P0340 & P0344

[sgesbeck]

A few days ago the CEL came back on with P0303. It seems to be driving fine though. I ordered the ThinkDiag2 scanner and it arrived tonight. The cam crank difference is 6650.60 deg and the cam crank learned is 2.60 deg. Cam Synch at Start is "Out of Synch". I'll adjust the OPDA tomorrow morning to try and get it closer to zero and then do a relearn. If the codes return the next step would be to replace the ignition coil. It's possible it got damaged when I replaced the spark plugs last November.

 

[Duner]

A few days ago the CEL came back on with P0303. It seems to be driving fine though. I ordered the ThinkDiag2 scanner and it arrived tonight. The cam crank difference is 6650.60 deg and the cam crank learned is 2.60 deg. Cam Synch at Start is "Out of Synch". I'll adjust the OPDA tomorrow morning to try and get it closer to zero and then do a relearn. If the codes return the next step would be to replace the ignition coil. It's possible it got damaged when I replaced the spark plugs last November.


View attachment 605015

When you go to adjust it loosen the plate enough so you can rotate it while the engine is running. I believe 6553.50 is -0.1 degrees. My cam sync at start is also out of sync, not sure how to get it in sync.

 

[sgesbeck]

The saga continues. I adjusted the cam crank difference between 0.20 and 0.40 and then I did a relearn with the ThinkDiag2 scanner. The next day, Monday 3/31/2025, I filled up the tank and as soon as I left the gas station the CEL came back on. When I got to the canyon where I planned to hike I checked the code and it was P0303 Cylinder 3 Misfire detected. After the hike I used the scanner and there were several misfires on Cylinder 3. On Tuesday, 4/1/2025, I installed a new Standard Bluestreak Ignition Coil. Before I reconnected the battery, I did the manual relearn by touching the positive cable to the negative post for 30 seconds. I let it idle in the driveway for 15 minutes and hooked up the scanner again. No codes and no misfires but the Misfire Monitor was still in waiting mode. I guess it needs some drive time. We were meeting my son and granddaughter for dinner so I didn't have time for a test drive. This morning I drove to the canyon for a hike and no CEL's. When I got home I hooked up the scanner and there were 35 Cylinder 3 misfires and it was continuing to climb while idling in the driveway.

I'll review all my written notes and think about it overnight and try to come up with a plan tomorrow. I'll continue to post updates until I have it resolved.

 

[Duner]

The saga continues. I adjusted the cam crank difference between 0.20 and 0.40 and then I did a relearn with the ThinkDiag2 scanner. The next day, Monday 3/31/2025, I filled up the tank and as soon as I left the gas station the CEL came back on. When I got to the canyon where I planned to hike I checked the code and it was P0303 Cylinder 3 Misfire detected. After the hike I used the scanner and there were several misfires on Cylinder 3. On Tuesday, 4/1/2025, I installed a new Standard Bluestreak Ignition Coil. Before I reconnected the battery, I did the manual relearn by touching the positive cable to the negative post for 30 seconds. I let it idle in the driveway for 15 minutes and hooked up the scanner again. No codes and no misfires but the Misfire Monitor was still in waiting mode. I guess it needs some drive time. We were meeting my son and granddaughter for dinner so I didn't have time for a test drive. This morning I drove to the canyon for a hike and no CEL's. When I got home I hooked up the scanner and there were 35 Cylinder 3 misfires and it was continuing to climb while idling in the driveway.

I'll review all my written notes and think about it overnight and try to come up with a plan tomorrow. I'll continue to post updates until I have it resolved.

Did you figure out the cam sync at start? Also, if you have a leak down tester that can be a quick way to see if your valves on that cylinder are leaking.

 

[sgesbeck]

Did you figure out the cam sync at start? Also, if you have a leak down tester that can be a quick way to see if your valves on that cylinder are leaking.

Still have the "Cam Synch At Start - Out of Synch". I can't find any information on what that is or how to get it in synch. No leak down tester.

 

[JKP]

The saga continues. I adjusted the cam crank difference between 0.20 and 0.40 and then I did a relearn with the ThinkDiag2 scanner. The next day, Monday 3/31/2025, I filled up the tank and as soon as I left the gas station the CEL came back on. When I got to the canyon where I planned to hike I checked the code and it was P0303 Cylinder 3 Misfire detected. After the hike I used the scanner and there were several misfires on Cylinder 3. On Tuesday, 4/1/2025, I installed a new Standard Bluestreak Ignition Coil. Before I reconnected the battery, I did the manual relearn by touching the positive cable to the negative post for 30 seconds. I let it idle in the driveway for 15 minutes and hooked up the scanner again. No codes and no misfires but the Misfire Monitor was still in waiting mode. I guess it needs some drive time. We were meeting my son and granddaughter for dinner so I didn't have time for a test drive. This morning I drove to the canyon for a hike and no CEL's. When I got home I hooked up the scanner and there were 35 Cylinder 3 misfires and it was continuing to climb while idling in the driveway.

I'll review all my written notes and think about it overnight and try to come up with a plan tomorrow. I'll continue to post updates until I have it resolved.

Can't remember everything you have done, but for a single cyl misfire:

Swap the spark plug. Does misfire follow?

No, then swap the injector. Does misfire follow?

No. Check the compression, leak down.

And if you don't "exercise" the tach often, put some full strength fuel system cleaner in it and do some high RPM pulls to blow the carbon out.

 

[Duner]

Still have the "Cam Synch At Start - Out of Synch". I can't find any information on what that is or how to get it in synch. No leak down tester.

