Help Diagnosing

[bmvalentine]

I’m having a couple issues that I am attempting to troubleshoot. Couple symptoms:
1. After restart when jeep has been running for a couple of hours and after sitting off for about 10 minutes; it will start and rough idle for a bit and then seem to even out, although sometimes it has stalled at a stop.
2. Also after running for a couple hours, when either getting over to pass on highway the transmission will downshift and the rpm’s will increase accordingly, but there is a lack of power/no acceleration. Similar experience when encountering a hill, jeep will downshift but lose speed.

*couple more notes, there has been a couple occasions that the jeep has lost a large amount of power and will start running quite rough forcing me to pull over. Upon restart the problem will cease and it will drive normal.

ECU codes
P0300
P0301
P0302
P0303
P0304
P0305
P0306
P0121

I know what the codes are, the P030x’s are a cylinder misfire/general misfire. P0121 points to the TPS.

My intention is to start by replacing the TPS, but want some input on what else it could be.

 

[macleanflood]

Things getting hot and affecting idle are often loose intakes.

Check those bolts.

Smoke test for leaks might help too.

-Mac

 

[bmvalentine]

I’ll check and see what happens. I got it back in October with about 74,000 miles on it; it now has about 80,000, for a little more context. I’m more used to working on my ‘89 Land Cruiser, so Jeeps are newer to me. There are some differences but there are a lot of similarities too.

 

[bmvalentine]

Well update time. I have replaced the TPS with a Mopar sensor, I have taken the throttle body off and cleaned it very well. I am still getting a P0121 code, the misfire codes have gone away. Acceleration from stop has gotten better but if I need to accelerate up a hill from a stop it will shift down and get high rpm’s but lacks power. It is most noticeable at 50 when I need to maintain speed up a hill, it just lacks power.

 

[bmvalentine]

I have not smoked test, and cannot locate any vacuum leaks.

 

[Moglocker]

I have not smoked test, and cannot locate any vacuum leaks.

Cat stopping up

 

[bmvalentine]

That crossed my mind too. Is there a way to test that?

Cat stopping up

 

[MBDIAGMAN]

Do you have access to a scanner that will give you fuel trim information? That will tell you if it is a rich or lean condition which is the next fork in the troubleshooting road.

 

[macleanflood]

IR thermometer before, on and after the CAT.

Also can pull the O2 sensor and cause an exhaust leak to see if things improve.

-Mac

 

[MBDIAGMAN]

Yes there should be 100 degree difference between inlet and outlet of the cat if it’s doing its job. If the trim shows it to be rich and it has been rich for an extended period of time then the cat may very well be toast, but unless it is plugged, it shouldn’t cause much trouble beyond nuisance codes. In other words, if the cat is toast, replacing it is necessary, but probably not the root of the problem, rather is a result of the problem.

 

[macleanflood]

but probably not the root of the problem

Unless it's completely or partially plugged.

-Mac

 

[bmvalentine]

Do you have access to a scanner that will give you fuel trim information? That will tell you if it is a rich or lean condition which is the next fork in the troubleshooting road.

Yes, I do. Im not sure what is a good reading and a bad reading though.

 

[bmvalentine]

These were taken at idle after sitting for 30 minutes after driving just over an hour on highway and back roads.

SHRTFT1 ranged from 3.6-7.0%
LONGFT1 ranged from 8.6-11.7%
SHRTFT2 ranged from 0.0-6.3%
LONGFT2 ranged from 7.8-11.7%

 

[ItchyDong]

How does a P0121 code turn into a melted cat, loose intake, or looking at fuel trims? The PCM isn't seeing the correct voltage from the TPS signal wire, or, is incorrectly interpreting the correct voltage.

You asked for help troubleshooting. Here you go. Different DTC, same testing procedure. You can also short cut this whole process and look at live data on your scan tool if it has a data pid for throttle position voltage. But, always verify scan data with a multimeter as shown in the video.

 

[MBDIAGMAN]

Yes, I do. Im not sure what is a good reading and a bad reading though.

No problem just put the long term fuel trim value here and we will see what we can do with it. All we need for the next fork in the road is to know how rich or lean it is.

 

[MBDIAGMAN]

Whoops I posted before itchy was on it. It doesn’t take much, to get ahead of this old retiree these days. Once the TPS is sorted, there may be more to come.

 

[ItchyDong]

Whoops I posted before itchy was on it. It doesn’t take much, to get ahead of this old retiree these days. Once the TPS is sorted, there may be more to come.

I may actually be eating crow here. Looks like I’m mistaken in what the 121 actually means. This is straight from the 2004 manual. My bad fellas.

 

[ItchyDong]

Looks like you still need to run that test shown in the video, but if it checks out, testing of the map sensor needs to be accomplished as well. I can walk you through it if you get to that point.

 

[bmvalentine]

I may actually be eating crow here. Looks like I’m mistaken in what the 121 actually means. This is straight from the 2004 manual. My bad fellas.

View attachment 622624

Interesting, this would indicate a MAP sensor or a wiring issue, given that the TPS is a brand new mopar unit.

 

[MBDIAGMAN]

There should never be crow to eat when troubleshooting. Everyone pitches in with constructive thinking until it’s solved. Egos get in the way when team troubleshooting.