WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing - Jeep Garage - Jeep Forum

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Old 09-21-2014, 02:25 AM
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WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

Hi all, most of my forum comments are typically regarding TJ's as it is my jeep that I take wheeling. TOday's post is regarding my DD. My DD is an 01 WJ, 4.7, and 95k on the clock. I need your help.

Today drove an hour away from my home to deliver a snowmobile I just sold. Ran great. Stopped at a gas station on my way home to pick up a soft drink, and seemed to be running fine when I shut it off to run inside.

I came back outside just a few minutes later, jumped in, turned the key to start it and it came to life with a horrible knock, like a LOUD rod knock, not like a metallic pinging. I immediately killed it and looked under the Jeep to see the only liquid dripping on the ground was condensation from the A/C. (I thought that it may have thrown a rod) Coolant level checked out, engine oil in the "Safe" zone, I did not see anything abnormal on the dipstick.

Went back start it again, knocking was still there, but much more subdued than it was just a few minutes before. Oil pressure gauge was reading normal, engine temperature was right at 210, or slightly below it. After just a very short time, the knocking completely left, it is now non-existant. HOWEVER, it runs extremely rough, I know for sure it isn't firing on all cylinders, likely more than 1 is not firing. The wind was blowing just right so that I could smell the exhaust and could smell unburned fuel.

Thought for some reason that the ECM had a freak out session, disconnected the battery for 15 mins, and reconnected it, nothing changed. I called around, and got it on a trailer, now its back at home.

The starter does not labor heavily when turning the engine over, I can hear the fuel pump prime when the key is turned on, and will even rev when throttle is applied though it still runs rough.

I am clueless as to where to start, is this a common occurrence with the 4.7? Any ideas of what it can be? How can I check it before taking it to a mechanic?

After reviewing the situation multiple times in my head, the only thing that I can think of is that the timing chain skipped a tooth, or broke which allowed the valves to come in contact with the piston(s) and bending. I assume that this could produce a loud knock while they are bending, and after being bent, they won't make much racket. From my research, the 4.7 is an interference motor, is this correct?

At any rate THANK YOU so much for the time you have taken to read this, and if you have any suggestions of what could be going on, I would appreciate your assistance.

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  #2  
Old 09-21-2014, 09:00 AM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

Do you have a check engine/service engine soon light? Try the switch "on/off/on/off/on" and watch the odometer.

As for the 4.7 jumping I have heard of it. The early chain tighteners are known to wear. If that is the case I would expect it to be difficult to start and to run rough.

I hope some of our other members can help.
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Old 09-21-2014, 09:15 AM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

Welcome to the garage.
The 4.7 is indeed an interference engine. The chain could have skipped teeth, or a sticking valve and it can have a bend valve stem now. But indeed you should have a check engine light with a P030- code (- = cylinder number) or P0300 for multiple cylinder misfire.
The keydance as described by Travis should give you the DTC´s, or when not, you will need a scanner to check them. My first action would be a compression check and cylinder leakdown check, to confirm low compression on the respective cylinder(s).
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Old 09-21-2014, 09:38 AM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

Quote:
Originally Posted by Trav1s View Post
Do you have a check engine/service engine soon light? Try the switch "on/off/on/off/on" and watch the odometer.

As for the 4.7 jumping I have heard of it. The early chain tighteners are known to wear. If that is the case I would expect it to be difficult to start and to run rough.

I hope some of our other members can help.
Quote:
Originally Posted by Frango100 View Post
Welcome to the garage.
The 4.7 is indeed an interference engine. The chain could have skipped teeth, or a sticking valve and it can have a bend valve stem now. But indeed you should have a check engine light with a P030- code (- = cylinder number) or P0300 for multiple cylinder misfire.
The keydance as described by Travis should give you the DTC´s, or when not, you will need a scanner to check them. My first action would be a compression check and cylinder leakdown check, to confirm low compression on the respective cylinder(s).
Thank you for your input. I failed to mention that I did do the Key Dance last night, and it pulled nothing. After doing so, all it read was "done".

When I get time, it looks like I will be doing some diggging of my own.

If indeed the piston(s) have come in contact with the valves, can I expect the motor to be a several hundred pound paperweight?
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Old 09-21-2014, 09:46 AM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

If it misfires, a code will be set. Not sure at what point it will be set, it maybe has to run at a higher rpm.
If the pistons contacted the valves, you will be looking at doing the heads and probably new timing sets. What also happened a lot on these engines was that they drop a valve seat. The seat can be crussed and cause damage to the cylinder wall, piston and head. Compression test will show you which cylinder.
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Old 09-21-2014, 03:48 PM
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I rebuilt my 02 4.7l heads to be inspected, decked,repaired, cleaned, new seals,etc... no new valves or springs was 500/600. Alone. Then i didn't do timing properly on driver head and sheared off the cam gear dowl pin, no valves bent. Paid another few hundred to repair the pin. So yeah.

Like frango stated about the seats, mine were already repaired as they were dimpled/crimped/secured as both machine shops stated that to me. Must be a common issue
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Old 09-28-2014, 10:02 PM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

Dropped the Jeep off at a mechanic, he told me that a valve seat dropped in cylinder #2. He quoted me $2100 to replace the one head or $3100 to replace both heads. Because of this I am going to tackle this project on my own to save a couple thousand.

Questions: Is it worth replacing both cylinder heads? Should I just do the one affected head? Can I put 4.7 H.O. heads on it instead? I've read that on the earlier 4.7's that the timing chain tensioners wear out prematurely. Should I replace all components to the timing while I have it apart? Thank you for the help!
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Old 09-29-2014, 07:07 AM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

Did the mechanic remove the head to check for further internal damage to piston and/or cylinder wall?
I don´t know when you send a cylinder head to a machine shop, if they will redo all valve seats or not. If they do, then it would be worth it to do the other head as well. Just to prevent you to take it apart again lateron with a possibility of more damage to pistons and walls.
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Old 09-29-2014, 09:48 AM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

If the seats have not been repaired, do so will save you a world of hurt later on. H.o heads i believe are same just the cam is different and intake manifold
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Old 09-29-2014, 07:01 PM
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Re: WJ Mechanical Engine Woes... 4.7 W/ Cylinder(s) not firing

Quote:
Originally Posted by Frango100 View Post
Did the mechanic remove the head to check for further internal damage to piston and/or cylinder wall?
I don´t know when you send a cylinder head to a machine shop, if they will redo all valve seats or not. If they do, then it would be worth it to do the other head as well. Just to prevent you to take it apart again lateron with a possibility of more damage to pistons and walls.
He did not pull the head off, just the valve cover. I did not want to pay further money for him to tear it apart. So, no he does not know whether it has a damaged cylinder or piston. I asked him about it and he did not seem too worried about a damaged piston or cylinder wall. The seat wedged the valve open, so I'm crossing my fingers that it bent the valve only and the seat didn't destruct itself.

I called him today and told him that I needed him to put it back together because I do not have money currently to have him do the work. Later this week I should get it back, and begin the tear down process.
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