I have to go get my daughters 2004 Jeep Grand Cherokee and fix the engine. She came home for Xmas and her eng. light was on so I hooked it to the scanner and it said PO301 cyl. #1 missfire so I put a plug in it although the one in it looked OK. It was also a 1/2 gal. low in coolant and I didn't see a leak. She went on home 4rs. away and all seemed OK. Now it is in a shop up there and they say it has a flashing PO303 cyl. #3 missfire. They tried a plug and coil and it did not fix it. They are telling me now it has a lot of valvetrain noise and only 90 psi. comp. on that cyl. Are these engines having problems? Broke spring or rocker? Blown gasket between 1 and 3? I know 5.2's and 5.9's like the back of my hand, but have never even had a valve cover off a 4.7. HELP!!!!

The 4.7 is an OHC engine so it shouldn't have rockers. I've had the covers of my 4.7 once to clean them up for paint but that's it. They are a pain to get off too. They aren't as bad as some people make them out to be but I had to remove the A/C compressor and move it out of the way. That made life a lot easer. Good luck finding the problem. Sorry I can't help much. I'll be watching to see how things go.

man good luck with that.i had a code like that after 20,000 miles acouple of times in 1 yr.i ran some red line injector cleaner in the system[added to fuel]it got better after a while.i am not saying it is your problem but i dont want you fixing it if it aint broke.redline is at the autoparts store maybe 15$

I thought about injector trouble. Maybe trash getting in the injectors and sticking them part open and fuel washing down the cyl. and making the comp. low and making it miss. I always do a dry comp. test then squirt a little oil in and do a wet test. If it is injector trouble then what is the valvetrain noise?

I had a burned valve on my own 2000 4.7 when I got it. IIRC, the lifters set in the head and the roller followers bridge across the tops of the lifters and tops of valve stems. It would seem strange to have the misfire go from one cyl to another. Is easier said than done, but you should get it back to where you can look at it yourself if you can. I've had 2 rather high mile 4.7's, and they are so far, quiet runners at all times.

How many miles did yours have on it when it burnt a valve? This Jeep only has 68,000 mi. on it. I don't think it is a burnt valve because it happened all of the sudden on this cylinder and it has a noise under the valve cover that was loud enough for me to hear over a cell phone. Did you pull your heads? Do you have to pull the front off too? Was it a big job? I am NOT looking forward to this!

It was easier than it looked, had 92k, and had the funny cranking sound too. Had only 70 psi on that cyl and did set a misfire code only while idling. Mine was cyl #7 and was not too bad to pull the head, and I did not have to pull front of eng. Jeep may be more of a challenge.

Most of the times a burnt valve will try to hit when you get up some speed and just idle rough and have that funny cranking sound. The mechanic and my daughter says this runs bad on the road, jumping and jerking and trying to cut off? What kind of chain tensioner does it have? Do you have to wedge something in it so it won't jump out when you pull the gear off the cam?

There is a small torx or allen headed bolt that holds the tensioner that you take out and then can slide the tensioner straight out the top. I did have a diagram of the chain layout to be sure it was going together correctly. Keep in mind, I dealt with drivers side head and did not have too many issues, pass side may have been more of a pain. It's not a great big deal to pull a valve cover to see what you got, maybe you can luck out and only have a follower prob.

Cylinders 1 & 3 are on the drivers side also arn't they?

I was a chrysler tech a few years ago and our shop had 2 grand cherokees with 4.7 's and both had a burnt exhaust valve on # 7 cyl. The first on came in with only 18 k on the odometer and the second one came in with about 23 k. on it with the same cyl. I did both of those repairs. Those 2 jeeps came in about 3 weeks apart. I couldn't believe at low miles and the same cyls. on two different vehicles. Sent both heads out to a local machine shop and the shop stated that the exhaust guides had not been machine correctly and the valve wasn't seating properly. If I remember they were both 2000 models. This was about 2001 before I had left the dealership. At the time I had a friend that worked at another dealership and had ask him if they had seen any issues with 4.7's and he said they haven't. This was several years ago. Not sure if this is your problem, but thought I would let you know..

Must be a pattern there, I had put both new valves in that cylinder along with a new injector, as long as the party that sold it to me was paying for the parts. The truck now has 130k and has not done it again......so far.

If you have some noise also,I would pull the valve cover.Had one a couple weeks ago with a problem.the rocker had popped out of place.yes ohc, but it still has a rocker under the camshaft.compression will show ok,but that is because the valve isn't opening.Do a google on the problem.there are valve problems,also claims of carbon build up causing the problems(rockers popping out of place)pull the valve cover.

Thanks for all the info Guys. I am going to get it tomorow and I will pull the valve cover first. I thought maybe it was still under warranty, but she said it has 70,200mi. on it now and she doesn't think she paid to have it transfered in her name? She's had it about 1 year.

Just give the dealer the VIN. They won't be long telling you if they can help or not. 70200 mi if the dealer is decent at all should be able to get warranty. I didn't have to pay anything when I bought my 03 Ram to transfer the warranty.

Kevin

Almost all leak at the thermostat--slow but sure.replace the stat and maybe the water neck to prevent the coolant loss My wifes 01 Grand Cherokee has been a PITA on trouble but she LOVES that thing! Heater door flaps is a $$ big one--window motors ( go aftermarket 1/2 price ) rear end whine--let it whine... oil sender bad shows NO oil pressure--thats good on Monday morning! New brakes all around and the pedal still goes way down oh..don't forget that power steering hose coupler that is a POS and cost $175 to fix but I have to put up with it so I can be a Mopar man--right?