LS3 Cutting out at Full Throttle

30-ish AFRs shouldn’t backfire… Can you smell fuel when that happens? Plugs look black? If so, I wouldn’t trust that reading at all.

My guess is the new O2 sensor (happens) or its wiring (possibly grounds since the TPS was reading crazy as well) is fucked.

What happens when you just unplug the sensor? Clean up?
 
Waiting for my cam sensor to show up from Amazon (so I'm bored / anxious as f) - and figured I'd share what I'm hoping is the problem. I googled how to test cam and crank sensors with the Holley software and came across the video below...Basically "Diag" 6 is the crank sensor and the 97 I have circled looks to be how many times it had an issue...also noted the error on the RPM reading at this same time.
Anyway - cool video...sure fing hope it is my problem...crank sensor. All wiring looks good to it...



Screenshot 2024-11-16 121338.png
 
Well - it wasn't the cam sensor...My next maybe is the alternator. I've been reading that an alternator can cause CAM sensor issues...and if you look at the log below, the volts are all over the place at the same time the CAM sensor wiggs out. I did replace the alternator, so it's not too far fetched...but man, WTF will be very odd if that's the cause..

See two logs below - one from when the car has issues, and a different log from when it wasnt...

and @Rockwood - no fuel smell...havent tried pulling the O2 sensor yet...not sure if it will run without it - but with the new sensor exact same symptoms.

No issues:
1731806345075.png

Issues:
1731806444449.png
 
Looking at the pic in your earlier post.

I think you have a sensor reference voltage issue, or a sensor ground problem..

Your TPS, RPM, and AFR go nuts all at the same time. For the first 100~ seconds of that graph it is all cool. When it goes to shit after that, they all go to shit.

What changed around the 120 second mark in post #11?
 
when i installed my holley there were labels on the power and ground wires that said they wanted them connected directly to the battery. i did connect them to my battery switch hasn't been a problem i ran ground wires from battery to chassis and battery to block if i remember correctly there was a few ground wires from the holley harness going to the head as well. it looks like you have multiple sensors and battery voltage going out at the same time i would go over all the wiring and the relays i have had the relay for the fuel pump act up where it was sending low voltage to the pump
 
@wesinls multiple sensors shitting the bed at once means something common is fucked, as @Kraut_n_Rice and @Jersey_Jeff73 say.

Check common ground on a failing sensor for continuity to the battery negative and measure total resistance. Shouldn’t be nearly zero.

Check reference voltage on the same sensor. Should be 5V (or battery voltage, 12-ish) on the dot.

If that checks out, jiggle shit and see if it fucks off.
 
Last trip of the season in May car was not producing voltage...Assumed alternator, changed it, no fix - got it back home and noticed ignition switch had some loose terminals - changed it, same issue...Then found that on the dash there's a red idiot light for the alternator and it had a loose connection - changed out that light, and boom - good voltage and assumed my car was back to normal (so 2 dollar part was my problem all along).

Given I am getting good voltage and the idiot light works - I haven't changed out those two items yet...dumb ino - but a new alternator producing good voltage and the idiot light works...that being the cause of my issues just seems unlikely to me / makes no sense. But given the weird voltage jumps and from I've been reading, it's a possibility it is the alternator. So today - swap out alternator and bypass that idiot light...if that 2 dollar idiot light is my problem I'll just laugh.

I also added a race radio - and had to add it to my battery...but all connections look tight, Odyssey battery, etc.

So yes @Sandkist alternator swap and issues began (plus a few other things noted above)
@Jersey_Jeff73 - ran direct to battery already and I've checked all grounds - they look good
@Kraut_n_Rice - the 120 second mark was my first hard blip on the throttle...before that was idling and a slow cruise out of camp.
@Rockwood if issues continue after alternator swap good idea.

Hate to admit I like having these issues as it forces me to learn more about the Holley software and my engine in general....and if all current sensors are good I'll have a complete set in stock in camp for future issues for myself of someone. :)

Video showing alternator causing cam codes fwiw.
 
Just some thoughts. You didn’t accidentally short anything when replacing the alternator or other electrical items? I seem to recall a few members over the years having issues with their radios/intercom interfering with their ECMs. Faulty battery (internal connection) could also be something to look at.
 
wesinls said:
Well - it wasn't the cam sensor...My next maybe is the alternator. I've been reading that an alternator can cause CAM sensor issues...and if you look at the log below, the volts are all over the place at the same time the CAM sensor wiggs out. I did replace the alternator, so it's not too far fetched...but man, WTF will be very odd if that's the cause..

