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Unread 08-05-2010, 01:03 AM   #1
VegasMatt
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Jeep cranks and cranks, will not fire

Hey Guys,

So I drove my Jeep to the gym, no problem. I come out of the gym, and the engine will crank and crank but will not fire. The battery is charged. I checked all fuses and relays, and could not see any that were obviously toasted. Ended up having the Jeep towed back to my house. After doing some searching, I have four competing theories right now:

1) I installed a kill switch into the ASD relay per Jerry B’s instructions. It has been working perfectly for several months, but perhaps I had a solder fail? I will trace the wires, but I put everything together pretty solid so I’m not sure it could just work itself loose.

2) There is a component failure in my plugs, distributor, wires, or some combination of the three. I will check for sparks and see if I am getting power or not.

3) The Crank Position Sensor has failed. I will pull it off and see if a check engine light comes on, or if I notice any change in behavior on my gauges.

4) The fuel pump and/or fuel filter is bad. I really hope this isn’t it, because I understand this is a major PITA to replace.

Can you guys think of any other possibilities I may have missed? Really frustrating as the damn thing worked an hour before, and then refuses to fire and run now.

Thanks,

Matt

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Unread 08-05-2010, 02:47 AM   #2
BYuen
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Quote:
Originally Posted by VegasMatt View Post
Hey Guys,

So I drove my Jeep to the gym, no problem. I come out of the gym, and the engine will crank and crank but will not fire. The battery is charged. I checked all fuses and relays, and could not see any that were obviously toasted. Ended up having the Jeep towed back to my house. After doing some searching, I have four competing theories right now:

1) I installed a kill switch into the ASD relay per Jerry B’s instructions. It has been working perfectly for several months, but perhaps I had a solder fail? I will trace the wires, but I put everything together pretty solid so I’m not sure it could just work itself loose.

2) There is a component failure in my plugs, distributor, wires, or some combination of the three. I will check for sparks and see if I am getting power or not.

3) The Crank Position Sensor has failed. I will pull it off and see if a check engine light comes on, or if I notice any change in behavior on my gauges.

4) The fuel pump and/or fuel filter is bad. I really hope this isn’t it, because I understand this is a major PITA to replace.

Can you guys think of any other possibilities I may have missed? Really frustrating as the damn thing worked an hour before, and then refuses to fire and run now.

Thanks,

Matt
Sounds like it is your fuel pump assembly. Mine just went out a few weeks ago. I went ahead and replaced the whole unit. You can diagnose whether or not it's your fuel pump by checking to see if you're getting ample fuel pressure at the fuel injectors. To do this, find the schrader valve on the fuel injector rail. Remove the cap then press down on the valve with a small object just as you would air down your tires. If fuel shoots out of the valve under high pressure, then you know your fuel pump/filter is good and your problem lies elsewhere. If it kind of just dribbles out, then you know the problem lies with the fuel sending unit.

Replacing the fuel sending unit might seem intimidating at first, but it's really not bad! I've had to drop my gas tank twice and it's an easy afternoon project. Just do your research before hand and you'll be fine. Stu-offroad.com has a good write up for replacing the sending unit. If it is your fuel pump assembly, just let me know if you have any questions about the replacement. Our TJs should be exactly the same Good luck with the rest of the diagnosis.
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Unread 08-05-2010, 10:47 AM   #3
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Thanks BYuen! I had a suspicion it might have been something in the fuel pump assembly, as it seemed like the engine was ready to go but had nothing to burn.

Still hoping it's something easier though... Might as well change all the plugs and wires while i'll be testing them anyway.
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Unread 08-06-2010, 08:24 PM   #4
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So, I'm trying to drop the fuel tank, and I can't remove one of the two nuts on the front side of the tank that are right next to each other. The nut and bolt both turn, and I cannot loosen or tighten the nut. Any ideas for getting this nut off? I'd rather not use a cut-off wheel, with all the gas fumes around.....
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Unread 08-06-2010, 08:52 PM   #5
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have you checked fuel pressure at the fuel rail on the motor first?
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Unread 08-06-2010, 08:57 PM   #6
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Yes, nothing came out of the schrader valve - not even a dribble. I also eliminated the CPS and ASD relay relay as a cause of the problem.
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Unread 08-06-2010, 09:46 PM   #7
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Well, not wanting to throw sparks everywhere so close to fuel vapors, just ran out and got a $5 hacksaw at Lowe's. First thing in the morning i'll spend an hour or two and cut off that bolt.

