ls3 416 0411 ecu . hard cut at 6300 rpm with backfire.

[boback1]

hello i'm new to this forum I have an issue with my vehicle and hoping anyone here can help me. i'm sorry in advance if my post is not correct. any pointers on how to make a better post next time is also welcomed.

my car used to have an ls1 with a ls1-b ecu speed density tuned. i replaced it with an ls3 416 but still cathederal heads and went from ls1 to ls3 coils. I did the gen 3 to gen 4 conversion with all the extension harnesses and all new sensors and parts. Got the car running fine. went to the dyno and the car wouldn't rev past 6,300 rpm when we did a pull on the dyno then it would backfire hard, shoot flames out of the exhaust, and then car would go in some sort of a limp mode. you have to cycle ignition then car runs fine again. if you rev it in nuetral it'll rev to the normal redline of 6,850 rpm but would backfire hard when it hits rev limiter and runs bad again, i have to cycle ignition again then it runs normal. here's the things i've done already to try and fix it with no luck.

replaced crank sensor with 2 new ones and a known good one from my old engine while performing crank relearn everytime.
replaced cam sensor twice with 2 new ones.
removed timing cover to verify cam gear is not loose or moving.
measured cam gear to cam sensor air gap and it measured good.
added more good engine to chassis grounds
installed brand new 145 amp alternator
replaced knock sensor and verified all extension harness's are good.
knock sensors are next to headers now but my tuner says he didn't see any knock and even did something to make the knock sensors less sensitive.
scoped cam and crank signals and found signals are not cutting out.

my ve map isn't tuned optimum for the setup right now but it's safe in WOT areas. just wondering if there's something we missed in the tune or anyone have similiar experience. This problem is driving me crazy. i'm not a tuner by any means but i bought a cable just to try and figure this out. I've uploaded my file into the attachments. any help is greatly appreciated thanks.

[2xLS1]

Did you switch to a 24x reluctor on the crank or are you using the lingenfelter converter box? I noticed the coil dwell times haven't been changed from the stock LS1 coil settings. Not sure if that really matters nut when you are grasping for straws.....
Have you looked into the possibility of high rpm valve float?

[GHuggins]

All of your rev limiters haven't been adjusted. Such as etc in gear = 6200 = throttle closing with no fuel cut = spitting fire capability / then there's some cold start modifiers that look really low even at operating temperature...

Things to try anyways...

[2xLS1]

All of your rev limiters haven't been adjusted. Such as etc in gear = 6200 = throttle closing with no fuel cut = spitting fire capability / then there's some cold start modifiers that look really low even at operating temperature...

Things to try anyways...

It's a cable throttle calibration and the ETC Limit is set to disable anyway.

[boback1]

The reluctor is 24x no conversion box. My valve springs were checked and machinist said they are good. Springs are more than capable of handling the cam. But like you said at this point it could be anything. If it makes any difference I ran it in 2nd gear till 6,000 didn't let it hit rev limiter then shifted to 3rd and it ran all the way out till 6,000 again the. I tried to grab 4th and it happened even without hitting rev limiter. Backfired and lost throttle response and I had to cycle key again to get it to run good again. I'm hooking up a fuel pressure gauge into the car right now to verify its holding fuel pressure again. I'm running an oreilly brand fuel filter. Just checking anything and everything at this point.

[2xLS1]

Does it set any codes when it happens? My guess is you are losing spark or losing accurate spark timing which make me think it is somehow reluctor/crank sensor related. Can you post a datalog of it happening?

[boback1]

No it does not set any codes. I'll get some logs tomorrow. Crank sensor didn't drop out when I scoped it.

[boback1]

i made a log this morning. only thing i see a little weird to me is the ignition voltage drops down to 10.5 volts when I start the pull. Is that normal ?

[2xLS1]

Your narrow band O2s are 0-10MV at WOT. It is lean as fark. You shouldn't need 31 degrees of timing either. Kind of explains reving in neutral but not under load. It's starving for fuel.

[boback1]

ok what should the MV be at full throttle ? i hope i didn't damage this engine. It's a built engine i hope it's ok.

How about the ignition voltage ?

also thank you for your input so far.

[2xLS1]

Narrow bands aren't accurate for setting WOT fueling but you should be seeing them north of 850mv and I like to see them in the 900s. Typically anything below 450mv is leaner than 14.7:1. The lower the leaner so when you see them 0-10mv you can imagine. Was there not a wide band O2 on it even on the dyno?

[boback1]

yes i have an extra o2 bung on my pipe and we used the dyno wide band to tune it. it was going good afr's were in the 11:8:1 to 12:2:1 are for the whole tune while this issue was happening. Then all of a sudden it was starting to go up to 13:1 afr when we were tuning and making more power(n it made 559 hp and 555 tq) so i we assumed i maxed the walbro 255 out. so my tuner threw about 15 % more fuel and it wouldn't go past 13:1 afr so we stopped. I replaced that pump with a walbro 450. possible bad o2 sensors? the tune shoulkd actually be pig rich in that area because he didn't take the additional 15% fuel out.

[2xLS1]

Narrow bands while not accurate outside of 14.7:will definitely show what the A/F trend is. And 13:1 would still be above 450mv, not 0-10. All I can go by is the 1 log you posted.

[boback1]

I hear you. I'm gonna replace both o2 sensors and do another log . So I'm assuming the ignition voltage is not an issue?

[2xLS1]

I hear you. I'm gonna replace both o2 sensors and do another log . So I'm assuming the ignition voltage is not an issue?

Either are your O2s.. They are not even used at WOT but will give you an idea of what the A/F is. Your problem is not O2s.

[boback1]

ok with that said i have absolutely no idea where to go from here. everything else looks to be good nothing is dropping out or losing signal.I can't find anything in the tune like a rev limiter that i've missed. this thing is so consistent it hits the same rpm everytime. i've done at least 30 2nd gear pulls till it hits the 6300 rpm where the issue is and still can't figure it out. anything you recommend i should be logging for next time?

[boback1]

i just looked at the log again and it looks like the cam signal stops moving at 4200 rpm till it hits the problem then goes back down to 4200 rpm and starts moving again under that. The cam signal is reading 3200 when it stops reading and as rpm goes back down it's moving again. I'm pretty sure it's not supposed to stop reading.

[2xLS1]

Fix the lean issue first. Do you have logs of it on the dyno? Should have been logging it. If you say the WB was never leaner than 13:1 then the narrow bands should be above 450mv. Engine will run without a cam sensor signal. I would have a FP gauge on the rail first while doing a pull. If FP stays up then you need to look at the tune.

Observe that as long as the PCM receives the Crankshaft Position sensor 24X signal, the engine will start. The PCM can determine top dead Center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The Camshaft Position sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes if incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.

[boback1]

Ok thank you for the explanation. I do have a fuel pressure gauge on the rail and it never goes below 55 psi during the pull. Unfortunately no logs were taken during the dyno. I'll try and get a wide band in the car a start logging afr.

[2xLS1]

Looking again at the tune I'm betting it is a fuel pressure problem. Are they 52lb@4 Bar injectors? I noticed only the IFR table was changed and none of the other injector tables were. I don't believe that is causing your lean condition. The VE at WOT looks like it should be providing plenty of fuel.