random misfire, WJ 4.0

tonwantonga · Jul 12, 2010

I rebuilt the 4.0 in my 02 WJ in Jan/Feb after #2 piston exploded. Once back together and back in the Jeep, it ran 'okay', similar to how it ran before the piston took a permanent vacation, the occasional miss or two. About a month later the CEL came on, giving a cylinder #5 misfire. didn't run any different, so I didn't do anything for about a month. Then I got the multiple misfire, #2 and #5, and of course it ran like crap. I thought that meant the coil rail had a bad 2-5 coil, so I replaced the rail. no help. Pulled the #5 plug, it didn't have any soot at all on it, like it hadn't been firing, but of course it only had 1000 or so miles on it. Switched it with #1 plug (which did have a little color), no change. Ran some Seafoam, replaced the #5 injector, and moved the camshaft position sensor a little bit ( I never had it synched after rebuilding) and the engine started running better, the CEL went away. a month later, it was back. same symptoms, same cure. just did it again almost a month ago, this time I went further, checked the crank position sensor, got what I thought was a bad ohm reading, and replaced it with a new one from the dealer. while I was there I got a can of Mopar Combustion Chamber Cleaner, ran it through, back to running oaky, and the CEL went away. However, after that it needed cranked longer to start, and seemed to be a little short on power.

So last week the CEL is on again, same #5 misfire. you can hear the miss. It should become a multiple misfire here in a few days again, just like it has 3 or 4 times before. It shouldn't need a can of Seafoam every month. I have I think eliminated a spark problem, a fuel problem, a sensor problem. That leaves an air problem? is it possible that the IAC is screwed enough to cause this? a leak in the manifold gasket? an O2 sensor?would a code reader from the parts store tell me any more than I already know?

AndyZJ · Jul 13, 2010

What all did you replace in the head when you rebuilt the motor? Bent valves maybe.

tonwantonga · Jul 13, 2010

the head looked fine other than the crushed #2 plug, so I didn't do anything to it.
I am wondering about the IAC because it seems to run fine above idle, at least until it starts the multiple misfire. I never had the computer throw an IAC code during all this, so I doubt if this is the problem, but it does affect the idle. Compression checks out fine in cylinder 5.

AndyZJ · Jul 14, 2010

I would try swapping the coil pack on the misfiring cylinder to another spot and see if the misfire moves. Then you can rule out the coil pack.

tonwantonga · Jul 14, 2010

the coil rail was replaced, and that didn't change anything.

tonwantonga · Jul 15, 2010

well, as of last night I can rule out the fuel filter as a possible cause of a lean misfire. I believe the one I took off is the original filter. 127,000 miles is probably too many. the stuff that dumped out of the filter when I took it off is still on the floor this morning, so it did have something other than gasoline in it. One thing to note, when I took the cap off the fuel rail to bleed the pressure off, nothing came out. zero. it had been 3 or 4 days since it was driven, but there should have been some pressure still in it. that probably explains the occasional longer than normal crank time to start. The miss is now a definite miss, obvious at speeds higher than idle, so if it is getting more noticeable, it should become easier to find the problem, right?

tonwantonga · Jul 16, 2010

so today sure enough, it progressed to multiple misfire, 2 and 5. well, I figured maybe I should start back at square one, test everything again. first thing I checked was vacuum. pulled off the air horn, pulled the PCV hose off the manifold. of course the engine speed picked up, but the odd also happened. The check engine light went off, the codes are gone. now at this point I should have took a bow and said "ta da!" but the engine was still running poorly. hooked up the vacuum tester, it is sitting pretty steady at 14 psi. still messing, I unplugged the IAC. a little change in engine speed, still missing. pulled the coil rail and #5 plug. check compression, about 140 psi. it held 140 for 20 minutes. I put the pulled plug in the coil rail at number 2, grounded it, and cranked the engine, then again at 5. good spark. still had the compression tester in number 5, now it is up to 160. got fuel. So I have fuel, air, spark, compression. new #5 injector, fuel filter, crank position sensor, coil rail is only 4 months old. harness around engine looks ok, no rubbed through areas to indicate wire damage. threw a P0505, bad IAC, when the IAC was unplugged. one website I looked into said a P0305 could be caused by the obvious cylinder 5 items, or bad fuel pump, clogged cat, vacuum leak, and I had one person mention a bent valve. I guess maybe I'll pull an O2 sensor and see if that lets the engine exhale better. I mentioned before that I didn't go and have the engine synced after I rebuilt it, could this be the problem?. I have moved the cam position sensor a bit both directions, far enough to make things really bad, then back to where the marks on the clamp indicated it was before the rebuild. I'm stumped.

