When a few months ago my truck was running rough I twice got plug misfire codes only. After replacing all plugs/wires ( #4 plug seemed a bit rusty and worse looking than the others)things were fine till CEL comes on again with the PO171 ,174 codes showing up. ( bank 1 /2 lean codes). Cleaned the MAF ,could not find any air leaks anywhere. Somewhere ( I dont seem to recall when,where or why) the CEL in on again and now I was getting the 401 code only. ( EGR system ) After reading so many threads and posts on here and another Ford forum I try the easiest fix, replace the DPFE.( $50) wasted, still get 401 code. So many people said they had major carbon buildup in the throttle body passages.Assumed this has to be it, but mine were really clean though.I snapped the left egr bolt during this process giving me more work . Drilled out the bolt using larger and larger bits, and just ran a new bolt with a nut to fix it as the threads were shot. I am doing all this mainly as my smog check was due and need to get rid of codes as we all know. Smog guys do a quick test with vacumn gauge and think EGR is fine as they got the required reading then all of of sudden the reading is gone Tell me my EGR solenoid must be bad, so I get that ,install new ($35) clear codes but 401 comes back. Replace the EGR valve ( $55 ish ?) Clear codes and they dont come back after 40 plus miles so I think I'm good to go. One thing though, truck still runs funny,but no CEL. Will not pass smog but have no new code reading. We started pulling the grey electrical plugs to the injectors 1 at a time to see where the bad plug may be . # 4 does not change ( to rougher running ) when lead pulled. Smog guys assume its the corresponding coil pack but were perplexed why no new codes were coming up. ($45) more for a CP ( truck has two) and no change , motor still a bit rough. I decide something I should have earlier and replace that plug #4. That was the problem!!( or at the problem now). Truck is running smooth and passed test. NOW, I think that the #4 cylinder has a coolant leak into it. It must be slight, as I lose little water , but think this must /may be the case. ( IE think it was the one that fouled in the beginning as it was a bit rusty as I said earlier and must/may have again ) . Maybe it was a fluke the 2nd time but I will see. After my long novel, is it possible the Gunk or other type aluminum seal for radiators may fix the leak? Or I guess I could/should just wait to see what happens ( if it starts to run rough again). Any suggestions, comments, input etc is welcome. I'm sure this kind of thing may have been covered on here before, but maybe this will help someone else with similar issues.

 

If you've only driven 40 miles, the tests probably haven't run. Contain your enthusiasm until all monitors have run successfully. Only THEN are you in the clear.

 

if you determine that you have some head gasket or cracked head leak... use this stuff, it works-- permanently.

Bar's Leaks Liquid Copper Block Sealer

 

Project, you were right, my CEL came back on within 10 miles of my smog cert.Its just that that period of time was longest light stayed off, so I may have gotten a little over confident things were going to be fine. At least I already got smogged , so I'm not so worried about it. Truck still seems to run good despite the new CEL. Will look into it eventually ( no hurry now)as I'm curious what is up. Steve, used some Gunk aluminum seal? , will see and may try the Bars Leak as I have heard others say good things about it.