91 Jeep YJ - Cranks but No start - Have spark and have fuel at fuel rail

RJones

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First post. I'm still learning so be gentle. :) I have a 91 Jeep YJ 6 cyl 4.0 automatic. Jeep has been running fine until 3 nights ago and hasn't started since. I went to start it and it acted strange. Almost like the ignition hung in the on position and kept starting. I turned it off and then it hasn't start since. Cranks fine but no start. (Actually ignition still seems to be hanging some in case that could be the problem)

I have test for spark coming out of the coil and have spark. I have pulled spark plug wires #1 and #2 and have spark coming out of distributor. It is more like a slow pulse spark and seems a little weak, but I do have spark.

The CEL flashes as normal and fuel pump kicks on to prime as normal. I have what seems to be plenty of fuel at the fuel rail.

I want mention, I had problems about a year ago with my jeep dying when I slowed down and them some times it would start. Same thing, had fuel and had spark. Even sent the computer off to be checked and it checked out fine. Finally had it towed to a guy and he replaced ignition coil and I'm not sure if he replaced the camshaft position sensor inside distributor or not, but it looks new. I think he mentioned setting the compression stroke #1 at TDS but wouldn't swear to it. Anyways, got it back and have had no problems since, until 3 days ago.

Problem seems like the same exact thing. I do have spark and I've done the ohm reading test on the crankshaft position sensor and it reads fine.

Any ideas would be much appreciated. I also checked all fuses under the hood and they are fine. I was thinking about Making sure the compression stroke for #1 was still sitting at top dead center (TDS) and checking to see if the rotor under distributor cap is sitting at the 5:30 or so position after I set at TDS. I understand that's where it's supposed to be when adjusted at 0 TDS. I am wondering if that has possibly skipped and is a little off causing me an issue. If that's even possible. I'm thinking that might have been the problem last time, but it could have been a weak coil I guess or maybe even the camshaft position sensor if that was even replaced. (Tried calling him a couple times but haven't been able to reach him)

Again, any advice from any of you experienced pros would be great! Thanks in advance.
 
In a nut shell there are 2 TDC's. One is the compression stroke and the other between exhaust and intake cycles. if it ran fine until whenever, then suddenly died It is possible the dist rotated a bit if it was not tightened down to begin with,unlikely, but many things are possible. That being said the computer adjusts the timing once the initial is set basically. From my experiences and generally speaking if a engine has its timing off,even 180 degrees off on the distributor, it will crank over, backfire, crank slow like its struggling ect. Ive never seen an engine with the timing off act 100% dead and not try to do something like I mentioned above. FYI, if an engine is at exactly tdc on the compression stroke you can basically drop the distributor in at any position as long as the rotor is pointing at the #1 plug wire/terminal when its seated and snugged up. Yeah you'll have to set the initial as mentioned. I stuck a new dist in my 91 and was a tooth off or probably 20-30 degrees off and it still started after cranking it a bit and was driveable sort of, My SNAFU there. Im sure a few others will chime in with some ideas on whats going on to get you going.
 
Thank you for the response. I really appreciate it. I have noticed a slow start at times, but I know a lot of people complain about that with the yj's. I had also noticed a rare backfire when starting, but it was very rare but would happen every once in awhile. Not sure if any of that is related to the issue I am having now or not. I guess I could try and make sure it's set to TDS and all that. I had one guy tell me once it's set that should not change. But I'm not sure if it can or not. I did talk to the guy a few minutes ago that fixed it over a year ago and he couldn't remember what all he did other than replace coil. He suggested it could be the camshaft position sensor or even the plugs fouled. He also said I should check my injectors to make sure they are pulsing and getting the 12v needed. I'd have to research how to do that. Thanks for your information.
 
