CEL was throwing miss on cylinder #5 and the Jeep would stutter/skip/miss at 4,000 rpm. I changed plugs, wires, rotor and cap. CEL still throws cylinder #5 miss and p1391 (CMP). Any thoughts?

1998 XJ, 4.0L

 

More specifically, would a bad CPS cause the engine to miss at a certain rpm (4k in this case)? And, could it be related to a miss in cylinder #5?

 

Anybody?

 

Yeah any one, as my XJ has a miss at 4000rpm. I have a new CPS but not really looking forward in replacing it than finding out it had nothing to do with it. But my XJ is not throwing codes.

 

Is it doing this while in motion, or revving in park/neutral?

 

Under load whilst driving. Starts really well, idles perfect, and tends to lessen when it warms up. Last week when I went to pick up my new rims, it got really really bad and felt like I lost more than 50% of power, at one stage I could not even rev past 2500rpm and when I put my foot to the floor, it just did not go anywhere past 2500 revs, even back fired a few times.

I thought seeing I live in the country it could have been bad fuel, I got fuel at 1/2 full tank, and filled it with the best fuel I can get being 98ron, and my Jeep seem to drive better, power was back again. But I still have this stutter/miss in second gear when it hits 4000rpm's, but no backfiring of any kind.

Prior to this about 2 weeks ago I had a parasitic draw that was draining my battery flat in less than 2 days, but I found the problem, it was the service light under the hood, so I pulled the fuse and left it out, and that fixed the drain, a few days after that the miss started.

My plugs and leads are about a year old, same for the air and fuel filter, and I also replaced the IAC at that stage. I have ordered new plugs, new fuel filter, new map sensor switch and TPS and a new coil is all coming in the mail this week. I already have the crank sensor switch, and will have a go at changing that out the next day or so (not looking forward to it with a bad back) to see if that fixes the problem.

Any input or help or feedback would be greatly appreciated, and seeing I have ordered a fair amount of replacement parts I will do one by one and test it to find out what the cause of this miss is, so to give feedback via here to help others that have a similar problem in the future.

 

OK, I changed out the crank sensor switch, and it was not that hard to change. But guess what? My XJ now stutters around 2000rpm, stutters around 3000rpm, and still stutters just past 4000rpm. But where it has gotten really worse whilst driving in Drive, it feels like it is kicking back a gear while I am doing about 80 k's/50 miles. It still starts up the same, idle is the same.

As much as I have other parts coming this week and the next few weeks as well, its really got me stuffed, I was open to the fact replacing the crank sensor switch might not fix it, but why did the whole stuttering thing get worse is beyond me!

Help guys! Anyone?

 

I readjusted the throttle valve/trans kickdown cable just to insure that was fine, and it made no difference. I went for a drive and it is now as bad as it was last week, it stutters really bad, and bucks for a split second, and jolts the whole car, it is now even affecting the idle as that is not so smooth anymore. I also did the keydance, and no error codes.

 

It has gone downhill even more, it now burps, stutters in park, not under load, and even stalls now if you don't ride the throttle when reversing or driving at lower revs. It is night time now and cold, but will in the morning change over the crank sensor switch but to the old one that came of my XJ, just to see what that does. Could it be a dying fuel pump? Could it be a coil that is going downhill fast? As it sounds to me like an ignition miss, or fuel problem of some sort.

 

Posted my problem on http://www.ausjeepoffroad.com/ (aussie site) and 2 members think it is the oxygen sensors, any one think the same?

 

Test your fuel pressure.

 

First thing I did this morning was to put back the crank position sensor that came off it. And presto, it runs normal and idles perfect sitting in park, revs clean and no sign of anything wrong, now that was what it was like before I change out the CPS, I still had that miss at 3000 and 4000, but at least now the car is driveable.

I took it for a spin with the front O2 sensor disconnected, it still had a slight miss at 3000 and an oh so slight miss at 4000, but it does not buck like it did the day before, so what other words the new CPS is a dud and gladly leave the old one in it. I will have to let the car cool right down to drive it again to see what it does with the front O2 sensor being disconnected, to really give my spin on it if it is the culprit or not. The exhaust tip is also extremely black, indication it is running very rich, and it seems to be going through juice more as well.

The cat has no rumble or makes any sort of noise indicating it is coming apart. I just received a new fuel filter (old one is 12 months old) a new coil is coming this week from Melbourne as it could still be why it has that miss, new plugs (old ones are 12 months old) are on their way, a MAP sensor switch is on its way as well, and a new TPS sensor has been ordered as well. I am about to order a new upstream/pre-cat O2 sensor as my XJ has got over 320,000 k's on it and unless they were changed at one stage they will be truly stuffed or on their way out.

So at this stage, the original problem of that miss is still there, although seems a fair bit less with the upstream O2 sensor disconnected, I am letting the car cool right down, and than reconnect the O2 sensor to see how it acts, than disconnect it again to see if there is a difference. I only have a new fuel filter to put in at this stage, but will start replacing one part at the time as they come in to insure that if it is not the O2 sensor to at least solve this problem and pin point what the problem part was.

My money is still on the O2 sensor as the best milage I get out of a tank of fuel is at very very best 350 k's, and lately (last few weeks) I was under the impression it was using more fuel again.

Thanks so far for all the advice and input, and keep the suggestions coming, and I will update after I drive it late this afternoon after cool down and re-connect the O2 sensor. Stay tuned.

 

I forgot to mention, no check engine light came on or error codes via key dance whilst driving with the upstream O2 sensor being disconnected, really thought the ECU would at least warm me some how that it was disconnected.

 

It should, at least on a US-spec engine.
The key trick never worked on my '96. Does the CEL light up when you first start the engine?

Keep an eye on the cat, '96 has a lifetime recall due to early failure. Mine broke apart internally and partially clogged the exhaust.

 

Yeah the CEL comes on at start up, and even tested it the other day by pulling a vacuum hose off, it came up with the CEL light straight up. My key dance has always worked, but last year I bought one of them hand held scanners, connected it to the ECU under the dash, and it just sat there telling me ''connecting to ECU'' and never worked that way, hence I do the key dance as it seems to work. The cat has no rattles or any weird sounds are coming from it, but I am sort of tempted to take a hammer and long piece of steel to it, as the 02 sensor that is on the cat is there to only tell the ECU if the cat works or not, I am sure I read that a 1996 XJ O2 cat sensor just senus if the cat works or not, and has no impact on how the engine runs.