sheky1

Hello,

I am new to the forum, I have a 2004 Grand Cherokee since new and I want to keep it going.

I found the forum by searching my issue, hoping to find some help and offer what I can.
Jeep has 211 k, 4.0 L inline 6 cylinder.

I was stuck in traffic on the interstate this weekend, when the traffic broke the truck started bucking and cutting out on acceleration.
I was able to maintain steady speed of 50 MPH, but on an incline it started bucking and cutting out again.

I limped the truck home, then it would stall stopped at traffic lights but would restart.. Pulled the codes and had PO122 Throttle Pedal Position Sensor Switch Low Voltage.
Changed the TPS, truck started fine drove a mile at 25 MPH, ok. Accelerated up to 35 MPH got slight buck, left off the throttle and it was ok.

Stopped at a traffic light, truck stalled and would not restart, had it towed home. Tried a few times to start the truck the same day, would not start.
After the truck sat over night, it started in the morning. I didn't try to move it.

I have seen several threads from several years ago with similar issues. Does anyone have any suggestions or can point me to relevant threads?
Any help will be greatly appreciated. I have had this truck for almost 20 years!

Thank You,
Sheky1

Caish

I fought similar issue, like it was vapor locking.
00 LAredo 4.0
Finally I decided it had to be fuel pump related, but how to check it for sure.
I had 49 psi so that was good, but revving it dropped to 0 at 3000 RPM.
So then pulled the Schrader valve in the fuel rail,
Jumped the fuel pump relay with a paper clip.
Ran hose in a 5 gallon bucket.
After 30 seconds or so it had barely a pint, just a really weak stream.
It should be very close to a gallon after 60 seconds.
There is a pressure regulator/filter in front of the tank, looks like a fuel filter with three lines on it.
Can pop a line loose back there and recheck the volume.
We fought this for over year because I knew I replaced the pump when installed the engine in #BastardHeep
I was bullheaded and didn't want to drop the tank again.
Chinesium parts strikes again...

sheky1

Caish,

Thank you for the information. The homework I have been doing has been leading me down an electronics / sensor road. Fuel delivery issue makes sense. When the truck first started acting up on the interstate, it would cut out on acceleration. I will take a look at the fuel system.

Another question, do you have any suggestions for replacing shift cable linkage retaining bushing. I notice my retaining bushing on the transmission side is missing.

Sheky1

oddballracing

One more thing:

If your tool supports PID reading and not just code reads.

I had an issue in my '98 that had me committing the sin of not looking only at the facts, but a preconceived notion that it was due to my replacing the stolen catalytic converter (still angry) with just a pipe and a new downstream sensor.

Comparing the upstream sensor to the downstream sensor I saw they were wildly different (front was reading >1V and rear almost zero. As the upstream sensor was consistently reading 1V (rich), the ECU was attempting to correct this by leaning the mixture right out, while the rear sensor was reading completely lean (with a working Cat this would have immediately triggered me to know it was BS). I'll admit i had very little understanding about how the common automotive O2 sensor worked, and after some reading realized how off the mark I really was. Before going full parts cannon on it, I used just a simple Bluetooth OBDII ELM327 interface (they are something like $20 on Amazon), and a free android tool like "Car Scanner" (up to two sensors real-time graph in the free version) to visualize the sensor data at the ECU, it started to make more sense.

Only in closed-loop was I getting this problem (idle, cruise), but in open-loop (cold, WOT, decel) everything was fine. It was only in closed-loop where the O2 reading was considered, did I get this. at 390,000km, it seemed acceptable that an O2 sensor had outlived it's usefulness after learning these are only rated for less than half of that. Replaced the upstream O2 sensor with a Denso unit from RockAuto (not promoting them, just happened to be the cheapest option while I was ordering parts for other vehicles) and she's been running like a top for a week now.

This should be an additional check if you continue to have issues after verifying fuel pressure, strong spark, etc. I don't see any reason that the O2 would cause a no-start condition, even when warm as that should also be an open-loop mode.

Do you get the same bucking whether you are WOT (pedal to the flow) or when the vehicle is cold?

Also, is that a drive-by-wire or cable operated throttle system? (I don't have any Jeeps that new). I had a 2010 chevy truck that went into a reduced power mode with a bad TPS on a drive-by-wire throttle body (i know you say you replaced yours, may not hurt to inspect and test the wiring). The reason I ask about the DBW, is your description of the P0122 code states "Pedal position sensor" which implies drive-by-wire, even though the code also carries a description not containing "Pedal" in the statement.

sheky1

oddballracing,

Thank you for the information. I investigated fuel delivery. My fuel rail does not have a schrader valve so I pulled the fuel line from the rail, pointed it to a bucket and had a helper turn on the key. I only saw a trickling flow. Changed out the filter regulator, it was hard starting but did, ran at idle for about 10 minutes, engine died and would not restart. Went to check fuel delivery, started to remove the fuel line from rail, now had high pressure at the rail fuel, started spraying when I tried to release the line. Engine was hot and I didn't want a fire, I decided to move to test spark.

I pulled the coil, checked for spark with one of those spark plug looking tools that has a grounding wire. I was checking one cylinder at a time. #1 cylinder always had a good spark. I wasn't getting consistent result testing #2-#6. It seemed like I never got a spark on #6. It was getting dark and I was able to see air arching in one of the boots.

Changed the coil, tested each cylinder individually for spark. Cylinder #1 had consistent spark, didn't get consistent results testing #2-#6. Again it seemed that I never had a spark at cylinder #6. The coil rail only has three coils; pairs of cylinders fire together (#1- #6), (#2-#5) & (#3 -#4). It didn't make sense that I was seeing spark on #1 but not #6.

I got an old spark plug and made up a grounding cable, went back to test the cylinders in pairs. With the new coil, a spark tester in boot #1 & #6, good spark at both, same for the other two pairs. Again with a plug tester in each boot I wanted to check spark individually. I did this by disconnecting the ground for the spark tester. Spark was still strong, even the cylinder where the ground was disconnected still sparked. Lesson relearned, do not hold the ground cable in your hand! Did that once.

Finished installing the new coil, now it had been running strong. Hasn't stalled or cutout while driving, haven't been out on the highway with it yet, but I think it will be good.

I will look into my scanner to see if I have have PID. Also thank you for the lead on Bluetooth OBDII interface. I know better but fell into the "part changing" trap. We are up and running again and I think I am a bit smarter now.