I have a 01 4.0. I wasn't driving at the time but a coolant hose broke and I believe the car was overheated for a long time. I repaired the coolant leak. I didn't run the car long enough to bleed coolant because of the ticking and misfiring. The misfire code is for cylinder 8. I changed the spark plug and coil pack but it is still misfiring and ticking? Now Im thinking the valve spring might have broken? I do have a real time obd II but not should what I should be looking for.

 

are you sure you changed out the right coil ?

 

From the front of the car. I replaced the last right plug on the driver side. Is this cylinder 8? The code was P0308. The coil pack was a spare from when changed all the packs about 500 miles ago with the ebay special.

 

Two thoughts... One, the replacement coil is crap. Two, make sure the fuel injector harness is firmly pushed into cyl #8 injector. (Cyl #8 location - drivers side - closest to firewall)

 

I bought a new coil and I still the same issue. I'm going to pull the valve cover off and check the spring. If the spring is bad is it possible to replace without pulling the head off?

 

I also checked the injector plug connection and voltage. Im reading 13 vdc. I checked the coil plug and I saw pulsing voltage.

 

We've not had valve springs reported as problems so it's highly unlikely to be that.

 

How much do you know about your car?

Are you aware of the timing chain tensioner problems? Have you looked to see if they have been changed?

Not much use repairing a 4.0L until you fix the big problem. Car may have already jumped time.

Many, many threads on here about the repair. How to do it and where to get the parts.

It is a big job if you DIY it!!
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I read about the timing chain tensioner issues. I only had this car for 5k miles. It has been running great until it was badly overheated. I pulled the driver side valve cover off today. I do have the old tensioner. The chain seem to be tight with no slack and when I pushed down it did not move down much. Wasn't able to see the cylinder 8 springs, but I was not able to push the lifter down and the cam lobs had no gap or play. I pulled the spark plug out and it seem that it has sparked. Could there be another cylinder misfiring to cause this, bad fuel injector or a intake gasket? I was think also thinking of doing a compression test.

 

whats the actual code

 

the code is P0308

 

ok, that is cyl 8.

does the code return when cleared, you could have another faulty coil causing misfires and no codes.

 

I cleared the code and replaced the coil and plug. I ran the car and it was missing at 40 mph and at idle. The same code came back after a short 100 yard drive.

 

ok, it my be worth doing a compression test.

another thing to consider is i believe a faulty/sticking injector can sometimes throw a misfire code on other engines not sure about the aj engines

 

You can swap injectors to see if that is the problem too.
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I have a big depressing 0 compression on cylinder 8. I was thinking for a minute that my gauge was broken so I also checked cylinder 1 and had a good 125 psi reading. I'm going to be done with working on this engine. Now Im thinking of junking the car or a engine swap. Thanks guys for your help.