Running a bit rich...suggestions anybody?

[red.EDDIE.4x4]

ok so i have a pretty much bone stock 4.0 in my 93 x.
on my most recent trip to firestone the manager took it for a test drive for final inspection. and he told me that the plugs were pretty black for only being 2 years old and that my fuel mixture was pretty rich. i know him on a personal level and he and i were going to trouble shoot it at my house.

so i would like to know...is this a common problem?
does anybody else have a similar problem?
what things would you go about checking first?

PS, i have a check engine light that comes on...but only on occasion. thinking maybe its an O2 sensor...? MAF?
any advice is welcome, Thanks!
-Tyler

 

[shaggymane]

Pull the codes, post them here, use your DVOM to check volts and resistance on the MAF & O2.

Put a fuel pressure tester on the Fuel Press Regulator.
Pull the vac line off the FPR, see if there's any gas in the line = bad FPR



A bad FPR running high will give codes MAF out of range, O2 sensor not switching, stuff like that, when there's nothing wrong with the MAF or O2. So, don't just replace them & make that mistake.
Test don't guess. It costs less

Black plugs, oil or gas? oil fouling usually doesn't happen in all plugs at once unless it's from something like a the vac modulator.
leaky injectors will black plugs up but again it's odd for *all at once*. How many plugs are black?

 

[red.EDDIE.4x4]

Black plugs, oil or gas? oil fouling usually doesn't happen in all plugs at once unless it's from something like a the vac modulator.
leaky injectors will black plugs up but again it's odd for *all at once*. How many plugs are black?

im not sure how many are black. but he pulled a few and told me they were pretty black for only being 2 years old. ill prob take a look later when i get home.

 

[Tony H]

Air filter really dirty?
A sign of a faulty Fuel Pressure regulator is Rich running condition. Teh fuel that gets past the leaky Diaphragm gets fed into the intake manifold
The Code light coming and going might be a sign of a lazy O2 sensor.

 

[red.EDDIE.4x4]

Air filter really dirty?
A sign of a faulty Fuel Pressure regulator is Rich running condition. the fuel that gets past the leaky Diaphragm gets fed into the intake manifold
The Code light coming and going might be a sign of a lazy O2 sensor.

how might i go about changing this fuel pressure regulator? and where is it located? Thanks!

 

[Tony H]

Located on the passenger side of the Intake Manifold. look for the Steel Braided line