QwkTrip

iTrader: (23)

Remember, valve train is part of the air system too.

I don't know how a stock ECM behaves, but my Holley EFI was able to mask a failing fuel pump for months before I noticed it in the driver seat. ECM kept increasing fuel trims to compensate for dropping fuel pressure. Didn't notice anything from driver seat until one day the engine lost some pep at high rpm due to knock retard. I never have knock retard so that clued me in to look at things and I found fuel pressure dropping ~10 psi at high engine loads. AFR was fine, but sparks plugs were reading lean. That knock sensor saved my engine and my bank account.

AndyLS1

Great info and definitely something we all need to be aware of and pay attention to. I'm not sure how intuitive the stock ECM is, but it's definitely worth investigating further.

Y2K_Frenzy

It wouldn’t be the O2’s because they aren’t being used during wide open throttle.

AndyLS1

ok, good to know, thank you! One thing I can remove from the check list!

AndyLS1

If you like motorsports and you like puzzles, this thread is for you! Ha!
I did some additional testing today and found that this RPM limit of around 6000 RPM is not consistent. I put it in neutral and floored the accelerator and the first rev went up to 5500 RPM and hung there, the second and third revs only went to 4500 RPM and hung there. I don't think it's an ECU issue because of the inconsistency of where it seems to give up the ghost on the RPM range.
I also tried flooring it while in 3rd gear and it would not progress any further than around 5000 RPM.
I cannot get it to the rev limiter of 6700 RPM anymore.
This weekend I am going to replace my 4" 90 degree intake hose with a new silicone one and clean the K&N filter properly and fully. This will rule out some of the more simple items.
Appreciate any thoughts on this as I am a bit baffled at this point.
Thanks,

bobcratch

hook up a fuel pressure gauge as well.

AndyLS1

I will test this too, thank you

Y2K_Frenzy

I think it’s going to be a fuel or spark issue more so than air.

AndyLS1

I have an extra set of plugs. I'll put them in and see if that makes any difference. Appreciate all the great ideas and input.

AndyLS1

UPDATE: The issue seems to have been a dirty MAF. Once I cleaned the MAF I was able to regain full rev range up to the mapped 6700 RPM redline. I really appreciate all of the great advise and troubleshooting steps from all of the good folks here. Hopefully this thread will help others in the future.
Thanks!

G Atsma

NICE! At least it was an easy AND cheap fix!
I bet you'll be keeping the can of MAF cleaner closer at hand..... lol

AndyLS1

Ha! Yes indeed, the MAF cleaner can will always have a place on my shelf now!

QwkTrip

iTrader: (23)

Good job figuring it out.

AndyLS1

Unfortunately, it appears as the MAF was not the culprit in this troubling LS1 issue. I took it out for a bit of a shake down, cleaning out the carbon, the other day and it still seems to just bog down at higher RPMs and not progress to redline. I can stand on the throttle in 2nd, 3rd (probably other gears too) and it just sort of falls flat around 5500-6000 RPM. The ECU is set to 6700 RPM for the redline. I am going to try to swap out the ECU with a buddy's LS1 ECU and see what happens with that. This build has all new internals and all new accessories/sensors, etc except for the coils, these are from the original motor. Is there any way to test the coils to ensure they are not the reason for the breakdown at high RPMs? I also plan to run a fuel pressure sensor at the rails and somehow have this where I can see it while running at high RPMs to see if there is a fuel breakdown in that rev range. Any insight is very welcome on this and hopefully this thread will help others dealing with this same challenge in the future (I know I have learned so much about my build from reading past threads on this site!). Thanks all!

Redlined2000SSLS1

Main problem or not, get rid of that K&N. The oil from the filter collects on the MAF and throws off the airflow calculation. This happened on my bone stock SS several years ago. I called my dad, who is a GM tech with 30+ years experience. He correctly diagnosed the MAF issue over the phone. Apparently K&N filters are the culprit almost every time this problem rolls into the shop.

Y2K_Frenzy

It’s after one cleans and then re-oils those type of filters is when the problems happen. People will put on too much oil & it doesn’t dry so it gets sucked into and on the MAF wires.

AndyLS1

I actually have the K&N cleaners but was hesitant to use them, the red oil especially, for this very reason. I use my air compressor and pushed air from the inside out as best I could but did not re-oil the filter. I have run it with this filter for a few years without issue but will replace this as it's a cheap potential fix. I would like to rule out as many easy/cheap things I can before getting into the more difficult/expensive items. I will clean the MAF again today and take it for a test run and see how it behaves.

AndyLS1

I just cleaned the MAF again and let it dry before re-installing it. I let the car warm up and then, with the car in neutral, floored it. The first run it went quickly to the rev limiter and pinged it as should. The second and third runs, the car went quickly to around 500 under the rev limiter and fluctuated within around 100 RPM up and down from there, not hitting the rev limiter. I then took it for a drive and in 2nd & 3rd gear with my foot on the floor it just stops going at around that 500(ish) mark before the rev limiter. I think I may need to just replace the MAF and see it that corrects the issue.

Y2K_Frenzy

It runs fine everywhere but at “redline?” A new MAF might do the trick, I dont know. But it seems like it’d run crappy all the time, even at idle, if the MAF was “bad.” Unplug it with it running and see what happens maybe. If it runs worse then I’d kind of think that the MAF was good. If you want to clean the MAF really well remove the screen & put some 90% rubbing alcohol in a squirt bottle (mist) and spray the bars and wires real well. Spray some alcohol on a Q-Tip & rub the bars until they’re shiny. You can clean the wires with a Q-Tip as well, just make sure the cotton is real wet so it won’t leave lint and be real gentle.
Did you look at a spark plug to see if it’s getting fouled out or anything?

AndyLS1

It does make sense to try to deep clean the MAF more than just with the MAF spray cleaner. I will take it off and clean the wire filaments as you mentioned, gently of course. The car runs great at idle and up to around 5000 RPM. Under the heaviest load (6-7000 RPM) is where it starts to give up the ghost. I'll try the deep clean on the MAF and run it and see if that helps before buying a new MAF, thank you for the suggestion.
Spark plugs look great, not fouled or oily, all look good. I even replaced them with new ones and replaced the wires to rule all of that out.