199 YJ 6 4.0 died (sometimes starts and sometimes doesn't)

RJones

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Feb 17, 2022
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Hey all. I've been dealing with this issue quite sometime now. I'll start from the beginning, because it could have been the culprit all along. I bought the Jeep around 4 years ago. Didn't drive it much, but never had any starting or dying issues. Started good, ran good. I had it probably 6 months and my son was driving it and ran it out of gas. We all know the fuel gages can be wonky. Anyways, it ruined the fuel pump. I got the fuel pump replaced and it fixe the issue but jeep has ever really been the same since. It started dying when coming to a stop. Most of the time would start back up right then. If not, a day or two later would start up and run fine for a month or two. Died on me once coming up and hill and I never could get it to start back. Had ignition coil replaced and seemed to be fix yet again. Ran almost a year and I noticed it really started noticing it was taking longer to start. Well it died on me a couple weeks ago and I've been pulling my hair out.

So even now, sometimes it fires right up and will run awhile. Sometimes it takes a while to start and then dies. And sometimes it will crank, crank, crank and no start. Next day might fire up. Started up earlier today and ran 10 minutes. Tried 20 minutes later, cranked but no start. Sometimes I can give it some gas by pushing pedal and it will start up and idle a little rough. It has never really been the same since fuel pump went out and was replaced over 3 years ago.

Currently here's what I have. I have spark, I can hear the fuel pump prime. Occasionally it doesn't when it's already primed, but I was think that was normal??? I have 31 psi at fuel rail when turning ignition on. It will eventually bleed down to 0 (zero) but it does have pressure when you turn key over. So gradually losing fuel somewhere. Maybe check valve. I've swapped and tested relays. I've checked voltage going to fuel pump and getting 12.65 volts. Jeep has new plugs, wires, distributor, crankshaft position sensor, Temperature coolant sensor. Fuel regulator seems to be working. I can disconnect it and pressure will jump 8 -10 psi. I did find the connector for fuel pump on the jeep harness side had a aftermarket connector and butt joints were near broken from wires and the orange power wire near connector was pulled back and so was ground. I thought maybe it was shorting out and causing it to die. Fixed all that with solder and heat shrink.

If anybody has any ideas of this intermittent issue, I most certainly welcome it. I'm desperate at this point! Could I have gotten a faulty fuel pump and causing me problems all along and its getting worse? I'm pretty sure check valve isn't great but should stat if I'm getting that kind of pressure at rail? Also, I am pretty sure the fuel sending unit is wonky based on resistance readings form sending unit wire (brown) to ground If fuel level in tank stays the same it should not be getting polar opposite readings. Any thanks in advance for any help you can provide!
 

Gilaguy23

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I didnt pay 100% attention to all you did so far and dont recall seeing anything about a filter, but since you run the tank dry and likely sucked up and crap in it so have you changed the fuel filter? My 91 2.5 has one mounted on the frame up above the rear tire basically. Just a thought.
 
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RJones

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I didnt pay 100% attention to all you did so far and dont recall seeing anything about a filter, but since you run the tank dry and likely sucked up and crap in it so have you changed the fuel filter? My 91 2.5 has one mounted on the frame up above the rear tire basically. Just a thought.
Yes, I replaced the fuel filter after the new fuel pump was installed. I can't remember exactly when, but it was after that when I started having some problems and thought that might be the culprit. I'm guessing it's been maybe 2000 miles or less, so hopefully it's still okay. Thanks for your response. Much appreciated!
 

redbullet

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Might be the ecm/computer…some parts stores can test them. I had mine rebuilt by SIA on eBay for $125 and it fixed an intermittent reliability issue
 
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RJones

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Might be the ecm/computer…some parts stores can test them. I had mine rebuilt by SIA on eBay for $125 and it fixed an intermittent reliability issue
Thanks for the response. That has crossed my mind. Did your check engine light come on and then go off as normal when you started your jeep? I understand that's one sign your computer is bad if that stops working Mine comes on normal and I can check it for codes, but not getting anything outside the normal codes/flashes. I sent the computer off a little over a year ago when I was having problems, but it tested good. I'm getting proper voltage to the different areas I've tested, so I think my computer is good. However, at this point I'm really not sure of anything. I tested the TPS yesterday and it did not read properly based on the range I saw that it was supposed to. Going to try and replace it today and see if that might be the issue. We'll see what happens. Thanks
 
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RJones

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UPDATE: Likely still not fixed, but I was getting odd readings on the TPS when I test it. Range is suppose to be .2V - below 5 volts. I first read 5 volts right off with throttle closed and that's the low end. Way to high and means it's bad! However, I think maybe I did not have a good connection with the paper clip I used to back probe the wire to check it. Readjusted that and got .7 volts and opened throttle all the way up and got only 2.95 volts. Thinking that was low, decided to replace TPS. Keep in mind, after probing wired on harness, jeep fired right up, with old TPS. Also, fired right up today before I replaced TPS. I thought, maybe power wire inside harness wasn't making good connection? But doesn't really change anything when I wiggle it. Anyways, replaced TPS and it also fired right up. Readings on it were a little higher but not a lot. .8v (throttle closed) - 3.25v (throttle fully open).

