Lean conditions on both banks. What could it be?

[chrisblue23]

Hello all,

I got check engines codes on both banks for running lean. I bought a Bluetooth obd and have been trying to diagnose what it could be. I replaced the pcv hose because it had a hole in it and didn’t have a stable idle. The idle is now stable and I even replaced the pcv valve itself just in case. I did this a week ago and the check engine light has yet to go off. I took readings during a drive and for some reason the 2nd O2 sensor isn’t giving short fuel trim readings. Is it likely that sensor might be faulty?

 

[chrisblue23]

 

[Killer Ride]

Check fuel pressure and catalytic converters

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[stamp11127]

In order to be running lean one of two conditions must exist - starving for fuel or an air leak on the intake system. A smoke test is the easiest and fastest way to find a vac leak.

 

[Killer Ride]

A clogged catalytic converter will do the same thing.

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[chrisblue23]

I’ll check the converter. Do they go bad after 242,543 miles?

 

[chrisblue23]

I don’t know if it helps but some days it takes 4-5 seconds of cranking to start. Could a dirty fuel filter do it? Probably has never been replaced?

 

[Killer Ride]

Oh yea,
at that mileage I would probably just replace them. Remember there are 4.
I deleted the upper 2 and replaced the back 2 for even better breathing. It's cheaper still smogs fine. If you live in Ca. you are stuck with doing all 4. Unless you core out the top ones so it looks like they're still there.

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[stamp11127]

I haven't read any article or emissions book that states a clogged cat will effect the air fuel ratio. Where are you getting your information from?

Most cats go bad from raw fuel being dumped into them from misfires.

 

[Killer Ride]

Not saying anything about air fuel ratios but a clogged cat will make air fuel rates bounce all over the place OP stated he had lean codes which COULD be a result of clogged cats. And it is sporadic, depends on how it is driven I only have my own experience with the last 4 vehicles I own since 2011 3 fords and 1 dodge and a Lexus all with varying mileage from 50,000 to 435,000mi plagued with clogged cats.

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[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

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[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.