Just a quick history. I bought this Cherokee about 2 years ago. It's a 2001. Was losing coolant and found out about the 0331 head issue. Oil looked fine, I never could find a crack, but decided to proactively go ahead and do the cyl head swap. Went with Clearwater.

New head went on, new gaskets as well obviously. Also bought a set of 784 injectors, and new O2 sensors. Replaced all cooling system components.

Long story short, got it back on the road about 2 weeks ago. I've driven maybe 75 miles since. Plugs are all brand new, gapped correctly. NGK's.

It seemed a little sluggish, and under load it sounds like a faint exhaust leak can be heard. However, it idles fine, right at 750, no surging. I just figured the sluggishness was because I hadn't driven it in nearly 2 years and have been driving a 15 ecoboosted f150 as my daily driver. I just chalked it up to that. No codes/diagnostics.

It bothered me enough that I decided to do vac test/comp test/and check fuel pressure.

Vacuum test was a little concerning as I was only able to pull about 16 in. That seems low to me. Located in Central IL, so elevation is only 650 feet.

Fuel pressure seemed fine at 48 psi.

Compression test came back fine as well as can be seen below. So, I started thinking vacuum leak/lean mixture. But I'm not getting any codes. None.

Plugs look hot to me. They only have about 75 miles on them, and some idle time. If it's a vac leak, and leaning out the mixture this much, why does it idle fine? Why am I getting no air/fuel errors?

I'm new to the jeep stuff, so looking for some help!

Thanks everyone!

 

Dumb question but.... how old is the fuel ? how long did it sit ? Two years ?

 

No, not a dumb question. Fresh tank as of now. Used Stabil before I tore apart.

 

The plugs look pretty good, compression looks good. The vacuum is a bit low, but 15-20hg is within the normal spec.

 

Could it be a minor vacuum leak? A can of carb or brake cleaner sprayed on the lines, fittings and gaskets might be a simple check.

 

With my '00 vacuum leak problem areas have been the front two lines on the intake manifold. The rubber elbows attached to the plastic lines turn to crap. The very front one is easy. Piece of hose will replace it. The nipple on the intake manifold and the plastic line are the same size. Middle is different sizes. Used this: Dorman Part # 46022 or Part # NOE 6301670 at NAPA. I also replace the little elbow under the MAP sensor. Bought that from Jeep. Part# 53009672.