Squeek

Hey guys, I'm new to these forums but a handful of you may have seen me on crownvic.net or taurusclub.com. Yesterday I bought my first truck EVER (craigslist) and I'm excited because I think in the worst-case scenario I got a great deal.

The vehicle is a 1997 F150 4x4 Supercab, 4.6L with a 4R70W. Previous owner said the transmission was going out, and let it go for $600. After test driving it, I gave it a 15% chance the transmission will need to be torn apart, but I'm certain there are some very inexpensive things that may be suspect.

Here are some symptoms of irregular operation:

1.) Engine seems to run fine, but from a stop at WOT, there is a lack of power. Strangely, the RPMs increase, but the acceleration is inconsistent with the RPM increase--it's much slower, and tops out at about 30mph; I don't know if there is a rev limiter at 3500, but the vehicle stays steady and won't accelerate further until letting off the gas. The feel is very similar to a dirty MAF (which is bypassed under WOT of course). I got three PID snapshots--one at idle, one idling at 2000RPM, and one driving with throttle wide open from a near-stop. Below are some screen shots of OBDLink that show 3500 RPM at 28mph. The snapshots at idle were just data I wrote down because I forgot that I could just take a screen shot

2.) The main reason the previous owner thought the tranny was going out was because it would slip out of OD at highway speed. I thought this sounded a lot like a bad MLPS (transmission range sensor).

3.) When driving home, my girlfriend was driving my Taurus exactly 55mph, and I was behind her at about the same speed, but the F150 speedo only read 50mph. Later she tried 60mph and the F150 read about 55mph. I suspect there may be an incorrect or worn/damaged VSS (vehicle speed sensor). I believe the Taurus, while not calibrated, is pretty spot-on for speed. It's usually consistent with in-town "Your Speed Is" signs.

4.) There were stored codes of P0171 and P0174, System Too Lean. LTFTs at idle are showing -25% to -27% on both banks. STFT is about normal at -1.5% to -2.5%.

5.) 2WD, 4HI and 4LO are working correctly. Slight leak in the back of t-case.

6.) Data for idle:
Closed loop
CLV.................27.45%
ECT................188.6°F
STFT Bank 1.....-1.56%
LTFT Bank 1....-25.78%
STFT Bank 2.....-2.34%
LTFT Bank 2....-26.56%
RPM................703.25
VSS......................0
Ignition timing advance
for #1 cylinder....14.5
IAT...................64.4°F
MAF..................0.88lb/min
TPS abs.............20%
O2 B1S1.............0.08V
O2 B2S1.............0.76V
Scan tool input....14.4V

7.) Data for idle at 2000RPM:
Closed loop
CLV.................15.69%
ECT................199.4°F
STFT Bank 1...........0%
LTFT Bank 1......-4.69%
STFT Bank 2.....-2.34%
LTFT Bank 2.....-3.12%
RPM...............2060.25
VSS.....................0
Ignition timing advance
for #1 cylinder....29.5
IAT...................73.4°F
MAF..................1.86lb/min
TPS abs............22.35%
O2 B1S1.............0.66V
O2 B2S1.............0.11V
Scan tool input....14.4V

8.) Screen shots of WOT holding steady at 28mph@3500RPM are found in the pics below.