now i just sold my 4.2 but i ran into the problem that everyone else did with the 4.2 and the check engine light. i replaced all the sesors fuel filter and everything and couldnt get it off. so heres what you all been waiting for. take off your upper plenum on ur manifold and you should notice that all the rubber used for the vacum lines beneath the plenum are rotted from the heat. go spend 20 dollars on a new plenum gasket, three feet of 1/4 in vacuume hose, and also a foot of vauccume hose the next size up and replace those vacum lines(make sure to buy new plastic 90's) need about three.. i did this and it took my light right off and i got aroung 5-6 more miles poer gallon. but this is for those with codes saying running lean bank one or two.(po171 and po174) if i remember right. i guarantee that for 90 % of you this will cure it. e-mail me at zbbt@aol.com for detailed instructions.. but i wanted to shoot myself over this check engine light and am so relieved to have finally found the solution!!!!!!

 

Great info! If you post the instructions in detail it could become a sticky for this section.

 

thanx for the info,my engine lights been driving me nuts.....

could you post some more info about this procedure.....

 

wow its been about a year since ive been here, i have since sold my lifted 4.2 in place of a 2001 bmw 325. i wanted to see if this thread was still of use to anyone as my cure for those dreaded po171 and po174 codes were effecting everyone is still holding up in my old truck. the new owners check light is still off and he gets an estimated 5mpg better fuel economy, any questions ask here and ill explain the procedure better

 

and for kicks here are some picks of my ole rig, she was a great truck, still cruisin to this day same lift and tires with over 150,000 on the clock

 

how biga lift and tires is that
looks real nice

 

this is the answer ive been looking for!!!

thanks for the insight man! mine hasnt come on since i replaced my plugs and pulled out my PCV valve just to check and make sure it was vacuuming ok. but it has come on 2 or 3 times since then(about 2 1/2 months ago)

how often did urs, or anybosy's for that matter, come one? my would light up anythime i had a atmosphere temp change of 10+ degrees...

 

thanks guys, my lift was a 3in spring up front with a 3in spindle, in back i just had 2in blocks with hancook 53 in mudders. My light once it came on stayed on. after being on this site i noticed every v6 was having the same problem. well all the rubber under that intake plenum basically didintegrated in my hand when i touched it. any hole in your vacuume line will get you horrible gas mileage as your engine thinks its lean and dumps fuel in like crazy.

 

Hmmm....my CEL has popped on a few times in the last month but I looked it up but have long forgotten what the code was and cleared it. If it ever pops up I'll look into this. Can anyone backup that 5-6 mpg claim? I'm already doing a 17.6/21.3 average, and I doubt it'll go up 5-6 mpg.

 

well with my lift and 4.2 i was getting 8 mpg, once repaired i shot up to about 14. In your case i dont feel its the same lean codes as your light comes on and off. these symptoms i described are when the shoddy ford rubber deteriorates and leaves holes in your vacumme. once that occurs your computer begins dumping gas as fast as possible to compensate for the excess air so as not to burn up your top end

 

Everyone listen to this guy. I spent over 600.00 trying to figure out my check engine lite. At the end it was just a 30 dollar in parts. Now I have all new sensors and mufflers and vacumme lines. If I didnt plan to keep this truck forever I would of been pissed. Ben

 

same here, bought numerous sensors and replaced every filter, connector and injector, only to find some rubber saved the day as usual ; )

 

alright if someone explains what this upper plenum thing is im gonna jump on this to see if it fixes my codes!!

soo...anyone? haha

 

your intake manifold bolts onto your engine block, the plenum is the aluminum riser that attaches to your manifold and directs the air from your MAF to your valves. pop your hood and look at what the MAF is bolted to. i cant recall the count but theres around 8-10 small baolts that conenct it to your manifold you need to remove

 

ok thanks for the clarification

im gonna look into that tomorrow actually

is there any seals or gaskets that ill need to change or anything?