I just recently had a cat back system installed 3" pipe with a flowmaster on my 2002 F-150 4x4, 5.4 Lariat supercab. About 3 hours after I had this done my "service engine soon" light came on and I was wondering if this was because I had the cat back done and the computer detected a change or something like that.

About a week later I installed a FIPK F&N Generation II air intake and when I hooked the battery back up the light was gone but again it came on in a few hours. I was just curious if this was a common thing because I really don't want to take it in to the dealer and get raped for something simple. I do plan on getting a superchip tuner for my truck as well and if I remember right it can clear the service engine soon light but I won't be able to swing that for another month or so. I guess you can say I'm parinoid about this light so any help would be great.

Worried in Idaho.

 

I did 2 different 3" exhaust mods on my 2000 5.4 F-150 and never got any codes. No codes with the K&N FIPK either. I haven't read complaints like this either. The solution will only be speculation until you get the codes read.

 

Make sure your gas cap is on tight. I got the “Service Engine Soon” light treatment about 3 weeks ago. I have a little less than 9,000 miles on. After reading several posts on this forum I checked my gas cap, sure enough it was loose. I tightened it up and drove about a week and the light stayed on. The Owner’s Guide, on page 251 says the light will go out after three driving cycles if the malfunction is corrected; well it didn’t so I disconnected the battery for about a minute and the problem was apparently solved. I think if there was something seriously wrong it would have re-set the code and the light would have come back on. Good luck with it.

 

I had a Cat-back exhaust put on my 2000 about a year and a half ago. A few days after my light came on too. I made and appointment to take it in and have it put on the analyzer even though everyone told me it was probably because of the exhaust. The morning of my appointment when I started the truck the light was off and it hasn't come back on since. I took it in anyhow and had it put on the analyzer. The code we got read as a "random engine misfire" The guy at the shop said the same thing everyone else was saying, the computer sensed a different airflow and had to "learn" the new system causing the "random engine misfire" that made the light come on.

I also had the light come on once as a result of a loose gas cap...something to check if it persists.

 

In some instances a less restrictive exhaust installed on a higher mileage engine can cause a lower than normal EGR flow and trigger a CEL. A few members have resolved this by cleaning clogged or partially clogged EGR ports.

Just a thought ........... good luck.

 

Well, last night I got under my truck and started to look around and I noticed that the O2 sensor was just hanging there so I looked around and discovered where they put the new pipe coming out from the cat there was a bolt screwed in that looked brand new. Which I thought was odd so I took it off and screwed the O2 sensor in and then took the battery cable off for 15 minutes and now the light has gone off and has stayed off.

Jeez, the only thing I can think of is that they took the sensor off (so they didn't fry it when they welded) and inserted this bolt for when they were doing the weld so nothing could get in the hole and then just forgot to put it back on. Man, I was stressing my self over this and it was something simple. I should have took my truck back and chewed some a$$ but sometimes my temper gets the best of me so I decided it wasn't worth it. Won't ever take my truck back for any more work for sure!! I just want to say thanks for all of the help I have received here. I've learned so much in just the few weeks I've discovered this wonderful site. Once again thanks!

Royer