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10-08-2021, 06:57 AM #1
Will a bad tune cause random misfires (P0300)?
I'm chasing a p0300 code and I am curious as to whether the tune itself could be causing it. I replaced the PCM and on the stock tune it was running rich, had misfires on cylinders 2 and 7 at startup but then they cycled out. Had the tune flashed back in and now it runs like shit. Misfires on cylinder 8 constantly and 2 and 7 at idle (when it will idle). Should I go to a different tuner or continue to chase the misfires? I have a new throttle body and coil packs on order, sprayed starting fluid to check for vacuum leaks but couldn't really tell because of the idling issue. Any thoughts/inputs?
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10-08-2021, 09:44 AM #2
- Join Date
- Jan 2016
- Location
- US
- Posts
- 14
A second opinion is always a good idea
And sometimes a third!
Sounds mechanical to me, valve issue maybe
Sent from my SM-G988U using Tapatalk
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12-02-2021, 06:13 AM #3
I'm in the same boat as you. It's a new build. The tuner states that he's not done. I hope it's not mechanical.... but it's on him.
`99 Trans Am: Vigilante 2600, Stroked (383), Cammed, TSP Catback and Headers,Strano/Koni STR.T, Strano 35/22 Sway Bars, Elite E2 Catch can, 400,000 miles
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79 Firebird: Pontiac 400 4-speed, Borg Warner Super T-10, XE-268 Cam, Hedman headers, Edelbrock RPM intake, dual exhaust & Flowmasters
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`08 Corvette Base M6 LS3, Morimoto Headlights and Taillights, SLP Blackwing CAI.
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12-06-2021, 08:16 AM #4
- Join Date
- Feb 2009
- Location
- Florida Man Status Acheivement
- Posts
- 11,785
Navy Blue Metallic- 98 T/A, 00 FBVert, 78T/A
Check the plugs and wires. Plugs crack. Also check the wire harness for the coils to insure no crack or broken wires.
Common causes for P0300
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure (Carb only)
- Faulty fuel injector
- Vacuum leak
- Low fuel pressure
- Camshaft sensor defective
- Crankshaft sensor defective
- Engine timing off
- Leaking head gasket
- Low engine compression
- Poor quality fuel
All of these you can do and not have a mechanic charge you for.
Now regarding the ecm and tuning. This is a difficult answer. Meaning it could be a bad tune, ecm or tuner.
Do you have the correct ecm? There are different years of ecm's 98, 99-00, 01-02. 99-00 and 01-02 have the same pin out for the harness for the ecm while 98's have a much older and different pin out for the ecm. You can get a 99-00 ecm and have the software upgraded to 01-02.
How much tuning experience does the tuner have with LS1's?
You need to rule out the mechanical issues first, otherwise your tuner is chasing ghosts. For example when tuning mine after my 403 build I would have an idle issue all over the place but once I got above 2k rpm it would smooth out and have zero issues. After going thru 2 sessions of tuning and a different tuner, the 2nd tuner figure out that my map sensor was cutting out. I pulled my intake off to replace and relocate it and found that the seal on the FAST intake was torn and causing a 8" vacuum leak that would seal once I got into the pedal. Fixed those two issues and bam smooth idle and was able to finish tuning.http://www.ls1.com/forums/f7/my-6-liter-build-174257/
http://www.ls1.com/forums/f8/my-8-8-rear-build-165553/
6.0L Block - Forged 403ci , Polluter Stg3 Cam, FAST 102mm Intake, NW102 TB, MSD wires, NGK TR6 plugs, Truck Coil Packs, LS3 Fuel Injectors, CC Pacesetter LT Headers, TS&P ORY, QTP e-Cutout, Magnaflow Muffler, 104mm Air Lid & Line Lock, Catch Can, Stage 2 T56 w/Viper shaft, PRO 5.0 Shifter, Tick MC, SPEC Stg3+ Clutch, QT SFI BH, MWC DSL, Full UMI Performance Suspension, Viking Coilovers, YR1 Snowflake Wheels wrapped in NT555 tires & Custom Fab Ford 8.8 rear w/Wavetrac Diff 3.93 Yukon Gears, WSQ Hood, 3"CM Strange Eng Drive Shaft.
00 FB Vert - "Stockish" Belstein Shocks, Hotchkis Springs (1" Drop), C7 Snowflake 17" Wheels
78 FB - Just getting started......
Horsepower never lies, but is often lied about!
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01-31-2023, 12:56 AM #5
Yes, a bad tune can cause random misfires (P0300). A misfire can occur when the engine is not firing the correct amount of fuel or ignition timing is off, which can be caused by a poor tune.
how to change notes password
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02-01-2023, 01:26 PM #6
- Join Date
- Sep 2010
- Location
- Bel Air, Maryland
- Posts
- 1,719
Silver- '02 Trans Am WS-6, 6M
First thing I would do, is move ignition coils to different cylinders, and see if the misfire codes move with them.
SLP Air Lid/Smooth Bellows
L76 6.0L block, PRC Ported 243 heads, Texas Speed 224R cam.
Kooks Emissions LT Headers/Catted Y pipe
NGK TR55 plugs
Magnaflow Cat-back
Spohn Front Upper Tubular Control Arms
UMI Front Lower Tubular Control Arms
UMI Front Sway Bar
UMI Rear Lower Control Arms/ Adjustable Panhard Rod
UMI Welded-on Two Piece Subframe Connectors
Factory C5 Z06 17x9.5 wheels w/ 285-40-17 Continental Extreme Contact Sports all the way around.
Dyno Dynamics dynoed @:
415 rwhp
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