Eagle Posted May 13, 2012 Share Posted May 13, 2012 This is in the Pub because it's about my wife's 2000 XJ, so there's no cross-over to the Comanche. I'm stumped and I need diagnostic suggestions. My wife is away and I've been driving her XJ because my newer one is overdue for an oil change and my old one needs a front hub. About ten days ago, I stopped at the post office. When I came out and fired up the engine, it sputtered a couple of times, ran VERY rough for a few seconds ... then stalled. When I restarted it, the check engine light was on. It idled much slower than normal for a few seconds, then stalled again. Restarted a second time, NO check engine light, still ran rough, but it kept running. I knew I was long overdue for spark plugs, so I grabbed a set and installed them. It seemed to run smoothly/normally -- for a day or so. Then I began to notice that, when stopped at traffic lights in Drive, every few seconds the engine would give a little skip/burp/stumble. Twice it died, but restarted immediately. Then it seemed to smooth out. Until today. Today it got MUCH worse, and late this afternoon it lit up the check engine light and threw a code. P0306 -- Cylinder #6 misfire. Okay: The code tells me #6 is misfiring, and that's how it felt -- like I was only running on 4 or 5 out of the 6 cylinders. But the code doesn't give me any hint WHY it's misfiring. This is a 2000, so it has coil-on-rail ignition. I can't just pull a plug wire and check for spark. I have a bottle of injector cleaner in the tank, and that has been working for several days. What else can I do to try to zero in on what the cause of this is? I need to get this fixed before my wife gets home. (Fortunately, I have a couple/few weeks, but I would rather get it now rather than wait for the mast minute. Any suggestions? Should I swap a couple of injectors to see if the misfire moves to another cylinder? I know they are rated for less flow, but could I pull an injector from a Renix engine (of which I have multiple) and try that? I never drive hard in the XJs, so the injector would never need to put out full capacity, and I would use it only for diagnosis. If that shows the injector to be the problem, I'd buy the correct replacement. Got any other suggestions? Link to comment Share on other sites More sharing options...
jimoshel Posted May 13, 2012 Share Posted May 13, 2012 Swap injectors. See if the code stays with the injector or the cylinder. Link to comment Share on other sites More sharing options...
Eagle Posted May 13, 2012 Author Share Posted May 13, 2012 Swap injectors. See if the code stays with the injector or the cylinder. That was my first thought, but I figured it wouldn't hurt to ask the resident Jeep techs here if the factory has any diagnostic tree to follow for such symptoms. The XJ has 96,000 miles on it, BTW. Link to comment Share on other sites More sharing options...
Automan2164 Posted May 13, 2012 Share Posted May 13, 2012 Ever think of changing the coil? Rob Link to comment Share on other sites More sharing options...
Eagle Posted May 13, 2012 Author Share Posted May 13, 2012 Ever think of changing the coil? Rob What? 2000 XJ. Coil-on-rail. There are three coils, and each fires two cylinders. If one of them was bad, I should have lost both #5 and #6. Link to comment Share on other sites More sharing options...
Comanche County Posted May 13, 2012 Share Posted May 13, 2012 Continuity on the wire? Link to comment Share on other sites More sharing options...
1987Comanche Posted May 13, 2012 Share Posted May 13, 2012 Heat soak on the injectors. It's a well documented problem on the 00-01XJ's. The Mopar TSB "fix" is to zip tie insulation on the injectors (I think #3 or #4 is most common). I might have the TSB floating around if you want to PM me. Link to comment Share on other sites More sharing options...
ComancheKid45 Posted May 13, 2012 Share Posted May 13, 2012 ^ Beat me to it, i would definently start there ;) Link to comment Share on other sites More sharing options...
Eagle Posted May 13, 2012 Author Share Posted May 13, 2012 I found the TSB on-line. My problem is #6, not #3. I get rough starts with COLD starts -- like after being parked overnight. And it doesn't go away a few seconds or a minute after a rough start. Also, this XJ doesn't have the retro-fit leaf guard on the manifold, so there's less heat to trap. And it isn't that hot here -- today was the hottest day since early April, and it only got up to about 72 degrees. This is a 12-year old vehicle that has gone 96,000 miles, and this problem just showed up within the past ten days or so. I'll think about wrapping some insulation on the injectors, but it doesn't sound like a slam dunk from here. Link to comment Share on other sites More sharing options...