tonwantonga · Jul 18, 2010

another day,another appearance of the code. I cleared the codes and used Seafoam twice, after removing the fuel rail and injectors to check it out. the rail is clean inside. drove 70 miles with a 1/4 tank of gas and half a can of Seafoam in it. I could feel it missing some, and at 80 miles the CEL light came on again. misfire in 5. filled up the tank and headed back. 20 more miles and the light started flashing, the engine started chugging like my old CJ used to when the dist. cap got wet. misfire in 2 and 5. pulled over and shut off the engine, then turned it back on. light stopped flashing, the chugging stopped, although it was still missing on one cylinder. 15 miles later, the problem came back, popped it in neutral, and turned the key off and on again, drove ok the rest of the way home.

If I had a bent or sticking valve in cylinder 5, or bad compression, air delivery, or fuel delivery, I could see the misfire in 5 being mechanical. but that wouldn't spread to cylinder 2. I understand that the PCM decides which cylinder misfires by measuring the time lag or whatever, so maybe it is not actually cylinders 5 and 2, but some other wild vibration that is misinterprets. but there is definitely a miss that gets worse, and then can be made to get better or go away. I'm running out of ideas other than maybe the PCM is screwy.

other things I did this time around, checked compression, pulled the IAC and cleaned it, checked the injectors, checked the cam position sensor. if I had an int. short in the wires, why would it always affect number 5 for awhile, then always get worse and toss a number 2 misfire as well? I have to get this figured out, my wife is eyeing an Acadia, and we've got a 1000 mile trip coming up soon, that this Jeep was supposed to go on with us.

AndyZJ · Jul 22, 2010

You've pretty much gone over every conceivable cause to the problem and still not found a solution. All I can say is I'm pulling for you dude. If a car at my dad's car lot gave us this much trouble we would just put it in the salvage yard and part it out. The only idea I can come up with is that with the misfire coming and going and then spreading to number 2, it must be some sensor getting interfered with while running. The crank or cam sensor is a likely candidate. I know its not the same year, but in my 1993 Grand Cherokee I used to have a problem where after decent distance driving my distributor would foul. There was a sensor for number 1 cylinder under the distributor assembly. There was an oil passage that lubricated the gear for the distributor shaft and the seal in it was old and had allowed oil to come up and splash on the sensor for telling the computer when number 1 was TDC. If I'd shut the engine off it would not start right back up, but let it sit for an hour and it would be fine as soon as the oil dripped off it. Not saying its the same problem, but I just wanted to explain that oil can screw with sensor readings. Since you rebuilt the motor are you sure that everything is correct about the crank and cam sensors?

