Hey guys, when I put on my super loud "off-highway use" exhaust system. (dual 2.25", H-pipe. Magnaflow glasspacks as resonators into a dual in/dual out Flowmaster Super 40 dumped before the diff) I also opened up some rather loud unwanted backfiring through the pipes. It would backfire between every upshift, and backfire massively on throttle tip-in after engine overrun.
Although shooting a fireball from the exhaust is cool, the loud gunfire booms were grabbing the wrong attention and were getting downright embarrassing. I imagine I can't be the only one experiencing this level of exhaust backfiring after playing with loud exhaust so just in case you are interested in resolving it too here is my solution.
While watching my wideband o2 gauge I noticed my backfiring would coincide with decel fuel cut-off. More specifically the fueling re-entry protocol coming out of decel fuel cut-off when throttle is applied. And yes, the computer does go into fuel cut-off in between shifts.
I wanted to trick the DME into thinking my foot was still in the throttle while shifting to prevent it from going into fuel-cut mode which is does every time the engine is above 1000rpm and the throttle/TPS is closed.
I attached a capacitor to the TPS signal return going to the DME and then grounded the - of the cap. I started with a 100uf cap, it cured around 40% of my backfiring. Now I'm up to a 470uf cap and backfiring is completely gone, however the exhaust does still pop and gurgle on engine overrun once it does go into decel fuel-cut after the cap has bled down. Yet the backfire from the throttle tip-in coming out of decel fuel cut-off is completely gone.
Side note; I would only do this mod on a manual trans car. Automatics use TPS signal, along with MPH for trans shifting. Delaying the ramp in and ramp out of the TPS sig will make for some unusual, lazy, delayed shifts and gear hanging. (theoretically).
While watching the TPS signal on my piggyback not only did I successfully delay the TPS ramp down it also slowed the TPS ramp up/in because now the TPS is charging a cap too and it's charging a cap though a resistor, the TPS itself. It sounds counter intuitive. Why would anyone want to delay the TPS throttle apply ramp signal, but on the street the car drives beautifully. Since the MAF has the major control of fueling and AFR's I'd imagine the TPS is mostly used for load calculating. I was afraid of perhaps causing a lean stumble due to tip-in acceleration fuel because the TPS signal was moving slower then actual throttle opening. But really, on the test drive throttle was nice & crisp it even felt snappier and high rev pull feels much better.
The only side effect I've noticed is that once the engine is reving down it takes an extra second for it to land on low idle. Which I can live with that.
Please excuse my messy wiring, my DME compartment is getting crowded with the Ostrich chip emulator and MAFT-PRO
Although shooting a fireball from the exhaust is cool, the loud gunfire booms were grabbing the wrong attention and were getting downright embarrassing. I imagine I can't be the only one experiencing this level of exhaust backfiring after playing with loud exhaust so just in case you are interested in resolving it too here is my solution.
While watching my wideband o2 gauge I noticed my backfiring would coincide with decel fuel cut-off. More specifically the fueling re-entry protocol coming out of decel fuel cut-off when throttle is applied. And yes, the computer does go into fuel cut-off in between shifts.
I wanted to trick the DME into thinking my foot was still in the throttle while shifting to prevent it from going into fuel-cut mode which is does every time the engine is above 1000rpm and the throttle/TPS is closed.
I attached a capacitor to the TPS signal return going to the DME and then grounded the - of the cap. I started with a 100uf cap, it cured around 40% of my backfiring. Now I'm up to a 470uf cap and backfiring is completely gone, however the exhaust does still pop and gurgle on engine overrun once it does go into decel fuel-cut after the cap has bled down. Yet the backfire from the throttle tip-in coming out of decel fuel cut-off is completely gone.
Side note; I would only do this mod on a manual trans car. Automatics use TPS signal, along with MPH for trans shifting. Delaying the ramp in and ramp out of the TPS sig will make for some unusual, lazy, delayed shifts and gear hanging. (theoretically).
While watching the TPS signal on my piggyback not only did I successfully delay the TPS ramp down it also slowed the TPS ramp up/in because now the TPS is charging a cap too and it's charging a cap though a resistor, the TPS itself. It sounds counter intuitive. Why would anyone want to delay the TPS throttle apply ramp signal, but on the street the car drives beautifully. Since the MAF has the major control of fueling and AFR's I'd imagine the TPS is mostly used for load calculating. I was afraid of perhaps causing a lean stumble due to tip-in acceleration fuel because the TPS signal was moving slower then actual throttle opening. But really, on the test drive throttle was nice & crisp it even felt snappier and high rev pull feels much better.
The only side effect I've noticed is that once the engine is reving down it takes an extra second for it to land on low idle. Which I can live with that.
Please excuse my messy wiring, my DME compartment is getting crowded with the Ostrich chip emulator and MAFT-PRO
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