TPS? Vapor Lock?

Serbonze

TJ Neophyte
Original poster
Supporting Member
Joined
Nov 12, 2015
Messages
1,879
Location
USA
Something really strange happened with the TJ (4.0) today. I drove it to and from work (about 25 miles each way) and it was fine. I got home, parked it in the driveway and went inside. About ten minutes later I went outside to move cars so I could put it back in the garage. I started it, and it ran REALLY rough. I shifted into reverse (auto) and it moved really slowly. I shifted to drive and gave it gas to pull into the garage and it stumbled all the way in. Giving it more gas didn't do much, it just kind of crept into the garage.

It was about 90 degrees and sunny today.

I cleaned the idle control valve and throttle body about 2,000 miles ago.

Thoughts?

Throttle body position sensor? Vapor lock?
 
I would go along with your first thought, sound like you may have had a heat plume that cooked the rail. Was it running ok later on.
 
I didn't have a chance until just now to go back out and start it. It's idling fine now.
 
Heat soak issue. Number 3 cylinder?

I did a little more research on it last night, and it certainly describes what happened. I've owned this Jeep for almost four years now though, and that never happened before. I also found this service bulletin:

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Thanks go to Mrblaine. He just had a similar issue with a customer and was kind enough to explain it on this forum.
 
Thanks go to Mrblaine. He just had a similar issue with a customer and was kind enough to explain it on this forum.

Do you happen to remember which thread? I just searched TPS, Vapor Lock, soak, etc and I'm coming up empty.
 
Check page 2 of "35s Performance."
Got it, thank you sir. I'm not sure why that didn't come up under my search terms. I going to repost is reply below to hopefully help someone in the future.


BTW Frank, I needed you here yesterday. I installed a Super 16" kit on a TJ Rubicon along with new rear pads and rotors. I get it all done, have a very nice time chit chatting with the owner and then go do the break in. I need to center the steering wheel due to swapping out his dropped pitman arm so I get back from the break in and do that. Then I have him drive it and a mild toe tap will lock up his 33's at this point and he seems to like his brakes and the steering.

It's an 04 and I notice on the several times I've had to stop and then restart it that it appears to have the injector heat soak issue but it goes away pretty quickly.

Get done and he leaves and leaves at full throttle for some reason and I hear the engine missing as it goes up the hill. I'm putting a few tools away and he whips back into the driveway, sticks his head out the window and hollers at me that he has a check engine light.

I say Okay, you have a check engine light.
It wasn't on when I got here.
Yes, I understand that but there is nothing related to working on the brakes that will throw a check engine light.
I didn't have one until you touched my Jeep.
Yes, I understand that, but again, there is nothing about the brakes that will throw a code. But, I did hear your engine missing as you were going up the hill so I suspect you have a cylinder 3 misfire due to a heat soaked injector.
I didn't have a CEL when I got here.

I tell him to hold on a second and I'll get the scanner and we'll see what it is. I scan it and the code pops up, Cylinder 3 misfire. I flip the screen around and show him and say see, just like I said.

I get a blank stare so I tell him to hold on and I cleared the code. Tell him to start it up and listen to the motor. It will idle rough and then in about a minute the intake will cool down, heat soak will go away and the idle will smooth right out. He starts it, it idles rough and then cools down the injector and the idle turns to a smooth purr.

I get another blank stare and I explain yet again, I didn't do it. You have an 04, there is a TSB for the heat soak issue, go look it up.
Still a blank stare so I needed you here to slap him in the back of the head and tell him to listen to someone because he sure wasn't listening to me.