Quikchevy

i am not new to FI nor these trucks but this one has me stumped!

I'm looking at a 98 with the 5.7 and a Whipple S/C that was installed back in 1998 at 4700 miles (new) basically. It is for sale by the second owner. The truck throws a P0171 code basically every day or close to it as I am told.

I went to test drive it yesterday with my tech2 scanner in hand. When I drove it around town it felt good. Once I got on the freeway and stabbed it to WOT it felt flat, like it didn't want to pull very hard.

The seller told me when he bought it, he was given a hand held scan tool to clear the pesky SES light that always comes on. The shop that put the kit on back in 98' tried to fix it back then with no luck??!!

Now, the truck comes with all the records from day 1, impeccable maintainance records!

This does NOT seem right to me. The original owner is a VERY wealthy older guy who also did other mods, spent about 20-25k before it hit 5,000 miles. Why would he just accept that his brand new truck throws a code everyday?!

As I remember the freeze frame showed the code triggered at about 1650 rpm, not heavy load, not high speed, ect.

Now it kind of makes sense a S/C blasting in air could cause a lean, but that is only is the rest of the system can't keep up right? I doubt Whipple really would have built a kit that throws a code on every truck!

If it's actually true though, where would you look first for the issue? I am thinking a pro tuner should be able to get in there and modify the fuel maps to dump more fuel when needed? It's obviously pulling timing or cutting power somehow.

Any any any help on this would be great before I drop the $$ on this rare truck and chase a supposed 17 year old problem!

Thanks in advance

fastassls1maro

iTrader: (22)

if its only throwing a p0171 code then its not a tuning issue but more then likely either a vacuum leak/boost leak or possible lazy o2 sensor. P0171 system lean bank 1 means that it is seeing a lean condition on bank 1 only which is cylinder 1,3,5, and 7. Look at your freeze frame data and see what it shows for short term fuel trim b1 and long term fuel trim bank 1. If either of those are around 20% it either has a fueling issue on that side or boost/vacuum leak. I dont think would drive the truck for 17 years with a lean code running boost though(seems kind of odd).

tblentrprz

In general, lower speed lean codes due to vacuum leak or exhaust leak and high speed/heavy load lean codes due to fuel supply issues.
Suggestions
1. Pull B1 upstream o2 sensor (B1S1) connector and make sure the PCM is indeed seeing B1S1 with problem and o2 connectors are not swapped (I've seen it before).
2. Make sure no exhaust leaks upstream from upstream O2 sensor (usually leaks affect idle trims only).
3. Monitor fuel trims (Short term and Long term 1 and 2) while power through 1650 to 2500 rpm. If fuel map is correct, LTFTs and STFTs should stay below +10%. If fuel trims are above +10%, adjust tune.
4. If fuel trims are not close and B1 is above +20%, you could try and swap upstream o2s and see if problem moves. If still B1 problem, make sure fuel map and supply is good to 6K.
5. FTs close to same and below +10%, may be corrupted PCM file triggering code falsely. I would flash PCM with latest base and plug in tune tables and retest.
HTH

LilJayV10

iTrader: (39)

Good post.

I generally look at LTFT first because that's what the PCM has learned over time.