Geonovast Posted May 13, 2012 Share Posted May 13, 2012 Continuity on the wire? Link to comment Share on other sites More sharing options...
terrawombat Posted May 13, 2012 Share Posted May 13, 2012 What wire? I've had a similar, "out of the blue" problem like this with my 2001 XJ - and it conveniently happened when I was trying to get my XJ through inspection. Anyway, I tried changing the spark plugs and saw no difference. I had 300 people telling me it was the common heat soak problem. Okay - so why didn't it do it in year's prior when the temperature was much warmer? It turned out that the bolt holding down the crow's foot on my camshaft position sensor had somehow worked itself loose enough that the sensor spun itself a few degrees before re-lodging itself stuck. It seems that the Jeep PCM is able to compensate for the timing being out a few degrees and it seemed to run somewhat normal, except for those times when it didn't... Anyway, long story short - I found this article about timing your coil-on-plug XJ with a toothpick and haven't had a problem since (2+ years now). http://www.askamechanic.info/askamech2/ ... iew/55/47/ Could be a long shot, but still worth a shot... Link to comment Share on other sites More sharing options...
HOrnbrod Posted May 13, 2012 Share Posted May 13, 2012 Pull the Air Idle Speed motor from the throttle body and clean it all up with sensor-safe carb cleaner. Also clean the connector where it plugs in and check the o-ring. The #6 fault is common as it is the weakest firing cylinder. For sure this will help out even the idle if the motor functional. Link to comment Share on other sites More sharing options...
Eagle Posted May 13, 2012 Author Share Posted May 13, 2012 What wire? I've had a similar, "out of the blue" problem like this with my 2001 XJ - and it conveniently happened when I was trying to get my XJ through inspection. Anyway, I tried changing the spark plugs and saw no difference. I had 300 people telling me it was the common heat soak problem. Okay - so why didn't it do it in year's prior when the temperature was much warmer? It turned out that the bolt holding down the crow's foot on my camshaft position sensor had somehow worked itself loose enough that the sensor spun itself a few degrees before re-lodging itself stuck. It seems that the Jeep PCM is able to compensate for the timing being out a few degrees and it seemed to run somewhat normal, except for those times when it didn't... Anyway, long story short - I found this article about timing your coil-on-plug XJ with a toothpick and haven't had a problem since (2+ years now). http://www.askamechanic.info/askamech2/ ... iew/55/47/ Could be a long shot, but still worth a shot... Looks interesting. Any easy way to line up #1 at TDC/compression without having to remove the coil rail and the #1 spark plug? Link to comment Share on other sites More sharing options...
terrawombat Posted May 13, 2012 Share Posted May 13, 2012 Line up the notch on the crank pulley to the zero tick mark on the timing chain cover. Link to comment Share on other sites More sharing options...
terrawombat Posted May 13, 2012 Share Posted May 13, 2012 Line up the notch on the crank pulley to the zero tick mark on the timing chain cover. Link to comment Share on other sites More sharing options...
Eagle Posted May 13, 2012 Author Share Posted May 13, 2012 Line up the notch on the crank pulley to the zero tick mark on the timing chain cover. That presupposes two things that don't work on the 2000 4.0L: (1) You need to remove a spark plug to feel if #1 is coming up on compression or exhaust; and (2) You have to be able to see the timing marks on the front of the engine. I'm old enough to have grown up with points and condensers and actually setting the timing every time we did a "tune-up." Which, back then, we did every 10,000 miles. I know what the timing marks look like -- and they aren't visible on the 2000 XJ. And I don't feel like fighting the idiot coil rail a second time just to pull ONE spark plug so I can feel for compression while I crank. I was hoping you would tell me that Jeep thought about this and made provision for it. I guess not. Link to comment Share on other sites More sharing options...
dasbulliwagen Posted May 14, 2012 Share Posted May 14, 2012 Someone mentioned the cam position sensor. I have seen similar model years have the internal housing bearing go bad enough to cause the sensor wheel to jump around and cause a bad misfire, but is wasnt usually just on a single cylinder like yours. Take the little black cover off the top and wiggle the shaft around by hand to see how much play it has. You can also run it and watch it move around and cause the misfire at different RPM's if this is your problem. The only fix if this is it, is a new cam sensor/ oil pump drive housing (distributor). Good luck. Link to comment Share on other sites More sharing options...
terrawombat Posted May 14, 2012 Share Posted May 14, 2012 Line up the notch on the crank pulley to the zero tick mark on the timing chain cover. That presupposes two things that don't work on the 2000 4.0L: (1) You need to remove a spark plug to feel if #1 is coming up on compression or exhaust; and (2) You have to be able to see the timing marks on the front of the engine. I'm old enough to have grown up with points and condensers and actually setting the timing every time we did a "tune-up." Which, back then, we did every 10,000 miles. I know what the timing marks look like -- and they aren't visible on the 2000 XJ. And I don't feel like fighting the idiot coil rail a second time just to pull ONE spark plug so I can feel for compression while I crank. I was hoping you would tell me that Jeep thought about this and made provision for it. I guess not. I'd say sorry, but I wasn't the engineer at Chrysler who did the design and layout of the 4.0L. I didn't day that this diagnosis would be effortless. This is a Chrysler-made product, afterall. If you remove the aux. fan, you can shine a flashlight at a certain angle and get a glimpse of the timing mark. With the help of a fold-able mirror, it becomes a trivial task. As for determining if the #1 cylinder is at the top of the compression or exhaust stroke...if your alignment hole in the cam sensor looks to be 180 degrees out, then you're most likely on the incorrect stroke - spin the crank around another turn and you'll be there. Link to comment Share on other sites More sharing options...
