99' Wrangler Sport Bucking and Shaking

[diegoa1997]

I have a 1999 Jeep Wrangler Sport 4.0L 6Cyl. Whenever I am accelerating from a stop it will start bucking and shaking like if it was going to stall out. This only happens when accelerating from a full stop. When I first turn the car on in the morning, it accelerates fine for the first few stop signs and red lights but then it starts doing it at every single stop. Once it picks up speed the ride is smooth and has no issues. The check engine light came on the other day but turned off before I got home to check it. When I checked it, it gave me a stored code of P1391. When I read online I see that this can mean the crankshaft and camshaft sensors which I already changed along with the distributor cap, rotor, cables and spark plugs. Any suggestions as to what the problem could be?

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[WXman]

You're a couple of decades behind. This is a JL Wrangler forum and a lot of the millennials on this forum were in kindergarten when your TJ was built.

But... from what you describe I can tell you that you are likely in for a headache. I had a 2001 model WJ with that same engine and it developed the same issue. We tried everything imaginable. New plugs, new coils, new crank sensor, new cam sensor, fuel injectors, ECU, heck I even had the valves in the head machined again and installed new pushrods and valve springs. Nothing would fix it. It would drive fine until it got to operating temperature and then it would all go to hell with a flashing CEL and a bucking, kicking engine.

I finally got so tired of it that I sold that Jeep and moved on. It was my second 4.0L and my last. I swore I'd never touch another. Good luck.

 

[cbrenthus]

Error Code P1391 is defined as CMP or CKP Signal Intermittent Condition. It refers to intermittent conditions in the CMP (camshaft position sensor) or the CKP

I'd check the wiring to the sensors. There could be a minor short somewhere that is causing this even with good sensors. Are you sure that's the only code you're throwing?

 

[diegoa1997]

You're a couple of decades behind. This is a JL Wrangler forum and a lot of the millennials on this forum were in kindergarten when your TJ was built.

But... from what you describe I can tell you that you are likely in for a headache. I had a 2001 model WJ with that same engine and it developed the same issue. We tried everything imaginable. New plugs, new coils, new crank sensor, new cam sensor, fuel injectors, ECU, heck I even had the valves in the head machined again and installed new pushrods and valve springs. Nothing would fix it. It would drive fine until it got to operating temperature and then it would all go to hell with a flashing CEL and a bucking, kicking engine.

I finally got so tired of it that I sold that Jeep and moved on. It was my second 4.0L and my last. I swore I'd never touch another. Good luck.

Well this is a little discouraging, :/
Thank you for your input though

 

[diegoa1997]

I'd check the wiring to the sensors. There could be a minor short somewhere that is causing this even with good sensors. Are you sure that's the only code you're throwing?

Yes, that's the only code that appears. I will double check all wirings and see if I missed something.

 

[XJ253]

I'd guess either the fuel pump is starting to go or a damaged ECU (rare, but it happens).

 

[bwright1818]

My '97 had phantom issues that were solved by replacing the PLUG at a sensor. Mine happened to be CTS but if I were you, I'd try replacing the crank and cam sensor plugs. The metal sockets in the plugs can open up with time; so heat and vibration can start to do odd things to them.

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