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06-29-2022, 12:26 PM #1
- Join Date
- Sep 2014
- Location
- Roseville, CA
- Posts
- 1
Blue- 1999 Z28 & 2000 SS
Started Running Lean - Instantly and Can't Determine Cause
Hi, First time posting to the forum and needing some exert advice.
I have a '99 Z28 that has been stroked to a 383, heads, cam, etc. It was tuned by John Gibson @ Forced Air in Sacramento a few years back and has been a great (fun) daily driver.
I was driving it the other day and felt it go dead lean- nosed over and wouldn't accelerate, barley idle - exhaust tone changed as well. It was like a switch had been flipped. No funny engine mechanical noises occurred.
Towed it home - hooked up HP tuner and checked for DTC's - which there was none. Checked the current tune file against the old and there was no difference. I rewrote the file just to make sure. No difference in running condition.
Fuel pump with new filter sit solid at 58 lbs. - which it did before I changed out the filter
Replaced the MAF with another factory unit. - getting same numbers from it
Replaced the front O2 sensors (running long tubes no cats) - left bank was running just a little lower -replaced they are almost identical at 450mv idle 900 rpms
Still runs the same.
I have not changed out the MAP or IAC control - was hoping not to have to pull the intake to get to the MAP
I did and do have VCM files of the car idling (barely) - I think the readings look good except the MAP jumps up and down from roughly 75 - 85 - and the spark advance is bouncing up and down - I'm thinking the spark is bouncing due to the MAP moving around? Is it normal for the MAP to jump around (is this indicating a vacuum leak?
I'm not a pro at deciphering what the scanner is telling me and could use some help checking the numbers.
Any ideas on what I may be dealing with? I have VCM files I can upload as well to show it live running.
Hope I'm missing something obvious
Still trying to figure out how to upload images and or videos.....
Thanks for any help you can provide!
Bob S
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