Welcome Visitor! Please take a few seconds and nola mike
Well-Known Member
So I have intermittently had a CEL with codes p0171/p0174 (both banks lean) since i got the truck ('97 4.0 4wd) a few mos/11k miles ago. If i reset them, it usually takes at least a few hundred miles for it to return. Last time around (maybe 500 miles), i also got a P0402 (too much EGR flow) code. Replaced some vacuum lines, though didn't see a leak. Truck runs fine. I also replaced the DPFE, which had been reading higher voltage than spec. With my new fancy scan tool, I'm getting some curious readings:
1. There are no longer any codes, pending or otherwise. All of the I/M readiness codes are OK.
2. All of my O2 sensors read 0v. All of my FT readings (both SHRTFT and LONGFT, both banks) are pegged at 100%. It's been like this for a while. Not sure why this isn't triggering a code. I'm getting voltage at the sensors, and I removed one and torched it, and I got a signal from it.
3. My scan tool reads "modules". I don't understand what these are exactly, but here are the readings that fail:
$41 ID 12 Measured value FF38
$52 ID 00 Measured value 2AO
$10 ID 21 Measured value FFFF
So...I figure that
a) I really am running super lean. However, on startup, shouldn't I get different values, esp at the O2 sensors while I'm running in open-loop before the car warms up?
b) There's a problem maybe in the harness somewhere, where the computer isn't reading the O2 data correctly, and perhaps adjusting the FTs based on faulty O2 input of 0v? Although again, I would expect the computer to trip some kind of sensor code if they were misbehaving.
I'm at a loss as to where to go next...again, no driveability issues at all. I took it on a 9200 mi road trip with a slide in camper, several times over the mountains to 10k feet in 90' heat without a problem. I feel like that pretty much eliminates any fuel system problems.
1. There are no longer any codes, pending or otherwise. All of the I/M readiness codes are OK.
2. All of my O2 sensors read 0v. All of my FT readings (both SHRTFT and LONGFT, both banks) are pegged at 100%. It's been like this for a while. Not sure why this isn't triggering a code. I'm getting voltage at the sensors, and I removed one and torched it, and I got a signal from it.
3. My scan tool reads "modules". I don't understand what these are exactly, but here are the readings that fail:
$41 ID 12 Measured value FF38
$52 ID 00 Measured value 2AO
$10 ID 21 Measured value FFFF
So...I figure that
a) I really am running super lean. However, on startup, shouldn't I get different values, esp at the O2 sensors while I'm running in open-loop before the car warms up?
b) There's a problem maybe in the harness somewhere, where the computer isn't reading the O2 data correctly, and perhaps adjusting the FTs based on faulty O2 input of 0v? Although again, I would expect the computer to trip some kind of sensor code if they were misbehaving.
I'm at a loss as to where to go next...again, no driveability issues at all. I took it on a 9200 mi road trip with a slide in camper, several times over the mountains to 10k feet in 90' heat without a problem. I feel like that pretty much eliminates any fuel system problems.
