2003 Jeep Liberty 3.7 miss-fire

After getting codes of misfire on cyl #1, I swapped the coils, injectors with no help. Then, after performing a compression test the #1 cyl has about 30psi all others are normal at 140-150psi. I performed a cyl pressure leakage test no pressure was lost? After removing the cyl heads and found most of the cyl’s with a lot of black carbon, and all cyl head vlv’s with black carbon. Should I have the cyl heads sent to the shop and just clean this carbon off the cyl, or is there another test to verify the pistons are not a problem. Note I have the timing chains locked with tooling to prevent any misaligning when ready to instl.

You cand do a wet compression test if you havent already done that. When you get your cylinder head back on pull your spark plug for that cylinder and pour a little oil in the cylinder. The oil closes any gaps that the piston ring may have. After puttin oil in the cylinder do another compression test and see if that did it. If so…that fixed your problem and you should be fine. If not then you may have worn piston rings and you may need to replace them. Quite alot of extensive work for a do it yourselfer, very impressed.

Are you going to do a valve job on the heads and have them surfaced? What does the cylinder wall on that 30psi cyl look like? I cant help but think you are loosing that much compression through a valve.

The cyl heads will be going to the shop, but I’m still considering is it worth the money! All pistons have a lot of black carbon covering them. Is there a good chemical to clean the pistons? It’s hard to believe that regular gasoline created that black soot on the pistons. I’ve taken eng’s apart before finding pistons clean. I can’t see the #1 piston wall, but all others walls have a cross grain markings. Not sure what to do next, continue on or scrub the project and install an engine.

You really need to get a mechanic to examine the #1 cylinder wall and #1 piston and rings. What if you put it all back together and still had low compression?! Right now is an ideal time to put new piston rings on #1 piston, if need be.

The carbon build-up is from not using a TOP TIER gasoline. You can read about this subject here http://www.toptiergas.com/

When excessive carbon accumulates on the piston tops, this carbon can begin to glow red hot as the engine is operated. When the charge of air/fuel enters a cylinder this glowing carbon can ignite this air/fuel charge at the wrong time, and this causes a misfire. Or, if the backsides of the intake valves accumulate excessive carbon, this carbon can block the proper flow of air/fuel into the cylinders. And if there’s really excessive carbon deposits on the backsides of the valves, this carbon can absorb some of the fuel that’s supposed enter the cylinders. This can then cause a lean condition in the cylinders which can also cause a misfire.

The low compression on #1 cylinder is worrysome though. If it’s not being caused from the #1 intake valve being held open from carbon deposits, then the problem might be from stuck piston rings in #1 cylinder.


There are solvents that you can use to help clean the carbon off. I think WD-40 works also. I assume that the gas mileage you were getting was below the norm for the vehicle. I would suspect the engine coolant temperature sensor may be bad and causing the system to run rich. If this vehicle only has one injector then it may be leaking.

Along with Oldschool, I have to think that something more than rings is causing the very low pressure in #1 cylinder.

I’m taking the heads to a shop for rebuild, and wait for the results. If the heads are not a problem then; installing a short block engine will be an alternative. Thanks for everyone’s advise on this subject matter. I will post the out-come of this project.

There may be a problem with the valves for #1 but the others sound ok. It also doesn’t sound like you need a engine replacement. Maybe just some work on #1 piston. The problem with the engine running rich is due to something besides the engine itself, perhaps a sensor that was mentioned earlier.

The compression results you got may be a little low and if so you may be able to clean the engine an piston rings and get some better numbers. A product called Auto-RX can clean the engine in a safe way and you may get better compression like others have reported. Check out Auto-RX.com.

I recently finished my project; after removing the cyl heads I found the both springs and the valve was bent for that #1. But now after installing the heads, chains, cover, balancer, intake, fuel rail, the car started fine on the first start but it will not stay at idle. After a few mins at idle the car will shut down, it will only stay at idle or above with the foot on the gas pedal.

I found a bad vaccum system hose and that corrected the problem. thxs.

That’s great that you found the cause of the low compression (30 psi) on #1 cylinder; bent valve and springs! Any determination on why they bent? If the cause isn’t fixed, it could happen, again.

It’s too late now; but, test with a vacuum gauge, and a cylinder leak-down test, would have revealed the valves as leaking. FYI.

After investigating the problem, I found the valves were covered with carbon and suspect bad gas over the years. This excess amount of carbon caused the valve to stick causing the spring to break. Since my wife was driving this car home that day, she continued to drive it home with the backfire which caused the bent valve. After repairing the engine the engine is running fine. If any one needs tool number 6958 spanner wrench, used to hold the camshaft with removeing or installing. You can make one; buy two thin metal strips from homedepot, make a sissor with two holes on the end (5/16), put bolt with nuts on each end. This tool is sold for almost $90 on most sites.