Akula69 Posted May 14, 2012 Share Posted May 14, 2012 Had a similar problem with both my wife's and my daughter's WJ. After working with it for a long time it finally ended up that the injector harness had a spot that got too hot and melted the insulation on that cylinder's wire - causing a short that was throwing the code. Fixed short and wrapped that section of the harness with insulating fabric. Link to comment Share on other sites More sharing options...
carnuck Posted June 7, 2012 Share Posted June 7, 2012 Line up the notch on the crank pulley to the zero tick mark on the timing chain cover. That presupposes two things that don't work on the 2000 4.0L: (1) You need to remove a spark plug to feel if #1 is coming up on compression or exhaust; and (2) You have to be able to see the timing marks on the front of the engine. I'm old enough to have grown up with points and condensers and actually setting the timing every time we did a "tune-up." Which, back then, we did every 10,000 miles. I know what the timing marks look like -- and they aren't visible on the 2000 XJ. And I don't feel like fighting the idiot coil rail a second time just to pull ONE spark plug so I can feel for compression while I crank. I was hoping you would tell me that Jeep thought about this and made provision for it. I guess not. I'd say sorry, but I wasn't the engineer at Chrysler who did the design and layout of the 4.0L. I didn't day that this diagnosis would be effortless. This is a Chrysler-made product, afterall. If you remove the aux. fan, you can shine a flashlight at a certain angle and get a glimpse of the timing mark. With the help of a fold-able mirror, it becomes a trivial task. As for determining if the #1 cylinder is at the top of the compression or exhaust stroke...if your alignment hole in the cam sensor looks to be 180 degrees out, then you're most likely on the incorrect stroke - spin the crank around another turn and you'll be there. Chrysler "modified" the layout (I'd use an F word myself) Link to comment Share on other sites More sharing options...
Eagle Posted June 27, 2012 Author Share Posted June 27, 2012 Many thanks to those who offered suggestions, and especially 1987Comanche for digging up the TSB on doing a 'Mexican tuneup" to clean carbonized valve stems. Unfortunately, although we now have the cleanest upper engine in captivity, that wasn't the problem. After that didn't work, my fellow Comanche driver, Erich, dug out a complete fuel rail from a '99 and I swapped out the #3 injector out of that one for the #6 in the wife's XJ. Still no joy. The last gasp was to install a used coil rail I borrowed from the shop foreman at the dealership. BINGO! As they say in Little Italy, "She's a work." So I'm now looking at $125 (plus tax) for a new coil rail. I'm glad to have gotten the problem tracked down, but not very happy that this new-fangled ignition costs so much to repair. The vehicle has less than 100,000 miles on it. I should NOT have to spend $125 on a fairly low-mileage engine that has always been maintained and babied. A conventional coil would be a lot cheaper and a lot less work to change out. Oh, well. Rant over. I really just wanted to let y'all know what the problem was in case you ever encounter it. Link to comment Share on other sites More sharing options...
mountainman Posted June 28, 2012 Share Posted June 28, 2012 if i were you i would party that its only 125 bucks. To get 100k miles out of ANY coil is amazing. There are cars that need thousands... yes THOUSANDS of dollars worth of repairs at 100k miles. If thats all youve had to do to it and its given that many trouble free miles... you should be thankful. Link to comment Share on other sites More sharing options...
mvusse Posted June 28, 2012 Share Posted June 28, 2012 Sparkles is nearing 190K on the factory coil, 147K and 25 years on Wilbur, 90K and 25 years on the Purple People Eater. Come to think of it, I have NEVER had to change out a coil on any of my vehicles. Not even my then 29 years old F100 with 230K when I wrecked it. Coil going bad at 100K would mean bad quality craftsmanship. Link to comment Share on other sites More sharing options...
mountainman Posted June 28, 2012 Share Posted June 28, 2012 lol...SMH Link to comment Share on other sites More sharing options...
Eagle Posted June 28, 2012 Author Share Posted June 28, 2012 if i were you i would party that its only 125 bucks. To get 100k miles out of ANY coil is amazing. I don't think so. My '88 Cherokee is now at 287,000+ miles on the original coil. I fully expect it to reach 300,000. Link to comment Share on other sites More sharing options...
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