Missing on decel?

Black91TSiAWD · 04-30-2007, 12:12 AM

Ok I recently traded my gsx for a 95 tsi awd, I just put new bpr7's gapped at .029 and new plug wires as well. The car doesnt have a miss at wot or idle, only happens under a good engine brake.

It snaps and pops like an srt-4 almost. Fuel mods are a rewired 255hp and 550's, stock fpr for the moment.

Thanks alot, any help would be appreciated.

ZmanIV · 04-30-2007, 01:15 AM

Quote:

Originally Posted by Black91TSiAWD

Fuel mods are a rewired 255hp and 550's, stock fpr for the moment.

That is your problem.

Black91TSiAWD · 04-30-2007, 02:07 AM

Quote:

Originally Posted by ZmanIV

That is your problem.

Yeah no its not

, but thanks anyway.

pneumo · 05-01-2007, 12:17 AM

Check your TPS adjustment. The ecu is supposed to shut off the injectors when the throttle is closed and rpms are higher than 1200 rpm. If the TPS is misadjusted the ecu will think the throttle is still open, and it'll keep injecting fuel, resulting in misfires, backfires, or sputtering.

ZmanIV · 05-01-2007, 02:31 PM

what boost are you running?
What color are the plugs?
If your fuel system is overrunning the FPR when you let off the gas wont you will have excess fuel in the exhaust system causing the backfiring/popping sound.

srumel · 05-01-2007, 03:05 PM

might want to check your cam timing as well. my exhaust cam is advanced one tooth, and i have the exact same "popping" sound. how's your vacuum?

DGajre777 · 05-01-2007, 03:15 PM

Quote:

Originally Posted by Black91TSiAWD

Fuel mods are a rewired 255hp and 550's, stock fpr for the moment.

Quote:

Originally Posted by ZmanIV

That is your problem.

Quote:

Originally Posted by Black91TSiAWD

Yeah no its not , but thanks anyway.

Fuel overrun is when the stock FPR cannot route back enough fuel causing a crappy idle or stalling like symtoms on deceleration. Stock FPR overruns don't just happen at WOT or idle, they also happen at deceleration.

A 255 pump overruns the stock FPR. Get a rewired 255 and it'll overrun the stock FPR even more, since it flows more with increased voltage. According to RRE...

At 12.5 volts (non-rewired) the 255HP flows:
Fuel Pressure 43psi - 233 Lt/hr
Fuel Pressure 73psi - 189 Lt/hr (30psi boost, assuming you have a 1:1 AFPR)

At 14 volts (rewired) the 255HP flows:
Fuel Pressure 43psi - 264 Lt/hr
Fuel Pressure 73psi - 220 Lt/hr

I suspect the lack of an AFPR to be the culprit. Stock 2G fuel pressure is 43psi. Your stock FPR should raise fuel pressure on a 1:1 ratio with boost. Do you have a fuel pressure gauge to monitor your fuel pressure?

It could also be because you are running rich. Are you running without a cat?

pneumo · 05-01-2007, 06:39 PM

Black91TSiAWD, does the snapping and popping happen the whole time you're decellerating? Or does it snap and pop for a second or two just after the throttle is closed?

scottsee · 05-01-2007, 07:54 PM

Quote:

Originally Posted by pneumo

Check your TPS adjustment. The ecu is supposed to shut off the injectors when the throttle is closed and rpms are higher than 1200 rpm. If the TPS is misadjusted the ecu will think the throttle is still open, and it'll keep injecting fuel, resulting in misfires, backfires, or sputtering.

Exactomundo!

Black91TSiAWD · 05-01-2007, 11:07 PM

Ok to clear up a few things, even though Im fairly certain pneumo nailed it with the TPS, I just havent gotten the time to mess with it yet.

Yes it happens the whole time Im decelerating

car has a 1g head swap

plugs and wires are brand new and have maybe 50 miles on them

550cc injectors, safc2 at -10% correction

there is a rammed out high flow cat on the car with some shitty flanges that leaks a little

I do know the FPR is being overrun but wasnt too sure it was causing this problem or not.

timing was just set 50 miles ago when the head was re-installed.

boost ~19psi hrc 20g

no fuel pressure gauge, the a1000 is on its way.

absolute_DSM · 05-02-2007, 09:20 AM

Also, make sure if youre running a 1g TB, that youre running the 2G TPS with it.

SleeperG · 05-02-2007, 09:54 AM

exhaust leaks will cause popping under decel condtitions like engine braking.

i'd focus on eliminating every single exhaust leak you have. for one they rob your bottom end, two they make your exhuast raspy and loud, three it might be the problem.

ZmanIV · 05-02-2007, 10:22 PM

Quote:

Originally Posted by SleeperG

exhaust leaks will cause popping under decel condtitions like engine braking.

i'd focus on eliminating every single exhaust leak you have. for one they rob your bottom end, two they make your exhuast raspy and loud, three it might be the problem.

If the exhaust leaks are after the turbo what does it matter.
N/A motors need the exhaust system to be intact, turbos need to get the gasses out as fast as possible.