Starting issue, Possible timing problem

[Piston broke]

Hi Guys,
A few months ago I had a problem with the engine in my Jeep. It looked as though a valve seat dropped out and proceeded to chew up the head and piston.
I didnt have time to do the strip down myself so gave it to a mechanic to do. The bottom end was fitted with new bearings etc, new timing chain and sprockets and a new piston and con rod assembly fitted. On the top end, for cost reasons I purchased a complete used head assembly from a vehicle dismantler. I checked the head out for cracks, flatness etc and found it was in top condition. In fact the head looked pretty new. I have finally rebuilt the engine but now I have this problem! It wont start properly. By this I mean that before just one turn of the key and the motor would burst into life. Much like a dog when someone says Walkies! But now it just wont fire up. However, if i turn the key to ignition on position and then off quickly for a couple of times it fires up straight away when I turn the key to start. The check engine warning light stays on. A friend used a scanner on the car and told me the fault was due to low fuel pressure. I check the pressure myself and found I had about 55psi so I dont think that was the issue. I had another scan done and was told the problem was due to the relationship between crank and camshaft. I checked the positioning of the sprocket with cylinder 1 at TDC and found this to be correct. I also changed the cam position sensor but I still have the same problem. The only thing I can think of is that there is some difference between the Camshaft and associated parts between the original and new heads.
Anybody out there with any ideas????

 

[mx3_ryder]

Was it the passenger side head you replaced? What year was the cylinder head you bought and did you use your original cam sprockets or the one that came with head?

 

[van462]

On the fuel pressure check did you also cut off the jeep and see if the system held pressure. A leaking injector will cause fuel pressure to fall off.

 

[Piston broke]

MX3 Ryder,
Thanks for the reply.
It was the passenger side head, and I dont know what year it was but it looked pretty new.
I replaced the head complete with cam, valves, sprocket etc. From your reply I am guessing you know what the issue is. Is this a case of been there, done that?
If this is what I am begining to think it is I cannot use any parts from the old head as this head is probably coke cans by now. The guy I bought the new head from took the old head for the scrap metal. The reason I usd all the parts on the new head was that they seemed to be in better condition than the old parts.
Does this give you any clearer ideas?

 

[Piston broke]

Van 462,
Pressure held up fine for about 15mins

 

[jeffixertk]

wont start

with your scan tool check to see if cranking rpm is accurate, should be about 125 to 150 rpm. run a compression check at number one cylinder to verify cam timing, if very low possible cam out of time, also check for ignition spark at plugs. if no big eureka moment then try to start engine with ether to see if it will run which will then point to fuel problem.

 

[mx3_ryder]

What year is your liberty. The tone ring on the cam sprocket is used for timing so if you have the wrong year that would be your issue.

 

[TwoBobsKJ]

What year is your liberty. The tone ring on the cam sprocket is used for timing so if you have the wrong year that would be your issue.

X2 for sure.

If you have an 02 through 04 your KJ uses the JTEC computer; if you got a head from an 05 or later 3.7 liter then it used an NGC computer and they're not compatible. The number of slots in the cam sprocket are different (the cam sensor reads those slots as it spins) and so your computer is expecting to see one thing and it's seeing another.

If the cam sprocket is the same then my next suggestion would be the security chip on your key. My KJ doesn't have a chip but I've seen threads here where some sort of reset needs to be done so the security system will allow the engine to run. IIRC the engine will tun over but not run if the chip isn't communicating with the computer.

But my first guess is still the cam sprocket.

Bob

 

[Piston broke]

The tone ring seems to be the logical answer to this problem. My Liberty is an 05 limited.
How can I spot the difference between the two types of tone ring. It looks like a trip to the vehicle dismantler again but I think it would be a good idea if I knew what I was looking for. The guy at this place might not know the difference either.
Bob Strange you should mention the key The remote stopped working so I changed the battery in it. Ive read how to reprogram it but I need an original key to copy the program, Which I dont have, or take it to the dealer and pay a fortune to have them do it. Or live without the remote function for a while. Ummm let me think this one out for a day or two.
By the way the engine does run, a little rough though, so I dont think the key is stopping it. The tone ring is my first choice.
Thanks all!! will report back after I have changed out this part.

 

[TwoBobsKJ]

The tone ring seems to be the logical answer to this problem. My Liberty is an 05 limited.
How can I spot the difference between the two types of tone ring. It looks like a trip to the vehicle dismantler again but I think it would be a good idea if I knew what I was looking for. The guy at this place might not know the difference either.
Bob Strange you should mention the key The remote stopped working so I changed the battery in it. Ive read how to reprogram it but I need an original key to copy the program, Which I dont have, or take it to the dealer and pay a fortune to have them do it. Or live without the remote function for a while. Ummm let me think this one out for a day or two.
By the way the engine does run, a little rough though, so I dont think the key is stopping it. The tone ring is my first choice.
Thanks all!! will report back after I have changed out this part.

Pop the valve cover off the passenger side and look at the cam sprocket. There's a stamp on the face of the sprocket that will either say JTEC or NGC. If it says JTEC you found the problem.

Bob

 

[Piston broke]

OK, so I changed out the sprocket on the passenger side head and......
SHE LIVES. Running like a dream. I also found that I needed a special tool to stop the chain tensioners closing in, but with a little bit of British engineering managed to make my own.
All I have to do now is a whole lot of little things that I have been meaning to do for a long time now. But I am recently retired so these will keep me busy. Thinking about it I dont know how I found the time to go to work for all these years!!!
Anyway Guys, thanks for your help.

 

[TwoBobsKJ]

Congrats! Glad you've got her running again - and that you found the suggestions helpful.

Enjoy your KJ - Cheers! arty52:

Bob

 

[megatone]

Great job.