jdog Posted April 25, 2020 Share Posted April 25, 2020 can you pull a plug or two and see how they look. Link to comment Share on other sites More sharing options...
HellCreek Posted April 25, 2020 Share Posted April 25, 2020 14 hours ago, Green Mesa XJ said: Just catching up on the recent posts. Maybe the O2 sensor will fix it, they can cause all kinds of problems. The check light for a O2 failure on the 91-92(?) were a separate light from the check engine, that required a Chrysler/jeep tool to reset, many owners just pulled the bulb. I have two PCMs from when I was testing the pcm by swapping, on the original pcm the O2 light been reset by Jeep, the used PCM had the light come on. I think it was mostly a mileage thing or perhaps when it failed the light stayed on, i don’t remember correct the answer now. My random thought is if this Jeep still a random problem try swapping in a different PCM, they don’t often fail but when they do all kinds of crazy problems can intermittently appear. The odd problem we had I think was water from the windshield leaking got the brake switch and/or TCU and caused the situation where my in-laws thought they jeep didn’t have power on a hill, couldn’t accelerate, etc, I never saw it and most of that they describe about vehicles having trouble is normally wrong. On the fly I replaced the TPS and Brake switch, on the 91 up the brake switch surprising ties in to a number of systems like Cruise control and the torque converter locking up or not. Similarly TPS also ties in to a few systems. And tps could cause issues with power. I was never sure about what the problems was, I had to drive a ways to pick the Jeep up from the house where they left it parked, so I picked the parts up and took a chance on fixing it and driving back. Never gave me any trouble, been years and lot of miles and a few 3 hour trips on the highway since then. Of other odd problems those 91-up 4.0 Jeeps have is crank position and cam position sensors, crank position on the bell housing is famous for the woes it causes. Cam position is not as infamous but can cause all kinds of trouble, some times it’s actually the distributor physically wearing out wobbling around. On the 1991 4.0 the cam position sensor was a pain, I think it had to be removed by taking the distributor out and taking it apart, many years since I’ve messed with it so I might be wrong. But I do remember it was easier to replace it with a rebuilt, I pretty sure the later 94-95 distributors could be swapped in as the signal was the same and so were the plugs on the harness. The benefit being the cam position sensor was easier to replace. Sorry to ramble on randomly, maybe this helps somebody. Edit: I forgot about the MAP sensor, never actually had one fail on those jeeps. But if the vacuum line becomes disconnected it runs poorly. Sent from my iPhone using Tapatalk Pro I just replaced the O2 sensor yesterday. Since the problem is intermittent, I really can't tell if that fixed the surging problem, but I know it didn't fix the running-rich tail pipe odor. The windshield washer tank has been broken and dry since my son had the car (about 5 years), so I don't think that is the problem. I tested the TPS with an analog Volt meter, and it testes O.K. with a smooth, steady sweep, and the voltage was within specs. The CPS tested O.K. with an Ohm meter. How would one test the Cam position sensor? The MAP sensor tested O.K. with a volt meter using a vacuum pump as in Don's earlier post. The injectors were bench cleaned and tested about a year ago. I have not inspected the plugs yet, but I will do that next. In my experience, though, bad plugs or wires are usually not that intermittent. This vehicle might go a month without any problems and then mess up. Oh, and I also replaced the water temperature sensor (on the thermostat housing). So far I have used the shotgun approach, replacing parts and cleaning connectors. I would really like to find a solution to both these problems (surging and running rich) before I have replaced everything that can be replaced. By the way, the air filter is new also. Thanks, Tom Link to comment Share on other sites More sharing options...
gogmorgo Posted April 25, 2020 Share Posted April 25, 2020 When I had my cam (sync) sensor go out on me in my ‘91, it came with a code 54. I haven’t read through the entirety of the thread, but have you checked for fault codes? I don’t really remember doing anything for diagnostics other than pull the codes. I just swapped in the ‘94+ distributor. As Green Mesa points out, it really is just a drop-in swap. I did have to reclock my plug wires on the new distributor, because the newer style has a fixed ear for the hold-down bolt that only allows it to go in one way, as opposed to the earlier style with a hold-down clamp that allows for turning the distributor housing. There is potential for the cam sensor to cause running rich, I imagine. My understanding is the cam sensor is what controls injector timing, and when the signal goes bad it supposedly uses the crank signal and batch fires injectors. Don’t quote me on that though, I don’t know what leads me to think that, the research I did at the time of the incident was a good six years ago. Link to comment Share on other sites More sharing options...
jdog Posted April 25, 2020 Share Posted April 25, 2020 the plugs will tell us if it is running rich and which cylinders, they could be showing us that its running rich without giving fits Link to comment Share on other sites More sharing options...
HellCreek Posted April 27, 2020 Share Posted April 27, 2020 I pulled the plugs and they all looked the same and normal, according to the Haynes manual color pictures. The gaps on the plugs were .035. The plugs, by the way, were changed about a year ago with Bosch Platinum FR9HP. All of the plugs had a mild fuel odor, which, I think, would go along with the running-rich issue. While I had the plugs out I did a compression check with a screw-in gauge and got 130 psi on all cylinders, so we can rule out a blown head gasket or badly worn rings. Plus no oil on the plugs would indicate good rings, at least on the oil rings at the bottom of the pistons. Before I clean the plugs and re-install them, do I need to change them for any reason? I am going to install a new cap and rotor, just for the heck of it, even though this one appears to be o.k. By the way, Gogmorgo, the codes are 12 and 55. Is there a way to test the camshaft position sensor in the distributor? Thanks for all the help. Link to comment Share on other sites More sharing options...
jdog Posted April 27, 2020 Share Posted April 27, 2020 Nope you can Reinstall, it will be later today before I can get to a manual to inform you how to test the cmp Link to comment Share on other sites More sharing options...
jdog Posted April 27, 2020 Share Posted April 27, 2020 Altho I do gotta ask why platinum plugs? If you don't mind me asking Link to comment Share on other sites More sharing options...
