Misfire on Cylinder 2 & 5 after warm up

[RJC]

Hey everyone!

New guy here but, long time creeper.

I just picked up my first TJ, its a 2001 4.0 auto Sahara w/219,000 miles. It ran great when I bought it and I was able to get about 80 trouble free miles out of it before the fun started.

The Jeep threw 3 codes about a week ago. P0300 (multiple cylinder misfire) P0302 (cylinder #2 misfire) P0305 (cylinder #5 misfire).
If you start the Jeep cold with the codes cleared it starts and runs great, once you start driving you get about 5-7 minutes before it throws the cylinder #5 code and you can feel the studer when that happen. Within just a few minutes of that code, it throws the cylinder #2 code with the flashing CEL light and feels like it is in a limp mode.

I am not an electrical guru of any sorts but, my buddies put a meter on the injector plugs and it looks like I loose the pulsing ground on 2 & 5 once it warms up.

Things that I have replaced

-Spark plugs (Champion coppers gapped to .35)
-Coil pack
-Crank position sensor
-Cam position sensor
-Both upstream C02 sensors


Just some other variants to add to the mix. The guy I bought it off of did do a cut and splice on the fuse box under the hood, everything looks tight and right under there. The oil pressure gauge doesn't seem to work correctly so someone put a manual one inside the cab, it has roughly 55LBS at start up and gets down to roughly 25ish once warm.
The coolant temp gauge holds pretty steady right in between the first dot and 210 once "warm".

 

[macleanflood]

Grab the factory service manual under resources and start ohming and checking continuity on wires.

What brand crank position sensor?

Odds are the oil pressure sensor the PO installed was probably not a recommended brand. I went through a couple auto parts store ones before buying a Mopar.

Not sure but 2 and 5 might share the same coil pack...or does the 2001 still have the distributor? It which case check the cap and rotor.

-Mac

 

[OldBuzzard]

Not sure but 2 and 5 might share the same coil pack...or does the 2001 still have the distributor? It which case check the cap and rotor.

Yes, 2 and 5 share the same coil. Since those two are your misfiring plugs, the coil pack should be your first suspect. You might want to pull it and inspect it carefully, and ohm it out.

 

[OldBuzzard]

The 2001 Factory Service Manual on here is only about 1/3 of the size it should be — pretty useless. So use the 2000 FSM and the 2002 FSM. The ignition systems in those should be about the same.

 

[RJC]

Grab the factory service manual under resources and start ohming and checking continuity on wires.

What brand crank position sensor?

Odds are the oil pressure sensor the PO installed was probably not a recommended brand. I went through a couple auto parts store ones before buying a Mopar.

Not sure but 2 and 5 might share the same coil pack...or does the 2001 still have the distributor? It which case check the cap and rotor.

-Mac

It was a Duralast part.

 

[RJC]

Yes, 2 and 5 share the same coil. Since those two are your misfiring plugs, the coil pack should be your first suspect. You might want to pull it and inspect it carefully, and ohm it out.

Coil pack is new.

 

[macleanflood]

It was a Duralast part.

That might just be your problem.

What brand is the coil pack and what does it ohm out at? (Procedure in the FSM for testing the coil pack.)

-Mac

 

[RJC]

That might just be your problem.

What brand is the coil pack and what does it ohm out at? (Procedure in the FSM for testing the coil pack.)

-Mac

There has been no change since swapping. The coil pack is also Duralast.

 

[macleanflood]

I need @Jerry Bransford back!

-Mac

 

[Wildman]

Have you swapped the spark plugs from #2 & #5 to #1 & #6? See if it moves. Then swap the injectors the same way and see if it follows or the fault stays with the same cylinder.

Oil pressure seems about right with 55lbs cold & 25lbs once warm.

Have you checked compression in each cylinder? Also do a leak down test on each cylinder.

If you install the original coil pack do you have the same issues?

 

[RJC]

Have you swapped the spark plugs from #2 & #5 to #1 & #6? See if it moves. Then swap the injectors the same way and see if it follows or the fault stays with the same cylinder.

Oil pressure seems about right with 55lbs cold & 25lbs once warm.

Have you checked compression in each cylinder? Also do a leak down test on each cylinder.

If you install the original coil pack do you have the same issues?

I have changed the plugs and the issue followed with the new plugs.

That's good to know.

I have not done a leak down or compression test yet.

 

[RJC]

I have changed the plugs and the issue followed with the new plugs.

That's good to know.

I have not done a leak down or compression test yet.

I did swap injector plugs. I swapped 1 & 2 and 4 & 5. the next time it through a code it said cylinder misfire 1 & 3. That made zero sense to me, I never touched #3.

 

[RJC]

Good morning and TGIF!!

Yesterday I ohm tested all of the injector wires and coil pack wires and everything checked out good. While running I was able to confirm that I receiving spark to all 3 coils so it appears to just be a lose of power to the injectors (2 & 5).

I pulled the fuel rail off and I am going to clean and check the injectors for spray pattern.

Anyone have any fresh ideas as to why I am loosing 2 & 5 after the vehicle warms up?

 

[macleanflood]

Did you ohm check the coils? There's a specific procedure in the FSM to check for ohm values across contacts on the coils to determine if they're in spec. You could also swap your coil packs and see if the problem moves.

Next up would be compression and leak down tests.

-Mac

 

[RJC]

Did you ohm check the coils? There's a specific procedure in the FSM to check for ohm values across contacts on the coils to determine if they're in spec. You could also swap your coil packs and see if the problem moves.

Next up would be compression and leak down tests.

-Mac

I did ohm check the coil. This is a one piece coil design.

I'm struggling to understand the value of compression and leak down test for this issue.

 

[macleanflood]

Engine needs spark, fuel, compression and timing to run...right?

You've confirmed spark, fuel and timing...

-Mac

 

[Irun]

Just to rule out someone didn't replace the distributor and set the replacement one tooth off, share a picture the distributor, looking straight to the firewall.

 

[RJC]

I

Just to rule out someone didn't replace the distributor and set the replacement one tooth off, share a picture the distributor, looking straight to the firewall.

It’s a 2001 with coil pack. No distributor.

 

[Irun]

Technically true, so swap the term camshaft position sensor, in place of the traditional distributor, and take a picture of that.

 

[JKP]

Good morning and TGIF!!

Yesterday I ohm tested all of the injector wires and coil pack wires and everything checked out good. While running I was able to confirm that I receiving spark to all 3 coils so it appears to just be a lose of power to the injectors (2 & 5).

I pulled the fuel rail off and I am going to clean and check the injectors for spray pattern.

Anyone have any fresh ideas as to why I am loosing 2 & 5 after the vehicle warms up?

Did you check the resistance of the fuel injectors? Hot and cold.