HELLO, Thank you for your time to read this!!!

OK, its an 87 2.8 MPFI that i have had since 30k, it now has 230k on it and never had ANY major problems.

It seems to miss pretty badly, usually but not always, under load, or above 2000rpm. I replaced the fuel pump about 50k ago, so i don't think the fuel pump is the problem. This misses alot worse than when my fuel pump went bad.
I ran my scanner on it, the Oxygen sensor, and MAF sensor are the only thing that popped up. I then monitored the car during start up, everything read ok except my MAT manifold air temp read 286 degrees after the car sat all night in 30 degree temp. I replaced the MAT, now my temps are good.
I also got a new Oxygen sensor to put in, been around 110k since my last Oxygen sensor change even tho it was responding ok,(my voltages were good),
BUT when i went to replace the ox sensor i noticed a huge crack in my Y-pipe, i mean when i try and loosen the old Ox sensor it widens the crack into a gap. The carck is almost right where the y comes together.
I might be stupid when it comes to cars, but here is my idea...
If my Oxygen sensor is measuring my exhaust wrong( since i have a cracked Y pipe) that it could through off my other sensors when it tried to come up with the ideal fuel/air mixture. I notcied when I monitored my ideal fuel mixture, which is ideally a 128 on my scanner(14.7 to 1) to fluxuated quite a bit, trying to achieve the 128 it would jump down to 91 even. I have never seen it do that.

ANy ideas??????? Thanks, Mike OHIO

 

have you done anything about the MAF sensor?

 

no not yet, I do think i have an extra around somewhere, i'll try a swap and see. A new MAF is around $60 isn't it?

 

wow a new MAF is $244 at NAPA, I really wanna get it fixed, but I don't wanna end up with a pile of scrap with $1200 worth of new sensors either.

 

try finding one at a junkyard