Tacshrp

my wife's 2004 grand cherokee se with the 4.7L v8 has recently developed a pronounced tapping that sounds like it is in the top end and is running rough. i recently replaced the water pump and the spark plugs. the tapping actually sounds to me like it coming from the back half, just under the air intake body. (i probably am not using correct terminology. please, feel free to give me the correct names.) any suggestion?

does it have a power reduction mode like my chevy p/u?

tiwvr1

just a total guess, but sounds like a collapsed lifter, do you change oil regularly?

Tacshrp

Oil gets changed every 4,000 miles religiously. I don't know how overhead cams work. Do they use lifters?

tiwvr1

not to familiar with the 4.7, are they over head?

Tacshrp

It's a dual overhead cam engine with aluminum heads and cast iron block. It runs Great when it's running right. The problems with it all manifested at once. Water pump, tapping, and running rough. She said she didn't let it get over 240d When the pump let go. I don't think there is a bad head gasket cause the oil looks good and no excessive moisture from the tailpipe. I'm thinking you are on the right track. Something in the valvetrain.

Tacshrp

I was just looking out the window at it thinking about what could be wrong, when, for no reason, all of the lights came on for about 3 or 4 seconds and then went back off! Headlights, taillights, and interior lights! Holy cow! What's going on?

Tacshrp

It just did it again!

HCCAFan

Gremlins.

DOes it run good at all? If not, perhaps you jumped timing? How many miles?

Tacshrp

145,00 miles. I guess it could jump time. I don't know how the valvetrain works. Did a little research but it looks intimidating. It was running like a champ and then went to hell all at once. It runs the same driving or at idle.

HCCAFan

Those 4.7s do jump timing fairly often and with your kind of mileage. I hope it's something else.

Tacshrp

Do you know if the 4.7 is an interference type engine? Could it be catastrophic for the valves and pistons if it jumps time? It starts perfectly. Then, it starts tapping and rough idle.

HCCAFan

How long does it take? Yes, it will bend valves.

Tacshrp

Thanks for the input. It will be taking a trip to the shop.

HCCAFan

Could be "lucky" and it's a valve stem seal you caught early!

Tacshrp

Yeah. That would probably be best case scenario.
I hope I'm lucky.
Thanks.