Can clogged EGR passages foul spark plugs?

Maintenance/Repairs
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Ok here’s an update. I had the car diagnosed and the long and short fuel trims were way out of the normal range. Specifically long term bank 1 was 9 and bank 2 was 19.82. Forget the exact numbers for short term fuel trim but that too was definitely off.

Mechanic took off the upper intake manifold to clean carbon but upon removing it, there was not very much buildup present to actually clean. So he said we might have to continue the diagnostic…however he did notice the IMRC bushing was broken causing the IMRC arm to hang off and the butterfly valve on the drivers side to be stuck open. He put on a new bushing and put the arm back into place ensuring proper operation of the butterfly valve. We cleaned the small amount of carbon there was off anyway from the EGR passages In the lower intake and cleaned the upper intake passages too. Installed it back, and then did an induction service with seafoam to clean cylinders and pistons from carbon. Finally put a new set of oem spark plugs. After doing all that and driving it, the long and short fuel trims were back in normal range fluctuating within 5% of zero. This SHOULD fix the problem right? The fuel trims being off should be what was causing the spark plugs to foul with carbon right?

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Did he let the fuel trims stabilize on their own after the repairs? Or did he perform the repairs and immediately reset the fuel trims with the scanner?

If it’s the latter . . .

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He did the repairs and then connected the scanner to show the live data. He didn’t reset the fuel trims we took it on a drive and then checked again with car parked and both fuel trims were normal range. Should this fix my spark plug fouling issue?

44

I guess we will all find out in a few days.

45

Alright. Great info and responses from you and others on here. It does make a difference in predicting the outcome if he had reset the FT to zero. At this point waiting it out is wise. However, you should be able to narrow down the answers to few possible causes and effects. Let us summarize: Symptom: Dry Soot (carbon deposits on SP#4). Diagnosis: 1. Inefficient Ignition (example: weaker spark, bad connection, bad coil pack) 2. Too much fuel (but ECU compensates by decreasing LTFT up to negative 25% before engine check light kicks in- or worse. However, I think you stated LTFT shows positive 9 and 19 which is inconsistent with Rich condition prior to ECU adjustments). 3. Too much Air (Lean condition in which ECU will compensate by increasing LTFT up to positive 25% before check engine light kicks in. Your new finding confirms ECU positive increase to LTFT. So, Air blockage would not be an issue). 4. Too much fuel (without ECU adjustments due to incorrect sensors output) could result from leaky old injector or new injector cauing inefficient burning. 5 Incorrect sensor outputs or incorrect ECU commands (however, your O2 sensor showed rich condition but that could not have been specific to Cylinder 4 rather to the total fuel trim) which means ECU and sensor need to be tested (albeit, this is unlikely). 6 exhaust valve damage results in the above symptoms but also can be measured by measuring the compression in that specific Cylinder (also some would use the tail pipe or the valve cover oil port to confirm air is noticeably escaping at high velocity through the ports).

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What fuel are you using?

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So I read all the symptoms and ALL the responses (by the way guys, good job of having differing opinions at times and not pointing anyone out for the most part). I am very intrigued on the finality of all of the work and discussions. Did all the fuel trim numbers stay on track and the engine finally not misfire, and no more weekly cleaning of the plugs? Also Im not a Ford tech and I dont know what a "IMRC"valve is, its function and what issues it may cause… Anyone?

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intake manifold runner control valve

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Generally speaking, you likely won’t even notice a manifold runner has failed but it will set codes., It’s purpose is to lengthen the intake tract at low RPM and increase low end torque. At a certain RPM flaps close and the intake tract is shortened. That helps the engine breathe a bit better at elevated RPMs.

And Ford is not the only car maker to use them.

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Hey everyone,

As of leaving the mechanics 2 weeks ago, he tested the long and short fuel trims and both were in normal range. However that was 2 weeks ago and they have not been tested again since then.

The photo above shows what I saw when I pulled the spark plug in cylinder 4 today to check, after having driven it for the past 2 weeks since the repair and was happy to see the electrode and ground are not fouled and color seems normal. However as you can tell from the photo the tip of the ground appears chipped! (And it certainly wasn’t when we first installed it.) There also appears to be some carbon towards the bottom of the ground. Is this normal? The wet stuff on the threads is anti-seize by the way.

We put OEM motorcraft pre gapped spark plugs so heat rating or improper plug/gapping isn’t an issue. If you were me, would you replace the plug since it’s slightly chipped? Because…

Even after this repair, when I’m accelerating hard it will SOMETIMES hesitate just a little bit. (Does not do this everytime). The car is running 90% better after doing the repair 2 weeks ago, but especially under load, I can tell it’s still not 100% right. Again, only sometimes! Most of the time it will accelerate normally even when doing a hard pull. The times that it does have the hesitation, the best way I can describe it is I’ll floor it, the car sounds like it does when you’re hitting the rev limiter in park and it won’t rev any higher. Only it sounds like this WHILE accelerating. It basically sounds and feels like it’s bouncing off the rev limiter for a couple seconds while it’s speeding up before it downshifts and returns to normal. Not sure if I’d even call it a misfire, maybe for lack of a better word…on a scale of 1-10 on how bogged down the engine feels when it does have this issue, I’d say it’s a 2.5 or 3. Very minor but something still not right. Given the plugs aren’t fouling anymore just from a visual inspection, I’m not sure if this is happening due to the chipped plug. Also what would cause a chipped plug in the first place? Due to the plugs not fouling after 2 weeks, I think it’s safe to say the fuel trims being correct now but then why am I still getting this annoying intermittent hesitation under load?

Another thing to note is the mechanic had to use a different brand of spark plug wire he had lying around for just one of the wires because one of them broke when he was taking them off to put on the new plugs. The wire was the correct length for the respective cylinder and was new, it was just a different brand than the other 5…this shouldn’t make a difference should it?

All of the following have been replaced in the past 2 months:

IMRC actuator (the entire unit itself is brand new), one bushing on the actuator that somehow broke off despite it being a month old, fuel filter, fuel injectors for drivers side bank, MAF sensor, air filter, all o2 sensors replaced, TPS, EGR valve, throttle body cable, fuel pressure regulator, coil pack, OEM wires and plugs, ran bottle of cataclean through gas tank.

No codes before or after the repair

51

My guesses: either something physically hit the plug, or they’re counterfeit.
Where did you buy the plugs?
Does the mechanic have a borescope to look at the tops of the pistons?
I’d look for a mark on the piston where it hit the plug, or after so much time fouling the plugs there’s enough carbon buildup on the piston to reach the plug.