After replacing TPS, Jeep started up 3 or 4 times no problem. Let it set for about 30 minutes and it started, but was slow to start. So I really don't know.

Almost does seem like it is something with the throttle. IAC (Idle Air Control) valve) maybe? Idles just fine though, around 800 RPM's and not rough or anything once it starts.

Someone on another forum mentioned neutral safety switch possibly an issue. Anyone familiar with it? I know it's only on the automatic jeeps, which is what mine is. Manuals don't have it. Thanks
 

AbileneYJNewbie

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I've got an 87 2.5L 5 speed manual yj that had similar intermittent starting/running issues. After towing it back home two times in a row I decided to park it until I figured it out. Since it was mostly original and I bought it in 2020 the harnesses all looked like crap so I opted to get all new wiring. I kept the computer harness but everything else has been replaced. I still have a little to do before I can try it out and know this probably doesn't help in your situation. But you might just give all of your harnesses and grounds a once over. Mine was in such a mess I assumed that it couldn't hirt to replace the whole thing.
 
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RJones

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I've got an 87 2.5L 5 speed manual yj that had similar intermittent starting/running issues. After towing it back home two times in a row I decided to park it until I figured it out. Since it was mostly original and I bought it in 2020 the harnesses all looked like crap so I opted to get all new wiring. I kept the computer harness but everything else has been replaced. I still have a little to do before I can try it out and know this probably doesn't help in your situation. But you might just give all of your harnesses and grounds a once over. Mine was in such a mess I assumed that it couldn't hirt to replace the whole thing.
Were you able to buy all these harnesses in a kit or did you have to buy them all separately? Where did order or purchase them from? I have a few that probably would be better being replaced. Thanks
 

AbileneYJNewbie

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I bought a generic 25 circuit harness from painless performance. It came with everything for the entire vehicle. You can check on thier website, I think they do have different harnesses and setups. There are a few companies that sell the seperate harnesses, just have to do some searching. Painless did have a direct fit YJ harness setup but it either wasn't available or sold out when I purchased mine. My thoughts on the harness is that the original lasted a long time so this one should last as long if not longer.
 

AbileneYJNewbie

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AbileneYJNewbie

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I don't have a ton of electrical experience. Just some basic soldiering skills and common sense. I would definately suggest giving painless a look. All of thier wires are label number and color coded and with rhe installation instructions included it is almost as simple as putting a jigsaw puzzle together. Very easy to do yourself.
 
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RJones

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I don't have a ton of electrical experience. Just some basic soldiering skills and common sense. I would definately suggest giving painless a look. All of thier wires are label number and color coded and with rhe installation instructions included it is almost as simple as putting a jigsaw puzzle together. Very easy to do yourself.
That's really good information on the harness kits. Thanks for sharing.
 
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RJones

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UPDATE: And the saga continues.......... Remember, I replaced the TPS yesterday.. I started the jeep like 4 times today and it fired right up. Even let it run about 10 minutes. Idled great, no issues. This evening I thought I'd try it again and it wouldn't start after about 3 tries. Also noticed I could no longer hear fuel pump priming. I could still hear relay click under hood however. I decided to run the flash on the CEL and got a code of 24 which indicates TPS reading above or below normal voltage. Remember, new TPS. I checked the low and high voltage and they were not out of range. .80 -3.25 volts which is in range. I decided to put the old TPS back on and by this time I can hear the fuel pump priming again. Still received 24 code on old TPS however. Jeep started barely and I hit the gas a little and it caught up. Started it twice since and fires right up. I unhooked the battery to see if it would clear code but I'm still getting it. So both TPS are throwing a code now. I also checked wires going to TPS and middle wire reads 4.97 volts and wire to the right reads 5 volts. I will be taking the TPS back and getting another just because but I have no idea if it's really bad or not. I think the jeep is possessed. Any ideas, I'd be forever grateful. Thanks
 
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RJones

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UPDATE: Still having issues, but might have some more info. I have a new IAC valve and yet another new TPS since the last new one I put on threw a code. I am going to take the throttle body off this weekend and clean it really good and replace both the IAC valve and TPS why I have it off anyways.

However, jeep wasn't starting today after starting and running awhile yesterday before dying. Which is nothing new. I decided to check for spark again and did not have spark coming out of ignition coil or distributor. After a few tries I got spark and the jeep tried to start. Plugged wires back in and got it in to see if it would start and it tried but the battery is weak at this point. I have it on the charger now.

