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Old 11-07-2019, 07:15 PM
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92 4.0 5 speed wont start

Welp, I have not been active on here for quite some time, and the main reason for that, is the YJ has been dead, and I can't get her to fire. Cranks without starting, seems to be a spark issue, as it will not even sputter on starting fluid down the throttle body....
Have replaced the Crank sensor, Ignition coil, fuel pump, even the Caps in the PCM!,

So, would anyone have any clue at all what would be causing this behavior? any help would be Much Appreciated!

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Old 11-07-2019, 07:52 PM   #2
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Iíve never had that issue but is there a fuse that could be blown? Iím throwing darts haha, easy to check though?


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Old 11-07-2019, 08:10 PM   #3
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Hey, you and I seem to be having about the same problem. I have a 93 YJ, also 4.0 5 speed, that also has no spark. My Crank sensor tested bad, so I replaced it with no change in the no spark condition. Coil tests good, so I left it be. Rockgod, do you have any codes? I tried the key on-off-on trick and my CEL just stays lit solid, so maybe that in itself is indicative of an issue? I'm going to look over my grounds this weekend, as I have read one or more bad grounds can cause issues such as ours, especially those directly involving the distributor.

If it won't start on ether I can't imagine your problem is fuel. Regardless it wouldn't hurt to verify, if you haven't already, that you do in fact have no spark. I stuck a spare plug in my #1 wire and grounded it to the block, as well as in the wire coming directly from the coil, had a buddy crank the motor over for me, and sure enough no spark.
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Old 11-07-2019, 08:17 PM   #4
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Iíve never had that issue but is there a fuse that could be blown? Iím throwing darts haha, easy to check though?


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Absolutely, makes sense to check the simple things first. Now that you mention it, I think there's supposed to be an auto shut off something or other relay that can cause a no start. My fuses all checked okay, but I haven't fooled with anything else yet. That will be something else to consider.
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Old 11-07-2019, 09:02 PM   #5
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Stop throwing parts at it. Really you should diagnose it. How do you know you don't have spark? How have you tested it?
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Old 11-07-2019, 10:26 PM   #6
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Reread #5 post.

Find a post by Got it at last. In his signature there's a free link to several Factory Service manuals and a couple Factory Parts Manuals.
Open that link and click on the manual that you need.

The FSM should have a diagnostic flowchart. Follow the flowchart rather than replacing parts. You may need to buy or borrow tools to do so, but you can keep the tools you buy and might need them again. If you replace good parts, the good parts that you took off are of no value to you in a box under the bench.

Let us know what you find. We now have a race between rockgod88 and upnsmoke. Who's gonna get their Jeep running first and then let the other guy know what the problem was.

Good Luck, L.M.
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Old 11-07-2019, 10:28 PM   #7
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BTW, a belated Welcome to the Forum rockgod88 and a new Welcome to the forum to upnsmoke.

Good Luck, L.M.
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Old 11-07-2019, 10:49 PM
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Pretty sure we have checked all the fuses, but will go over them again, I believe the only codes were for the Battery disconnected within 50 starts, and the A/C code, Thanks LuckyMac, but I'll check over the Fuses and grab a spare plug and see what I can find tomorrow,
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Old 11-07-2019, 11:12 PM   #9
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Have you pulled the plug wire off the ignition coil and tested for spark? Let me know if you need directions on how.
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Old 11-09-2019, 02:25 PM
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Ok, just went thought the fuses and tested for spark at the coil again, and nothing, no spark at the coil, so possibly a dead coil? going to test that next...
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Old 11-09-2019, 03:41 PM
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Did some more testing, has the 12v constant on the yellow. When cranking seems to get some kind of voltage (green wire) on the meter, but I can't get a testlight to light on either 12v constant, or on the green while cranking... Have 2 coils, new one has about 1.2 ohms across each plug pole and around 12.9 main to plug pole, and the old one is about 0.9 ohms across the plug poles, and 10.5 ish on the main to plug. seems to be within range from what I have heard...
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Old 11-09-2019, 07:46 PM   #12
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It's probably best to test the power and ground of the ignition coil with a test light to ensure you have enough current. Just a DVOM won't do that unless the load is on the circuit. That being said the yellow is positive coming from the ASD relay. When you turn the ignition key and the computer has the right conditions, you will have batt+ on that wire. The green wire is a ground that is provided by the PCM. It will click on and off as the PCM fires the coil. Here is a link on how to test that circuit.

