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Discussion Starter · #1 ·
Background: Sunday morning, cold in the 20 degree range. Start the Smurf, let her warm up for a few. I drive to the stop sing leaving my neighborhood ~1200' and as I'm sitting there waiting to turn she starts idling rough. As I turn the corner she's still rough and the CEL starts flashing. I pull over and shut down for a couple minutes. I had problems connecting torque app, so I bit the bullet and started her back up, she ran fine the rest of the day. Torque did end up working and it pulled P0308 in the memory, I also have an EVAP code.

I checked the wiring on cylinder 8 from plug to coil, the wire harness from the coil, the wiring & plug for injector #8. All visually checks out and connections were solid.
Took my daughter to school & drove to work today, no issues.

Any thoughts??

96 Cougar 4.6 stock.
 

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First I would look for a cracked intake manifold leaking coolant into the spark plug well. Assuming no issues there, pull the #8 plug and see what it looks like. If it looks OK, switch the #7 and #8 spark plugs around, and switch the #6 and #8 injectors. Also switch the coil packs side to side. Clear the codes and drive the car. If/when the misfire comes back, what component it followed is the failed part.
 
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I'm with Mikey on checking for the coolant leak.
 
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Discussion Starter · #4 ·
I double checked, no coolant. About March 19th I swapped those items Mikey stated, no issues since. Until today. leaving work, it's chilly and damp, rained pretty good all day today. She was idling rough after work, sat in the parking lot for a couple minutes to let her warm up a little. Drove up the road and could really feel the miss, CEL flashing, code points to cylinder 8 again. I pulled over and shut her down for a minute or 2, started back up and drove home with no more issues.

The commonality between these 2 incidents is cold & damp. I'm thinking I've got an electrical issue, like connector, sensor, wiring, etc. Anyone have a solid understanding of how the ECU determines misfire and narrows it down to which cylinder? Like what sensors, data it uses to make the determination. Thanks.
 

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The flashing CEL is usually due to a misfire due to No spark / excess fuel condition. I would start with the ignition system first.

Misfires are sometimes calculated by the engine RPM .. as we all know, RPM is driven by ignition firing, so the crankshaft tends to momentarily speed up faster with each ignition event - not sure this is how Ford works their EEC, it's just one method to determine misfire via Crankshaft position. ( sorry I'm not sold on the rich spike theory ) 😉
 

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flashin ce light is the warning for catalytic converter damage is ongoing due to fuel excess.
 

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The flashing CEL is usually due to a misfire due to No spark / excess fuel condition. I would start with the ignition system first.

Misfires are sometimes calculated by the engine RPM .. as we all know, RPM is driven by ignition firing, so the crankshaft tends to momentarily speed up faster with each ignition event - not sure this is how Ford works their EEC, it's just one method to determine misfire via Crankshaft position. ( sorry I'm not sold on the rich spike theory ) 😉
May well be, that's just how I understood it
 

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I double checked, no coolant. About March 19th I swapped those items Mikey stated, no issues since. Until today. leaving work, it's chilly and damp, rained pretty good all day today. She was idling rough after work, sat in the parking lot for a couple minutes to let her warm up a little. Drove up the road and could really feel the miss, CEL flashing, code points to cylinder 8 again. I pulled over and shut her down for a minute or 2, started back up and drove home with no more issues.

The commonality between these 2 incidents is cold & damp. I'm thinking I've got an electrical issue, like connector, sensor, wiring, etc. Anyone have a solid understanding of how the ECU determines misfire and narrows it down to which cylinder? Like what sensors, data it uses to make the determination. Thanks.
swap the number 8 and number 7 injectors. Clear the code. Drive till the code comes back and see if the code moves to cylinder 7. If so, replace the injector. If it stays p0308, check back here.
 
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Discussion Starter · #10 ·
swap the number 8 and number 7 injectors. Clear the code. Drive till the code comes back and see if the code moves to cylinder 7. If so, replace the injector. If it stays p0308, check back here.
That's one of the things I swapped back in March and this was the first time the code reappeared, still at #8.

FWIW: I did notice the exhaust was darker and more pronounced while the misfire was happening. Like a dark & thick white smoke, if that makes sense.
 

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If it only happens when wet, try putting water in a spray bottle and spraying the plug wires. If they are slightly cut, the water can provide an easier path for the electricity to flow and cause a misfire. Also if you do this test in the dark, you will be able to see the spark jumping out of the wire to the engine.
 

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That's one of the things I swapped back in March and this was the first time the code reappeared, still at #8.

FWIW: I did notice the exhaust was darker and more pronounced while the misfire was happening. Like a dark & thick white smoke, if that makes sense.
Fair enough. Have you checked for vacuum leaks at the intake manifold gasket? Also, any chance you have a spare computer? I keep a PCM around for diagnosis on our cars. It has a known P0340 code because the PCM is bad. But When I swap it in I always know what to expect. Maybe you can grab a pcm from a junkyard and swap it in and see if the misfire returns that way.
 

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Spark plug wires been replaced? Not sure if Motorcraft are still available, but Autolite are also pretty good.

Al
 

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Discussion Starter · #17 ·
Last night I went out and fired up the Smurf, sprayed water all over the wires and especially around #8, NO sparks. Just to confirm, #8 is at the firewall, driver's side, correct?

FYI: I replaced all the vacuum lines, except the EVAP on the side of the gas tank 4-5 years ago also.

I'm going to look at my datalog to check the fuel trims, if there is a vac leak those should be elevated. Anything else the data might tell me?

For the intake leak, spray some WD-40 around the gasket while running and pay attention to the RPMs? It's been a while.

I'm leaning toward and electrical issue, maybe even ECU, since both times this happened I shut the Smurf down, let sit her sit for a couple minutes, started back up with no misfire and ran smooth for a while afterward. It's like she's running Windoze. 😁
 

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Last night I went out and fired up the Smurf, sprayed water all over the wires and especially around #8, NO sparks. Just to confirm, #8 is at the firewall, driver's side, correct?

FYI: I replaced all the vacuum lines, except the EVAP on the side of the gas tank 4-5 years ago also.

I'm going to look at my datalog to check the fuel trims, if there is a vac leak those should be elevated. Anything else the data might tell me?

For the intake leak, spray some WD-40 around the gasket while running and pay attention to the RPMs? It's been a while.

I'm leaning toward and electrical issue, maybe even ECU, since both times this happened I shut the Smurf down, let sit her sit for a couple minutes, started back up with no misfire and ran smooth for a while afterward. It's like she's running Windoze. 😁
You can carefully use brake cleaner to test for vacuum leaks. Typically if there is a leak where you spray the rpm will increase.
 
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Discussion Starter · #20 ·
I took a look at some recent data logs and will try to remember to data log my trip home. At any rate my fuel trims are about 8-9% high and tapers off to near 0 toward the end of the drive. about 1hr 15m drive. Looks like I may have a vac leak. Its a busy weekend coming up here, but planning on making time to hang out with some brake clean. I'll report back.
 
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