4.0 Multiple Cylinder Misfire (1,2,3)
 

Hi guys, this is my first post and would like to say thank you. I have learned so much just from browsing this site about Jeeps and cars in general. The Jeep community is awesome and I am glad to be a part of it!

To start off, I have a 2000 XJ with 4.0 and AW4 with 177k. I bought it a little over a year ago with a blown head gasket. I replaced that along with all other gaskets around the head, and inspected head for cracks, which it did not have the common crack between 3&4. I also replaced radiator because it was puking coolant, probably the reason the previous owner blew the head gasket. It was running great for about 5 months with no CEL. It does need about 2-3 cranks to start though unless I prime the ignition because the check valve in fuel pump is bad.

About a month ago it started randomly stalling on me until one day it stalled on my street I live on and I coasted home in neutral and it would not stay running for more than 2 seconds. I replaced Crankshaft Position Sensor and it fixed that.

Although, even before the stalling was happening, so for probably 6 months now it has had a CEL for multiple cylinder misfires. During the summer I would clear the light and it would be up to a week for it to come back, but now it comes back the next day or the day after I clear it. The first cylinder to come back with the light is 1, then a few days later cylinder 3 will pop up, and cylinder 2 would come up as a "pending fault" meaning it was detected once by ECU and it needs to be detected again before coming up as a fault.

To try and fix it I have changed spark plugs (NGK v-power), and used Mopar Combustion Chamber Cleaner incase it was carbon buildup on the exhaust valves. To note: I did swap injectors for Bosch 4 hole injectors a while ago, so it shouldn't be those leaking unless I somehow got bad ones when I ordered.

Some symptoms I am having: it has a pretty rough idle, around 650rpm and it shakes the whole jeep and even more so when I am in gear and at a stoplight. Sometimes it idles even lower than that. Reverse at idle is very slow so I basically have to give it some gas when reversing. I get pretty bad gas mileage for only having 31's, around 9-11. Also, it makes this popping sound at idle which goes away when I give it some gas I assume that it is because the whole motor is shaking and somethings probably hitting something else. I can only hear it with the doors shut, it sounds like its coming from the bellhousing area.

I don't think it's heatsoak because it is pretty cold out right now. I also don't think it is the coilpack because I read when those go bad the cylinders misfire in pairs, so it would be (1,2) and (3,4) misfiring but cylinder 4 never comes up.

I read it could be timing chain slack and it is possible to set the cam sensor back to compensate for slack by toothpick alignment. Do you guys think I should try that, and if alignment is perfect what do you recommend I check out/replace?

Thanks a lot, I know this was very long!

Compression test.

Are you able to log your o2 sensor (pre cat)?

Edit: as mentioned by Turbo, do a compression test as well especially with a previously blown head gasket.

You may want to use a scanner that shows live data so you can see what the Sort Term Fuel Trim are doing - adding or subtracting fuel. Running lean or running rich.

Alright so I did a compression test, they all seem pretty high except cylinder 3:

1- 160psi
2-155psi
3-95psi
4-180psi
5-180psi
6-180psi

Also my spark plugs were white and had a decent amount of carbon on them, I am assuming that's from using the carbon cleaner a few days ago. The plugs were about 3 weeks old, I replaced them with the old ones which were fine, they were only about 5 months old.

Pull the plugs on your injectors and check them. Start the jeep, let it idle. Pull one injector plug at a time and listen to see if the idle changes or starts misfiring.

The terminals on two of my plugs were so corroded that I couldn't even get a resistance reading with my meter. After I did a cap, rotor, wires and properly gapped new plugs it started misfiring. Cleaned the injector plugs and started running like a champ again. I saw you replaced injectors already but check the wiring harness side of the plug.

Thanks for the reply LACK,
i can see the injectors on the scanner my buddy has, we checked fuel trims etc, all look good, i ohmed each injector plug when this all started, i put noid lights on them looked good, i replaced one injector plug just because it looked pretty ratty, none of that has made any difference in resolving this, in fact its getting worse every time i try and run it, im hopinh something craps out all together at least i get a code or something to trace. i do not have a dist cap or rotor, i have a coil pack with a SYNC assembly were the distributor in yours would go, it has a cam sensor built into it which is also all brand new, its popping through the intake which means a timing issue and my can sensor will not sync it just flashs on and off lost sync in sync lost sync in sync, does it even with key off,
i started pulling the harness apart looking for shorts, with no codes even when its popping hard through the intake and studdering like hell not a single code will set and no pending codes,
any ideas?