The way to test is explained in this video at around 9 mins.
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Old 11-09-2019, 07:48 PM   #13
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Should have finished my thought before clicking post. If you have both power and a ground (switching on and off) but no spark at the ignition coil post, then you need an ignition coil.

If you you are missing either the battery positive or the ground from the PCM, then you need to go though those circuits deeper. Things like crank sensor and cam (distributor sync) come into play.
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Old 11-11-2019, 09:27 PM   #14
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Thanks everyone, for the kind welcome and advice so far. Rockgod, you will have a bit of a head start on me. I got busy with other things and have only had a little time here and there to play with the Jeep. I clicked the link in Got it at last's sig, but my computer doesn't like the page. Perhaps at some point I'll just invest in a paper service manual. Until then, I'll continue eliminating variables with the info I have and what you guys have provided in this here thread.

Sequel, thanks for the video. It has given me a direction to go in. I once dealt with the capacitor issue with another YJ, but that made the CEL be delayed in coming on. Now mine is staying on, and so far in my searching I can't find any info regarding that issue specifically. I tested the wires coil as instructed in the video. The power wire has 12 volts as it should, but the signal wire is constantly grounded, whether key on or cranking. My crank sensor is new, because my old one tested bad. I figure I'll turn my attention to the distributor and related wiring next. Otherwise, I'll be open to and grateful for any suggestions regarding what to look at next.
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Old 11-12-2019, 07:38 PM   #15
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The power wire has 12 volts as it should, but the signal wire is constantly grounded, whether key on or cranking. My crank sensor is new, because my old one tested bad. I figure I'll turn my attention to the distributor and related wiring next. Otherwise, I'll be open to and grateful for any suggestions regarding what to look at next.

That is not good if your control wire back to the PCM for the ignition coil is always grounded. Just to confirm your test, if you put a test light, clamp it to battery positive, and touch the control wire, it stays lit all the time? One test to do is unplug the wiring harness and see if it goes out? Sounds like you have a short to ground that you need to address.

When you said your crank sensor was bad...how did you test it?
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Old 11-13-2019, 07:34 PM   #16
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Hi, for the crank sensor I tested the resistance across the sensor itself with it unplugged. I don't recall the measurement, but there was a measurable resistance, which I have read indicates the sensor is bad.

For the control wire I back probed the connector at the coil and did put a test light on it. It was constant on- no change or flashing when cranking. I have not tested it with the harness unplugged, but that is a good idea. Next chance I get to look at the Jeep I'll start in on the wiring harness and see what I can find. I have a line on an original factory service manual. I should have it by the weekend. Hopefully that will take some of the guess work out of things.
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Old 11-13-2019, 11:07 PM   #17
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Hi, for the crank sensor I tested the resistance across the sensor itself with it unplugged. I don't recall the measurement, but there was a measurable resistance, which I have read indicates the sensor is bad.

For the control wire I back probed the connector at the coil and did put a test light on it. It was constant on- no change or flashing when cranking. I have not tested it with the harness unplugged, but that is a good idea. Next chance I get to look at the Jeep I'll start in on the wiring harness and see what I can find. I have a line on an original factory service manual. I should have it by the weekend. Hopefully that will take some of the guess work out of things.
So just to be clear, you did nothing to elicit the problem? Meaning, other than park it one day, and the next day it wouldnít light?
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Old 11-13-2019, 11:47 PM   #18
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I was actually going down the road, moving more or less constant speed and it just suddenly lost power. I was only about a mile from home. Called my pop up and he pushed me home with his truck. I thought I felt/ heard a stumble a few miles before it shut off, but other than that it was running fine prior.
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Old 11-14-2019, 09:27 AM   #19
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Hi, for the crank sensor I tested the resistance across the sensor itself with it unplugged. I don't recall the measurement, but there was a measurable resistance, which I have read indicates the sensor is bad.