tonwantonga · Jul 26, 2010

bad news for me. Over the weekend, I once again checked compression. 5 great cylinders, about 160 pounds. number 2 cylinder, 60 pounds. don't know why it didn't show up before. just a coincidence this is the cylinder that the piston exploded on back in December, that required the rebuild. new sleeve, new rod, new piston, new rings, so yeah, ugly coincidence. anyway, a shot of oil brought the compression right up, so it sounds like a ring problem. and you know, the vaccum tester read 14 pounds, right there on the gauge it says 'rings' in that range, but I didn't believe it. unless a ring broke, I can't think of a reason why the rings are leaking or aren't seated after 5 months of driving. the computer must be misinterpreting the vibrations and keeps telling me number 5 is a problem when number 2 probably was the culprit all along. possibly, I don't know why it would be in an engine just a few months off rebuild, but if the rings were carboned up, the Seafoam treatments actually did help some, but not for long. having the rings build up with carbon in a week or so after treatment doesn't really make sense. I'm probably going to have to pull the head to look, unless I can find a borescope to take a look in there. would't be much to see unless there was a broken ring that scored the heck out of the cylinder.
so, I put the plugs and the coil pack back on so I could move it out of the garage, and when I started it up, it acted like the TPS is screwed. barely running, no throttle response, random RPM changes while holding the pedal steady, etc. not throwing codes yet. anyway, I have my hands full this week, then hopefully I can find time to check this out some more. I have trouble believing all these things are failing at once, but it could happen.

tonwantonga · Jul 28, 2010

well, it's not the TPS. The IAC is wide open, I took off the air horn to look for disconnected hoses, wires, etc. and started it, I could hear it sucking like crazy. finally got it to throw some codes after feeding it some WD-40 for a bit ( I couldn't reach the carb cleaner), I got P0171 and P0174, lean on bank #1 and Bank #2, which if I read them right are v-8 codes, and this is the 6. no matter, the extra air it is sucking in is telling the O2 sensors it is running lean. the other code was P0320, which bothers me because I just replaced the crank sensor with a dealer part. once the engine warmed up the engine died and wouldn't start again. I guess I shouldn't have taken out the IAC and cleaned it last week. I didn't have time to test the IAC last night, so I don't know if it is good or bad, but I did unplug it with no change. i turned the A/C on a couple times and there was no detectable change in the engine speed. anyway, the IAC good or bad won't fix the low compression in cylinder #2.

tonwantonga · Aug 1, 2010

fuel pump pressure test - barely makes the gauge move. once in awhile the pressure will go all the way up to 10 psi. I guess I'll be spending some time under the Jeep dropping the tank, then under the hood looking at that low cylinder.

AndyZJ · Aug 3, 2010

I don't envy you sir. At what point would you say you'll cut your losses and move on?

tonwantonga · Aug 3, 2010

I'm going to bang my head against this brick wall a little longer. I'll probably cut my losses and move on right after I can't afford to. dropped the tank last night. the pressure gauge that Autozone 'loaned' me, I even hooked it up between the filter/regulator and tank to check it there. same near zero pressure. so the fun began. of course my WJ has a hitch so that complicated things (and the tank being half full is just icing on the cake), but the hardest part was figuring out which hoses to pull loose under the rear quarter panel. got lucky and all the bolts I twisted came loose. I usually break 1/3 to 1/2 of them, seems like. After I get the pump swapped and the tank on, the rocker arm cover, and probably the head, will be coming off. Hopefully it won't be too bad in there.

tonwantonga · Aug 7, 2010

well, maybe it is the TPS. today I've got it reading 4.48 volts closed, 1.245 WOT. It should be like 0.5 closed, 4.5 wide open. of course, I also have 120 pounds pressure showing in the cylinder that was reading 60 a few days ago. yeah, I guess this Jeep, given enough time off will heal itself completely. right. I'm not sure about the new fuel pump I put in, I have pressure at the rail some of the time, but not all of the time. I haven't put a gauge to it, but it appears screwy. I guess I'll have to ride my bicycle, the tractor, or the ATV the 6 miles to AutoZone to get a new TPS, for 35 bucks I'm going to go ahead and replace that sensor. I could wait for the wife to come back with the ZJ, but she could be gone all day. anyway, I'm sure you're all waiting for the end to this story, so I'm headed in.

tonwantonga · Aug 8, 2010

deceleration lag, backfire into intake on accel.

