CEL, Error Codes, And Ignition Issues

xhogboss

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Black Hills, South Dakota
2003 Wrangler Sport, 4.0/auto, 3.73 gearing, 22,000 original miles, clean CarFax. known owner and use/service history, off-the-showroom floor stock/no mods

Recently purchased. Hard starting but ran well otherwise. 80 mile drive on Forest Service/County gravel roads and notice I had a CEL. Plugged in my scanner and found logged P0301 fault - Cylinder 1 misfire - still running OK. Some internet research and decided to pull spark plug on #1 cylinder. Tan, normal-appearing plug, no evidence of arcing or spark tracing. A little more research and decided to replace plugs with Champion Dual-Platinum 7034 plugs. Gapped to .035", anti-seize on the threads (none on plug tip) and torqued to spec. Reinstalled coil pack and started engine - started easily but ran really poorly! Stumbling, missing, rough. Pulled codes again; P0300, P0301, P0303, P0304. Cleared codes, pulled and checked plugs, reinstalled and torqued plugs - ran poorly again on start-up. Same codes reappeared. Checked coil pack - front and rear packs were cool to the touch - center pack was HOT!

More research and found a YouTube check for coil pack - basically seeing if there is spark from all plug contacts/springs. to a grounded steel rod. Good spark from 1, 2, 5 and 6. No spark from center pack serving cylinders 3 and 4. Checked continuity between contacts/springs 1/6, 3/5,and 2/5. All read very close to 15.5/15.6. No continuity between any other combination of the contacts/springs > leads me to think secondary circuits are good/not open, and no shorts between coil packs. Don't have/can't find what the resistance readings should be between the four connector contacts at the rear of the coil pack.

I'm thinking the coil pack is bad at this point. I'm suspicious of the timing; CEL > P0301 code > new plugs > more and new error codes > lack of spark. The 'no spark' on #3 and #4 seems to be a good reason for the P0303 and P0304 codes. I know the 4.0 can be sensitive to odd spark plugs, but the 7034 plugs seemed to be on the "OK to use list". Doesn't seem like the wrong plugs would kill the coil pack.

What am I missing?
 
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2003 Wrangler Sport, 4.0/auto, 3.73 gearing, 22,000 original miles, clean CarFax. known owner and use/service history, off-the-showroom floor stock/no mods

Recently purchased. Hard starting but ran well otherwise. 80 mile drive on Forest Service/County gravel roads and notice I had a CEL. Plugged in my scanner and found logged P0301 fault - Cylinder 1 misfire - still running OK. Some internet research and decided to pull spark plug on #1 cylinder. Tan, normal-appearing plug, no evidence of arcing or spark tracing. A little more research and decided to replace plugs with Champion Dual-Platinum 7034 plugs. Gapped to .035", anti-seize on the threads (none on plug tip) and torqued to spec. Reinstalled coil pack and started engine - started easily but ran really poorly! Stumbling, missing, rough. Pulled codes again; P0300, P0301, P0303, P0304. Cleared codes, pulled and checked plugs, reinstalled and torqued plugs - ran poorly again on start-up. Same codes reappeared. Checked coil pack - front and rear packs were cool to the touch - center pack was HOT!

More research and found a YouTube check for coil pack - basically seeing if there is spark from all plug contacts/springs. to a grounded steel rod. Good spark from 1, 2, 5 and 6. No spark from center pack serving cylinders 3 and 4. Checked continuity between contacts/springs 1/6, 3/5,and 2/5. All read very close to 15.5/15.6. No continuity between any other combination of the contacts/springs > leads me to think secondary circuits are good/not open, and no shorts between coil packs. Don't have/can't find what the resistance readings should be between the four connector contacts at the rear of the coil pack.

I'm thinking the coil pack is bad at this point. I'm suspicious of the timing; CEL > P0301 code > new plugs > more and new error codes > lack of spark. The 'no spark' on #3 and #4 seems to be a good reason for the P0303 and P0304 codes. I know the 4.0 can be sensitive to odd spark plugs, but the 7034 plugs seemed to be on the "OK to use list". Doesn't seem like the wrong plugs would kill the coil pack.

What am I missing?

More research and head-scratching. It appears that one of the four contacts in the connector at the rear of the coil pack gets 12 volts. A crankshaft position sensor sends an intermittent ground signal to the coil packs from the PCM, to complete the circuit and that coil pack fires the matching cylinders; 1 on compression/6 on exhaust and so on; waste spark system. If the 3-4 coil pack primary circuit isn't getting a ground signal, it can't release the energy/fire the secondary circuit.

The four wires should terminate in one of the three large connectors on the PCM. Which terminals/contacts would I check to see if the wires from the coil pack connector have continuity?
 
Go to the Resources section and you can pull up the FSM for your year which will have the wiring diagrms, theory of operation, etc.
 
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Disconnected the PCM to isolate the wiring.

