopped by my local NAPA guy who had his own shop for 30-some years; discussed; I told him that my instinct was that it was a fuel-feed interruption issue and perhaps the system was working at cleaning out fuel residue resulting from the rig having been in storage for three years before the new engine insert; he suggested a shot of Techron (?) into the fuel as a first step. When I checked whether the fuel injector system had also been replaced with the new engine, it looks that it was not (not at all sure there was wisdom behind my trusted mechanic's decision to just remount the original set . . . ?!); thinking to get that replaced shortly.

Within the first 120 miles on the road, the bucking has repeated numerous times; stopped by O'Reilly Auto Parts and had the diagnostic hooked in; result: Code P0121, indicating Throttle/Pedal Position Sensor 'A' electrical circuit was out of range or had a performance problem for a predetermined period of time."

Yesterday: Now on a shops-are-closed Saturday in Anacortes, Washington; stopped by a NAPA store, and noticed a Current & Classics shop across the street with the shop door open; went over, met the owner, after a very brief description from me got his diagnostic, came out hooked it up, went back into his office/computer, and handed me a stickynote with the TPS part ## written on it (kindness beyond, on his part!); I walked back over to the NAPA shop and bought the part. All of the discussions along this journey were that replacing the small part was very simple; went back to the hotel, did a www.search and learned that the job is, indeed, something I could do..

Today: Went out to replace the TPS unit; the existing one looked new, which puzzled me -- wondering if my mechanic had already put a new one on . . . Tried to remove the two T20s holding it in place, but could not get the driver to "set into" a torx-head; now thinking there must be a different-head bold/screw in there . . . reconnected the line connector, started the engine, turned around and started to slowly drive; engine died; tried to restart, nothing, feeling like the starter had disappeared; gave it a 10-sec breather, turned the key, and the engine fired up again; started again to drive, and it died again.

Decided I am now at the get-a-tow-to-a-shop tomorrow (Monday) and go from there.

THE POINT OF THIS POSTING: Anyone know to recommend a good Jeep-experienced mechanic in Anacortes or Oak Harbor/northern Whidbey Island? Would be very much appreciated as I had planned to only be up here this week.

 

Ok, I cannot recommend anyone as I'm in Detroit & dont know anyone by you. But it sounds electrical. The code "TPS out of range" refers to the resistance "sensing circuit" that most of those sensors are on. Most including the TPS ground to a brown wire with a yellow stripe that can be found under your steering wheel if you have cruise control.
"Out of range" resistance can occur from low/high voltage if you have a shot battery like me, after just starting the car, gauges dont work until I start moving and the voltage rises lol. Or if I hit my EXT idle button and it idles up to 1100 rpm the gauges turn on.

**Sensors on brown ground with yellow stripe**
(Vehicle speed sensor, crank position sensor, cam position sensor on 00-01, Fuel sensor, Throttle position sensor, Manifold Actual Pressure Sensor, Mass Air Flow Sensor etc.)

Things to check yourself that are easy/cheap. 1, 2, & 3 are unlikely, I think its number 4.

1) Dying when driving (which is what it could be momentarily doing when "bucking") is a symptom of a bad ignition switch which you can replace with a phillips & flathead screwdriver in 1 hour. You can even pull out the one you have, lightly sand the contacts and put it back to see if that fixes the bucking problem. The momentary loss of power/voltage could cause sensors to go "Out of range" & throw a code. Unlikely as other sensors would have a problem but worth checking.

2) Having ACC power with the dash lights on but hearing NOTHING when turning the key and it happening intermittently is typically a NSS which wont allow you to start the Jeep when in anything other than neutral//park. You can jump the pins with a paper clip, there is a youtube video on "bypassing the neutral safety switch" which is a good way to test but dont leave it that way as it does throw an airbag code. Which can be cleared by unhooking the battery for 20ish minutes. If he swapped in a new trans that NSS may have been old, if its your trans, leaks from rear mains leak onto the NSS and typically make them fail. But like your ignition switch it can be pulled, cracked open, lightly sand contacts, use RTV to replace its old dry gasket and it should last another year or so with no dielectric grease.

3) Since there was a motor swap & this happens within a timed period of starting the vehicle, it COULD be a ground wire got pinched during the transplant. The PCM connector is easy to get to next to your air filter box. With no tools can be un plugged. Only do these with battery disconnected. There are 3 connectors, 1,2 & 3. 3 is closest to the driver, 1 is farthest away. You want connector 1. Find pin A23 on connector 1 per the included 99 PCM pinout from the FSM. its an orange wire with a dark blue stripe if that helps find the pin. Put your multi meter into 'continuity' mode (Looks like wifi symbol). If you dont have one buy a digital one at scamazon/hazard fart for 15$. In continuity mode, put one lead on pin A23, then the other lead on the middle pin of your TPS connector as per the included pinout from the FSM. If your meter beeps then thats good. Its just checking to see if there is a cut in the wire. Put it in horseshoe mode and do the same thing. If in beeped in the first test, it shouldnt say "OL" or "open loop" in this test. If the resistance is a number that does not rise then its fine. If it continuously rises. Then the ground that's meant to go to the PCM is skinned somewhere and touching the body, opening up infinite resistance.

4) A bad clock spring can cause high voltage to come out of a TPS and give that code. WITH THE BATT DISCONNECTED. Unplug the TPS, remove the plastic wire covering, ONE WIRE AT A TIME, cut one wire at a time making sure your cutting implement doesnt touch multiple wires when cutting the next wire. Cut one and bend them away. Strip the orange wire with a dark blue stripe a little long about 1 inch each side for testing. Then strip the rest and twist them back together to make sure they dont touch, put electrical tape over the orange wire to the one side. When twisting the orange wire with a dark blue stripe back together, twist them around the red positive lead of your meter to give you a free hand. Dont let any stripped wire touch the body at all.
Plug the TPS back in, double check that no wires are touching each other or the body then connect the battery. Turn the key to the ON position. Take your multi meter and put it in DC Volt mode. Its symbol is a straight line, usually next to a wavy line meant for AC voltage readings. Put your black lead on the stripped section of brown wire with the yellow stripe, and your red lead is already on the orange wire with the dark blue stripe. When the throttle is closed it should read 0.25 volts. Fully open it reads 4.5 volts. If it reads correct when closed, put your hand on the throttle and open it all the way up. If it goes over 4.5v you could have a bad clock spring. If when closed you're getting 0.35 volts or more. Bad clock spring. You definitely want a mechanic to do that as its behind the airbag and a P.I.T.A job. But at least you'll know for sure instead of costly guessing. The clock spring could be killing TPS sensors. Maybe clock spring got damaged during the swap? Dunno.

Doing these tests will avoid tows to mechanics who dont know about these jeeps and hopefully save you some money.
If you do these things and report back I'll do my best to help.

PS : I think its the clock spring as the first time wasn't for a while (5 miles) probably a limited amount of turning. Using the clock spring or "turning" probably causes the TPS issue by putting out too much voltage and then it bucks. In the one instance you said you turned the Jeep around then it died. I'd check the clock spring first.

- Drew