hello all, i got a new to me 98 expy eb, 5.4 4x4, with 180k on it. it started running rough and missing under load, but idles fine. checked the codes, and got the 171/174 banks too lean code. did the search and found all the threads that helped diagnose the problem. forum member glc said that its almost always a pcv leak, or a fuel issue. so 'ill get the valve and elbow and a new fuel filter and see what happens.
here's my question. everything i've learned would make me think that a cop or plugs had gone bad, not the pvc system.does it allow that much extra air into the induction, or is the ecm that sensitive?
be easy on me, i'm just trying to understand.
rick

 

What happens is it lets more air in than the system can compensate for. There are limits to the fuel/air mapping.

It sure wouldn't hurt to pull the plugs and replace them, unless you know that they have been replaced recently - I doubt that they have been changed more than once and 100k is pushing it a bit. It *might* need cops.

 

thanks glc, i've got new plugs and fairly new cops from my old expy that this one's replacing, also have injectors that have less than 5k on 'em, gonna do that,too. will pick up the pvc replacements tommorow. hope that will cure it. these trucks can be a pita, but i still think that this gen. are the best lookin' trucks out there.

 

Yea, this info isn't much good without knowing brand names of parts used...it matters.

Btw it's pcm, in case your unaware.

 

No, it's PCV..........positive crankcase ventilation. PVC is polyvinyl chloride and PCM is powertrain control module.

 

i've got motorcraft plugs, the cops aren't. the injectors are rebuilds that i got off of ebay, they worked well in the old expy. i know that i'm taking a chance by not using motorcraft cops, but i don't have an extra 400 bucks for this. i've not had the chance to get this done yet, hoping tommorow is the day.