Identified and rang out the coil pack connector wires; Blk/Gry is coil 1 driver, Dk Blu/Tan is coil 2 driver and Red/Yel is the coil 3 driver. None of the four wires is shorted to each other or to ground. Each coil driver wire has continuity to one pin in the PCM connector; coil driver 1 to pin 7 of PCM connector 1 (closest to engine); coil driver 2 to pin 9 of PCM connector 2 (middle of the 3); coil 3 driver to pin 1 of connector 1. DkGrn/Lt Grn wire shows common to lots of places; pins 4, 5, 6, 10, 11, 14, 15 of PCM connector 2, pins 8, 9, 13, 16 of PCM connector 3, and to fuse 28 in the Power Distribution Center.

Checking the PCM connectors - connector 1 is common to ground on pins 2, 6, 13, 22, and 23; connector 2 is common to ground on pin 23; connector 3 is common to ground on pins 1, 3, 4, 5, 11, 19, 24. None of the grounded pins are common to any of the pins having anything to do with the coil pack connector.

The wire bundle running side to side to the rear of valve cover is strapped tight into a hard-formed plastic wire loom. Can't move and chafe insulation. Close inspection of wire looms/bundles doesn't reveal any evidence of rubbing or chafing. Every wire bundle has factory clips/connectors and doesn't appear to be dislodged or out of place. I'm thinking this is not a wiring problem.

I cleaned and gapped the original NGK plugs and took the Champions out. I have a new coil pack that I will put in and I'll see how it runs. If there's still a problem then it's probably time for someone with a super-wazoo OBD scanner. I don't want to just throw parts at it, and I'm really hoping it's not the PCM.
 
Installed a new Blue Streak UF296 coil pack, pulled the Champion plugs, cleaned/gapped/reinstalled the original NGK plugs. Charged the battery and re-connected everything. Started the motor and noticed rough running. Checked OBD and discovered code P0353. Shut everything down and started checking... Coil packs 1 and 3 were unremarkable; coil pack 2 is noticeably warmer to the touch. That's a clue to me, but I honestly don't know where that leads - other than that coil isn't being told to release its energy.

So I'm kind of where I started but with different error codes. Doesn't seem like the coil pack or the plugs were the answer. There are so many inter-connected systems controlled by the PCM that I'm starting to look in that direction. Any help would be greatly appreciated.
 
Unwrapped the wire bundle from the PCM to the main bundle where it disappears into a hard-formed plastic channel going around the rear of the valve cover. No chafed or worn wires. Identified Connector 104 and checked continuity from pin 4 in that connector to pin 2 of the Coil Pack connector. Had continuity and no short to ground. Plugged in the coil pack and checked continuity from the coil driver pins in pcm connectors 1 and 2, to pin 4 in C104 - had continuity and no short to ground. Pulled the connectors on all fuel injectors and checked continuity from pin 4 in C104 to each injector - continuity with no shorts to ground. As far as I can tell, the wiring involving the coil drivers and the injectors is good.

Next step is to re-connect everything, start it up and grab/wiggle wiring bundles to see if I can locate an intermittent problem. If I can't locate a wiring problem that way and it still runs bad, I'll check for error codes and pack the PCM up for shipment to WranglerFix.
 
I wish I had some advice for you. I suck at electrical. I do want to say, though, I'm impressed by your approach and documentation. Sorry you've received so little input, but here's hoping that one day this thread may help others!
 
Talking through it helps me understand how it's supposed to work. If the repaired/new PCM works, I'll let everyone know. If not, then I really have some digging to do.

No update on the PCM replacement yet?

I'm following this thread as well, as I'm currently dealing with some sort of electrical issue as well causing no start condition, and appears to be no spark.

Already tried replacing crankshaft position sensor with no luck, may try camshaft sensor next. Also tried tracing wires yesterday and didn't see anything obviously bad to my untrained eye.
 
No update on the PCM replacement yet?

I'm following this thread as well, as I'm currently dealing with some sort of electrical issue as well causing no start condition, and appears to be no spark.

Already tried replacing crankshaft position sensor with no luck, may try camshaft sensor next. Also tried tracing wires yesterday and didn't see anything obviously bad to my untrained eye.

PCM is on its way back from WranglerFix...
 
No update on the PCM replacement yet?

I'm following this thread as well, as I'm currently dealing with some sort of electrical issue as well causing no start condition, and appears to be no spark.

Already tried replacing crankshaft position sensor with no luck, may try camshaft sensor next. Also tried tracing wires yesterday and didn't see anything obviously bad to my untrained eye.

Easiest thing to check/replace is the Auto Shut-down Relay. Since you have a no spark condition, it has to be something that effects all cylinders. Lots of posts point to the large wire loom that runs behind the valve cover. On some models, the wire bundle rides next to the studs that hold down the valve cover and the studs can wear into the bundle, creating shorts and or open wire conditions. On mine - an '03, the wire bundle is encased in a large, rigid plastic tray to avoid the chafing issue. Just one more place to look.