ENGINE BREAKING UP AND MISSING BETWEEN 5000-6000 RPM

[H2BRUTE]

Recently, when I happen to rev the engine between 5000-6000 rpm's (only to hear the exhaust with the QTP exhaust cutouts open) it starts to miss and break up. This never happened before. I have a magna charger supercharger installed with MSD wires, new plugs, 178 degree thermostat, dynatech long tube headers with flow through cats and a bassani dual exhaust system and a Volant cold air intake. For the first few months after installing the supercharger, this never happened. It Always ran smooth. Any ideas on what might be causing the problem?? As always, your help is greatly valued..BRUTE

[MVR 155]

I know you mentioned new plugs..... was that when the SC was installed a few months ago??? The first thing I can think of is to check the plugs, even though they are a few months old. You may be getting some detonation and have possibly damaged a spark plug(s). If you find that you have detonation I would suggest hooking up with a reputable tuner right away and have him add fuel or pull timing on your program. Right along with the first theory is that you may be starving for fuel up top, I would hook up a pressure gauge and check this..... if your starving for fuel you are definately detonating which can or has already taken its toll in terms of engine damage.

Good Luck in getting to the root of the problem..... keep us posted on what happens.

[H2BRUTE]

As always, thanks for the input. I take it in on Monday..Will keep you posted..BRUTE

[Desert Dan]

What is the redline RPM on your engine?
5-6000 rpms are pretty high for most V8s

[CONRAD II]

Do you have gauges monitoring your air/fuel ratios? If so, are you running lean, rich, or are you at 14.7:1? I have the mag charger also, and if I am at idle or under boost I never ever run lean. Sometimes while in vaccum I do notice that I am running lean (sometimes as much as 16:1), but my engine runs/sounds fine. I hope I'm not about to start having the same problems that you are....

[datapimp69]

my supercharged engine started doing this around 6 mounths after putting it in.

i still havent figured it all out yet but, i have figured out that is has something to do with the quality of gas i get.

i can only run 92+ octane now and i can tell when i get crap gas from somewhere.

i get on the highway and floor it and it starts breaking up. and throwing "random cyclinder missfires" errors. get better gass or add a octane booster and it goes right away.

[CONRAD II]

Originally Posted by datapimp69

my supercharged engine started doing this around 6 mounths after putting it in.

i still havent figured it all out yet but, i have figured out that is has something to do with the quality of gas i get.

i can only run 92+ octane now and i can tell when i get crap gas from somewhere.

i get on the highway and floor it and it starts breaking up. and throwing "random cyclinder missfires" errors. get better gass or add a octane booster and it goes right away.

Doesn't mag recommend that you use ONLY premium fuel after installing the super charger? I've had my charger on for about 6 months and have had zero problems other than workin out a couple bugs in the very beginning.

[H2 Bill]

I have had the problem a couple of times too. Once it was a burned ignition wire (actually twice) and the other was clogged injectors due to bad gas. Now I only run Chevron or Mobil. I found this out by running a couple of bottles of Techron through the tank and it cleared it right up.

[H2BRUTE]

It will be interesting to see what they find out when I take it in. My tach actually doesn't have a red line on it, but I would guess probably between 5000-6000 rpms would be it..The guy at the shop thinks it is a fuel filter since it is only doing it at high rpms. I have been using 93 octane since the s/c install, but maybe I will get some Techron and see if it helps before I take it in. Thanks again..BRUTE

[MVR 155]

Originally Posted by CONRAD II

Do you have gauges monitoring your air/fuel ratios? If so, are you running lean, rich, or are you at 14.7:1? I have the mag charger also, and if I am at idle or under boost I never ever run lean. Sometimes while in vaccum I do notice that I am running lean (sometimes as much as 16:1), but my engine runs/sounds fine. I hope I'm not about to start having the same problems that you are....

16:1 is waaaaay lean, if you are really at this A/F ratio I can assure you that you are very close to some serious problems (if there isnt already damage)...... even 14:1 is too lean, with a supercharged (or any other F/I induction vehicle) I wouldnt go over 13:1 personally since you want to leave a small buffer for bum gasoline and extreme conditions. Im a firm believer that whenever you do a major mod (such as internal motor work, forced induction, nitrous etc....) that it should be dyno tuned with a wideband A/F to get the max performance from the set up as well as be within safe parameters from detonation.