Just found this and sounds like the same problem I'm having. This guy seems to have way more patience than I do, but finally found the problem. Has be thinking problem could definitely be with the distributor or my rotor alignment has just been knocked off after setting compression stroke #1 at TDS. I'm going to try that this weekend and if it doesn't start I'll look into the distributor and camshaft sensor more.

https://Jeep Forum/threads/91-yj-has-fuel-and-spark-wont-start.1796873/page-6
 
Yes. After setting compression stroke to tdc it fired up! A couple starts after that it was a bit slow to start and actually had to give it a little gas one time and it backfired but started. Has started ever since so timing must have jumped somehow. Wish I knew what’s causing it. It is starting and running good again. I think I’m going to change spark plugs and wires and distributor cap and rotor button this weekend since it’s pretty cheap and I figure it can’t hurt. Ohm test on all injectors tested fine. One I couldn’t get connector off to test since there was something in the way but I imagine it’s okay since the other 5 were. They all read 14.2 ohms. I’m going to test it to just to be sure. Checked fuel pressure at rail and it’s 38. It does leak down slowly but its not bad. But after setting to tdc it did fire up and hadn’t started before that for about 5 days so that was apparently an issue. I might run some gum out fuel system cleaner through it too. That’s my update for now.
 
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In a nut shell there are 2 TDC's. One is the compression stroke and the other between exhaust and intake cycles. if it ran fine until whenever, then suddenly died It is possible the dist rotated a bit if it was not tightened down to begin with,unlikely, but many things are possible. That being said the computer adjusts the timing once the initial is set basically. From my experiences and generally speaking if a engine has its timing off,even 180 degrees off on the distributor, it will crank over, backfire, crank slow like its struggling ect. Ive never seen an engine with the timing off act 100% dead and not try to do something like I mentioned above. FYI, if an engine is at exactly tdc on the compression stroke you can basically drop the distributor in at any position as long as the rotor is pointing at the #1 plug wire/terminal when its seated and snugged up. Yeah you'll have to set the initial as mentioned. I stuck a new dist in my 91 and was a tooth off or probably 20-30 degrees off and it still started after cranking it a bit and was driveable sort of, My SNAFU there. Im sure a few others will chime in with some ideas on whats going on to get you going.
Reading your post again after I set to tdc on compression stroke and verified trailing end of rotor blade was pointing just past the #1 plug as specified in manual and got the jeep to start again. One thing I did happen to notice was the bolt holding down the distributor wasn’t very tight. Pretty loose actually. So you might be on to something there. I tightened it so we’ll see how it goes.
 
After you do the above, if it's still acting strange, you may have skipped a tooth on the timing chain. How many mi are on it?
Jeep has 166,000 miles on it but has a new crate motor with about 10,000 miles on it. However motor was in when I bought the Jeep a couple years ago. I have not looked at the timing chain and have wondered about it. Only set camshaft to tdc and verified rotor was pointing toward #1 plug. Could timing chain possibly have jumped a tooth but I was still able to get it to start by only setting compression stroke to tdc?
 
I have a 91 yj 4 cyl and I speak from this experience. My distributor timing is not operator adjustable. there's a tab on the engine block that prohibits it from being turned, the computer sets the timing from information collected from the engine parameters while it is running. That being said I had an experience similar to yours and replaced the timing chain and Timing gear and received no noticeable improvement in the engine performance. I will spare you the details and get right to my solution. i removed my exhaust manifold and inspected the underneath side to find 3 sizeable heat cracks that I could not see from above. Apparently fresh oxygen was being sucked through the cracks after the combustion process and the computer was seeing this from the oxygen senser. The computer rightfully increased the fuel ratio to richen what it perceived to be a LEAN condition. But in reality more fuel wasn't needed and it was over fueling the engine. open your hood and listen to your engine, if it seems loud you might check for exhaust leaks. I know some will call BS on this but let me say since I repaired this my YJ has passed California Smog with Flying Colors for the last 10 yrs. hope this helps
 
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Back again. Same problem as before. Posting new article below. This thing is driving me crazy.

