I have a 2003 F150 4.2L. I was doing a spark plug change & the original plugs were:
3 plugs on one side were #Motorcraft AGSF 34EM platinum

Then 3 plugs on the other side were #Motorcraft AGSF 34EGMplatinum.

I replaced the plugs wth AUTOLITE Xtreme Performance Iridium #XP5144.

Less than 100 miles of driving the "Check Engine" light came on; code P171 Potential Lean Banks 1&2.

I want to change back to Motorcraft AGSF 34EM platinum & Motorcraft AGSF 34EGMplatinum......

Does anyone know which side the three 34EM plugs fit ? (right or left) or does it matter?? Like a ******* I didn't pay attention when I removed the plugs??
Any help on this would be greatly appreceiated......

 

A waste spark ignition system fires two sparkplugs at the same time. (One cylinder will be on the compression stroke and the companion cylinder will be on the exhaust stroke. The spark going to the plug on the exhaust stroke is "wasted", hence the name "Waste Spark" ignition System, but it saves the engine having to have a mechanical distributor, etc.)
The current flows from one of the companion coil towers to the sparkplug center elctrode, jumps the gap to the side electrode, travels through the block to the companion sparkplug's side electrode, jumps the gap and travels up the center elctrode to the companion coil tower. So effectively, one sparkplug fires in the 'forward' direction and the other fires in the 'backward' direction.
So instead of installing zillions of double plat plugs at the factory, to save $ Ford buys single plat plugs, some with the plat on the center electrode and some with plat on the side electrode. They are installed in the proper hole to minimize gap erosion, depending on which hole fires forward and which fires backward.
The aftermarket only sells double plats to us 'cause we only buy 6 or 8 at a time and therefor we don't have to be concerned about which one have to go in which holes.

 

Why blame the spark plugs? Go back and check over your work for loose connections, broken cracked pieces that may cause the code.

OBD-II DTC: P0171 System Too Lean (Bank 1)

 

Good explanation pdqford. Here I thought it was to meet emissions at the factory.

 

I purchased this truck brand new 2003.

Today, 18 DEC 2012 it currently has 41,000 miles. I did check the work I did, but the code came up less than 50mi after the plugs were changed,
I have the code reader, so I did erase the Check Enging Light a few times since the same code poped up 3 more times. So, I believe changing back to the orig #Motorcraft plugs the check engine light will stay off. I will see & post if old plugs cure the problem or not...

 

The plug locations are listed in your owners manual. Cylinders 1,2,3 use EGM suffix. Cylinders 4,5,6 use EM suffix. If replacing plugs use plug with suffix EEM.

https://www.fleet.ford.com/maintenan...ls/default.asp

 

Awsome!
Thank you, I will put the old plugs in & see if code pops up...

 

Get rid of those Autolite plugs. I've heard several people have issues with them and have read thread after thread here with problems related directly to those pplugs.

 

What gap are the plugs?

 

.054 is the factory spec on the plugs it originally came with but if you're determined to use a different plug, I'd ask at the parts store.

 

I went to Ford dealer got the reccommended Part # ASGF-34-E-EM
FORD PART # FPC:010195656...

have driven over 270 miles, no "Check Engine Light"
I believe that it was caused by Autolite plugs....
Thanks for helping me out......This is a really good web site

 

thanks it was 34-eem!

 

Who would think a spark plug would make the difference? As electronics have become more pertinent making these engines run to strict standards I've become a believer in oem thermostats and spark plugs in the last few years. It's not easy on the pocket book though if your paying full oem retail.

 

The plugs are subject to different errosion conditions depending on the polarity of the spark in a waisted spark system.
Same thing with Mig welders that have reverseable cable connections depending on what your doing.
Everytime a spark is generated a small amount of metal is melted away.
The factory did the plug thing so all the plugs would age about equal instead of just 3 too early.
The difference is in the material hardness and resistance to spark errosion.
They don't miss much unless the bean counters over ride engineering, which happens a lot, just to save money.
Good luck.