Question is, it's so cramped between the tub and the crossmember-type thing where the bolt comes through, I'm not sure I'll be able to fit another bolt in there to replace the one I cut out.

Is 6/7 bolts asking for trouble?
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Unread 08-06-2010, 10:13 PM   #8
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Well, not wanting to throw sparks everywhere so close to fuel vapors, just ran out and got a $5 hacksaw at Lowe's. First thing in the morning i'll spend an hour or two and cut off that bolt.

Question is, it's so cramped between the tub and the crossmember-type thing where the bolt comes through, I'm not sure I'll be able to fit another bolt in there to replace the one I cut out.

Is 6/7 bolts asking for trouble?
You'll be fine. Once you drop the gas tank you can easily reach in and replace the bolts you had to cut off. The rear cross member is just a c rail

EDIT: Oh you mean the two bolts towards the front of the Jeep... I can't specifically remember how much space is between the tub and the crossmember. However, I do have a 1" body lift so I'll have more room than stock. You should be able to replace them easily once the tank is out. If not, you might have to unbolt one side of the body from the frame and jack it up a bit to get enough room to replace the bolt. It wouldn't make sense for Chrysler to design it that way... but a lot of things car manufacturers do don't make sense lol. I guess you really don't have another option other than to cut that bolt out
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Unread 08-06-2010, 10:47 PM   #9
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Same thing happened to me, except it happened once at home and once outside a hotel.
We replaced the ignition coil 3 or 4 times, then replaced the CPS and it fixed it right away. And it was easier than screwing around with the ignition coil.
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Unread 08-07-2010, 09:05 AM   #10
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And it was easier than screwing around with the ignition coil.
That's awesome advice. Anytime I have a difficult repair, I fix something else that's much easier to get to. This one time, there was a hole in the oil pan so I replaced the side mirror on the driver's door.
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Unread 08-07-2010, 09:54 AM   #11
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That's awesome advice. Anytime I have a difficult repair, I fix something else that's much easier to get to. This one time, there was a hole in the oil pan so I replaced the side mirror on the driver's door.
*sshole.
Next time, please try to keep your comments constructive and on topic. Less sarcastic would be a nice touch as well.

-Jason
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Unread 08-09-2010, 10:36 AM   #12
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Whoa Billy…..


Anywho, I finally got that bolt cut out, 2 saw blades later. Getting that lock ring out required the use of a BFH and a 2x4. I have reassembled the pump and will bolt the fuel tank back in tonight after work. Then we’ll add back a little gas, turn the key and see what happens…

The outgoing fuel filters were filthy. I wouldn’t be surprised that alone was enough to restrict my fuel supply.

I also swapped out the plugs with new Bosch stuff. FSM specifies a gap of .035”, the outgoing plugs measured .085”
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Unread 08-09-2010, 11:08 AM   #13
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Looking forward to see what happens. My hard start is getting very annoying.
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Unread 08-09-2010, 11:22 AM   #14
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Whoa Billy…..


Anywho, I finally got that bolt cut out, 2 saw blades later. Getting that lock ring out required the use of a BFH and a 2x4. I have reassembled the pump and will bolt the fuel tank back in tonight after work. Then we’ll add back a little gas, turn the key and see what happens…

The outgoing fuel filters were filthy. I wouldn’t be surprised that alone was enough to restrict my fuel supply.

I also swapped out the plugs with new Bosch stuff. FSM specifies a gap of .035”, the outgoing plugs measured .085”
Sounds great! Yea the external strainer on my old assembly was really gunked up too. I can't imagine what the internals looked like.

Let us know how those Bosch plugs work out for you. They have a reputation of not running well in the Jeep 4.0 .
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Unread 08-09-2010, 12:27 PM   #15
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Let us know how those Bosch plugs work out for you. They have a reputation of not running well in the Jeep 4.0 .
Yeah, i remember reading that on here as well - unfortunately, vatozone didn't have any Champion or NGK's. I got just the plain jane plugs, not the irridium coated or whatever the fancy ones are.
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