Check engine light yet again!!!!

[MY 85 GT]

I cant seem to keep this light off for anything now its pulling a P151 or maybe it was P0151 lean air fuel mixture?.....Whats causing this..I have a BBK cold air intake what is making this come on?????

 

[e8597cobra]

well if its a lean a/f mixture there are only 3 places to look first your air intake check the mass air for any obstructions or failure second check the inlet air temp sensor if its close to heat cause if it reads hot it will lean it out third if there is any rough running at idol check the iac idler air control valve for carbon build up. the next thing i would check for is a clogged fuel injector if they are not supplying the right amount of fuel that will throw a code and finally the worst one check the o2 sensors you can pull them out and clean them because i have had a lot of cars come into the shop over the years that have had codes thrown due to the o2 sensors i would check the o2 sensors first because they regulate the a/f for the on board comp use a little carb cleaner ( i use 2+2 myself) and give them a good scrub these are all cheap fixes and if you have a pep boys near buy they will clear the code for free if you do not have a scan tool. word of caution though be very careful with running the car lean it will cause a lean misfire and could result in engine damage i will check the thread to see how you are doing and any more questions feel free to ask

 

[MY 85 GT]

Thanks for the info..Let me say this light just came on last nite..I had it cleared this morning at an advance auto parts drove for awhile it came back on...I have a BBK cold air intake where the air filter is in the fender well...Yesterday i went to the shop i use to have both my motor mounts changed i had a broken passenger motor mount...he found the air filter off and laying in the bottom of the fender well...weird no check engine light them and i dont know how long it was off....So he did the mounts,changed the oil...replaced the serpitine belt...and i had a Leaky exhaust gasket on the passegner side were the BBK catted high flow X-pipe meets the stock header...Well that was a diaster the gasket isnt sealing and the cat back is toast rusted and doesnt seem to fit...i suspect its not the cat back for that car...My question is the light has never been on for a lean condition but now after he did all this work it came on in a matter of minutes...Weird no?....Could the MAF gotten dirty or something got sucked in there? I dont think so?...Im going to be buying a new Off road X-pipe and cat back so maybe i should buy 2 new O2s also?

 

[e8597cobra]

lol sounds like a mess but yah if you have a exhaust leak between the front o2's and the back o2's there is your problem i am a uti grad and have 12 credentials from ford motor company with 4 ase's and 4 years experience in the shops ive seen this tones of times but you might not need to buy new o2's just clean them first then if its still there then replace them it will save you around 200 dollars i put intakes in tones of cars epically fords and have never come across a lean a/f code when installing them but i would get the exhaust welded instead of bolt in stuff nothing seals like a weld i would look at that exhaust as the problem.

question did you have any check engine lights before the exhaust

 

[e8597cobra]

BBK OFF-ROAD X-PIPE STOCK/SHORTY HEADERS 4.6L 2V 1996-1998 - CJ Pony Parts, Inc.

BBK OFF-ROAD X-PIPE STOCK/SHORTY HEADERS 4.6L 2V 1996-1998
Part Number: XP11

BBK 2-1/2" Off-Road X-Pipe for 1996-1998 4.6L 2V Mustangs with Stock or Shorty Style Headers.

This BBK direct replacement X-Pipe features 2-1/2” diameter CNC mandrel bent aluminized tubing to ensure maximum flow and horsepower.

OEM-Original O2 sensor locations and factory style die-stamped flanges ensure a perfect fit and BBK In-house dyno-testing has shown solid gains of 15-20 horsepower depending on application.

ALL BBK full length X-Pipes are designed as a direct bolt on to factory headers o any aftermarket shorty headers as well as of course BBK shorty headers for weekend track or race use.


if you enlarge the pic you will see the o2 sensor holes at the down pipes towards the right of the pic if there is a leak at that connection on ether side it will cause that code i would get that checked first

 

[Mr. Rustypwnz]

you aint gettin 20hp out of those, although they are nice..

 

[bhuff30]

I gained .2s and 2mph in the quarter with an offroad H on my otherwise stock 97 GT. That's close to a 20hp gain, right?

Here's the thread I started way back when:
http://www.stangnet.com/mustang-forums/726056-off-road-h-pipe-track-results-before-after.html