car runs fine, then poof! lean

[MrdB]

i have 780cc with a fpr, 3" gm maft, safc... everything is set up fine.. while i am crusing alone.. car runs around 14.5a/f... then out of no where goes to 16-17a/f? i can set it on crusie and it does it.. i watch the safc and nothing changed, but the damn thing goes lean..? then if i let off the gas and back on its fine.. then a couple seconds later.. poof lean again? WTF?! HELP ME!!!

 

[bluetlr2001]

im sure you probally have but if not have you done a boost leak test. and when you do it try opening your throttle body while your doing it. to see if your seals are leaking any.

 

[Gary 420A RS]

lean or rich?? check on your fpr and make sure its still at the right preasure setting. if its changed put some thread tape on it and put it back together..

iam running 750's and with a fp of 18

 

[MrdB]

at idle my fp is 41ish

 

[MrdB]

i just went out and checked everything.. and drove it again... at a steady ride.. it runs 14.2-14.7a/f.. then it just goes to 16.9-15.6 a/f... but if i build boost it is fine? wtf. i think i have blown my intake gasket

 

[Gary 420A RS]

you got a vacume leak some where? or maybe a short somewhere.

 

[grnchevyz]

how old is the front O2? It could very well be on its way out. I had a similar issue where I would be 14.2-14.5 and for no apparent reason go to 15.5-16.2

No boost leaks, no vaccuum leaks, gaskets all good...replaced front O2 and boom problem gone.

 

[The_one]

I have a very similar problem. Basically, everytime i hit 3k rpm with 65-80 mp/h on the highway at a constant speed my a/f goes from 14.5 to 16-19. Whenever my a/f shows a 16-19 my car lost all its power.
I am in the process of changing the CAS, so if it solves the problem i will let you know

 

[MrdB]

hmm.. well lets me know if that helps? i am going to buy a o2 senor tonight and see what that does..

 

[Mindslayer]

whatever happen on this I have the same problem with 880 and MAFT and CHIP ECU, Supra FP rewired.