1996 cherokee 4.0 misfire

[adnanski]

I have a 1996 Cherokee 4.0 that started with a CEL and a "misfire in cylinder 1". After replacing all 6 injectors, all plugs for Champion copper plugs, Bosch plug wires, new air filter, new fuel filter, seafoam in the throttle body, as well as the oil and the gas tank, and a fresh oil change, I now have misfire on 1,2 and 6. Any idea about what in the hell it could be? I'm stumped. All the wires are in the correct place, not overlapping, and I've had the CEL cleared at autozone, and the jeep ran and purred for 3 days before the check engine light coming back on. I have bought a crankshaft position sensor that I have not installed yet. I've read about the CPS, the EMC, the cat being plugged, looks like mine has been replaced already. I took it to a machanic because I was sick of throwing money at it. He unplugged injector on cylinder #1, and the misfire didn't seem to change much as it did on let's say cylinder 3 or 4. He then pressure tested the #1 cylinder and said that the exhaust valve is sticking on that cylinder. He then took the air intake tube off and proceeded with slowly pouring water into the throttle body with the warmed, running engine while opening the throttle slightly. He said that the steam will more than likely clean up some of the carbon build up around the valves. I took the jeep home after he cleared the code. Jeep ran better than new for 2 days and then the check engine light came back on. I'm going to go buy the distributor cap for it tmrw and see if that does it, maybe even try to get the CPS on as well as unplugging the battery and trying to reset the EcM..(if that's how you do). I've read up about this misfire for 2 weeks now, and next to my machanic telling me to take the head off and take it to a machine shop and the of course I would just put everything new in the head (lifters, valves, rocker arms, head bolts, gaskets and so on) priced at about $250 for parts on Rockauto.com and about $200 for the machine shop to clean the head up. Rather than taking half the motor apart, which I can do myself but don't have time for, does anyone recommend anything else other than injectors, plugs, plug wires, and air filter that I can look into? Much appreciated, sorry about the long post, just wanted everyone to know what I've done so I don't waste anyone's time. -Adnan

 

[TerryMason]

Welcome to Jeepz.com
I don't have any suggestions for you - hopefully someone smarter than me will be along.

 

[JPNinPA]

A number if things can cause a misfire. Too much air, too much gas, stuck valve, timing. Each of these withanber of causes. Too much air being from the injector gaskets not seating or cracking even missing. Spark plug not seated. Leaky intake. Leaky TB. Stuck iac...

Go back through what you did and be sure plugs are correct pn and gapped properly. Snugged down to correct torque. Check for leaks by spraying WD40 around the TB, base of TB , around each injector and around each cylinder at the head.

Clean the TB and IAC. And verify your timing.


The water is a good way of cleaning carbon build up. You may need to do it again to correct a stuck valve. But the valves and springs are a common issue. Not real common but it happens. Taking the valve cover off to inspect the valve train would come before rebuilding.

 

[greg92jeepxj]

Read your post with interest and it seems to be something a bit common that has happened to your engine . We hear of this often and this malady attracts much attention. While it's true that a misfire will certainly cause carbon build up within the combustion chamber and the intake runner for the affected cylinder(s) , more diagnostics is always recommended. Just as your mechanic has done some diagnostics already and tried an old procurement ( steaming out the combustion chamber ) he was on track to leak down test the cylinder in question. He obviously isolated the miss to one cylinder and concentrated on it. Was the cylinder checked again after the steam trick was performed to verify results ? It is important to compare the affected cylinder to a good cylinder for balance purposes. Before tearing the top end down , concentrate on the ignition system for spark quality . You want to see if your getting the same readings equally in all cylinders. A kilovolt tester is a good substitute for an ociloscope is one is not available . Distributor caps are primary causes for this problem of the quality is lacking and carbon tracking is noted. I wouldn't swap out a perfectly good working crank or cam sensor unless found faulty , the OEM ones usually are best and parts store quality leaves much to be desired and are troublesome when it comes to sensors. You did not post a DTC for either of those sensors ( CPS & CMP ) so I would leave them in place. To remove the cylinder head for reworking is extreme so you want to be sure it's absolutely necessary. Has valve spring pressure been checked ? Although you've not experienced a loss in power due to compression which weak valve springs will contribute to , check this before getting into engine tear down . Not second guessing your mechanic or doubting him , only would like to know what he's found that firmly has him believing that cylinder head reconditioning is needed . It's thorough to do this to eliminate valve train problems but what has his leak down test determined ? What were the differences per cylinder ? If the valves are not rotating normally and causing sticking and carbon build up , I second his recommendation. But first sort out the ignition secondary problem before moving on to the engine. Please post what results your mechanic has found from the leak down test as well as any other diagnostics he's performed. I don't wish to capitalize on his findings but is the health of your 4.0 really at stake to this degree ? A cleaning with the cylinder head removed is the only thorough way to clean carbon so I will respect his decision if he feels it's that big a problem. Since you've stated the engine ran well after the "steam cleaning " , this leads me to believe your back to the original problem and building up carbon again. Would like to know leak down results for affected cylinder versus all cylinders and if possible a kilovolt reading for all plug wires . Are all spark plugs burning clean except cylinder one ? Please let us know what info you've got of his diagnostics to date. Thanks for your post . Greg

 

[eodcoffman]

Have you checked the ignition cool or distributor? In my experience most misfires are caused by dead coils. Just something else for you to check I guess