See two logs below - one from when the car has issues, and a different log from when it wasnt...

and @Rockwood - no fuel smell...havent tried pulling the O2 sensor yet...not sure if it will run without it - but with the new sensor exact same symptoms.

No issues:
View attachment 129284

Issues:
View attachment 129285
Click to expand...
 
at the 135 why did the voltage drop so far did you have to re start or the fans kick on or is there a loose connection. also you can adjust the frame rate to view the data from diag 6 and 9 for the crank sensor you want 20 mili second frame rate so you can see the pulses havent messed with the holley in a while i think you had to do a system log and set the frame rate. the o2 sensor shouldnt be a problem you can adjust the learn rate and limit the amount the holley will adjust the fuel or might also be able to run it in open loop
 
Last edited:
this was a data log a did a while ago if you want to compare to yours
 

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Put it on a Dyno and figure it out.
I had a miss and CBM ran into the Dyno. Turned out to be something wrong with computer. Swapped and ran great after that.
 
So it ran fine for 3 years then started acting up? Did you change anything over the summer?
 
Oreillys will bench test your alternator for free btw

Also, did you check the ground to your head for the computer/harness/sensors? Or just your chassis ground, and/or battery ground?
 
acefuture said:
Oreillys will bench test your alternator for free btw

Also, did you check the ground to your head for the computer/harness/sensors? Or just your chassis ground, and/or battery ground?
Click to expand...
All of the grounds look good - The 2 to the heads and the main on the harness...
Just got done swapping out alternator, trigger wire, spark plug wires, and MAP sensor...Seems like it's running better / doesn't cut out as easy, but IDK - if i push it, the engine will spit and die, but I seem to have to try harder...Revving the engine in neutral is starting to scare me a bit. The only sensors I haven't changed, and that I have now, are the crank and knock sensors...i might try to change them tomorrow.

Headed to Gordon's on Saturday and will be there all week...hoping for the best.

I'm going to give Redline a call and see if they'd be willing to look at the car while I'm out there...they made a stop at my camp last year to check on some things as a courtesy...maybe they have some magic to help me.
 
wesinls said:
All of the grounds look good - The 2 to the heads and the main on the harness...
Just got done swapping out alternator, trigger wire, spark plug wires, and MAP sensor...Seems like it's running better / doesn't cut out as easy, but IDK - if i push it, the engine will spit and die, but I seem to have to try harder...Revving the engine in neutral is starting to scare me a bit. The only sensors I haven't changed, and that I have now, are the crank and knock sensors...i might try to change them tomorrow.

Headed to Gordon's on Saturday and will be there all week...hoping for the best.

I'm going to give Redline a call and see if they'd be willing to look at the car while I'm out there...they made a stop at my camp last year to check on some things as a courtesy...maybe they have some magic to help me.
Click to expand...
i have my knock sensors turned off they pick up too much noise for the engine being mounted solid to the chassis. my friend has a drag car was having similar problems to you was caused by EMF electo magnitec interference holley systems don't work well with noise. you can try disconnecting the alternator power and field wires make a few passes and see if its better. also rewrought any power cables away from computer harness. testing the output of the alt in not going to tell you if the alt is making too much rf noise. when you changed your alternator did you put something with a real high output. also try calling holley their tech support is good. if you still have problems pm me i can get you a phone number to a guy that knows the systems in and out he did some of the original programing for holley
 
Jersey_Jeff73 said:
i have my knock sensors turned off they pick up too much noise for the engine being mounted solid to the chassis. my friend has a drag car was having similar problems to you was caused by EMF electo magnitec interference holley systems don't work well with noise. you can try disconnecting the alternator power and field wires make a few passes and see if its better. also rewrought any power cables away from computer harness. testing the output of the alt in not going to tell you if the alt is making too much rf noise. when you changed your alternator did you put something with a real high output. also try calling holley their tech support is good. if you still have problems pm me i can get you a phone number to a guy that knows the systems in and out he did some of the original programing for holley
Click to expand...
Will do and thanks...it's the same alternator that was in the car before I started having the issues.
 
Something I went through on my car last season (you were there to see it) is like @Jersey_Jeff73 mentioned, the Holley system is very sensitive to noise. One suggestion my tuner had is to make sure the alternator lead cable is isolated away from ANY other wiring. The noise it omits can interfere with sensor cables and throw off readings making the computer throw wild adjustments to make up for it. So check that your alternator cable is no where near any other wires.

We'll swing by your camp when we are out next week btw
 
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