Ok, new TPS. I figured from the readings I was getting from the old one that it was majorly screwed. interesting now,I have lag time on deceleration, and unless you open the throttle really slow, it'll bog down and actually backfire into the intake. is my new TPS messed up? any guesses? still working on a combination of problems, I think. not just one. is it the cam sensor telling the ECM to fire the plugs at the wrong time, an intake valve slow to close, the IAC? another interesting item to mention, when the engine dies, the IAC ticks like a clock for 10 seconds or so after. never heard it do that before. loud enough you can hear it a few steps away from the jeep. The IAC still sucks air like crazy and I am still getting only 10 inches vacuum at the manifold, I checked my gauge on the ZJ manifold and it is pulling 15 on it, so maybe my gauge is off a little, but vacuum is still low. however, after the engine warms a bit the sucking sound goes away almost completely, and the vacuum rises to 14. It looks like this WJ may be getting a rollback ride to a real mechanic, I have run out of ideas. I hate to admit defeat but it looks like Chrysler might have beaten me this time.

shayne_354 · Aug 8, 2010

have you watched a live data stream to see if it might be the injector driver? one problem is enough th deal with, but to have several issues at once really complicates things. try to find someone with a scan tool capable of showing live data. that may help. wish ya luck

tonwantonga · Aug 23, 2010

finally got the Jeep to the Dealer, guess how many parts I had replaced were crap? the new filter/regulator was screwed up, only was getting 10 pounds pressure to the rail. and, that new fuel pump that I spent 160 bucks on and all that stupid work pulling the tank, the check valve on it is crap. Dam AutoZone. 200 dollars worth of worthless parts. so a Mopar regulator, 260 dollar bill at the dealer( I wasn't going to fight the damn thing all the 8 miles back home again so I could replace it again) and I'm back to where I was before all this happened, a rough running rebuilt engine with low compression on cylinder 2. dealer measured it at only 30 pounds. I still have to pull the head.

thejeeper · Aug 24, 2010

Valves

I have been watching your thread and felt compelled to answer your questions for you. It seems like you have replaced everything, even items not related to a "hard" misfire. For a quick background of who I am, I worked in a Chrysler/Jeep dealership for 16+ years and am master certified with both Chrysler and the ASE program. Your problem is the valves. They are not bent or sticking, but the face where they meet the seat is not perfect. When you remove a head, it is always a good idea to remove the valves and use grinding compound to lap them back in for a positive seal. Valves spin as the engine runs, but on the 4.0 they do not start spinning until 2500 RPM's. That explains the 30-60 psi compression on one test and 120 on the next. The valve(s) have some pitting in it that needs to be removed. I like to use a reversible drill with a small section (3 inches or so) of 5/16" hose connected to the valve stem and a driver bit at the drill. Run the valve one way, then reverse it. Do this about five times each way for each valve and you will have a perfect seal.

Also, your O2 codes that you had are NOT V8 specific. Both the V8 and 6 use the same O2 codes.

I hope this helps you in your plight to fix your Jeep. Feel free to PM me for more information.

tonwantonga · Aug 25, 2010

Thanks for the reply, thejeeper. I drove the Jeep 60 miles yesterday, and during that drive, feeling the miss, and then feeling it get worse, then a little better by messing with the gas pedal, I pretty much decided that, with all the other bits and pieces of information I have, the problem pretty much has to be the the valves, particularly one of the valves on cylinder 2, probably the intake, as I was getting some backfire into the intake when it was barely running after replacing the pump. there's no way I can think of that bad rings could cause such a variation in the compression, and when I added oil to the cylinder and re-checked my compression, I put in too much oil, and it screwed up my comp tester. I'm going to start getting the parts together today to have everything on hand for a head pull starting Thursday evening, including a couple of new valves, and we'll see what we find. I looked over the head when I rebuilt the engine, and it looked okay, but then I didn't open the valves and inspect the seats. If I would have had the right tools and more time I would have. I was trying to save some money and time by not touching the head during the engine rebuild, looking back it certainly didn't save any time or any money, and now my wife has an incredible amount of resentment towards her Jeep that hasn't been right since Thanksgiving last year. hopefully, though, this weekend will bring about a change in the Jeep and her attitude towards it.

random misfire, WJ 4.0

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