code decipher please
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code
how serious is a vacuum leak? I've had my expedition for about 3 years and the check engine light has come on about three times and the diagnostic would read a vacuum leak. I would ask the mechanic (3 diff mech)well what exactly is a vacuum leak? They would tell me oh it's nothing serious. What we'll do is just reset the light for you. How serious is the "oh nothing serious?"
Logistics Pro
Joined: Jan 2001
Posts: 3,740
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From: Central NYS
Well, here's my take on a vacuum leak. Suppose one of the o-rings on bank2 cracks and allows some extra air to be drawn in to cylinder 6. The O2 sensor is going to see this extra air and tell the PCM. The PCM is going to drive all the injectors on bank2 to run richer to use the extra oxygen being leaked in to cylinder 6. This will cause cylinders 5, 7, & 8 to be too rich. Over time this extra fuel will wash the lubrication off their cylinder walls, causing excess ring wear on those cylinders.
I suspect that if you have a scan tool that will let you monitor LTFT (Long Term Fuel Trim) you will see it is running over 20%. This excess fuel will reduce the efficency of your catalytic converter when the PCM runs the Cat efficenecy monitor.
Since you have both banks running lean (P0171 and P0174), you probably have the beginings of the infamous PCV valve elbow leak. I'll let someone more knowledgable than me chime in as to where it is located on your '99 5.4L engine.
I suspect that if you have a scan tool that will let you monitor LTFT (Long Term Fuel Trim) you will see it is running over 20%. This excess fuel will reduce the efficency of your catalytic converter when the PCM runs the Cat efficenecy monitor.
Since you have both banks running lean (P0171 and P0174), you probably have the beginings of the infamous PCV valve elbow leak. I'll let someone more knowledgable than me chime in as to where it is located on your '99 5.4L engine.
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Joined: Feb 2005
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From: Ft. Worth, TX
The first place to look for a vacuum leak is the PCV rubber fittings on the plastic pipe. IF this is where your leak is and you fix it you will still have to have the CEL reset, it will not just go away by it self.
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