Thread: Engine Popping Noise at 6K RPM

Hey guys,

I have an '03 Impala LS with a host of engine and exhaust mods. Before I get into the issue here was my most recent mod: a PCM from INTENSE racing w/ 6K RPM WOT shift points and a 180 thermostat. The car runs beautifully until it hits exactly 6K RPM. It will occasionally short shift at 5900 without any issues. So here is the problem...When I hit 6K, it straight sounds like somebody took a handfull of firecrackers and threw them in a coffee can. It will pop rapidly for about 2-3 seconds, hesitate, and then shift into 2nd. The sound is coming from the engine bay, not the exhaust. Also, I am running 93 octane from sunoco. I have read about a million different solutions to this problem but its all very vague. Somebody told me that maybe my alternator isn't keeping up with spark demands at that high of an RPM. I got the stage 1 voltage boost from ZZP and installed it with the problem still persisting. I just replaced the fuel filter with a high flow unit the other week and my injectors are definitely good. My assumption is that I'm having an issue with timing being too far advanced, some sort of intake leakage, or I'm suffering an A/F lean-out. Any help from you guys would be GREATLY appreciated.

Well the stock PCM uses a 5800 RPM WOT shift point and I'm not having any problems until 6K. Yes, it would technically solve my problem but then I would lose all of my aftermarket PCM benefits and I don't want that haha.

I've got the ER rockers from ZZP on the valvetrain. It most definitely is not hitting the limiter and it doesn't sound anything like valve float. I'm considering putting in LS6 springs anyway but I doubt that has anything to do with it.

Originally Posted by Z34Phoenix

Im sorry but with stock springs 6k can cause float and with ER rockers you are asking more of the valve train and in more risk of float. i know after installing my HV3 i tested raising the shift point in the tune and it would float around 6000-6100 I ended up lowering it to 5800 as i wanted some wiggle room.

LS6 springs are too harsh from what i have been told. L76 springs are what most are recommending now. these are what i plan to run with my SLP rockers.

as for running too much timing, or lean A/F this is very unlikely as you would have detonation and the knock sensors would pull timing.

what could be happening is your spark or fuel cut off is set too close to your shift point. so during a shift sometimes when the shift takes a bit longer it is bouncing off the limiter.

Well, the limiter is set at 6200 rpm and its definitely not touching that. I'll just go ahead and put valvesprings in since everybody insists on it being float.

I think I'm going to wait it out and see what happens. If the problem cannot be solved with a tune (or an adjustment less than major) and it turns out to be valve float, I'm just going to have the shift points bumped back down to the stock 5800. I might put in heavier valvesprings, I may not. I have not really decided what I want to do just yet. I just figured I'd see if anybody had the same problem so I could get right down to it.

Clearly I'm not going to be doing any racing until I find out what the problem is -_____-