cjomanche Posted October 2, 2017 Share Posted October 2, 2017 Having a problem with my 91 Comanche Pioneer. 4.0 HO, 4x4, AX-15. When the RPM is sitting just below 3,000 RPM there is a "hiccup" that occurs randomly, but somewhat predictably. I've only been able to replicate it in 3rd and 4th gears, but it may happen with others. It does not happen at all when the RPMs are 2,600 or below, or above 3,000. Just in this one tiny range. Here is the video I took (sorry for the loud road noise.... cold air intake has gotta go)https://www.youtube.com/watch?v=k8p-...ature=youtu.be My buddy who knows a lot about these Jeeps had no idea what it was. Thought it might possibly be something with the distributor, or a sensor somewhere. Any ideas? Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 2, 2017 Share Posted October 2, 2017 Does the engine hiccup when this happens or is it just a tach skip? Since it's happening in both 3rd and 4th gears at about the same spot, I don't think it's related to vehicle speed, a loose cluster cable connection, tach input signal, or bad cluster printed circuit foil. I think the most logical cause would be a wonky tach meter movement. I'd pick up a used HO cluster and swap in the tachometer to see if it still happens. Also, why is the oil pressure gauge pegged? Link to comment Share on other sites More sharing options...
cjomanche Posted October 2, 2017 Author Share Posted October 2, 2017 46 minutes ago, HOrnbrod said: Does the engine hiccup when this happens or is it just a tach skip? Since it's happening in both 3rd and 4th gears at about the same spot, I don't think it's related to vehicle speed, a loose cluster cable connection, tach input signal, or bad cluster printed circuit foil. I think the most logical cause would be a wonky tach meter movement. I'd pick up a used HO cluster and swap in the tachometer to see if it still happens. Also, why is the oil pressure gauge pegged? It's the actual engine hiccupping. You can feel it. The tach needle bouncing is just the visible evidence of it to give an idea how much of a stutter is occurring and how long it lasts. I wish you could hear the sound in the video, but it doesn't really come through on the recording. Oil pressure gauge didn't work when I got the truck and haven't gotten it fixed yet. There's an aftermarket gauge installed right underneath that you can barely see in the video. Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 2, 2017 Share Posted October 2, 2017 In that case first check for fault codes: https://comancheclub.com/forums/topic/28111-reading-obdi-91-and-92-mj-fault-codes/ Link to comment Share on other sites More sharing options...
Jeep Driver Posted October 2, 2017 Share Posted October 2, 2017 Typical neglected Jeep wiring. Looks like your temp is high too. Link to comment Share on other sites More sharing options...
cjomanche Posted October 2, 2017 Author Share Posted October 2, 2017 1 hour ago, Jeep Driver said: Typical neglected Jeep wiring. Looks like your temp is high too. I just got the truck six months ago. Which wiring area should I check? My temp gauge reads about 15 to 20° hotter than it actually is. I installed a summit racing in line temp gauge and I haven't seen it go above 200°. Link to comment Share on other sites More sharing options...
Green Mesa XJ Posted October 3, 2017 Share Posted October 3, 2017 I’ve had a 91 completely lose the cluster while driving, never stoped running just instruments hiccuped.Not sure about this problem, could be electrical. CPS fails it shuts you down, cam position I think would shut you down too. I’d check the distributor for play, only happening at certain rpm is strange. Sent from my iPhone using Tapatalk Pro Link to comment Share on other sites More sharing options...
specauto Posted June 2, 2018 Share Posted June 2, 2018 Old thread but possibly a common problem. My Son's 94 XJ was doing the same thing, it was the crank sensor. Also, I'm a fleet manager at a Charter school, sometimes our buses, particularly the DT466s, do the same thing and 90% of the time its a cam sensor, which on those engines does the same thing as the CPS on the Jeeps. It hiccups and "blips" because its acting like you momentarily shut the ignition switch off. It should be replaced and if that is not the problem, keep the old one as a spare. Link to comment Share on other sites More sharing options...
omega_rugal Posted June 2, 2018 Share Posted June 2, 2018 mmm does this hiccup only show in the tach or does the engine feels like shutting down? i can`t hear it in the video... Link to comment Share on other sites More sharing options...
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