Lean conditions on both banks. What could it be?

[TobyU]

My scanner doesn't show the info that way. I get O2 voltage and I look for the downstream one to switch form low to high and back.
Then I have short term trims and long term trims.

When both banks are lean you usually have a fairly good size vacuum leak.
Intake gaskets are notorious for this.

 

[chrisblue23]

In Arizona all they do is check your gas cap and computer for emissions. I’ll just end up coring out the top ones and getting some nice aftermarket ones for the bottom 2. Maybe they are full of carbon. Just under pressure tags are up in a month and have the check engine light on.

 

[chrisblue23]

Should I replace the 02 sensors while I’m at it?

 

[chrisblue23]

My scanner doesn't show the info that way. I get O2 voltage and I look for the downstream one to switch form low to high and back.
Then I have short term trims and long term trims.

When both banks are lean you usually have a fairly good size vacuum leak.
Intake gaskets are notorious for this.

I’ll check that gasket tomorrow.

 

[Killer Ride]

Only if you are getting lazy or slow readings. You can get some from Rock auto for fairly good prices. A good exhaust guy can do a back pressure test or you can use an infrared thermometer to get a heat rating the hot side is the one with the clog

Sent from my SM-G950U using Tapatalk

 

[rjdelp7]

Test your fuel pressure, at the fuel rail. It should be 40psi or higher. Check all your vacuum lines.

 

[R0cketMan]

A quick test for fuel system issues would be to cycle the key several times before starting to build pressure in the fuel system. A dirty filter will only cause starvation under load when the engine demands a large constant flow rate. You’ll likely get some kicking and bucking if it is severe enough under acceleration. A clogged catalytic converter likely won’t cause an issue in both banks at the same time. A severely clogged cat will cause the engine to bog under load without kicking and bucking.

A vacuum leak is the likely culprit and can cause slow starts because a cold, lean mixture is hard to ignite. 20 year old vac lines or a bad gasket is not uncommon. Without knowing the engine speed from your data capture, your information doesn’t give much to work on. I assume your engine was running around 1700-1800. A higher engine speed compared to your MAF would indicate a vacuum leak. O2 upstream values are clearly lean, downstream (after cat) are showing proper voltage.

I hope this helps.

 

[Bruce Mitchell]

I had the both banks lean issue a few years ago. Replaced the fuel filter, cleared codes, hasn't been a issue since. I'm a big believer in Occam's Razor. (Also, I'm a cheap bastard.)

 

[TobyU]

I had the both banks lean issue a few years ago. Replaced the fuel filter, cleared codes, hasn't been a issue since. I'm a big believer in Occam's Razor. (Also, I'm a cheap bastard.)

You got lucky.

 

[bonasa]

Had same issue, replaced o2 sensor, fuel filter, intake manifold gasket, vacuum lines. turned out to be the fuel pump. plenty of pressure at idle, but as it warmed up it failed.