[CONRAD II]

Originally Posted by MVR 155

16:1 is waaaaay lean, if you are really at this A/F ratio I can assure you that you are very close to some serious problems (if there isnt already damage)...... even 14:1 is too lean, with a supercharged (or any other F/I induction vehicle) I wouldnt go over 13:1 personally since you want to leave a small buffer for bum gasoline and extreme conditions. Im a firm believer that whenever you do a major mod (such as internal motor work, forced induction, nitrous etc....) that it should be dyno tuned with a wideband A/F to get the max performance from the set up as well as be within safe parameters from detonation.

If I am really running as much as 16:1 wouldn't the engine run poorly because its starving for fuel? The only time my gauges show that I'm lean is randomly when I'm not in boost. The rpm's don't change and the engine doesn't feel any different though.

[MVR 155]

Originally Posted by CONRAD II

If I am really running as much as 16:1 wouldn't the engine run poorly because its starving for fuel? The only time my gauges show that I'm lean is randomly when I'm not in boost. The rpm's don't change and the engine doesn't feel any different though.

Probably just fluxuation in the gauge when on/off throttle, that is not uncommon..... I meant under acceleration if you were that lean you would have big problems. Probably wouldnt hurt to go one heat range colder on the spark plug and tighten up the gap a bit on them, if normal gap is .050-.060 run them at .035-.045

In the mean time pull your plugs and look for any signs of running lean... if there are tell tale signs then going a heat range colder as well as some tuning will definately help out big time.

[finall]

a) Kewl! Since very soon you will blow up your engine because you are running it up to 6K rpm. Chevy v8's are just not designed for it. Please post pics when you do!


b) Could be a computer safety cutoff feature of some sort, to keep leadfoots from doing a) above.

c) Could also be fuel, timing, etc. The guy who installed the screw should be able to figure this out really quickly.

[Humdingah]

Originally Posted by finall

a) Kewl! Since very soon you will blow up your engine because you are running it up to 6K rpm. Chevy v8's are just not designed for it. Please post pics when you do!


b) Could be a computer safety cutoff feature of some sort, to keep leadfoots from doing a) above.

So you're telling me a modern Gen III or IV small block V8 cannot be revved to 6,000 rpm? What's the redline on the new Vettes...6.5 or 7K? I'd have no problem spinning one to 6,000 rpm now and then...apparently you're well-versed in modern engine design. I've got the shift points on my Lightning, with a supercharged 5.4L and just about the longest stroke on a production motor, at 5,800 rpm with no issues.

You'll run into valve float issues long before you 'blow up an angine'.

And there is no computer safety cutoff feature that does what is described...they'll have a built-in rev limiter but nothing that will cause an engine to break-up throughout the rev range to protect against spinning to a 'stratospheric' 6,000 rpm.

[MVR 155]

Originally Posted by Humdingah

So you're telling me a modern Gen III or IV small block V8 cannot be revved to 6,000 rpm? What's the redline on the new Vettes...6.5 or 7K? I'd have no problem spinning one to 6,000 rpm now and then...apparently you're well-versed in modern engine design. I've got the shift points on my Lightning, with a supercharged 5.4L and just about the longest stroke on a production motor, at 5,800 rpm with no issues.

You'll run into valve float issues long before you 'blow up an angine'.

And there is no computer safety cutoff feature that does what is described...they'll have a built-in rev limiter but nothing that will cause an engine to break-up throughout the rev range to protect against spinning to a 'stratospheric' 6,000 rpm.

No problem spinning any of the LS-X engines to up near 7K on stock parts, the limiter on my Z06 is set at 6900 rpm. Now will the truck make power over 6K.... most likely not but that is due to tuning peramaters and camshaft profile.

[H2BRUTE]

Well, after taking the car in to check out why it was missing at high rpm's they diagnosed it as the REV LIMITER, which I never heard of..Guess it's something like a governor in the old days preventing you from going too fast or in this case revving the motor too high..Guess that's a good thing. Anyhow, it is running like a champ..Guess I won't be revving it up on idle that high with the exhaust cutouts open. BRUTE ps Thanks for all your comments..I learned a ltot from this little episode..

[pdsq99f4]

Did you have a professional tuner tune your H2 or is the program just the canned program that comes with the supercharger kit? Sounds like you need some fine tuning because a stock H2 can rev to close to 6K without a problem.

[H2BRUTE]

The program that was installed is from Magnacharger. From what I gather, (per the shop that did the install) they put the rev limiter at 6K so you never over rev the motor. That is the way they make sure your Hummer lasts for 100K miles or more. BRUTE