JMO413 Posted April 27, 2020 Share Posted April 27, 2020 You need regulator old copper plugs. I have seen this create problems with multiple Mopar vehicles. Platinum plugs are designed for newer coils. They do not have a clean spark on older coils. Link to comment Share on other sites More sharing options...
Pete M Posted April 28, 2020 Share Posted April 28, 2020 yeah, over the years I've known lots of members that had issues with the fancy plugs. Link to comment Share on other sites More sharing options...
HellCreek Posted April 28, 2020 Share Posted April 28, 2020 I used these because of the usual sales hype, i.e., more expensive is better. I wish I had known that before I re-installed them. Doesn't the fact that they were in good shape after a year of running mean that they are o.k.? Also, if the plugs were in question, wouldn't the issue be more frequent than a month or two apart? Just sayin'. I had a '72 Plymouth Fury that had a bad plug wire that was shorting against the block, causing a missing issue. but it was a lot more regular than that. Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted April 28, 2020 Share Posted April 28, 2020 I would think its more likely a compounding factor. Meaning the plugs are producing a not so great spark, but it works the vast majority of the time. Until this one sensor (the problem you are trying to diagnose) submits a reading of 4.75 volts instead of 4.80 volts because of whatever reason. Then you get a misfire, because that 0.05v was the difference between everything working and something borking. Sorry for the vague generalities here. But its how I would describe my concern. Link to comment Share on other sites More sharing options...
Pete M Posted April 28, 2020 Share Posted April 28, 2020 copper plugs are cheap. I would do that since nothing else has had an effect. can't hurt, right? Link to comment Share on other sites More sharing options...
jdog Posted April 28, 2020 Share Posted April 28, 2020 Next question is did this start after the plugs, but as Pete says plugs are cheap and easy on this one Link to comment Share on other sites More sharing options...
HellCreek Posted April 28, 2020 Share Posted April 28, 2020 1 hour ago, jdog said: Next question is did this start after the plugs, but as Pete says plugs are cheap and easy on this one Hard to say. Right after we got this, the fuel pump went out and it sat for about 5 years. We replaced the pump and tank about a year ago and cleaned the injectors and replaced the plugs and wires at the same time. Link to comment Share on other sites More sharing options...
HellCreek Posted April 29, 2020 Share Posted April 29, 2020 O.K. What brand and part number (heat range) plugs should I get? Getting the wrong heat range would probably be as bad as keeping the platinum plugs. Link to comment Share on other sites More sharing options...
jdog Posted April 29, 2020 Share Posted April 29, 2020 oe is champion 412, brand is a personal choice. just as long as its a copper core Link to comment Share on other sites More sharing options...
Pete M Posted April 29, 2020 Share Posted April 29, 2020 when you did the pump, did you replace the little hose that's on the assembly? Link to comment Share on other sites More sharing options...
eaglescout526 Posted April 29, 2020 Share Posted April 29, 2020 Mopar still has plugs for our trucks. I used Bosch Platinum plugs once and never had an issue with them. I might have even seen an improvement in fuel economy from using them but that was about three years ago. Link to comment Share on other sites More sharing options...
HellCreek Posted April 29, 2020 Share Posted April 29, 2020 3 hours ago, Pete M said: when you did the pump, did you replace the little hose that's on the assembly? Yes, I did - the second time. The first time it blew off. 3 hours ago, jdog said: oe is champion 412, brand is a personal choice. just as long as its a copper core I always preferred Autolite. No reason, just had good luck with them. Link to comment Share on other sites More sharing options...
JMO413 Posted April 29, 2020 Share Posted April 29, 2020 Champion or NGK. This is with reading IMHO. Link to comment Share on other sites More sharing options...
dustyniner Posted April 30, 2020 Share Posted April 30, 2020 ` Link to comment Share on other sites More sharing options...
HellCreek Posted May 9, 2020 Share Posted May 9, 2020 I finally got around to changing the plugs; thanks for the suggestions. I really can't tell if the intermittent surging problem is fixed, yet, as it doesn't happen all the time, but the strong exhaust odor is still present. Is there any way to get these engines to run a little leaner? Link to comment Share on other sites More sharing options...
JMO413 Posted May 9, 2020 Share Posted May 9, 2020 4 minutes ago, HellCreek said: I finally got around to changing the plugs; thanks for the suggestions. I really can't tell if the intermittent surging problem is fixed, yet, as it doesn't happen all the time, but the strong exhaust odor is still present. Is there any way to get these engines to run a little leaner? How far have you made it through cruisers tips. All the wiring tips are a must do. Link to comment Share on other sites More sharing options...
HellCreek Posted May 9, 2020 Share Posted May 9, 2020 11 minutes ago, JMO413 said: How far have you made it through cruisers tips. All the wiring tips are a must do. I have done all of them. Link to comment Share on other sites More sharing options...
jdog Posted May 9, 2020 Share Posted May 9, 2020 just a thought hows the exhaust system? Link to comment Share on other sites More sharing options...
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