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Misfire cylinder 5

XJensen

NAXJA Forum User
Location
Sacramento
I have had a misfire on cylinder 5 and swapped out the coil. That seemed to help a lot but is getting worse again and just threw another code, I still need to scan the new code....

Just wanted to start a thread and get ideas rolling. I need this fixed soon to pass smog...
 
What codes are you seeing ?

What brand/type spark plugs are installed ?

Have tested the injectors and injector wire harness ?
 
Fuel injector may be the problem mine keeps giving misfire on #2 changed that plug and wire keeps coming back .
 
Not home now and will check the latest code this weekend. In the past it has been the random misfire and cylinder 5 misfire.

I figured I will swap in new plugs while I was at it. What brand do you guys recommend?

How can I test the injectors and the injector wires?
 
First things first. Do a compression test. What do the plugs look like?
 
When you get a cylinder misfire, the ecu will always throw a P0300 too.

Now, a single cylinder misfire is easy to diagnose. It's either fuel, spark, or compression. Start with a simole compression test. Next, move around the ignition components. Move the #5 spark plug to the #4 spot. Drive it, see if the misfire moves. (Side note, always always always use OEM spark plugs) Next, swap the coil between cylinders 4 & 5. If it didn't move, swap the injector between 4 & 5. At this point, you should have only moved stuff and not spent superfluous money. When the problem moves to another cylinder, that's the component to change out.
 
Always buy genuine Jeep engine sensors. Regardless, the symptoms described do not suggest a Crankshaft Position Sensor (CPS) problem.


The Jeep 4.0 L runs best on basic Champion spark plugs. The 2000-01 runs well on those too, but runs a bit better on AutoLite APP-985. Confirm that the spark plug boots are not bunched up and that they are fully engaged on the spark plug body.

As suggested already, swap spark plugs first and injectors after a few days to see if the misfire follows either part.

Use your volts/ohms multi-meter to test the injector ohms, and to test the injector wire circuit continuity as you wiggle the wires.
 
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OK this has been a long while but is still an issue. I rolled the dice last I posted and passed SMOG then promptly blew up the front end on the first trip out. Front is finally all fixed up but I am still having trouble with the misfire in cyl #5.

I have completed the follow tests
compression, roughly 165 across all cyl
adjusted the CPS with a toothpick, it was slightly off
Fuel pressure - steady 45lbs
spark - seamed good
injectors - swapped and still an issue with #5
injector wires - pulse seamed normal
intake leaks - used carb cleaner and could not find anything
Cleaned up all grounds
Wrapped injectors with lava mat
Bought a new heat shield for the exhausts manifold - here later this week

I will test it out again this week but once the CPS was adjusted is seemed to run great cold the misfire when hot. I also bought the Torque Pro app but cant seem to connect to the Mode $06 misfire data. Any help there? I believe PID 06A6 data point C & B for the average and cycle counts.

Once warm would leave me to believe O2 sensor but would that cause an issue with only one cyl?
 
What did the plugs look like? Was #5 the same as the others?

Since it was mentioned about swapping the coils, I guess it is a coil on cylinder setup. Is there a possibility somehow the coil drive got swapped sometime in the past. That would cause a similar problem.

From here, I would get a NOID light and see if you can detect any difference between cylinders. The same cylinder swap issue can happen on injectors as well. On a Renix, #5 and #6 leads are almost exactly the same length. Check the color codes with the manual.
 
The plug looked a little discolored but not much different from the others. It still has the coil rail so no risk of switching those around.

I tested with a NOID and the pulse to the injectors all looked the same. If the plugs to 5 and 6 were switched wouldnt they both show a misfire? I dont think they are switched but will look
 
Update, all test have looked good... one this is the SMOG place couldn't run the test the last time I brought the jeep in. They claimed the test machine could not communicate with the jeeps computer.

I took it to a friends house to run it on his scanners and he was having trouble connecting as well. My bluetooth module does not seem to have any issues.... i still believe the misfire must be heat related. I had the exhaust manifold heat shield off when I ran over to my neighbors, injectors still wrapped, and threw a misfire on 3 & 5 when I restarted. This is what I would expect and the only lead I have to follow at this point.

I have a spare computer from my old jeep I might swap in as well. The one in there now is a re-manufactured unit.... I will look for leaks around the precats as well
 
Mystery solved. #6 tube is cracked on the exhaust manifold. Hooked up the shop vac and could feel the air, sure enough about a 1.5" long crack.

It is pointed right at the #5 intake just below the injector.
 
Replaced with a Banks Header, got it quick and it is CA CARB compliant. everything went great and runs awesome, or so I thought. It through a misfire on cyl 6 now and the SMOG shop claims once again that my jeeps computer will not talk to theirs.

I think it is throwing the code and the test machine is aborting the test. I am going to recheck for leaks and try it again at a new shop. The place I had been taking it to routinely leaves the jeep running before inspection, during test and during the visual with no airflow. while the jeep shouldn't misfire anyway this is not helping...
 
Alright, a lot has gone one since my last post and I would like to get it out to hopefully help someone.

I feel like I have jumped down a big rabbit hole. I swapped in my old ECU and it ran like a dream, I couldn't believe how smooth it ran and it has been so long I forgot how much better it could be. I went on a 20 minute drive and then it started running like crap again. I assume it was because it was running on default settings and once the data came in from the sensors the crap data screwed with the timing.

I started getting a misfire in cyl 5&6....

I pulled the Cam Sensor and the sensor looked to be in less than ideal condition and the oil pump drive had some play in it so I replaced it. I also found some small vacuum leaks in the lines feeding from the intake manifold. intake pressure got a little better but still weak at about 15# at idle.

This is where things started to get weird, but finally started getting other codes to help me out. I got misfire codes across more cylinders and a high voltage code on bank 2 downstream O2 sensor. turns out the O2 sensor wires were rubbing the bell housing and grounding out periodically.

I replaced the sensor, I had a spare set from my old jeep. I also got a temp moving pass from the DMV and ran the Rubicon for SierraFest with the Sierra Chapter!

Driving up the hill it was getting hot when pulling hills, 145 range. the dash gauge was crap and was not far from normal but I had my OBD2 hooked up to the Torque app. When I got to the trailhead at Loon it had codes for the bank 1&2 upstream sensors and misfire codes on a couple cylinders. I replaced the bank 2 upstream sensor, forgot the other sensor at home so only got to do one.

Ran the con just fine and running rough, first time up Soup Bowl too!

by the time I finished the trail I had misfire codes only but I had codes for cylinders 3,4,5 & 6.... I figure at this point, given the behavior with the ECU and the new Cam it has to be the crank sensor.

New mopar sensor arrived today so we shall see. Any other idea in case this does not work?
 
Swapped in the crank sensor. ran amazing for a few minutes then started up again. misfires on 3&5 and complaining about the TPS voltage reading. Swapped the TPS and still misfiring. This has got to be some kind of ground issue or something.....
 
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