1991 Jeep Wrangler YJ
6 cyl 4.0L HO, fuel injected – Automatic Transmission
166,000 miles – (Has new crate motor with only 11,000 miles or so on it)

Anybody that can help me with this issue, it would be greatly appreciated! I know just enough to be dangerous probably, but I feel like I’ve done enough testing and troubleshooting that the jeep should be at least starting. I’m about ready to give up at this point! Below are a couple of links that I found in another forum and my problem seems to be almost identical. (His problem ended up being with the new distributor and the gear being rotated and it was out 180 degrees or something like that.

91 YJ has fuel and spark, wont start | Jeep Enthusiast Forums (Jeep Forum)
91 YJ has fuel and spark, wont start | Page 6 | Jeep Enthusiast Forums (Jeep Forum)

(I also replaced the distributor like this guy did, because I have been wanting to due to some supsicions, and when it just died at a stop sign on me the other night, which it had done before awhile back, I decided to put in a new distributor. I was not getting spark, then I was getting spark. Very odd. I believe I have a timing issue of some sort and have had with this jeep for quite some time now. On a couple of occasions over the past couple of years the jeep wouldn’t start or it would just die on me. Setting to TDC at compression stroke piston #1 fixed the issue. If it is losing its timing after running great for a few months, I have no idea why.

Anyways, a year ago it did this same thing. I had it fixed, and the guy said it was the ignition coil, which tested out fine for me a year ago. This time it has a new position coil from where it was replaced then, Plus I am getting spark from coil and all 6 wires coming from distributor. I get voltage coming into the coil and also get a signal on the signal wire. The secondary resistance was reading low at 9.28K ohms so I thought it was bad. Haynes manual said it should be reading like 11.2K ohms to 15.3K ohms. I bought a new distributor just in case, but it reads exactly the same 9.28k ohms on secondary resistance. Plus I am getting spark so I have not replaced it.

I’m also getting fuel. One turn over of the ignition and not cranking it pressure gauge reads 31psi. Running (when it did run) around 38psi. It will leak down slowly and back to zero in a few hours, but it’s getting fuel. I can hear fuel pump prime every time. I did spray starter fluid in throttle body just to make sure and still won’t start. Does not appear to be a fuel issue.

The crankshaft position sensor reads good on the multimeter plus I get spark. However, I replaced it just in case. Both the old and new read the same so that shouldn’t be it.

I took camshaft sensor out of old distributor when I was having this problem before and suspected it. I put it on the bench and applied 5 volts to it and I could get it to drop voltage to zero by placing a screwdriver between the magnet and lead. I did this when I suspected it before. However new distributor came with new camshaft sensor. Camshaft sensor shouldn’t be the problem.

I have new spark plugs and wires and had been running them over a month before it just died the other night. Other than maybe a few slow starts which I think is pretty common with these jeeps, had been running good.

It has started since I put the new distributor on and even ran for like 10 minutes then died. Cranked it back up again ran without dying for a while. No rough idling or anything that I could notice. Now it will not start again and didn’t do anything to it since it last started. I have set TDC at compression stroke piston #1 yet again and even took distributor back out to make sure rotor was positioned just past #1 plug at around 5:30 position. It will not start! I also double checked myself by putting a little wooden dowel down in spark plug #1 hole before and after setting to TDC on compression stroke and dowel went from being 6 inches in hole to top of piston to less than 2 inches (to let me know piston was at top) once I felt the air coming out and set the camshaft to the zero (0) mark. Still will not start!

I think it might be a timing issue or I don’t have distributor set just right, but I don’t know what else to do if it isn’t. I do not have a timing light. It looks like the rotor is positioned right where it should be to at least start up.

I guess I could drop old distributor back in to make sure new one is not defective, but the jeep died the other night for a reason so I figured the old one might be an issue. Plus I am getting spark with new one so I would hope it would at least start.

I haven’t inspected timing chain due to having to take everything off and remove cover to do so, but I would hope with the newer crate motor with only 11,000 miles it would be okay, but can’t guarantee it.

