Diablosport Forums

Hello everybody, I have a 2002 Lightning with a couple mods that include 2.6 upper pulley and a K&N panel filter. My boost gauge usually sees around 13-14lbs, but on cool days here lately its been tickling 15. My L currently has 107,000+ miles on it. I have replaced the O2 sensors and fuel filter around 100,000mi. Just here in the past few weeks it's been throwing the lean codes. I have cleaned the MAF sensor elements and changed the fuel filter again still no change. I just can't figure out why. I put the pulley and tuner on back around spring and has had no problems and has been running the 93 Octane with Pulley tune. I have some readout info that may help.

Here is what my Diablo reads out:

while cruising (60mph)

STFTs are around 0-5%
MAF reads around 40gm/s
IAT2's are about 97 when its about 70 outside
Timing is around 23-26
Engine Coolant stays around 184

WOT

STFTs read around +22%
MAF reads around 277-302gm/s
IAT2s rise to around 110* at 70* outside
Timing is at max 17*
Engine Coolant stays around 184

I keep leaning towards the MAF sensor because I have an AWD Explorer that had leaning and timing problems and was cause by a bad MAF. Could I have a bad MAF sensor or a bad fuel pump?

could be an exhaust of vacuum leak.

I have checked for vacuum leaks and there are no noticeable exhaust leaks.

timing seems fine, supercharged cars run low timing at WOT. but stft that positive the car is dumping fuel in because it's so lean.
to test the MAF unplug it and drive the car, just don't hit WOT.

What would I be looking for when I unplug the MAF and drive it? How would I possibly be able to determine if I have a bad fuel pump without fuel pressure gauges and how would I hook up pressure gauges to a stock setup? I've had a '93 stang with a 306 and I had aftermarket fuel rails and regulator with an electronic gauge and same for my '97 cobra which had an '03 cobra engine and Kenne Bell and aftermarket fuel rails. On this truck I see no where to attach a fuel pressure sending unit on the stock fuel rails. This sucks because I'm on a pretty tight budget this year and can't take it to have it checked out. I have to shade tree this one.

unplug the MAF and see if the truck still gives a code for running lean. But don't go WOT, just cruise around, maybe 3\4 throttle max.

there is a vacuum line notorious for popping off towards the back of the block just above where the transmission mounts up
you can follow it from the top of the blower on the passenger side all the way back
if that line pops off it will produce that code

I have a 03 lightning with the same lean codes p0171 and p0174. My truck runs fine it does idle a little rough and does feel like it list some power. I uninstalled my program and the truck idled really bad and even shut off after reinstalling it ran ok .the check engine light didn't come back on yet,any ideas why this would happen?