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2000 Jeep Wrangler TJ 32RH 170k Miles I bought this last fall with intentions of making it my forever Jeep since it replaces an identical one I had back when they were new. It had its engine replaced by a sketchy shop. I have been fixing things ever since. Some of the things I have fixed will be listed at the end of this post. In the interest of thoroughly understanding why this is happening and learning as much as possible, i`d like to keep this limited to diagnostics, testing, and troubleshooting rather than buying parts and bolting them on. I am well versed with the FSM, standard tools, and with Jeeps in general having owned everything from a CJ-5,7, XJ, WJ, YJ, TJ (twice). What I currently do not have is a DRB III - if anyone has one they`d like to sell please let me know. The problem: Random misfire flashing check engine light starting just over 3000 RPM and happening any time up to redline. Appears to happen more when cresting a long pass and then engine braking down the other side. Cannot feel any actual misfire. Over a long enough timeline codes will set for all 6 cylinders. No particular cylinder sets it off, but I tend to see p0306 earliest. Data includes fuel trim, TSB 09-003-03, vacuum, fuel pressure, and leak down test results: Fuel trim at idle is approximately 10% positive. And a snapshot at the time of the code being set is also usually around 10% positive. Photo attached shows the fuel trim at the time of a misfire, as you can see I floored it, light started flashing, and I took a screenshot, very simple. I have not replaced the intake manifold gasket yet, but have thoroughly checked all vacuum lines with propane, and brake cleaner. Have replaced a few that were suspect, but did not actually respond to propane. My understanding is even if this were an issue with the intake gasket, it should not affect under heavy load - but maybe when engine braking? For further proof of this, I capped off all vacuum lines at the manifold including the master cylinder, and was able to reproduce the error in first gear at 3100 rpm driving up my street. A vacuum meter (mityvac silverline) shows the needle bouncing/vibrating wildly at idle - but only within 1 or 2 marks on the gauge. This is indicative of leaking or worn valve guides? Vacuum test does not indicate exhaust restriction at any RPM level. TSB 09-003-03 - removed all rockers and verified a bullseye pattern is present. Did not rotate valves yet as I didn`t have a compressor available, and honestly I fully expected to be pulling the head during this process. Have run seafoam top end cleaner through the throttle body according to directions. Spark plugs are very clean and nice. Leak down test (cold engine): I have bad hearing, but could not hear or feel anything coming out of the throttle body, or the exhaust. No bubbles in the radiator. cylinder 6: set at 69, observed 62.5, percent difference: 9.88% cylinder 5: set at 70, observed 68, percent difference: 2.89% (was holding pressure by hand, cylinder may be lower in the bore than others) cylinder 4: set at 70, observed 64, percent difference: 8.95% cylinder 3: set at 69, observed 62, percent difference: 10.6% cylinder 2: set at 69, observed 60, percent difference: 13.9% cylinder 1: set at 69, observed 65, percent difference: 5.9% Fuel pressure: I had a crappy HF gauge but did not observe any negatives on fuel pressure at any RPM. I can retest if someone would like to see specifics. I did swap in a fuel rail with a shrader valve, this is one of the things that led me to believe the engine is a later model. Things that have been done - most of these are routine or were observed as being broken, missing, or neglected. I may have forgotten some but will update this list. 1. APP 985 plugs, removed AP985 plugs - this was done on day one. 2. Removed 180 degree thermostat, replaced with 195 - day one (the first time i drove it at the shop, didn't even have a thermostat in it) 3. Swapped in a known good coil rail from my XJ. No change whatsoever. 4. Built all new battery cables, soldered, marine heat shrink, direct cable from battery to body, and battery to block. ¹ 5. Swapped crank position sensor - not because it was suspect, but because it was BROKEN, and eventually did die causing a no start. I assumed the shop broke it when they installed the new motor. ² 6. Crank position sensor died again, 6 months later. ² 7. Correctly rerouted the belt, and installed a new one along with idler just because - this was done in the first month, did not observe any overheating or charging issues. 8. Fully disassembled and cleaned the throttle body. Noticed the IAC casting has been replaced and is not a good fit - so lapped all surfaces on a machinist surface plate, then reinstalled with aircraft form-a-gasket. No improvement, if anything the idle stays a little high at times. 9. Have done the disconnect, ground, reconnect, lights on, lights off thing at times just to force relearn (if that even worked on later models?) ¹ When doing the leak down test today I realized there is NO ground strap from the block to the head - will be repaired shortly. Edit: Added the strap, did nothing. See the last screenshot of current results. p0306 the first code to pop up this time. ² What I thought was top end noise all along was one of the four torque converter bolts riding around inside the tone ring of the flywheel. I dropped the trans to replace the flywheel thinking it was cracked, and discovered the bolt. Pic attached. Removed and inspected the flywheel, noted that it does not have the exact same tooth count or tone ring setup as the autozone replacement I bought, so reinstalled. It was in good shape anyway. Used ARP bolts to the torque converter, properly torqued. Also finally got the throttle valve cable perfectly adjusted, it needed an extra click on the tension side in order to shift properly. The bolt riding in there is what broke two crank position sensors - its amazing that they still worked for months with the magnet not even attached. Additional observations: I do not have proof but it almost feels like the misfire code is set at the same time the clutch fan is operating. In other words I can feel the sluggishness of the fan as well as some minor vibration at the time the light flashes. I am considering upgrading to a mishimoto electric fan and not because of current issues. I have noticed the ever so slight loss of coolant - where after 2 weeks or so it will be down to the top of the tubes when looking through the cap. It does not ever pull fluid from the reservoir, and has not dripped on the ground. Was able to pressurize the system and observe minor dripping from both hoses - going to write this off as solved. This is a 0331 TUPY head. The mileage, make, model of the engine are unknown - I am not entirely sure but it may have come from a WJ. I believe the date code reads 3 12 mx 17. Which is 2003-12-17