Tuned with vacuum leak, then fixed
12-24-15, 05:43 PM
#1
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Thread Starter
Tuned with vacuum leak, then fixed
What would be the result of someone getting dyno tuned with some sort of bad vacuum leak, and then later fixing the leak without getting retuned?
I've never had a MAP tuned car before, just MAF.
Rich all the time? Lean all the time? Only lean/rich at idle or full boost?
Apologies if searching just failed me; thanks!
I've never had a MAP tuned car before, just MAF.
Rich all the time? Lean all the time? Only lean/rich at idle or full boost?
Apologies if searching just failed me; thanks!
12-24-15, 05:58 PM
#3
Full Member
Thread Starter
He's dead Jim!
I keep finding out more and more about my new and dead car, the most recent being that this situation occurred some time before I bought it.
Last edited by Lord Bro; 12-24-15 at 06:55 PM.
12-30-15, 04:37 PM
#4
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Thread Starter
My logic
This is how I'm thinking about the system:
With a MAF tuned system that has a leak post-compressor and post-sensor a couple of different circumstances can occur. You're not in boost and unmetered air is entering the engine, or you've built some boost pressure and metered air is escaping the system before it gets to the engine. Fuel trims or some such might help compensate slightly, but this would generally result in a lean condition while in vacuum (low rpm or idle), and rich while in boost/at WOT.
With a speed density tuned system that has a leak post-compressor but before the intake manifold (pre-sensor), you're decreasing the effectiveness of the turbo while in boost, and perhaps decreasing measured vacuum due to the leak. Due to the nature of the system fuel trims get adjusted, and under boost the wastegate duty cycle decreases and the turbo works a little harder to hit expected boost pressures. If it were a perfect world your turbo could be working inefficiently and IAT *might* go up a bit, but there wouldn't be a huge difference.
We don't live in a perfect world though, so I imagine like AFRs would be off and you might run a bit lean while not in boost, and a bit rich and slightly warmer while in boost. If this were then accounted for in a tune (if it could be, if the leak was incredibly consistent), that would mean increasing fuel at idle and decreasing the amount of fuel provided while in boost/WOT.
All else held equal, if the leak were then fixed after the tune was done there would be extra fuel being provided while the intake was in vacuum, and not enough while diving hard. Rich at idle, lean at WOT.
I understand it's a bit of an oversimplification of the control system, but would that generally be the net effect of fixing an intake leak after being tuned?
With a MAF tuned system that has a leak post-compressor and post-sensor a couple of different circumstances can occur. You're not in boost and unmetered air is entering the engine, or you've built some boost pressure and metered air is escaping the system before it gets to the engine. Fuel trims or some such might help compensate slightly, but this would generally result in a lean condition while in vacuum (low rpm or idle), and rich while in boost/at WOT.
With a speed density tuned system that has a leak post-compressor but before the intake manifold (pre-sensor), you're decreasing the effectiveness of the turbo while in boost, and perhaps decreasing measured vacuum due to the leak. Due to the nature of the system fuel trims get adjusted, and under boost the wastegate duty cycle decreases and the turbo works a little harder to hit expected boost pressures. If it were a perfect world your turbo could be working inefficiently and IAT *might* go up a bit, but there wouldn't be a huge difference.
We don't live in a perfect world though, so I imagine like AFRs would be off and you might run a bit lean while not in boost, and a bit rich and slightly warmer while in boost. If this were then accounted for in a tune (if it could be, if the leak was incredibly consistent), that would mean increasing fuel at idle and decreasing the amount of fuel provided while in boost/WOT.
All else held equal, if the leak were then fixed after the tune was done there would be extra fuel being provided while the intake was in vacuum, and not enough while diving hard. Rich at idle, lean at WOT.
I understand it's a bit of an oversimplification of the control system, but would that generally be the net effect of fixing an intake leak after being tuned?
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wthdidusay82
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12-16-15 09:14 AM