I know there are a few fellow jeepers here on the board and thought maybe I could get some insight on some issues I am having with my wifes 2001 Cherokee.
It runs really well around town and such, but if I hit a hill or put any kind of load on the engine, it has a pinging sound and cannot maintain speed. Im not sure if its detonation or something else. I have heard this is a common problem with the 4.0 due to either a cracked manifold or gummed up valves.
I have replaced the spark plugs and checked the wires.
I would have changed the plug wires as well, but it has some kind of funky plug in setup.
I have also tried higher octane gas and it made no difference.

Any other suggestions?

Thanks in advance

 

Check the timing but I'm no 4.0L guy.

 

I agree with 2500Ram. Might be a timing issue.

Britt

 

Sounds like a bad camshaft positioning sensor. Are there any codes? Take to Autozone or one of these places that will read codes for free and see what you get.

Tye

 

Do you have the long coil pack that covers all the plugs? It is considered a 'wear item' since it contains the 'plug wires', however short they are. It's a bit pricey, but a friend with a GC said it fixed their pinging problem. I have yet to do it to my GC, but it's on the list.

 

Yeah, it has the weird coil/plug pack. I will have to look in to replacing it.

Because it is computer controlled, could the timing really be off that much?

 

Be sure your intake manifold is not pulling air ion, where it attaches to the head. BIG MIKE

 

There's a cam sensor where the distributor used to be on older models. You can loosen the clamp and turn the sensor clockwise just a hair to retard base timing. I actually jsut advanced my GC a couple weeks ago and picked up some pep and highway MPG. If it runs, it's unlikely the cam sensor is faulty. Try retarding it (just a wee bit) and see what happens. It's free to try, just mark the original so you can go back.

g

 

You might also check and see if there is a knock sensor present. If there is, it may not be doing the job it was built for, which is to sense spark knock, or ping ( detonation ) and advise to retard timing accordingly.

 

There are a couple things that it could be. Most common is piston slap, nothing wrong, just the sound they make. You have to be used to Jeep 4.0s to know if its piston slap or actual pinging. There is also a common problem with the exhaust manifold cracking where the 2 large tubes come together into 1 pipe. No recall on it unfortunately. When the cracks are real bad, you can definately hear that its an exhaust problem, but when they are just starting it can sound kind of like a ping.

Timing isn't adjustable on these engines. You can move the sensor a tiny hair, but not enough to really do anything. There is a TSB for certain years, and I think '01 is one of them, that tells about a problem with the valve springs. The actual symptom is a misfire or skip, but a minor skip can feel and sound like pinging.

Jim

 

I had heard about the tsb and it I think this is probably the problem.

Any ideas about how to repair this?

Any other ideas?

 

There is an updated valve spring with more tension. You will need to replace them all. I can't remember if they do anything about cleaning the valves...i think they just run cleaner theough the fuel system. The problem, according to the TSB (if i remember it right), is that the valve springs are a little too soft. When deposits build up on the valve seats, the valves stick open slightly.

Changing the valve springs is easy on that engine. Use any common method to hold the valves in place (air line adapter into the spark plug hole, long string stuffed through the plug hole, etc.), remove the valve cover, and remove the 1/2" (on the older ones...probably the same for your year) bolts holding the rocker towers on. Compress the valve spring, remove the retainers, and let up on the valve spring. Put the new spring in place, compress it, put the retainers in, let up...and move onto the next valve. If you take time to have a few beers it would probably take a couple hours to do the whole job. Put someone experienced, with the proper tools, on it and it should be done in well under an hour.

Jim