rdr8887

I’m trying to fix my son’s jeep. Giving me a tough time. It’s throwing the following codes:

P0351
P0300
P0301
P0306

I know cylinder 1 and 6 share the same pulse. Replaced the coil pack and spark plugs with NGK. No change.

potentially unrelated. He was having heat soak issue. Restart when hot was causing cylinder 3 misfire. Sluggish start then cleared up.

I verified continuity between pin 7 at the PCM and the connector to the coil pack. Wires don’t appear to be issue. Even jiggled around and kept continuity.

fuel pressure around 50psi.

Took coil pack off again and checked for spark. Had spark on 1 and 6. Used test light.

Compression test between 165 and 172 on each cylinder. No coolant in oil and coolant still looks good. Popped off valve cover to replace gasket and didn’t see anything of note.

im stumped. Any ideas? Plan to pull off fuel rail and injectors tomorrow. Watch them spray.

when I cleared codes after putting everting back together, it ran well for a mile or so until I gave it the beans. Didn’t like that. Started misfiring again. Same codes.

bluejeep2001

when you say coil pack, you mean the entire coil rail I hope...They sell a heat soak protection kit for 50 or 60 bucks...easy to install and seems to work well

rdr8887

yes. The rail.

Dave51

1/6 coil driver?

Do you have 4 oxygen sensors or 2?

What kind of OBD reader do you have? You could look at (waveforms, preferably) for O2 sensors, fuel trims, open vs. closed loop discrepancies and do a PCM reset, but since the issue involves 2 different banks I'm thinking you're looking at a PCM.

rdr8887

I have an Innova 5610. It’s kind of fancy. But, not snap on fancy. Live data doesn’t work on the Jeep.

not sure on O2 sensors. I’ll have to check when I get home. I want to say 4, but, that’s a guess at this point.

I also never tested the injectors.

I thought PCM as well. I need to pull mine to get a matching unit. Looks like $200 or less on eBay. I’d love to know for sure, but, I can get one to try it. When I tested for Spark, I was getting it. But, it also drove well for a mile or two before it started missing.

Dave51

You can but it would come with a price, somewhere between $60 to $200.

With a basic oscilloscope you measure stuff. This is from a current clamp on the 3 feeds into the coil rail:



You could probably clean those signals up a bit too, that's from just slapping on the clamp.

Measuring other stuff gets to be a PITA cause of the COP system. You have to yank off the rail and stick in short plug wires to measure signals from the coils to the plugs. Or get a COP probe, another 90 bucks. But you'd get nice clean signals.

But if you could try a new PCM for free I'd totally go that route.

Dave51

Or spike in up here, run 3 channels, compare, whatever:

rdr8887

I actually have access to an oscilloscope. But in this case, seems to make more sense to throw a part at it. All signs seem to point to PCM.

rdr8887

Okay. Definitely should have done some more research. Bought a PCM with exactly the same part number as this one. Installed today. Now it’s starting for about 1 second then dies. Might need to get this one programmed at dealer? My local dealer couldn’t even make me a key. I have my doubts they will be able to flash a PCM. Anyone know rough cost for that service?

Also, not sold it’s PCM anyway. What else could it be?

Dave51

Did you clear the codes and check for new ones? Do you or the new PCM have SKIM? Are you sure the "new" PCM works?

Dave51

IIWM I would monitor fuel pressure, CKS and injectors to see who's doing what when it shuts down. Sounds like it can't get out of Start-Up Mode when

rdr8887

cleared the codes, yes. Prior to starting. Haven’t re-read them yet.

Not sure about “new” PCM. But, i think my sons has SKIM. Had to get a new key programmed and it’s a light gray OEM key. Will check under dash to confirm when I get back to car.

assuming it works. Advertised as functional from reputable seller on eBay.

rdr8887

fuel pressure seems okay. 50PSI. Doesn’t drop much under load. Can repeat test while driving.

thought about injectors, but, the two cylinders I’m having misfires on are on the same ignition circuit. They fire together (1 and 6). Not sure if injectors share the same wire.

lawsoncl

Each injector is a seperate wire, which gets grounded to fire. They have a common power wire.

This would imply that the driver in the PCM is okay. Test light was checking at the input to the coil? Possible you have bad replacement? Can you swap coils and see if the problem moves?

rdr8887

I assumed this meant the driver was okay as well. I don’t have individual coils. One long coil rail that connects to all injectors. I loosened them removed the coil rail and attached a couple spark plug testers from 1 and 6 to spark plug with coil pack laying to the side. Pulled fuel pump relay and got to cranking. Was seeing spark on both cylinders.

it’s possible I have an intermittent issue. But, I assume that would still not point to the driver being the issue. I figure with that, it either works or it doesn’t.