I have checked my grounds best I know how. All the ones I could find, I was able to get continuity back to the battery ground by using a multimeter. I have also checked my fuses and checked my relays.

Anybody that can help me figure this out before I just give up and get rid of the jeep, I will be forever grateful! I am at my wits in!
Thanks in advance!
Randy
 
I have a 91 yj 4 cyl and I speak from this experience. My distributor timing is not operator adjustable. there's a tab on the engine block that prohibits it from being turned, the computer sets the timing from information collected from the engine parameters while it is running. That being said I had an experience similar to yours and replaced the timing chain and Timing gear and received no noticeable improvement in the engine performance. I will spare you the details and get right to my solution. i removed my exhaust manifold and inspected the underneath side to find 3 sizeable heat cracks that I could not see from above. Apparently fresh oxygen was being sucked through the cracks after the combustion process and the computer was seeing this from the oxygen senser. The computer rightfully increased the fuel ratio to richen what it perceived to be a LEAN condition. But in reality more fuel wasn't needed and it was over fueling the engine. open your hood and listen to your engine, if it seems loud you might check for exhaust leaks. I know some will call BS on this but let me say since I repaired this my YJ has passed California Smog with Flying Colors for the last 10 yrs. hope this helps
Thanks for the info. I can't rule this out. Something is going on for sure. The engine doesn't seem to be unusually loud to me. Over fueling the engine does make sense. Any other way I would be able to tell?
 
If you have not had the computer tested or rebuilt, give that a try. I just had mine done by these guys:

 
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If you have not had the computer tested or rebuilt, give that a try. I just had mine done by these guys:

Thanks for the info. I sent the computer off a couple years ago or so and they tested it and didn't find anything wrong. I can't remember what problem ended up being but seemed like same issue as I'm having now. I have expected timing issues with this jeep for about that long. I get voltage, signal an spark to the coil and pump kicks on and primes and check engine light flashes as normal so I think computer is working. Its not throwing in engine codes though.
 
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Thanks for the info. I can't rule this out. Something is going on for sure. The engine doesn't seem to be unusually loud to me. Over fueling the engine does make sense. Any other way I would be able to tell?
Might crawl underneath with a bright light and small mirror to do a visual inspection. Let me say I suggested this to a member on a different forum and he found cracks in his exhaust manifold. This problem is more common than might be expected. The exhaust manifold can be removed in 90 minutes +/-. While it is on the bench straight edge the mating surfaces of the exhaust and intake manifolds. Also , use a new gasket for reinstalling . A new exhaust manifold cost under $100 when I did mine. As a comparison, with a new exhaust manifold and muffler my yj is so quiet I can sneak up on people!

An after thought would be to take it to a smog shop. They can tell by your read out if you have exhaust leaks . That's how I found mine. The tech said to look for leaks after the combustion chamber. A smog test is $45 and a cheap diagnostic test ! I saved my paperwork, so if your tech won't play ball let me know and we can compare test results
 
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Might crawl underneath with a bright light and small mirror to do a visual inspection. Let me say I suggested this to a member on a different forum and he found cracks in his exhaust manifold. This problem is more common than might be expected. The exhaust manifold can be removed in 90 minutes +/-. While it is on the bench straight edge the mating surfaces of the exhaust and intake manifolds. Also , use a new gasket for reinstalling . A new exhaust manifold cost under $100 when I did mine. As a comparison, with a new exhaust manifold and muffler my yj is so quiet I can sneak up on people!

An after thought would be to take it to a smog shop. They can tell by your read out if you have exhaust leaks . That's how I found mine. The tech said to look for leaks after the combustion chamber. A smog test is $45 and a cheap diagnostic test ! I saved my paperwork, so if your tech won't play ball let me know and we can compare test results
I'll do that. Certainly wouldn't hurt anything, and would be worth a quick inspection. Especially if I found cracks. Thanks