we were just driving down the highway going up a hill, heard a loud knocking so we pulled over and POOF! the shop can't really figure out how it happened and we can't fathom losing 6 quarts of oil from the last time we checked at a stop (30 minutes prior).

regardless, here we are. we use this vehicle as our main mode of transportation and rely on it to make money, so we're trying to get this resolved quickly and (hopefully) without dropping much more than the $4,500 than we already have.

 

A lean code is set whenever the PCM has to increase fuel mixture past a certain threshold to maintain the correct ratio as indicated by the oxygen sensors. It has a base fuel map that indicates how much fuel is supposed to be needed for the amount of metered air going through the throttle body.

So if you're having a lean code there are a couple of things that could cause it. Either you have unmetered air entering the intake tract past the MAF that the PCM isn't counting. This could be a problem with your intake plumbing, or something not sealing past the throttle body which is known as a vacuum leak. I'd check all your intake plumbing and make sure that everything is tight and sealing well.

You could also have a fuel restriction. I don't believe your engine uses a fuel pressure sensor, so the PCM assumes that the correct fuel pressure is reaching the rails to deliver the proper amount of fuel. Lower than normal fuel pressure would cause less fuel to be delivered by the injectors than the PCM is counting on, resulting in the PCM having to command the injectors to stay open longer to compensate.

So at this point I'd check your fuel pressure at idle, and pull the freeze frame data for the codes. That will tell us what operating conditions were present when the codes were set. If the engine is under load it would suggest a more likely fuel restriction, and if at idle it would suggest a more likely vacuum or intake leak.

I've never seen 171 and 174 caused by oxygen sensors before. It seems downright unlikely that both sensors would have died at the same time unless your engine sent a lot of oil down the exhaust. If that happened you'd probably need catalytic converters too.

 

Do I even want to know what that would look like for my wallet?

 

I've been quoted somewhere between $400-500 for an aftermarket cat, labor included. This contrasts sharply with factory cats, upwards of $1700-2300 just for the parts.

If you do go aftermarket find one of the larger chain store muffler operations, demand the better grade if available and/or the part with the best nationwide warranty.

 

Thanks for the info!

I think my next step is to get a proper smoke test done and have actual diags run by people with more smarts on this than me

I'm just REALLY wanting to count out the small stuff before jumping into the big stuff.

I have a buddy that used to work for a dealership that told me to be careful of people saying the cam phasers are bad seeing as it's 5.4...

 

My point is that if your engine was that bad you'd be seeing other symptoms. Without cat inefficiency codes, stop worrying about the oxygen sensors. Because one would almost certainly cause the other.

Check over your intake piping, check the fuel pressure, and get back to us.

 

Those people are either unaware you have an E-van, or they don't know what they're talking about. The Econolines never got the 3V engines, so you have no cam phasers to fail.

 

Thanks for the info, Tom!

This place in general is fantastic!

 

Hmm........Missed Quoted here???

Nothing I ever wrote/said about the 5.4......which I don't have/work on.

I'll stick to my 5.8

 

For sure bro, vacuum leak. I'll bet you a cheeseburger. Vacuum leak vacuum leak vacuum leak.

These suggestions above are spot-on.

 

Ha ha, yup. Looks like I goofed that one up.

 

Vacuum connection AT throttle body that goes to PCV valve may be bad.

Pic of PCV valve appears ok but actual hose is covered by insulation....

Another way to find vac leaks is with a stethoscope....

 

Update:

While I haven't had time to get a smoke test done on the vacuum lines, I took it to get an oil change and may have stumbled upon the problem...

While the tech was refilling the oil reservoir, he noticed oil leaking from the area right where the hose meets the "oil intake" (if you will). He pulled the hose out and the gasket or little rubber seal that connects the two was sliced almost completely in half. We replaced that seal and I have had no CEL come on in almost 40 miles after clearing the code.

Does anyone know at what milage after a code is cleared that the computer will not report a recently cleared code?

I'm going to drive it a bit longer and if I don't get a CEL, put this to bed.

Thanks!

 

If any condition exists after clearing codes they'll re-appear almost immediately for the most part. Within 10 miles max, my experience is its sooner rather than later.

Hope this does clear the problems for you--small causes like this can be a nightmare sometimes.

 

That seal that you replaced at the oil fill tube, could have given you a slight vacuum leak, that set off the CEL.

Generally, as JWA wrote, a major problem, the CEL will come back on really quick, like as in a mis-fire (bad coil pack), Once codes are cleared, minor problem need approx 50+ mile of run time, at engine operating temperature for the sensor/problem to trip the CEL on.

Also, do hope that the crack seal took your problem away