2001 with AW4 to 242, 287k on it

Randomly, the transmission will miss or jump when im driving along causing the vehicle to "buck". sometimes it will happen once, sometimes a few times in a row, sometimes not for a hundred miles. No correlation to how long it's been running or temperature. Kickdown cable is adjusted properly, fluid is clean and proper.

Recently, I had a NSS issue, which threw the CEL light. Whenever I would experience this "buck" in the tranny, the CEL would briefly turn off and back on.

Fixed the NSS, no CEL now. When I drive and this happens, the CEL will flash on the a half of a second and then turn off so I can't catch a code.

Weirdly, the RPM's don't really change when this happens, but the speedometer will drop despite my speed staying the same. If I'm cruising at 45, the speedo will suddenly drop to like 20 and then surge back up to reflect my real speed. Could this indicate a t-case issue?

 

It seens more likely that your Jeep is misfiring. That blinking CEL indicates a multiple cylinder misfire. Good news is you probably don't need a new tranny. But you're gonna have to do some diagnostic tests to find the root of it.

Multiple cylinder misfire is usually a result of specific root cause such as a faulty sensor rather than something like spark plugs or fuel injectors. Not that it can't happen, but a single cylinder misfire is much easier to trace back to a specific cylinder, where a multi misfire means the engine is straight up not running right for whatever reason.

However, spark plugs are simple and cheap enough to quickly check or replace to rule this out as an issue first

If it's happening intermittently, I would bet it's an electronic issue like a loose wire creating a short when conditions are right. Clean your grounds. If you have a multimeter run some tests on your 5v line components TPS, Crankshaft sensor, Cam sensor, MAP Sensor, Vehicle Speed sensor, oil pressure sensor to insure they are performing at the right capacity. Carefully check around all sensors for frayed or broken wires as the often break at harnesses.

If electrical seems up to spec, I would run a fuel pressure test. Perhaps a faulty fuel pressure regulator or bad fuel pump could be causing improper fuel ratio, thus a misfire.

Check/listen to vacuum leaks. You can also use an open propane torch (flame off gas on) with the Jeep running to inspect for leaks. If the engine idle increases with the torch in a certain area you have found the leak.

I saved the cracked head spiel for the end because I hope it's not that. Usually it isn't the case but there's always a coupleI out there If you start seeing coolant or milky residue in your oil, you have really found the problem

Good luck! Misfires are tricky. I couldn't even tell my Jeep was misfiring for a while until it started throwing codes

 

The check engine light doesn't need to remain on for a code to have been set.

Use either a scan tool or a code reader or go to a parts store like Autozone where they will read the codes for you for free. Post the EXACT CODE(S) here for comment, not just a description of the code.

Interpreting OBD codes is often (usually) not straight forward and can require further testing/troubleshooting.

 

My symptoms were the same but couldn't pinpoint it. No codes. Thought it was the CPS but it checked out. Finally got real bad and threw the CPS code. Changed out CPS and solved problem. CPS issues can be intermittent (yet are often thermally-related).

 

This sounds more like an electrical problem, possibly a bad ground somewhere. The transmission and it's seperate computer have nothing to do with the speedo.

 

I think you may be right. I used a fuel gauge and did a leak down test and with the key on, but without starting, it jumped nicely up to pressure, but leaked down in about 1 minute. It seems to hold ok at idle, but it may explain my intermittent missing.

287k, stock fuel filter, pump, and regulator - should I just replace it all when I drop the tank? thanks

 

Yes.

Dropping the tank is a PITA - you don't want to have to do it 2x just because you thought you'd save a couple bucks.

Also put new tank straps on your shopping list - especially if you live anywhere where you get rust.