YJ 4.0 turns over but won't crank

Yeah, this thing ran like s**t. It’s still running like s**t. It runs smooth if I’m just coasting, but if I give it any gas it’s rough.

When you say it's smooth while coasting, does it idle normally but stumbles under load? If so that can be classic symptom of a weak coil.

So trying to put together the whole picture, was this thing running like garbage before you got involved? Like maybe they were having issues with it prior, parked it for awhile, the thing sat & eventually wouldn't start, you changed the plugs, wires, cap & rotor and now it's right back to where it was?

If that's the case after a basic tune-up & top engine clean I'd move on to diagnosing mechanical issues.
Compression checks are real easy to do, here a copy & paste from our manual (this is from my '99 but the precedure is the same & I'd assume the pressure specs are as well):

Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise the indicated compression pressures may not be valid for diagnosis purposes.
(1) Clean the spark plug recesses with compressed air.
(2) Remove the spark plugs.
(3) Secure the throttle in the wide-open position.
(4) Disable the fuel system. (Refer to Group 14, Fuel System for the correct procedure)
(5) Disconnect the ignition coil.
(6) Insert a compression pressure gauge and rotate the engine with the engine starter motor for three revolutions.
(7) Record the compression pressure on the 3rd revolution. Continue the test for the remaining cylinders.

Pressure Range . . . . . . . . . . . . . 827 to 1,034 kPa (120 to 150 psi)
Max. Variation Between Cylinders . . . . . 206 kPa (30 psi)
 
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When you say it's smooth while coasting, does it idle normally but stumbles under load? If so that can be classic symptom of a weak coil.

So trying to put together the whole picture, was this thing running like garbage before you got involved? Like maybe they were having issues with it prior, parked it for awhile, the thing sat & eventually wouldn't start, you changed the plugs, wires, cap & rotor and now it's right back to where it was?

If that's the case after a basic tune-up & top engine clean I'd move on to diagnosing mechanical issues.
Compression checks are real easy to do, here a copy & paste from our manual (this is from my '99 but the precedure is the same & I'd assume the pressure specs are as well):

Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise the indicated compression pressures may not be valid for diagnosis purposes.
(1) Clean the spark plug recesses with compressed air.
(2) Remove the spark plugs.
(3) Secure the throttle in the wide-open position.
(4) Disable the fuel system. (Refer to Group 14, Fuel System for the correct procedure)
(5) Disconnect the ignition coil.
(6) Insert a compression pressure gauge and rotate the engine with the engine starter motor for three revolutions.
(7) Record the compression pressure on the 3rd revolution. Continue the test for the remaining cylinders.

Pressure Range . . . . . . . . . . . . . 827 to 1,034 kPa (120 to 150 psi)
Max. Variation Between Cylinders . . . . . 206 kPa (30 psi)
Idle is ok. When under load it stumbles. It’s not smooth. I smell gas occasionally too. I just replaced the coil yesterday. That was the last thing I replaced before it finally started.

I asked the guy how it was running. He said it was running good. I need to clarify with him what good is. 🙄 Last time it was driven was about 3 months ago
 
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Ok, the owner told me that they thought someone had stolen the gas and that this had happened several times. Possibly they put water in the tank. It’s sat for three months or so without starting. Then it came to me to fix it. Of course, the coil got it going but it’s running really rough under load. So? Could it be water in the gas?
 
Ok, the owner told me that they thought someone had stolen the gas and that this had happened several times. Possibly they put water in the tank. It’s sat for three months or so without starting. Then it came to me to fix it. Of course, the coil got it going but it’s running really rough under load. So? Could it be water in the gas?

Haha sounds like your case is really coming together there Detective @JMT !

What kind of dick would steal gas and THEN replace it with water?

If the quality of the gas is suspect I'd absolutely replace it. You can't get any kind of good diagnosis if you're not sure about the fuel. Spark, air, fuel, compression are the four cornerstones of a running engine. Sounds like you've checked off spark and air so far.
 
