I am trying to tune my 400 small block. I have a huge stumble when I am trying to do a burn out. The car stumbles every time and sounds like it is off for about 3 seconds and then comes back too. If I freeze my snap on scanner I find the car is sensing knock and retarding the timing any ideas what the spark advance should be while doing a burnout mine is around 11 degrees My knock sensor is very very close to my exhaust could this make a difference???? when the car is just sitting in park running the blm goes all the way down to 108 and if I change the default to lower it will drop down even lower. What causes a low BLM

low blm is usually a sign of running rich. If your BLM's are higher than 128 you are lean. What is your o2 voltage when your blm's are that low?? Is the o2 switching or is it staying about 500mv?

I will have to double check but I think it is just staying at about 500 mv

This is probably because your neighbors own one of these new devices on the market called the "pubescent burnout neutralizer", and it works by emitting an EMP when it detects the sound of tires screeching on the pavement. The EMP momentarily disables the offending vehicle (for roughly 3 seconds).

Recommended workaround: Don't do burnouts.

nice real nice mangus

I'm so funny.

Hrm, my neighbors must have a more advanced one. It made my oil pump go out during a burnout. However my fix was more costly. Wonder if i can find a anti-pubescent burnout neutralizer on e-bay.

On a more serious note i'd make sure nothings causing false knock first then you may have to do some fuel/spark tuning.

seriously any idea what could be causing this stumble I have been working on it for about a year and a half.

I have a 400 small block with an 86 tuned port on it. it is running a 92 computer with the egr and cold start injector bypasssed

here is the car

I think i would try and get the 108 blm issue resolv. I know my ol' roc liked to hesitate upon sharp throttle jabs. What is the engine combo your working with? what size cam, etc?

Could be a lot of things. Here are some terms that I'll throw out for you to investigate: false knock, Acceleration Enrichment (AE), failing fuel pressure, vacuum leak.

Most masks have an upper limit of the spark that can be pulled out during knock detection (mine is 9 degrees), so if the engine is trully falling flat on its face (stumbling heavily), then it's likely not because spark is being pulled out.

This may sound like brutal honesty, but I find it curious that you've been working on it for a year and a half and you don't know what causes low BLMs. Sounds like you should start at ground level and do a bunch more reading. I know that doesn't help the matter at hand, and I'm sorry about that, but the more information you're armed with to start, the better off you are at understanding the solution.

So you've dispensed with the MAF and installed a MAP?

It might take a VERY CONSERVATIVE timing table, with alot of timing ramping out rather quickly.

An exhaust rattle (actually any rattle) can easily mimick the sound of knock in such a way the knock sensor reacts to it. How much retard are you seeing?. IF YOUR EXTREMELY careful, and only seeing a few degrees of knock try turning off the K/S (set the amount of retard possible to 0) and see if you hear any pinging, or traces of detonation on the plugs.
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That's not a 3rd Gen......... <G>
Whatcha trying to sneek past us?.
BTW, looks nice.