Random Stall / Misfire

[Zach O'Neill]

Firstly apologies, I’ve posted quite a bit about this in the past but I’m at a loss and don’t really know what else to do. So here I am again , I’ve had some major issues with my 2004 4.0 Auto TJ that I’ve posted extensively about and had some really helpful conversations about , but unfortunately I’m still having some problems. To recap I got my Jeep at the end of last year and on the way home it seemed like the power was dipping and coming back, dipping coming back etc, it didn’t fully die , just lost some acceleration and then returned to normal. Since then it’s also had a very severe intermittent misfire when under power that kills all acceleration and also it stalls at idle intermittently unless shifted into neutral and reved to stop the stall. This from my understanding is mostly random however I’ve never had an issue when cold. I replaced all spark plugs, changed the oil, changed all O2 sensors, the crankshaft position sensor was changed , it’s got no lights and rarely stores codes, the only thing I know for a fact is the barometric pressure reading is really far out , was reading like 700ish when it should have been up over around 1020 in Scotland. it’s been to 3 garages who couldn’t find anything wrong , one found a P1793 for a TRD Link communication error however my mechanic didn’t know how to fix. I went to a Jeep dealer and they pulled a stored code for a P0124 on the TPS however have said the TPS sensor is working as normal and expected so have put it down to a suspected intermittent wiring fault. Does anyone have any ideas ? Could it just be the PCM that’s gone ? Jeep want £150 per hour to diagnose and suspect it could take up to 8 hours to find the problem , so don’t really want to spend that money if I end up needing to replace the PCM after all. This video is what the misfire is like, no matter how hard you push the accelerator the speed barley increases and then all of a sudden it just kind of clicks the revs jump and it’s back to normal

Original post https://wranglertjforum.com/threads/stalling-when-at-running-temp.58677/

 

[Jerry Bransford]

What brand of crankshaft position sensor and especially what brand O2 sensors did you install?

 

[Zach O'Neill]

What brand of crankshaft position sensor and especially what brand O2 sensors did you install?

O2’s were NTK and the crankshaft sensor was mopar

 

[Jerry Bransford]

O2’s were NTK and the crankshaft sensor was mopar

Well that eliminates one of those as an easy fix.

 

[Zach O'Neill]

Well that eliminates one of those as an easy fix.

It’s the codes that don’t add up , my mechanic took it out a road test and it preformed flawlessly, had it sitting at idle and it eventually played up , he then managed to pull the P1793, however it didn’t store this code. We couldn’t find anything on the forum or online for this so were at a loss and he suggested the crankshaft sensor , unfortunately that didn’t help. Then the Jeep dealer got the tps sensor code but they’ve assured me that the sensor is preforming perfectly. So I presume what ever caused the false TPS DTC also caused the TRD link error , but I’m completely unsure as I don’t really have a clue what I’m talking about. As I said the barometric pressure was reading off but I presume that would just send my fuel economy to the floor and not cause anything else

 

[JKP]

The MAP sensor tells the PCM the manifold pressure (or vacuum if you prefer) and uses that with the TPS to determine the load on the engine. It is also used at startup to determine your atmospheric pressure from which it derives the air density which varies depending on your altitude.

Sounds like you need a new MAP sensor.

 

[Zach O'Neill]

The MAP sensor tells the PCM the manifold pressure (or vacuum if you prefer) and uses that with the TPS to determine the load on the engine. It is also used at startup to determine your atmospheric pressure from which it derives the air density which varies depending on your altitude.

Sounds like you need a new MAP sensor.

That’s definitely interesting , my mechanic was under the impression that the sensor that took barometric pressure readings was integrated into the PCM. But if it’s as youe saying it could definitely be the MAP that’s causing that , a faulty MAP sensor can also cause hesitation and stalling if I’m correct ? No idea how that would cause the TRD link error coming from the TCM though or what even causes that as I can’t find out much about it