Dahnkey

Hi. I have a 96 f150 4x4 w/dual tanks & an inline 6 4.9 and I just failed emissions. And they gave me these 4 reasons. Im lost and if anyone can help i would love it. Reason 1. P0411 "SECONDARY AIR INJECTION SYSTEM INCORRECT FLOW DETECTED. Reason 2. P0401 EXHAUST GAS RECIRCULATION FLOW INSUFFICIENT DETECTED. Reason 3. P0171 SYSTEM TOO LEAN (BANK 1)(2). Reason 4. P0174 SYSTEM TOO LEAN (BANK 2).

13Harleyfan

Did you disconnect all the emmision equipment?

Dahnkey

No. But what exactly does that mean? I don't know too much about this stuff.

13Harleyfan

Just from personal experience I have seen the air pump under the hood disconnected or disabled. There should be a diagram near the radiator or on the hood that shows all the emission parts attached to the motor, if they have been disabled or removed it will cause the problems you are having.

Dahnkey

Ok I understand. I will check. I do know the owner before me replaced the air filter w/a high performance air flow master. Any chance there could be an issue because of that? And thanks for you help.

13Harleyfan

Not unless it's very dirty or he left a bunch of stuff disabled. You could need a good tune-up, there are a lot of things than can cause these type of failures. I'm not a code chaser so one of the other guys can help you thru getting those corrected if everything else looks good. If the previous owner disabled the system, and you are not mechanically, you might want to get it into a shop for an estimate. Post a picture of the engine compartment so we can see what is hooked up.

Crowder

P0401 is egr valve. Sounds like a vacuum leak to me. Check all your vacuum lines going to the egr valve. And vacuum lines going to the evr as well

imp

He's running lean, which rules out clogged air filter. Shut off air, runs RICH, not lean.

EGR valves are known to get stuck, due to the crap sucked into them out of the exhaust gas stream. It might need to be replaced.

Auxiliary air is pumped into the exhaust gas stream to help burn unburned hydrocarbons. The so-called "smog-pump". Air pumps wear out and lose efficiency, (if not disconnected, check hoses). It may need to be replaced, too.

The entire engine running lean could be caused simply by a partly clogged fuel filter. Check fuel pressure, under load if possible. If it's low even at idle, replace the filter. Other causes for lean running, oxygen sensors, would be picked up by the computer and called out trouble codes of their own. imp

sdmartin65

Im with Crowder vacuum leak. You'll find it and only part needed with be some vac line, maybe. But it could a substantial leak to be causing the lean codes.

imp

I need to see things in a simple way, consider: A 4-inch hole (the cylinder) is sucking in air, that all must go through the mass air sensor and gets measured as to quantity. Now, if a 1/2-inch hole opens up say at the manifold, or a busted hose, yer letting in just about 1% of the air being measured, unmeasured. 1% is pretty small, 1/2" is a BIG vacuum leak, so I have trouble accepting a vacuum leak as throwing big lean codes, unless the manifold is busted open, or something really radical.

The added air due to vacuum leak results in a leaner run, O2 sensors tell PCM about it, and it can add fuel to compensate, to brings things up to "spec", up to a point.

Or, I could be full of ****! So, if a vacuum leak is found, and fixing it solves the lean code(s), please let me know, and I can slink away! imp