LS3 Cutting out at Full Throttle

wesinls

wesinls

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LS3 crate engine tuned by redline and has run flawlessly for 3 seasons. It will cut out at full throttle, back fire violently through exhaust, and after a second or so back to normal. All other throttle positions it runs perfectly.
Cleaned fuel filter, checked wiring, good fuel, good fuel pressure, swapped fuel pumps, good voltage...I'm going to turn on logging on the Holley and read the file when I get home (forgot my cables).

Any thoughts on other things to check? It's a new alternator and I changed out my ignition switch, but given its only at high rpm I can't see how those could be the cause.
 
What ecu? Can you data log it? How do the spark plugs and wires look?
 
If it’s back firing it’s dumping too much fuel, so could just need to reset the TPS
 
Redline uses Grade 5 hardware on the cam, not sure why, i have had a couple of the cam gears from them get loose, pull the cam sensor and see if the gear moves,

Also try replacing the Cam and Crankshaft sensor, and replace the relay on the system might be getting hot at full wack
 
J Alper said:
Redline uses Grade 5 hardware on the cam, not sure why, i have had a couple of the cam gears from them get loose, pull the cam sensor and see if the gear moves,

Also try replacing the Cam and Crankshaft sensor, and replace the relay on the system might be getting hot at full wack
Click to expand...
Replacing both sensors work for me a couple of years ago. I have some with me in wash 28.
 
Open up your laptop and see where it is on the fuel map on the live view. We had a MAP sensor go out and it would drop into a section of the fuel map that would almost kill the engine. Like it should be in WOT area and it would bounce to a section in the idle range and choke it out.

If you have not you can order every sensor on that car off amazon and keep a spare. With Holley you can read every value live so you can just start swapping them out one by one and see the results.
 
Do you have a paper fuel filter post pump?
If so, I would replace.
Buddies car did the same thing this past weekend.
Replaced filter and all good now.
 
While a long shot, I've had low compression in other motors that caused me to lose top end and produce this result.
 
maybe a long shot, but hows the air filter look? Ive seen engines similar situation with the air filter completely packed with sand/silt. Worth looking at.
 
wesinls said:
LS3 crate engine tuned by redline and has run flawlessly for 3 seasons. It will cut out at full throttle, back fire violently through exhaust, and after a second or so back to normal. All other throttle positions it runs perfectly.
Cleaned fuel filter, checked wiring, good fuel, good fuel pressure, swapped fuel pumps, good voltage...I'm going to turn on logging on the Holley and read the file when I get home (forgot my cables).

Any thoughts on other things to check? It's a new alternator and I changed out my ignition switch, but given its only at high rpm I can't see how those could be the cause.
Click to expand...
On the Screen is the Voltage smooth on the TPS, same issue i had with mid throttle, but no backfire, fuel filter issue the car for me just died then had to wait to start,
Back fire feels like it is loosing ignition, fuel is getting dumped in then gets fire up and lights the fuel,
 
Just got home and did a few rips this morning with data logging turned on - made the car do it's thing 4 or 5 times to get some good readings...Aqua is my AFR, yellow is the target - thinking it's an O2 sensor?

And thanks to all for the advice, tips - I checked all of them / reset TPS, looked at all my sensors for something obvious.

I attached my data log too for anyone interested in looking at it.


1731371193037.png
 

Attachments

Did it cut out on a couple pulls, but not others on this graph? I'm seeing right at 200 and right at 250 it looks like 2 almost wide open pulls where your AFR did not reflect the TPS and RPMs
 
Anytime I go above 80ish percent throttle it has issues...Here's another view. I like to buimp the throttle a lot when i drive, so not sure if that TPS is bad or not in this example.


1731464544057.png
 
wesinls said:
Anytime I go above 80ish percent throttle it has issues...Here's another view. I like to buimp the throttle a lot when i drive, so not sure if that TPS is bad or not in this example.


View attachment 129020
Click to expand...
the green is your tps you can see where at first its reading than goes out reading all erratic and in that pull it realy never goes above 50 percent
 
Jersey_Jeff73 said:
the green is your tps you can see where at first its reading than goes out reading all erratic and in that pull it realy never goes above 50 percent
Click to expand...
I ordered every sensor on Monday to have as a backup, the TPS being one of them...hoping to change out one at a time this weekend to see what the issue is.
 
Maybe it's already been said but check your Alternator. Had this exact issue with my LS2 and CBM found it on their dyno, at high RPM the Alternator quit charging which caused the computer to freak out, it would cutout then cause a big backfire....just a thought!
 
Meter Tech said:
Maybe it's already been said but check your Alternator. Had this exact issue with my LS2 and CBM found it on their dyno, at high RPM the Alternator quit charging which caused the computer to freak out, it would cutout then cause a big backfire....just a thought!
Click to expand...
I unplugged my alternator with a full battery charged and the issue was the exact same - although not a perfect test, i'd assume that worked as a test. Voltage also was above 14 the entire time. But fwiw, i was also thinking that might be the issue.
 
Still trying to figure out my cutting out issue on the buggy...So far swapped MAT, TPS, O2, IAC, fuel pump, cleaned fuel filter...
Parts in route:
Alternator (i switched it out at the end of last season so maybe, although voltage is good) -
MAP, Crank, cam, and knock sensors (all coming in the next few days)
New plugs and wires - I always wanted nice ceramic wires - so figured why not
Electronic fuel pressure sensor (i only have a manual one currently) - makes looking at data logs a bit more complete
Battery post- I'm not happy with how many things I have direct to my battery to the small M6 stud...going to clean it up, move things around, etc.

I changed ignition switch out at the end of last season - and the idiot light on the dash for the alternator...I might bypass them as a troubleshooting step, but makes no sense that would that cause my issue.

So ya - throwing money and parts as I have no clue on the issue...But if anything, it will be nice to have all the spare parts.

Car runs lean...when I blip the throttle...AFR goes up to 30ish plus...backfires and or dies...

Dirty injectors, man I don't know. Could replace them all but that's a costly guess.
 
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