@sab linked me the power train pdf from the sticky thread which had the step by step diagnosis procedure for misfires. It might be worth following that to help with this. Misfires can be a multitude of things, being electrical or mechanical. My misfire (knock on wood) randomly stopped. It was still occurring after I changed the spark plug and the coil pack, then it randomly went away.

 

[Duner]

Can't remember everything you have done, but for a single cyl misfire:

Swap the spark plug. Does misfire follow?

No, then swap the injector. Does misfire follow?

No. Check the compression, leak down.

And if you don't "exercise" the tach often, put some full strength fuel system cleaner in it and do some high RPM pulls to blow the carbon out.

An in-line fuel pressure gauge is a good way to see if a fuel injector is leaking without pulling the rail. But that wouldn’t tell you if one is gunked up or not. I agree with your process tho, simplest way to do it with minimal diagnostic tools.

 

[JKP]

Yeah, it's a pain to test the fuel pressure on the ones after they removed the schrader valve on the rail.

My 06 would develop a cyl 1 misfire when I was driving it 5 mi to work daily and sitting in line to get on base for 10 to 20 min.

A can of techron fuel system cleaner and running it up through the gears would cure it every time.

 

[Duner]

Yeah, it's a pain to test the fuel pressure on the ones after they removed the schrader valve on the rail.

My 06 would develop a cyl 1 misfire when I was driving it 5 mi to work daily and sitting in line to get on base for 10 to 20 min.

A can of techron fuel system cleaner and running it up through the gears would cure it every time.

Why they removed that valve is beyond me. I’ll add a picture of what I made when I get home.

 

[TerryD]

Why they removed that valve is beyond me. I’ll add a picture of what I made when I get home.

Can you swap on an older rail with the port? I've got to pull my rail this weekend

 

[JKP]

I'm pretty sure you can. And you'll also get rid of the damper that can leak.

 

[Duner]

Can you swap on an older rail with the port? I've got to pull my rail this weekend

I'm pretty sure you can. And you'll also get rid of the damper that can leak.

This almost seems like a preventative maintenance upgrade everyone should do. Along with drilling access holes to the rear bumper body mount bolt nuts.

 

[JKP]

If I remember correctly, they came with just the schrader port, the schrader port and the damper, and finally no schrader and the damper.

 

[macleanflood]

There's lots of pretty anodized aluminum ones on Amazon and eBay too. My 97 has the Shrader valve...I added a Racetronix QD adapter so I could hang a fuel pressure gauge near the rail.

The problem I see with all the aftermarket ones is they only have provisions for one test port. I want both a Shrader valve and a gauge. Need the valve to bleed off pressure and double check the accuracy of the installed gauge.

-Mac

 

[TerryD]

Sweet. Looks like I need to make a trip to the salvage yard Friday

 

[sgesbeck]

Today I swapped #3 Fuel Injector with #2 to see if the misfire would follow the injector. This is where it gets interesting. After reinstalling the fuel rail I was getting misfires on Cylinder #3 (the original issue), Cylinder #5, and Cylinder #6. I could hear a hissing sound like a vacuum leak too. I took it for a test drive while I monitored the misfires and the misfires would stop when the rpms were above about 1,000. I removed the fuel rail again and realized the lower injector O-rings weren't seated correctly on #5 and #6 but #3 looked fine. I reseated the O-rings, reinstalled the fuel rail and I was back to just #3 misfires. When I switched #2 & #3 injectors the lower O-rings stayed with the cylinder so this got me thinking maybe it is just the O-ring. I took the fuel rail off again and removed and inspected the #3 lower O-Ring. It appeared to be fine and I couldn't see obvious deformation. I had a set of spare upper O-rings which are just a little bigger, so I tried that and the misfires got much more frequent. I took it for a test drive, and again the misfires only happen at lower rpms. The Jeep seems to drive fine.

I ordered a set of injector seals (2 O-rings) for one injector from Extreme Terrain. They'll arrive next week but I'll be out of town all next week so it will be a while before I post another update.

If anyone has any other ideas on what to try, please share.

 

[Duner]

Today I swapped #3 Fuel Injector with #2 to see if the misfire would follow the injector. This is where it gets interesting. After reinstalling the fuel rail I was getting misfires on Cylinder #3 (the original issue), Cylinder #5, and Cylinder #6. I could hear a hissing sound like a vacuum leak too. I took it for a test drive while I monitored the misfires and the misfires would stop when the rpms were above about 1,000. I removed the fuel rail again and realized the lower injector O-rings weren't seated correctly on #5 and #6 but #3 looked fine. I reseated the O-rings, reinstalled the fuel rail and I was back to just #3 misfires. When I switched #2 & #3 injectors the lower O-rings stayed with the cylinder so this got me thinking maybe it is just the O-ring. I took the fuel rail off again and removed and inspected the #3 lower O-Ring. It appeared to be fine and I couldn't see obvious deformation. I had a set of spare upper O-rings which are just a little bigger, so I tried that and the misfires got much more frequent. I took it for a test drive, and again the misfires only happen at lower rpms. The Jeep seems to drive fine.

I ordered a set of injector seals (2 O-rings) for one injector from Extreme Terrain. They'll arrive next week but I'll be out of town all next week so it will be a while before I post another update.

If anyone has any other ideas on what to try, please share.

Isn’t at idle is when the engine is at higher vacuum? My misfires were also occurring at low rpms.

 

[JKP]

If the O rings are old, replace all of them.

 

[Duner]

If the O rings are old, replace all of them.

Also lubricate them before insertion