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Ok, the owner told me that they thought someone had stolen the gas and that this had happened several times. Possibly they put water in the tank. It’s sat for three months or so without starting. Then it came to me to fix it. Of course, the coil got it going but it’s running really rough under load. So? Could it be water in the gas?
What @qslim says is absolutely correct. I bought an '87 Saab that had been sitting for 6 months with 1/4 tank of gas in it. Ran like crap. Did nothing more than add five gallons of fresh mid-grade gas in it, and within a mile and half, she was purring. Obviously, if some jerk put water in the tank, you'll need to get as much of that out as possible before adding new stuff.
 
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Oh boy, this is going to be fun getting the tank drained. I don’t have any place to put all that gas.
 
In my experience bad gas will cause a rough idle. Stumbling on acceleration or rough running under load is more likely timing or lack of fuel flow. If you added 8 gallons and didn't notice much change, if you have a smooth idle I personally wouldn't suspect water or bad gas.

Edit: I have an old ford six and you can't adjust the idle speed, timing and dwell if the fuel isn't fresh. The idle is just not stable enough and it's obvious
 
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In my experience bad gas will cause a rough idle. Stumbling on acceleration or rough running under load is more likely timing or lack of fuel flow. If you added 8 gallons and didn't notice much change, if you have a smooth idle I personally wouldn't suspect water or bad gas.

Edit: I have an old ford six and you can't adjust the idle speed, timing and dwell if the fuel isn't fresh. The idle is just not stable enough and it's obvious
I think the gas is good. I did a test where I siphoned some out, added an equal amount of water, shook it for 10 seconds and let it separate. If water is in the gas it’s supposed to pull the water out. All the water will go to the bottom. If there is more water than gas you have water in your gas. Mine was equal.

I did check the fuel pressure at the rail, but I did it while turning it over rather than simply with the ignition on. Now that I’ve got it running I could go up to O’Reilly’s and do that test again in the lot. If that’s not it, I think I’ll look at timing.
 
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Update @qslim, @pagrey , @Mike_H , @Squatch et al engine geniuses.

this thing is running so weird I decided to check the timing. When I remove the spark plug one, it was all fouled with carbon as you can see in the pic. What I found on the Internet says that it’s running too rich. I don’t even have an air filter on this Thing right now and the throttlebody and IAC have been cleaned. So it should be getting plenty of air unless there’s something else stopping it. I also open the distributor cap to check the position of the rotor. The rotor looks damaged. I just put this rotor on last week. help!

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Update @qslim, @pagrey , @Mike_H , @Squatch et al engine geniuses.

this thing is running so weird I decided to check the timing. When I remove the spark plug one, it was all fouled with carbon as you can see in the pic. What I found on the Internet says that it’s running too rich. I don’t even have an air filter on this Thing right now and the throttlebody and IAC have been cleaned. So it should be getting plenty of air unless there’s something else stopping it. I also open the distributor cap to check the position of the rotor. The rotor looks damaged. I just put this rotor on last week. help!

View attachment 162712

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That plug is definitely fouled. Just because the engine can get enough air, won't necessarily mean its not running rich. The sensor that measures air flow (MAP or MAF) might be bad. If its reading high (more air), the ECU will bump the duty cycle on the injectors to feed more fuel so it doesn't run lean.

That rotor is messed up! Did they give you the right one? Did it look the same as the one you replaced? That is mechanical interference. What does the underside of the cap look like? I bet its messed up too!
 
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Yeah that plug isn't healthy at all, especially if you just replaced it recently. The dizzy rotor is trashed too, I'd look into @Mike_H 's suggestion as to whether that was the right one, or look into whether the cap is the correct part.

As for the fuel/air mixture, I'd personally look to the O2 sensor before the MAP (I'm assuming these things have a MAP sensor, like I said before I don't know a thing about the '94). MAP sensors in my experience are very reliable and less prone to failure than O2 sensors. One is a solid state pressure sensor that lives in the intake manifold, the other is a galvanic battery that lives in the exhaust stream. They work in concert, the MAP sensor measures intake manifold absolute pressure to determine how much air is entering the engine, the O2 sensor measures the oxygen content of the exhaust to provide feedback to the PCM as to how much air is being burned in the cylinders.

