Help! Mystery "miss" Cylinder 6 While Warming Up

yudy69 · September 17, 2009

OK, about 3 months ago I started up the truck and when pulling away from curb felt a slight miss/hesetation (almost like a bad carb feel...but of course it's fuel injected). After running for a min or 2 the miss goes away and truck runs FINE until the next time it is started. The scenario continued intermitentantly after that first time but has slowly built itself into about 95% of the times the truck is started (even after only sitting for 20 mins)and the "miss" has gotten more pronounced. One of my best friends builds transmissions at AMCO so we've had it down there after hours on the scanner etc.

Started throwing P0300 general miss codes cylinder 6 about 8 weeks ago and here's what I've done:

1. all new iridium plugs

2. swapped plug and wires 4 & 6 and still misses on 6

3. Scanner showing that 6 is flooding and computer is telling it to "back off" fuel (something around -31 bank 2)

3. NEW coil, New Injector, New Fuel Pressure Regulator, NEW computer, Re-Sealed Intake, Checked all vacum hoses going to/from intake manifold, checked fuel pressure (around 55lb's), checked compression cylider 6 (OK), Hypertech III was de-programmed for all above

WHAT THE HECK!!! any other tries before having to pull the head???

Please HELP ME!!!!

Truck:

2000 Silverado LT3 4X4 Prerunner

Custom front LONG travel (12inch) suspension with King remote res coil overs and extended Arms axles and tie rods, K&N intake, Headers, Hypertech III engine management, dual exhaust dumped with 2x Magnaflo behind cab, caged through bed, rear is end to end fully trussed CURRY Ford 9" with high pinion 3rd member 456 gears with Trutrac locker, deaver prerunner springs strapped at 20" of travel with King 18" triple bypass remote res, Painted Glass at all 4 corners (extended min 6x6) and glass hood.

asilverblazer · September 17, 2009

Injectors? Could be faulty and dumping too much fuel in. The computer is trying to lean it out unsuccesfully.

I wonder how the computer has determined that 6 is flooding? It can detect mis fires, and lean rich conditions, it might be presuming that based on the #6 misfire and a rich condition in the exhaust that 6 is the culprit and be flooding... I just didn't think the computer had that much logic built into it.

You could swap injectors similar to plug wires to see if the problem follows the injector.

yudy69 · September 17, 2009

Injectors? Could be faulty and dumping too much fuel in. The computer is trying to lean it out unsuccesfully.

I wonder how the computer has determined that 6 is flooding? It can detect mis fires, and lean rich conditions, it might be presuming that based on the #6 misfire and a rich condition in the exhaust that 6 is the culprit and be flooding... I just didn't think the computer had that much logic built into it.

You could swap injectors similar to plug wires to see if the problem follows the injector.

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Reply: Did coil first, then put a new injector in 6. Still says "miss on 6". fuel flooding does NOT say on 6, but the scanner is showing (in real time) that it's flooding on Bank 2 which is the 2,4,6,8 side. THANKS for the input...keep it comming!