Eagle_SX4 Posted February 25 Share Posted February 25 I am having a strange misfire at part throttle. Between 30-35 position reading on my TPS from my R.E.M. It doesn't happen while idling or any position of the throttle above or below 30-35. I can see my knock sensor reading spike when it happens but there are not any codes or other anomalies in all the read outs that would point to a source of the problem. I have swapped out my TPS with a spare I had and set it properly with no change. I have also changed my spark plugs distributor cap/rotor. I am heading towards it being an ignition problem maybe the coil, ignition control module or distributor stator pickup. There is an I.S. note about the distributor stator going out (I think it is 36e). Which is probably the next thing I will change out. Any help would be greatly appreciated. Link to comment Share on other sites More sharing options...
Ωhm Posted February 25 Share Posted February 25 Sometimes a kick and a buck are caused when ECU drops out of Closed Loop (LP) for an instant period of time. See if that correlates with the REM. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted February 26 Author Share Posted February 26 8 hours ago, Ωhm said: Sometimes a kick and a buck are caused when ECU drops out of Closed Loop (LP) for an instant period of time. See if that correlates with the REM. The R.E.M. shows it stays in closed loop while it misfires. It is worse when the engine is cold than when hot. Link to comment Share on other sites More sharing options...
Ωhm Posted February 26 Share Posted February 26 Should have asked earlier, what are the Fuel Trim values (ST<)? Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted February 26 Author Share Posted February 26 ST fluctuates based on throttle input any where from 80-150 but stays about 120 when cruising at 30 TPS. LT is at 105. Link to comment Share on other sites More sharing options...
Ωhm Posted February 26 Share Posted February 26 Thanks, on those fuel trim values. As you already mentioned, ST< read outs look good. Good call on possibly an ignition problem. If you haven't moved your distributor, it should be ok but still look at indexing (cruiser tip #13). Link to comment Share on other sites More sharing options...
ja_racing Posted February 26 Share Posted February 26 Can anyone take a pic of the wires or know how they go for the stator pickup i need to install a plug on my harness to connect it its cut off Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted February 27 Author Share Posted February 27 On 2/25/2025 at 6:55 PM, Ωhm said: If you haven't moved your distributor, it should be ok but still look at indexing (cruiser tip #13). Good news I got my distributor indexed properly and the misfire issue has gone away. Looking at the old cap the spark was arriving early catching just the edge of both the rotor and the cap. Surprised it ran as well as it did. Bad news is my distributor gear is very worn and I will need to get it replaced soon. Link to comment Share on other sites More sharing options...
watchamakalit Posted February 27 Share Posted February 27 Might be worth sticking a camera down the hole to check the condition of the drive gear on the cam. Link to comment Share on other sites More sharing options...
Ωhm Posted February 27 Share Posted February 27 If your misfire just showed up one day, I’d wonder if that gear jumped a tooth. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted February 27 Author Share Posted February 27 35 minutes ago, Ωhm said: If your misfire just showed up one day, I’d wonder if that gear jumped a tooth. It may have I don't remember it misfiring when I got the truck. 6 hours ago, watchamakalit said: Might be worth sticking a camera down the hole to check the condition of the drive gear on the cam. I have a borescope and will look at the cam gear when I get a new distributor. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted February 28 Author Share Posted February 28 On a hunch I thought I would see if my extra 4.2 liter distributor had a better gear. It did and was a direct swap for the old worn out one. I looked at the gear teeth on the camshaft and they look like they are about as worn as the old distributor gear. Yet another project for down the road. When that happens I will probably take the opportunity to swap to a 7120 head with H.O. cam and intake manifold. Link to comment Share on other sites More sharing options...
pizzaman09 Posted February 28 Share Posted February 28 I'm not sure I'd bother with an HO cam, they are extremely similar to the Renix cam. https://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted February 28 Author Share Posted February 28 36 minutes ago, pizzaman09 said: I'm not sure I'd bother with an HO cam, they are extremely similar to the Renix cam. https://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm Good to know after comparing cams from several different places the same cam is listed for 87-95. Link to comment Share on other sites More sharing options...
Ωhm Posted February 28 Share Posted February 28 Check and make sure that the drilled hole for the spring pin alignment is in the same location on both gears. Link to comment Share on other sites More sharing options...
Eagle_SX4 Posted February 28 Author Share Posted February 28 4 minutes ago, Ωhm said: Check and make sure that the drilled hole for the spring pin alignment is in the same location on both gears. I did check that both holes were in the same location both in relation the gear teeth and the bearing surface. I also used a added a lot of engine assembly lube to the "new" gear before reinstalling the distributor. Link to comment Share on other sites More sharing options...
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