So, could this be the Crankshaft Position Sensor even though I've already replaced it? My jeep is an automatic so I have to order them. I can not find a Mopar. I got this one from Rock Auto. It's WVE Brand but has NTK/NGK industries on box. I could have got the NTK from Rock Auto but the WVE was $3 more and had a 3 year warranty versus the the NTK that has 60 days. They look identical. Both the old CPS and the new one I ordered read the same no the multimeter. So either they are both good or both bad, likely.

So, should I order another Crankshaft position sensor? If so, does anybody have a recommendation on what kind and a link where to get it? Remember the CPS for automatics (one holt bolt down) is different than the CPS for the manual transmissions (2 hole bolt down). Plus, mine has the round connector and uses a paper spacer. Anyways, maybe I got a bad CPS or need to go with a different brand. Any ideas and suggestions would be greatly appreciated. Thanks
 

redbullet

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I buy all my sensors from autozone as they have a lifetime warranty and I can switch them out without the hassle of mailing. Many haters of autozone on here, but I like the price and convenience. I have replaced all sensors with autozone ones, they are reasonably priced and have not had any issues. One exception is the sensor on the distributor…went to Napa for that. I am part Irish and may be a little lucky, but that’s my approach…I hate having to return warranty items by mail, pay and wait, when using online stores. Good luck.
 
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RJones

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I buy all my sensors from autozone as they have a lifetime warranty and I can switch them out without the hassle of mailing. Many haters of autozone on here, but I like the price and convenience. I have replaced all sensors with autozone ones, they are reasonably priced and have not had any issues. One exception is the sensor on the distributor…went to Napa for that. I am part Irish and may be a little lucky, but that’s my approach…I hate having to return warranty items by mail, pay and wait, when using online stores. Good luck.
Thank you for your response. I actually like autozone as well. However, this having an automatic transmission and using a different CPS than the manuals they didn't have one. O'Reilly's didn't either. Autozone said they couldn't get it and O'Reilly's could order it but told me they would just order from Rock Auto if they were me. So that's what I did. The CPS I got might be good. I would like to get a Mopar, but haven't been able to find one for the automatic transmissions. Thanks
 
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RJones

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UPDATE: (RESOLVED)

I wanted to put this out here to help maybe anybody that might be having intermittent and hard to figure out Jeep issues. I waited a couple weeks to make sure I found the problem and it appears I most definitely did. I was still having problems with the jeep sometimes starting and sometimes not. I knew there was times I was not getting spark so I could narrow it down to something electrical. After several suggested I replace CPS which I had already done, I decided to order yet another one. Since I could not fine a Mopar I went with a NTK from Rockauto since it worked well with Rockeway's automatic 4.0 jeep just like mine. See above post.............

I received the new CPS and did a ohm test first thing with multimeter and it read identical to the other two I had. I was then convinced it was not the CPS and thought it had to be in the wiring harness or something. I started the jeep and this time it did start. I began checking the wiring for the CPS by wiggling wires or doing whatever I could. Never found any problem. Not there anyways.

I kept going since I was convinced it was a wiring issue somewhere. Got down near the alternator and ignition coil, (ignition coil had also been replaced) and when I wiggled the wire that was spliced from the coil to the alternator the jeep died. I knew I was on to something. Started it back up and could get it to do it again. If it didn't start, I would turn the ignition switch on and start with a hand held starter under the hood and wiggle wire unit it started and then I could kill the jeep again. Found my problem, well sorta. I took wires off alternator and was going to fix the spliced area but could not duplicate problem with multimeter continuity check.

Long story short, I found the problem by doing a lot of test with meter and found I could duplicate problem while wiring was plugged into ignition coil and that's where I found the culprit. The problem was the plug/connector to ignition coil. I could wiggle it and jeep would die. I noticed a small piece of plastic had chipped off on the side of the connector plug and was causing the one pin to be loose. Finding the plug was a problem but found a used one on Ebay. Got it in cut off plug and soldered new one on and it starts and runs like a champ!

I knew it would end up being something weird like this since I had literally tested or replaced everything else. So there you have it. I believe this has been a problem possibly since having the jeep but has gotten worse. Even a year ago when I had a mechanic look at it and he replaced ignition coil. I don't think it was the coil then. The primary and secondary resistance read fine for me then but I was at a loss. I believe when he put new coil on and plugged harness back up and it fired up (Not uncommon now that I know) he assumed coil was problem. It did go about a year without having too many problems other than really slow starts at times, but didn't think much of it.

Just a word of warning, those plugs are not easy to find if anyone ever has to replace theirs. I wanted to put this out there to possibly help anybody else that might be having similar issues. Never rule out the the harness/wiring or the connector itself. This problem almost drove me crazy so I now how frustrating it can be.

For all that added suggestions, it was much appreciated! I'm sure I'll have something else go wrong eventually with the jeep that will leave me scratching my head again. Thanks all!
 

skiznits

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Jun 2, 2022
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Damn, good job. Im certainly impressed about the troubleshooting you did. I started reading when I saw your section about the gas tank going dry and messing things up bc Ive done that myself at least 10 times. Anyhow...nice enjoy it til the next issue.