not a misfire issue... im not great at internal mechanics but ive never heard or read anything about lifters causing a misfire...

 

I'm inclined to agree with you, huntingman. Maybe it's a valve problem though - it is possible that when the head was replaced, the valves were installed wrong, or they're just not seating right.

 

The head was factory reconditioned, so I'm guessing the valves were properly installed and seated.
The mechanic is saying that he thinks there are several lifters that are not collapsing as they should and therefore keeping the corresponding valve slightly open, thereby resulting in apparent misfire. It would not really be a misfire, using his logic, but a leaky valve resulting in what seems to be a misfire.
His theory goes that, when the engine is cold, the lifters have leaked some of the oil and the engine runs fine until it warms up, then the lifters have filled up again and won't allow the valves to close completely.
I'm having a problem understanding this, but the notion that it could be something wrong with the lifters makes sense.

 

Just because a head was factory reconditioned, doesn't mean that it won't fail in some aspect. It isn't likely, but it can happen. I don't quite understand the mechanic's theory, but I'm not a mechanic either. Good luck and let us know what you decide to do with it.

 

It's hard to believe, but a single can of CD-2 oil detergent eliminated the "misfires" in a matter of minutes. The engine bucked and shook so bad, particularly under acceleration, that it seemed like it had to be something requiring mechanical or electrical repair. It's amazing that a little varnish could cause so much trouble.

I am now a believer in some of these additives. I thought it was just a bunch of advertising hype.

We'll probably try a can of Seafoam just to be sure it's all cleaned out before doing a final oil and filter change.

Thanks to everyone who chimed in with thoughts. It's good to be able to bounce ideas around among the serious enthusiasts.

 

Ok, its been almost 24 hours since you used this CD-2..... any follow up results. Just wondering if it is still helping or what.

 

Not sure if problem has been solved but just throwing in my 2 cents, Have u checked the CPS ( Crank position sensor) That will through of your timing of ignition from the spark plugs. also when you replace the wire and spark plugs did u replace the distributor cap. u may have to adjust the cap. also the rotor. I could be wrong though good luck

 

ken72: it's now been nearly 3 days. It is much better than it was, but I overstated the improvement in my previous post. It is driveable now, it wasn't before, but it runs a little rough between 1500 - 2000 rpm and sometimes won't go over about 3k rpm. A second can of CD-2 was put in a little while ago, so we'll see how it does next time it's on the road.

98jeepsrt6: there hasn't been a code set for the crank position sensor, and the mechanic said the problem isn't there. This is a 2001 and it doesn't have distributor or wires. There is a coil pack strip that fits directly over all six plugs. A new coil pack was installed, but it made no difference.

The jeep is still setting codes, but we haven't read them yet. Presume it will still be the misfire codes, but we'll check that tomorrow.

 

ok if your coils are good wires are good plugs are good. Then it has to be a sending problem from a sensor. If you havent checked the sensor yet never hurts to do it. On my 95 eclipse i had this problem only two cyl worked, coils were good but no spark and no power at coils 2&4 Went through everything ended up being a cam position sensor that controls two cylinders and crank sensor controlled the other two.

It seems we've gone the right way of eliminating possible causes. if you have power from coil to plug and u still have a misfire. then its a sensor guaranteed. You just have to figure out what controls those cylinders.. Ill see what i can find. .

Have you done a compression or leak down test yet?? Whats the code that its showing, went back through and didnt see one mentioned.
http://www.jeepsunlimited.com/forums....php?p=4499705
Heres another forum with ur same ? doesnt have the fix but will give you more ideas.

 

98jeepsrt6: Codes are 300, 304, 306 - multiples misfires, misfires cyl 4&6

Compression test was good, all cylinders.

It has improved a little with the CD-2, my son has been driving it everyday and reports the rough running between 1500 - 2000 rpm, low idle speed.

When we get a chance we'll do a vacuum check. My son is a cop working night shift so it's hard for us to get together to work on it. Also planned is Seafoaming, and if we can locate a good code reader that will monitor all sensors real time, we'll spend a while looking at that. We also need to check the camshaft position sensor for correct timing. It was removed in order to prime a new oil pump, so it might be slightly out of position. The CPS on this vehicle controls fuel injection timing.

Thanks to everyone for following our progress.

 

My $$ is on this /\ /\ guessing an incorrect valve job/ seat angle. check the cyl compression cold vs hot ??

 

Captainwoot and firstime00XJ:
I can understand the possibility of the valves not fitting properly, even though we installed a factory reconditioned head. But how do you explain that with two different heads the misfire codes are always on the same 2 cylinders. Seems like too much of a coincidence to me.

 

Any luck finding out what is causing your misfires?

Another thought not mentioned here it could be detenation in those cylinders, i also had that problem with my eclipse, it sounds like a valve tapping or exhaust leak, that caused the death of my eclipse..

 

After a lot of trial and error, a good deal of reading on the www, it seems that the misfire has cleared up almost completely. You may recall that the original violent misfires in cylinders 4 & 6 began about the same time as an overheating event. I really can't recall if the engine began misfiring before noticing the overheating or simultaneously. In any event we first had to replace the head with a rebuilt one because the old head had a crack and had been the cause of the overheating.

After replacing the head the misfires continued. We tried using a code reader but only got misfires codes and nothing else seemed to be malfunctioning. A new set of plugs and new coil pack did nothing to ease the misfiring. Cleaning injectors and moving them around also made no difference - the same two cylinders misfired. A mechanic looked it over and pronounced it to be a problem in the valve train, probably lifters. He was right.

My son put in a can of CD-2 and the engine smoothed out almost immediately. A second can of CD-2, then half a can of SeaFoam and it's running pretty well now. There is some valve tapping noise, particularly during warm-up. The engine pings some on regular gas when going uphill. But, other than those things the only problem left is low oil pressure.

When they replaced the head, they also replaced the oil pump because of persistent low oil pressure. However, they failed to install the gasket between the pump and the block. Oil pressure is slightly better than with the old pump, but not much.

Is it possible that the gasket could make that much difference in pressure? After warm-up, using 10W30 with new filter, the best it gets is about 20psi, dropping to zero on the gauge at idle. If we drop the pan to put the gasket in should we also replace rod bearings?

Thanks for your suggestions.

 

3 Month follow-up. The Jeep continued having problems, sometimes setting misfire codes, sometimes running okay, but usually running a bit rough above 1500 rpm. We finally concluded that there must be something wrong with the lifters as the mechanic had said last summer. Pulled the head again over the holidays and found that 3 lifters showed signs of wear. Two were badly worn, one of them had a hole. Needless to say the camshaft was badly worn on two lobes, cylinders 4 and 6 of course.
Now with a new cam and lifters smooth running has been restored.
Final judgment is that the head cracked, water was seeping into cylinders 4 & 6, washing over the lifters and cam and resulting in the serious wear we found on 2 lobes. The top of piston #4 was completely clean indicating the water leaking from the crack above.
Now, if we could just solve the low oil pressure at idle, we'd be happy. Have replaced the oil pump, filter, and rod bearings, but still have almost no pressure at idle after warm-up.

Thanks to all for your comments and suggestions.