Agreen
NAXJA Forum User
- Location
- Charleston
I see that the P0121 is a common issue with the 4.0, and often erroneously replaced. I hate replacing parts without diagnosis first, so I will not just throw a TPS at it in hopes of fixing it. I have an ELM327 Bluetooth scanner that shows it at 12.5% key on/engine off and at idle. At wide open it reads about 88%. Voltmeter test confirms about 0.6v and 4.5v, smooth sweeping motion between. I have tested this at the sensor and at the ECM. The wiring and TPS checks out, even with a wiggle test of all wiring.
I have looked more into it and found that it's an issue of the TPS not matching expected position based on MAP signal. This problem *usually* happens when I downshift to maintain speed going down a hill, with no throttle.
I noticed also that my AC went from recirc to defrost while going uphill. I haven't been able to locate a vacuum leak (yet) but I am suspicious of the manifold gasket. I replaced the exhaust manifold with a dorman unit like 2 years ago, and I've just started getting another exhaust leak. I read that the dorman gasket is kind of trash, but unfortunately after I had already installed it.
So I'm thinking this weekend I'll be ripping off the manifold again, inspecting for cracks, and replacing the gasket at a minimum.
Has anyone else experienced a P0121 because of a manifold leak? I'm going to document this as I go so hopefully others don't waste their time and money throwing TPS's at their own.
I have looked more into it and found that it's an issue of the TPS not matching expected position based on MAP signal. This problem *usually* happens when I downshift to maintain speed going down a hill, with no throttle.
I noticed also that my AC went from recirc to defrost while going uphill. I haven't been able to locate a vacuum leak (yet) but I am suspicious of the manifold gasket. I replaced the exhaust manifold with a dorman unit like 2 years ago, and I've just started getting another exhaust leak. I read that the dorman gasket is kind of trash, but unfortunately after I had already installed it.
So I'm thinking this weekend I'll be ripping off the manifold again, inspecting for cracks, and replacing the gasket at a minimum.
Has anyone else experienced a P0121 because of a manifold leak? I'm going to document this as I go so hopefully others don't waste their time and money throwing TPS's at their own.