Spark Plug experts - rough idle thoughts

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David Schmidt

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2003 sport trac 4L.



ok - I've been chasing a "missing" or "burp" in my engine for a while now. Misses every time a/c cycles , put in / out of gear, press on gas first time, etc. Just a little burp. Previous post said to go back to stock so I took my demon coil and put stock back in - no difference. So I took out all six Denso Iridium spark plugs and wires and replaced with Motorcraft platinum and some 8mm oe fit wires. Car still has miss of course but does run smoother. My new problem is the plugs. All three plugs on drivers side - the tips were basically melted off. All three plugs on passenger side looked like the day I installed them. This thing ran pretty darn good and got good mpg. The gaps on left side were like off the chart .70+. I think the scremin demon coil may have helped with the big gap. I took a picture of the plugs as they were removed in order. You can clearly see a difference. I'm assuming I'm not talking about a valve issue or piston issue or even a fuel injector issue. Whats different on this side of engine? I recently replaced the Oxygen sensors (upstream ones) - not sure when the plug damage occured though. No check engine lights, etc. Thoughts?



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The plugs to be worn like that tells me that you are running lean on the left (drivers) bank.



I need to think about this for a while.





Tom
 
What did you install them at for gap ???? I still run the Stock gap, There was no difference with the higher gap on a NON FI Sport Trac 4.0,....



Todd Z
 
plugs have about 35K on them. I installed at stock gap - probably around .054 for all of them. New pugs are set at .053 right now and are OEM Motorcrafts.



Could the demon coil act different on one side? Engine has never overheated and runs very cool - no issues there.



On my idle problem (missing) I'm going to try a OEM IAC valve and see if that does the trick. I have an aftermarket on right now. I did order a motorcraft IAC from Amazon because the price was really, really good but when it arrived the connector was pointing the wrong direction. (second time thats happened to me). Can't believe they build these things backwards. I hope the MAF sensor and the throttle body are OK but those will be my next purchases -maybe a coil pack??????



Too lean...more heat - maybe the new oxygen sensor I recently put in fixed that problem? Never has any new or pending "codes" in my OBD scanner. Unless starts to run real bad I'll pull a plug and check condition in a few thousand miles or so and monitor more carefully. Weird plug condition for all three on one side.

 
I do not have any idea how cleaning or replacing the IAC will help with this issue.



The IAC simply allows enough air into the intake manifold to keep the engine as an idle. If there were a separate manifold and IAC for each bank.





Tom
 
I have seen auto zone try to give the wrong IAC many times. Myself included for a t-bird 5L. I told them give me the one with the connector turn the other way. They told me thats the book one. If I buy the other, no warranty. So I left.
 
IAC will not stop your miss or plug problem. The MAF and TB wont either. If they did all plugs would look the same.

Which O2 sensor did you replace? There are 3. The last one after cat monitors emissions. The 2 up front both exhaust banks control fuel air per bank.
 
That is a crap load of wear for 35K miles. Why one bank wearsworse than the other has me stumped. I know on the OE plugs, the left and right banks have different part numbers, but the replacement plugs for both banks are the same.



Maybe this is a gross example on why it is that way from the factory?





Tom
 
Tom & Eddie,



What I said was that cleaning or replacing would "help &/or contribute" with a smooth running engine, and I was in no way implying that it was the entire problem. I will be interested as to the resolution of this problem, and find it very interesting that the OEM right & left bank spark plugs have different part nos. and the replacement ones do not.

 
I changed the plugs on my 03 at 30K before the major performance upgrades and I changed them again at 60K..........



the first 30k was on oem coil and wires and the second was with the PD coil and wires..



They looked better on the second set after running the xcal. I am running autolites app103 plugs now..... Will see at 90 k if they held up better then the 2 sets of oem plugs...



These ST's tend to run a little on the lean side, And with the Xacl and the richer mix i noticed the second set of plugs held up much better then the first set..



Todd Z
 
interesting...I replaced the oxygen sensors - upstream - two of them with Bosch with OE connectors, etc. Not motorcrafts but I'm told Bosch makes a great sensor. They seemed to work fine. I did not replace the one after the CAT. The web sites say their are "two" but I could only see the one after the CAT. I was told that one won't affect much - the two upstream are far more important.



I'm hoping the left original oxygen sensor was bad but not throwing a code. I will monitor the plugs and get a factory IAC in the very near future and get rid of the Advanced Auto part one - at least the connector was pointing the right direction.



Should I get a after cat oxygen sensor?
 
Caymen said:
The plugs to be worn like that tells me that you are running lean on the left (drivers) bank.



I need to think about this for a while.
Click to expand...

You're getting warm.

I have it on good authority from someone on another Ford board who knows his ignition systems very well that the late-model Ford ignition reverses the polarity, or rather the direction the spark fires, on one cylinder bank. In other words, on the driver's side the spark actually fires from the electrode to the tip...which is why multiple electrode plugs don't work well in Fords.



The Motorcraft Platinums should be fine, assuming you got double plats which I think Motorcraft plugs are anyway.
 
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