sunny5280

Hi everyone. I am a new member to this forum and new to Grand Cherokees. A couple of months ago a friend of mine purchased a 2000 Grand Cherokee Limited with 150K miles on the clock.

It seemed to run well for a couple of months but has recently developed a slight hesitation at highway speeds. Nothing that I've been able to notice while in the passenger seat. On Wednesday she went to the mountains and observed the hesitation became more pronounced while driving up hills into the mountains. Unfortunately I can't give a better description as I have not witnessed the issue personally. We will be heading back to the mountains tomorrow at which time I'll be driving and will hopefully (odd to say that) be able to replicate the issue. She states the problem only seems to occur at highway speeds and I'm thinking it may become more pronounced as the air thins (i.e. heading into the mountains).

The check engine light is not illuminated nor are there any codes (we had them read at Autozone with a generic OBD-II code reader and also performed the off-on, off-on, off-on key sequence and the computer returned "done" without displaying any codes). Does the Jeep store manufacturer specific codes which cannot be read with a generic OBD-II code reader?

Over the weekend we're going to replace the spark plugs and the PCV value (inexpensive and easy to do and probably needs to be done anyway). Any other suggestions? I was thinking O2 sensors but at $70 each that seems like something I'd like to avoid unless I have reason to believe they need replacing. We don't mind spending some money on repairs. In fact we expected we'd have to put some money into it (got it at a good price) but we don't want to blindly be throwing money at things.

We've already put some work into the vehicle as we didn't know how well it had been maintained previously: Had the water pump replaced (it was leaking), replaced the front and rear transfer case seals, changed all the fluids (brake, transmission, differential, oil, coolant), new CV joints (because we had new parts and figured why not), replaced the shift cable (was kind of jerky going into gear), and a new air filter. Except for the seals and water pump most of the work has been maintenance. None of this work was done in an effort to troubleshoot this issue. Just things we wanted to do (I'm a big believer in regular maintenance).

I've searched the forums and the Internet and I didn't see anything that would help me narrow down the issue. Most posts had some form of code and check engine light illuminated.

Thanks for any assistance you can offer.

GI-Jeepin'

What engine does she have?

sunny5280

Whooops, and here I thought I had included all the relevant information. It's a 4.7L with four speed automatic.

GI-Jeepin'

I am not overly familiar with the 4.7l V8 but as with any engine, a good tune up is the basis for any trouble shooting. Pay particular attention to what type and brand spark plugs she gets. I know that with the 4.0l engines Autolites plugs can and have caused issues with smooth operation. I would also use a can of Seafoam and add that to the tank. Change the oil if you haven't already, just to see what it looks like when it comes out and do not buy a Fram filter.

sunny5280

Thanks for the information. I just returned from picking up some diagnostic tools from Autozone (great tool loan program they've got). I picked up a compression gauge (I figure if we're going to be pulling the plugs to change them may as well take a compression level reading) and a fuel pressure test kit. Picked up the PCV valve and a new fuel filter (which also incorporates the pressure regulator). And of course the appropriate Haynes service manual. Oil had already been changed by my mechanic. All the fluids have been replaced. Hopefully the plugs, PCV value, or fuel filter/regulator will solve the problem.

GI-Jeepin'

let us know how it works out

Gee oh Dee

Wow thats alot of text to read.

Can someone summarize for us? Please?

GI-Jeepin'

In Short, it needs a tune up.

sunny5280

I wanted to follow up with my findings for those who may come across this post in the future. Nothing more annoying than searching and finding a post with no resolution.

With that said I drove the vehicle to the mountains over the Memorial Day weekend. I did not observe any hesitation or poor performance from the engine. Everything seems to be running OK engine wise.

I suspect the problem my friend observed was an issue with the driveline which she mistook for an engine issue. The transfer case seems to have issues (occasional rough shifting between 4H, neuteral, and 4L). I suspect this is the result of the previous owner having driven it with low fluid for a period of time. There's also a high speed vibration which we suspect is due to one (or both) of the drive shafts or the CV joints are worn. Having those looked at tomorrow.

With that said I did put in new spark plugs and a new PCV valve. Not because I had to but because it was time to do so. Unfortunately the compression gauge I had did not function correctly (no more than 30 psi in every cylinder despite the fact the engine is running fine) so I could not take compression readings. I intend to do so in a week or two just for curiosity sake. The plugs we removed looked good with no obvious signs of engine issues. No fouling, deposits, or burns. Engine is probably in great shape.

Hope this helps anyone who may come across this in the future.

pkess3

Thanks for the follow up to this. I myself just bought an 04 WJ with the 4.7L V8 (HO though) and although I'm not having hesitation, we ran across some blue smoke yesterday after taking it on a drive through the mountains. Perhaps it could use a good tune-up as well. I'll be looking at doing what you've done to yours. I've also experienced the driveline vibrations at highways speeds (around 65mph, gets worse the faster you go) and I've noticed leaking out of the rear end of the transfer case. I'll be having these looked at by our local driveline shop this week hopefully.

Anyway just wanted to say thanks for following up with your post. It is frustrating to be searching for something and come across a dead end. I'll be sure to follow up with any of my posts as well.

sunny5280

As an additional follow up we traced the high speed vibration to the front drive shaft. My mechanic removed it and the vibration disappeared. He took the drive shaft to a drive shaft specialist who confirmed it needed to be rebuilt. I believe I had started another thread on this subject and that's why I didn't have a resolution here.

Good luck with your new Jeep!