On our TJs I've noticed that the monitoring strategy for O2 sensors is much more analogue and loose than the Japanese motors I'm accustomed to - I replaced the O2 sensor in my '99 and, despite the absence of a MIL/CEL, it cleared up a lot of my driveability problems.

And when you said you decided to check the timing, what exactly were you checking?
 
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Sure looks like it was either the wrong rotor, or the distributor shaft has a wobble to it that allowed/caused the rotor to make contact (no pun intended) with the distributor cap. I've experienced both scenarios before, so it can and does happen. And like @Mike_H said, I'll bet the cap is toast, now.
 
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Hey, @JMT, when you put the rotor in, did you turn it with some downward force, and feel it line-up and drop in slightly? Seeing the top of your rotor, I can see it's pretty chewed up, almost like it wasn't completely seated (assuming that it was, in fact, the correct rotor). If it's the wrong one, then it might also explain the damage.
 
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Could this be because it was running like crap due to the damaged rotor and cap? I mean, it fouled so quickly because it wasn't firing consistently?

Yeah you might be onto something there... Maybe check to make sure that rotor was seated properly huh. If the button wasn't pushed down all the way the thing might have been chewing up the cap & arcing all over the place, that's a good call (assuming they are the correct parts).
 
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I don't think that plug is bad at all, if they all look similar it's just because it isn't running smooth yet. That plug is definitely not going to cause any issues by itself if you were concerned. It'll clean up the second you get whatever is wrong fixed.
 
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I don't think that plug is bad at all, if they all look similar it's just because it isn't running smooth yet. That plug is definitely not going to cause any issues by itself if you were concerned. It'll clean up the second you get whatever is wrong fixed.
I agree. The plug is just showing the results of something else that's not right. As you said, it'll clean up just fine. I think the big issue is what's happening with the dizzy. Can't wait to see a picture of the inside of that cap!
 
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Yeah that plug isn't healthy at all, especially if you just replaced it recently. The dizzy rotor is trashed too, I'd look into @Mike_H 's suggestion as to whether that was the right one, or look into whether the cap is the correct part.

As for the fuel/air mixture, I'd personally look to the O2 sensor before the MAP (I'm assuming these things have a MAP sensor, like I said before I don't know a thing about the '94). MAP sensors in my experience are very reliable and less prone to failure than O2 sensors. One is a solid state pressure sensor that lives in the intake manifold, the other is a galvanic battery that lives in the exhaust stream. They work in concert, the MAP sensor measures intake manifold absolute pressure to determine how much air is entering the engine, the O2 sensor measures the oxygen content of the exhaust to provide feedback to the PCM as to how much air is being burned in the cylinders.

On our TJs I've noticed that the monitoring strategy for O2 sensors is much more analogue and loose than the Japanese motors I'm accustomed to - I replaced the O2 sensor in my '99 and, despite the absence of a MIL/CEL, it cleared up a lot of my driveability problems.

And when you said you decided to check the timing, what exactly were you checking?
Good call on the O2 sensor. I forgot about the feedback loop. You're also correct that it's much more likely to be bad. I was hyper focused on intake, and forgot there was a system!
 
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I agree. The plug is just showing the results of something else that's not right. As you said, it'll clean up just fine. I think the big issue is what's happening with the dizzy. Can't wait to see a picture of the inside of that cap!
Yeah you might be onto something there... Maybe check to make sure that rotor was seated properly huh. If the button wasn't pushed down all the way the thing might have been chewing up the cap & arcing all over the place, that's a good call (assuming they are the correct parts).
I don't think that plug is bad at all, if they all look similar it's just because it isn't running smooth yet. That plug is definitely not going to cause any issues by itself if you were concerned. It'll clean up the second you get whatever is wrong fixed.

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C’s
 
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Have someone crank over the rig while you look down at the distributer shaft (cap and rotor off, obviously). Look for any signs that it might be bent. It's not likely, but it is possible, if someone else had ever been in there trying to remove it or an old rotor with a BFH, or something. Eliminate that as a possible cause.