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Discussion Starter #1
I'm having an annoying issue which is being hard to narrow down, mainly because it only happens some of the time.
The situation occurs after a pull where the car has seen ANY boost (anywhere from 1-9lbs, currently). After the pull, i'll tip back in on the throttle, and get a large hesitation, with sounds like the car is "trying to clear its throat". Then after about 1-2seconds, it will clear out, and drive completely normal.
This happens maybe 50% of the time, and will follow anything from a slight acceleration that sees boost, to a WOT pull. It does not seem to occur ever after acceleration where boost is not achieved.

The car:

349 a4, 10.5:1 comp, ported highports, f cam, trickflow r intake
76mm precision turbo, intercooled. 90mm PMAS calibrated for 60lb inj.
a9l tuned with moates quarterhorse.

Checked the usual suspects: Mass Air is clocked properly, TPS is fine, Wideband seems to stay in an appropriate area of lean state for 'off throttle' position, no o2's. Ignition is a msd 6al, msd HVC coil, msd pro billet dist, plugs, wires etc all new. No vacuum leaks that I can find. Car is not burning any oil.

Car runs, idles, and performs great... just this damned hesitation.
Any insights or recommendations?

Thanks!
 

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put a fuel pressure guage on it and see what it does. i assume you have a boost referencing regulator on there. i have seen the diaphrams on those wear out and cause an overly rich condition sort of like what you're describing which would explain the hesitation kinda like it's loading up. your wide band will help a lot but it can't tell you what's going on at the fuel rail or the regulator. also have you pulled any plugs and read them?
 

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Discussion Starter #3
put a fuel pressure guage on it and see what it does. i assume you have a boost referencing regulator on there. i have seen the diaphrams on those wear out and cause an overly rich condition sort of like what you're describing which would explain the hesitation kinda like it's loading up. your wide band will help a lot but it can't tell you what's going on at the fuel rail or the regulator. also have you pulled any plugs and read them?
thanks for the reply

the fuel pressure reg is an aeromotive a1000, and it doesnt appear to be sticking open after it boost references. (dips into the high 30's psi on decel/off throttle, comes right back to around 40psi on tip in, under boost it references properly at 1:1)
Wideband is reading appropriate conditions while the car is stumbling/hesitating (usually the car is coming out of decel when im tipping in, so it's fairly lean, but not overly so)


One other thing worth adding that may help... after some more seat time over the weekend, i have also discovered that this same condition occurs when the car is going downhill, even if it had not been in boost. I checked this multiple time to confirm that it was downhill which caused this scenario. Gas tank was FULL.
I feel like there is an obvious connection here that I am missing...
 

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Why no 02 sensors?

Why calibrated maf when you have a QH?

What type of WB , Lab grade?
 

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well good info with the pressures man um probly a dumb ass question but you said going downhill and on tip in after decel correct? so here's my only other question is there any way at all a plug wire or two could be grounding out like are all of them secure? if one or two wires are say hitting a hot ass header only when accelerating after decel or going downhill that could explain the poor driving condition. Now that we know where the fuel is at man honetly there's only 3 things that motor needs to run and you know for sure you got one of them... see where i'm heading with this check your ign sys man that's about the only thing i can come up with right now. -Or- maybe it's in your tune. can you adjust your light load tables? what kind of advance do you have in it at that rpm? could there be a dead spot in your tps when you sweep it? hope this helps point you in the right direction man. - Jimmy
 
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