For the control wire I back probed the connector at the coil and did put a test light on it. It was constant on- no change or flashing when cranking. I have not tested it with the harness unplugged, but that is a good idea. Next chance I get to look at the Jeep I'll start in on the wiring harness and see what I can find. I have a line on an original factory service manual. I should have it by the weekend. Hopefully that will take some of the guess work out of things.
Regarding the crank sensor test. I too have seen that on a website and I think it's a bum test. Doesn't tell you anything. The proper way to look at a crank signal is using an oscilloscope. Unfortunately, it's an expensive tool to buy to test a crank sensor. I have seen a youtuber (scannerdanner...one of my favorites) use a DVOM to test it but he rotated the engine over by hand. Crank and Cam signals are really fast square waves. 8V to 0v to 8v over and over. Hence the need for a scope to test. But if you slow it down, aka crank over using a breaker bar, you should be able to see your dvom go 8v then 0, then 8.

I am really curious for you to do the test I mentioned. Sounds like you have a short to ground. Question is it in the harness or is it in the PCM.

As for the service manual, very handy to have. I have a '92 and I am pretty sure we can walk you through finding the problem.

If you have a chance, one of the users on the YJ forum has a drop box that has a FSM. Grab the '94/5 and the powertrain diag manual. The 94/95 is almost identical to our 92. Wiring colors are different on the wiring diagrams (in some spots) and there are a few mechanical changes but not much. Also with the issue you are facing the powertrain diag manual is actually more helpful. It talks more about sensor data, PCM connections. It's more about fuel injection troubleshooting.

Either way, I bet we can get you through the problem on this thread.
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Old 11-14-2019, 10:57 AM   #20
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FSM's Below, Good luck
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Old 11-14-2019, 06:41 PM   #21
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Thank you, guys. I really appreciate your input. Sequel, If nothing else I will test the new sensor the same as I did the old one. I bet you are right about the test and the old and new end up being the same. If I have a helper available this weekend I'll try cranking the motor over manually and test it that way as well, out of curiosity if nothing else. I will start in on the wiring harness this weekend and see what I can turn up.

Got it at last, my computer is having trouble opening the link. I'm going to try it on one of our work computers tomorrow. I have access to a printer there as well.

Thanks again guys. I should be able to put some time in with the Jeep on Saturday, and will post up what I find (or don't).
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Old 11-15-2019, 01:47 AM   #22
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hi guys, i'm new to the forum but am jumping into this thread because I'm having the same issue as upnsmoke. I was on day 4 of a hunting trip and my 93 yj had been running fine, occasionally needed a few extra cranks to start up but otherwise no problems. I was driving back to camp and it just shut down. Right now I'm doing some research to come up with a plan of attack for diagnostics and repair. Thanks for the good ideas in earlier Posts. Seems like testing the crank position sensor is a good place to start. I'm wondering if anyone knows about a cam position sensor located inside the distributor and if that could be a possible culprit. thanks for letting me barge into your thread and ill keep you posted on anything i discover.
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Old 11-15-2019, 09:16 AM   #23
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hi guys, i'm new to the forum but am jumping into this thread because I'm having the same issue as upnsmoke. I was on day 4 of a hunting trip and my 93 yj had been running fine, occasionally needed a few extra cranks to start up but otherwise no problems. I was driving back to camp and it just shut down. Right now I'm doing some research to come up with a plan of attack for diagnostics and repair. Thanks for the good ideas in earlier Posts. Seems like testing the crank position sensor is a good place to start. I'm wondering if anyone knows about a cam position sensor located inside the distributor and if that could be a possible culprit. thanks for letting me barge into your thread and ill keep you posted on anything i discover.
For me, crank sensor or cam sensor are not the place to start. We can get to that later. When you have a no start, lets start with the basics. Fuel, air, spark.

Given that it look longer for the jeep to start, I'd almost start thinking fuel pump. But what you should test for is put a fuel gauge tester on the fuel rail and test your fuel pressure.

