Carnith Boring

Hello all,

New (to me) Jeep owner and new forum member.

We have a 2000 Jeep Grand Cherokee Laredo 4WD with the 4.0L automatic. I noticed shortly after we got it that there was a ticking in the engine that seemed like some bad lifters.

Not wanting to wait through the winter and hope it didn't get any worse we decided to install new lifters before the weather got bad. Seemed like an easy enough job... can I say I hate the design of the intake/exhaust manifold & bolts/nuts.

We removed all of the stuff that was in the way.

- fan, fan shroud, alternator, power steering pump a/c compressor, air breather & air box, throttle body cables, valve cover, disconnected wiring harness from fuel injectors, thermostat housing, intake manifold O2 sensors, a/c compressor and exhaust O2 sensors.

- Removed the intake manifold and moved the exhaust manifold.
- Removed the head
- Removed and inspected the lifters (5 of 12 were bad)
- Installed new lifters and reversed the process

After getting it all put back together we start it up. The engine immediately revs to approx. 4500 rpm so I shut it off. (the valve on the throttle body was closed and stayed closed)

We checked the vacuum lines and found one of the boots on the line that went to the Leak Detection Pump was worn. We replaced the boot, started it up and the same thing happened, 4500 rpm.

Talked to a guy we know who is a mechanic and he said it sounded like a vacuum leak.

We rechecked the torque on the intake/exhaust manifold and all were good. We are still getting the same results and no one we know seems to have any ideas as to how/why this is happening. So I'm reaching out to seek if anyone else has had/seen this problem to get some direction as to where to go next.

Thanks in advance.

dave1123

welcome to CF!

First of all, lifter noise is a long established trait of the 4.0. They ALL make noise. It's nothing to worry about. I replaced my 0331 head because it cracked (that's another story) and put new lifters in at the same time, even pumping them full of oil before installation. They were quiet for 3 days before they started to rattle again. It has to do with the oil supply ports to the lifters being small and not supplying enough oil at idle to keep them quiet. Except for modifications by Chrysler, this is an AMC designed engine that is known for longevity and good service life. It is, however, heavy and the wrong shape for modern vehicle design. That's why it was replaced by the 3.7 V6.

Yes, it sounds like a massive vacuum leak. Check the plastic elbow on the CCV valve (PCV) on the valve cover. It may have cracked when you took the valve cover off. Also check any other vacuum lines for being disconnected, specifically the MAP sensor, power brake, heater vacuum supply and the canister purge lines. There is a plastic "T" fitting near the firewall that supplies the heater and the cruise control that can be damaged in the head job.

If all that fails, there is a procedure known as a "smoke test". Smoke from a generator is connected to the throttle body and pressurizes the intake system. Then you look to see where it comes out.

As you can see by my signature block, I own the same model with 180K miles on it.

Carnith Boring

dave1123,

Thanks for the quick response. We figured it was a vacuum leak but every where we had checked was good. I'll check the T fitting tomorrow and as you said, if all else fails we'll try the smoke test.

But thanks again for the info and quick response.

Take care and God Bless!

dave1123

Thank you for that. I enjoy passing on my experiences with the younger generation. I'm 70 and have worked on vehicles a long time. My first car was a 37 Dodge I turned into a hot rod.