Learn me 2004 grand Cherokee 4.7 L weaknesses

I have a chance to pick up a pretty clean 2004 grand Cherokee that was towed home due to "Losing power going down the road."  Seller is 0% car guy, so the description I got is the best description I'm going to get. I'm looking at it tomorrow. What should I look for?  What are the known failure modes with the 4.7 L at around 125,000 miles?

Losing power could be anything.  Bring a scan tool and check for codes.  The 4.7 is known for valve train noise.  Especially on cold starts.  They also can have exhaust manifold issues, not all but worth looking at.  Sludge build up seems to be common issue with Chrysler products, hope he changed the oil.  Also, misfire issues seem to crop up, may be coils.   Good luck on your possible purchase.  The inline 6  seems to be more reliable.

A really clean 2003 popped up for sale near me.  I keep looking but have resisted so far.  

Dirtydog said:

The inline 6  seems to be more reliable.

Not in a WJ (99-04) except maybe the 04s.  The 4.7s tend to mostly die of abuse while the 4.0s have bad cylinder heads in those years (20 - 30 percent will crack on the top and dump coolant into the oil without ever being overheated or anything).  And the 4.0s randomly break pistons sometimes.  The 4.7 came with a better trans too. 

As far as weak spots on the 4.7, they HATE being overheated.  Get it hot and you're looking at possible cracked heads and/or dropped valve seats.  Keep them cooled properly and the oil changed and they're pretty reliable (not perfect, but not bad at all). 

Pre 99 inlines were pretty much reliable.  The 04 was ok.  My son had a 2004 Durango 4.7,  it was OK, but had valve noise, his friend has a 2010 Ram 4.7 with same issues.  A little under powered though, on the larger trucks. Chrysler products pretty much demand scheduled oil changes.

Valvetrain noise is the name of the game with that era of Chryslers.  4.0s usually clatter quite a bit too.  And yeah, the pre-99 or 2000 (depending on which model Jeep) 4.0s were much better (those heads didn't have issues).  Pre-96 were the best of them though, as 96 was when they changed pistons to the explody version. 

3 issues I've seen repeatedly: Valve seats, galled cam journals, and Head Gaskets

I don't know why, but the head gasket seems to blow on the rear cylinder toward the rear  water jacket.  It will actually wear a little grove in the head and cause it to skip

Valve seats are also a known issue.  Even Chrysler knows because the automotive engine rebuilders association has a bulletin on it.  The seats are just a hair too small, so when the engine over heats the valve seat falls out.  (And sometimes pops back into place which can make diagnostics difficult.)  Hopefully the owner quit driving once it started skipping, if not the seat will come apart and send little bits of metal bouncing around from one cylinder to another ruining the pistons.  

I'd peak down the oil fill and see if there is sludge in the valve train.  The dirty oil will cause the cam journals to gall, heat up and then seize.

Loosing power while going down the road.

Here's to hoping it is just a bad alternator and the battery got drained completely while driving. 

Did this "loosing of power" happen in the dark which would mean driving with the headlights on and possibly draining the battery pretty quickly?

When you go look at the Jeep, check to see if the lights will come on. No lights, dead battery. 

In reply to John Welsh :

I wouldn't be surprised if it was something simple like that.  I didn't ask if it was nighttime when he had to get towed home.  

Backstory:  this is the same guy I got my E60 from 2 years ago.  I did a brake job, rear axle bearings and seals, and replaced the LR wheel speed sensor on this GC about 18 months ago.  At that time it seemed pretty nice, but in need of a good cleaning.  He's not a car guy at all, and is ready for the GC to go away.

I put 190,000 miles on my 04 Grand Cherokee 4.7, before I had severe rocker rust and sold it recently.  I can't recall any significant mechanical repairs. I think I did a drive shaft at some point.  I know I replaced the factory cats with an aftermarket system that mostly worked and only occasionally threw a code.  I can't recall if the cracked exhaust manifolds were on my jeep or on my Explorer.  It was very reliable and I miss it.  Good luck and I hope your issue is something simple.

Since you have worked on this GC, hopefully it gives you a leg up on it.  Good luck, hope it pans out for you.