YJ 4.0 turns over but won't crank

JMT

JMT

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@qslim and others like @Goatman and @k-huevo and @Chris. OK, so the YJ forum is not very active and I’m trying to get this jeep fixed. It’s a 94 with a 4.0 so it has a distributor. I’ve got fuel pressure at the rail. I have no spark. The starter was bouncing around as my son turned it over. So I tightened it back up. I started removing the spark plugs and they don’t look very good. But they weren’t getting any spark anyway. What should I check next?

It’s not my YJ, but it needs some love.

Thank you,
JMT
 
I don’t know a damn thing about the YJ specifically, others might chime in with more focused feedback.

As far as getting no spark, how far have you chased it back? Are you getting high tension voltage from the coil to the middle of the distributor? How do the distributor contacts look?

And what do you mean by the starter “bouncing around”? Like it wasn’t securely fastened?

Edit: this is a great cheap tool to have in your toolbox - you can just hold it next to any plug wire and look at the filament to see if there’s voltage flowing through the cable. They’re like $10 at Walmart or parts stores.

1589501713413.jpeg
 
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If you tested the main coil lead to make sure it sparks I'd check for voltage at the coil. I assume all the fuses are good. If you have a decent meter or a dwell meter you can check for signal at the coil after voltage. Coil is the easy target with no spark.
 
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qslim said:
I don’t know a damn thing about the YJ specifically, others might chime in with more focused feedback.

As far as getting no spark, how far have you chased it back? Are you getting high tension voltage from the coil to the middle of the distributor? How do the distributor contacts look?

And what do you mean by the starter “bouncing around”? Like it wasn’t securely fastened?

Edit: this is a great cheap tool to have in your toolbox - you can just hold it next to any plug wire and look at the filament to see if there’s voltage flowing through the cable. They’re like $10 at Walmart or parts stores.

View attachment 161405
Click to expand...
Thanks. I’ll get one of those tools.

Yeah, by jumping around I meant loose. Of course, I just tightened it down.

Also, it’s pretty much just a 4.0 Engine. A few things are moved around or different. Same principles I think, but IDK or I wouldn’t be asking you smart engine people!
 
Start with a tune up. Rotor, Cap, wires, and plugs. Even if that doesn't fix it, those parts are cheap and should be replaced if there is any question. Next, check the coil. With electronic ignition, that's pretty much it for the "easy" stuff. the signal from the coil is going to come a black box.

There is always the possibility that you are getting spark, but the engine is out of time...How do you know you don't have spark?
 
Mike_H said:
Start with a tune up. Rotor, Cap, wires, and plugs. Even if that doesn't fix it, those parts are cheap and should be replaced if there is any question. Next, check the coil. With electronic ignition, that's pretty much it for the "easy" stuff. the signal from the coil is going to come a black box.

There is always the possibility that you are getting spark, but the engine is out of time...How do you know you don't have spark?
Click to expand...
Ok, I have spark at the coil, but not at the plugs. I’m going to get new plugs, spark plugs and distributor cap.

I guess if that doesn’t solve it I’ll check my voltage at the coil and the cam and crankshaft sensors. Am I getting the hang of this?
 
JMT said:
Ok, I have spark at the coil, but not at the plugs. I’m going to get new plugs, spark plugs and distributor cap.

I guess if that doesn’t solve it I’ll check my voltage at the coil and the cam and crankshaft sensors. Am I getting the hang of this?
Click to expand...

You're on the right track. How did you check for spark at the coil?

If you have spark there but not at the plugs you're going the right way. Like @Mike_H suggested, there may also be a timing issue. What's the context of the failure? Did it have work done recently or did it just give up the ghost after running normally?
 
qslim said:
You're on the right track. How did you check for spark at the coil?

If you have spark there but not at the plugs you're going the right way. Like @Mike_H suggested, there may also be a timing issue. What's the context of the failure? Did it have work done recently or did it just give up the ghost after running normally?
Click to expand...
It’s not my rig so I really don’t know what happened. From what I gathered, it was running about three months ago and then it sat for a while and then it’s no longer running.

I checked for spark at the coil by removing the plug at the center of the distributor, putting a spark plug on it and grounding it and then turning it over by the short circuiting the starter. I had spark at the plug
 
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pagrey said:
Don't forget the rotor, just mentioned it cause you didn't, probably just missed it.
Click to expand...
What’s the rotor? Is it something in the distributor? Something I need to replace?
 
JMT said:
What’s the rotor? Is it something in the distributor? Something I need to replace?
Click to expand...
Sometimes I forget that you haven't worked on cars your whole life, as involved as you've gotten with your Wrangler.

I should have posted a picture for you...Here is a CDI style ignition system, like what the YJ should have.

1589567149911.png


And a picture to show what the cap and rotor are:

1589567201112.png


By the way, the ignition on your TJ is like the picture of the V style engine (distributorless) There are three coil packs on the rail...each one handles two cylinders.
 
Mike_H said:
Sometimes I forget that you haven't worked on cars your whole life, as involved as you've gotten with your Wrangler.

I should have posted a picture for you...Here is a CDI style ignition system, like what the YJ should have.

View attachment 161530

And a picture to show what the cap and rotor are:

View attachment 161531

By the way, the ignition on your TJ is like the picture of the V style engine (distributorless) There are three coil packs on the rail...each one handles two cylinders.
Click to expand...
OK, very helpful. Yeah, not been working on these all my life. We’re at three years and six months and I really haven’t had many mechanical problems.

here’s the status on the YJ. I replaced the distributor, rotor, spark plugs, and wires. I still couldn’t get it to start. I checked my voltage going into the coil. I have 11.87 V. That sounds to me like it’s not enough. At the battery I have about 12.4. what now?
 
Seems like you've tested for and have spark. It would at least try to start with that. When you pull the plugs after trying to start do you smell gas, are they wet? I might be looking into why the injectors aren't firing at this point.
 
I'd get a spark plug tester to verify that you don't have spark at the actual plug. I'd probably try to find a known good coil to put in and see what happens. I'd also throw that battery on a charger. Don't forget to check grounds...You don't have a terrible voltage drop on the coil, but checking grounds is easy and cheap.
 
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JMT said:
OK, very helpful. Yeah, not been working on these all my life. We’re at three years and six months and I really haven’t had many mechanical problems.

here’s the status on the YJ. I replaced the distributor, rotor, spark plugs, and wires. I still couldn’t get it to start. I checked my voltage going into the coil. I have 11.87 V. That sounds to me like it’s not enough. At the battery I have about 12.4. what now?
Click to expand...

Have re-verified for spark at the plug? Nice & healthy white or bright blue is what you're looking for. They make testers too like @Mike_H mentioned, makes it a little easier to determine the quality of the spark.
 
Ok, no spark at the plug. I went back to the coil. I did get spark there earlier with a plug, but when I used a spark plug tester it wouldn’t light the bulb. Not enough. Voltage going into the coil is 11.8 as mentioned before. But not enough spark coming out of the coil. So I’m gonna go buy a coil. I hope this is the right thing to do
 
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