I'd also test for spark. Either pull a spark plug or at least pull the wire off the distributor going to the ignition coil and test for spark. A test light is my preferred method. Take the test light, clamp to a good ground (usually not battery post because of risk of spark). Then hold the tip of the test light near the plug wire and see if spark will jump to the test light.

Start there, report back. But I'd stop with this "testing the crank sensor" by checking resistance. Never works for anyone. The way to test a crank sensor is with a scope that most people don't have. There are some other tests you can do that can get you close but we'll cover that if you don't have spark.
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Old 11-15-2019, 12:07 PM   #24
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Thank you sequel, I was planning on testing crank sensor for intermittent voltage when I turn it over by hand. I haven't tested fuel pressure but I was thinking with the suddenness of the problem, meaning instant shut down while driving that fuel was less likely. I removed and cleaned my air filter and checked for spark when I was broke down in the field, no spark. BTW a jeep that was flat towed to hunting camp is a lot better than a broke down truck when you're in BFE. Do you have a suggestion on the order of things to check when no spark? Coil first? I am fairly handy and can follow directions but definitely not a mechanic. Thanks for any help and advice.
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Old 11-15-2019, 01:25 PM   #25
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Welcome back aguagrande,

See post #5 in this thread.
Follow the diagnostic flowchart for no start.
In the index, it might be in the "engines" section or in the section that deals with the specific engine (2.5, 4.2 or 4.0).

Good Luck, L.M.
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Old 11-15-2019, 03:10 PM   #26
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Thank you sequel, I was planning on testing crank sensor for intermittent voltage when I turn it over by hand. I haven't tested fuel pressure but I was thinking with the suddenness of the problem, meaning instant shut down while driving that fuel was less likely. I removed and cleaned my air filter and checked for spark when I was broke down in the field, no spark. BTW a jeep that was flat towed to hunting camp is a lot better than a broke down truck when you're in BFE. Do you have a suggestion on the order of things to check when no spark? Coil first? I am fairly handy and can follow directions but definitely not a mechanic. Thanks for any help and advice.
When you originally described the problem of shutting down and before that taking a while to start, I thought fuel pump. So they do fail that way.

But it is interesting that you say you don't have spark. My next step would be to check the ignition coil before going after Cam/Crank sensors (although you may end up there). For spark, you have to have a few things to work. The ASD relay needs to provide power. So you have some circuits involved with the ASD relay that have to work. You also have to have the PCM provide ground to the ignition coil (switches on and off). The video I posted on post #12 has how to test it.

I'd really go after testing the 2 wires that are on the connector. If those aren't there the coil cannot work right. Report back and we can go from there.

Btw, the cam and crank sensor are needed for the PCM to provide that ground.
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Old 11-15-2019, 09:17 PM   #27
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Thank you guys for your patience and willingness to help. today I had time to actually try out some of the things Ive been reading and learning about and embarrassingly discovered that I do indeed have spark. I'm not sure what I did wrong when I checked for spark in the field other than being tired and it being dark and cold. I depressed the schreoder valve while turning the engine over and didn't get any fuel to come out, something I didn't know to try when I originally broke down. I guess I'm going to start researching fuel pump diagnostics and take it from there. I did verify that my fuel system fuse is good and has power. Thanks again sequel, you where right from the start!!
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Old 11-15-2019, 11:20 PM   #28
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Thank you guys for your patience and willingness to help. today I had time to actually try out some of the things Ive been reading and learning about and embarrassingly discovered that I do indeed have spark. I'm not sure what I did wrong when I checked for spark in the field other than being tired and it being dark and cold. I depressed the schreoder valve while turning the engine over and didn't get any fuel to come out, something I didn't know to try when I originally broke down. I guess I'm going to start researching fuel pump diagnostics and take it from there. I did verify that my fuel system fuse is good and has power. Thanks again sequel, you where right from the start!!
Don't worry it happens. Really first step in fuel pump diag, is go rent a fuel pressure tester gauge at the auto parts store. Hook it up to the schrader valve on the fuel rail. Attempt to prime the pump by turning the key to on or start. Read the value on the gauge. I think our jeeps are mid 30s psi but would need to look it up to be certain.

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