LS 4.8 Backfire/Stutter Issue
04-09-2018, 03:05 PM
#1
Staging Lane
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LS 4.8 Backfire/Stutter Issue I have a 4.8 and T56 that I put in a tube frame car I'm building. I have had stuttering issues/non drivable and recently decided that I was going to redo it all to make sure I fixed it. So I bought a new 6014 and a new Holley 650 DP. Car idles great and will move no problem at low speeds, but if I get it rolling and stomp on it the car bogs completely and backfires a 2' flame out of the carb.
I have a LC-2 Wideband installed and the motor is running rich at idle ( 10.5-11). It appears by watching the gauge that it is leaning out when I stomp on it. I have 6.5lbs of fuel pressure and should be plenty to keep up.
I am at a loss!
I have a LC-2 Wideband installed and the motor is running rich at idle ( 10.5-11). It appears by watching the gauge that it is leaning out when I stomp on it. I have 6.5lbs of fuel pressure and should be plenty to keep up.
I am at a loss!
04-10-2018, 05:33 AM
#2
How can you be at a loss, you just got started tuning.
Yep, you are stupid rich at idle, almost fuel leak type numbers, and that is undoubtedly masking a lean condition off idle.
There are lots of tuning guides on line. The good ones start with going over the carb mechanically to make sure everything is square, gaskets are good, all orifices unblocked. Set a base timing curve, nothing too aggressive. CHECK FOR VACUUM LEAKS. The missing bolt hole on the Edlebrock intakes is notorious.
Go though the stickies on this forum and check your carb/timing settings against a known good set up. Take good notes on everything you do so you can back out bad changes.
Yep, you are stupid rich at idle, almost fuel leak type numbers, and that is undoubtedly masking a lean condition off idle.
There are lots of tuning guides on line. The good ones start with going over the carb mechanically to make sure everything is square, gaskets are good, all orifices unblocked. Set a base timing curve, nothing too aggressive. CHECK FOR VACUUM LEAKS. The missing bolt hole on the Edlebrock intakes is notorious.
Go though the stickies on this forum and check your carb/timing settings against a known good set up. Take good notes on everything you do so you can back out bad changes.
04-10-2018, 11:22 AM
#3
Staging Lane
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I’ve read a ton and messed with a bunch of settings on the last carb. Decided I may have a bad rebuild so I bought a brand new 650 to put on top.
Ive checked for vacuum leaks already thinking that was the issue. I can’t figure out why it’s leaning out so fast. The factory jets should be plenty for a fairly stock 4.8.
Ive checked for vacuum leaks already thinking that was the issue. I can’t figure out why it’s leaning out so fast. The factory jets should be plenty for a fairly stock 4.8.
04-12-2018, 02:43 PM
#4
Something that seems to get over looked is the coil harnesses. Sounds like you have them both flipped over backwards. The ones that are plugged directly into the coils. Happens a lot. Car will run fine at idle and part throttle. But when you stomp on it It will break up. Something quick and easy to check. If it was only one it wouldn't run very good at all. Hopefully it's that simple.