[bx4525]

Hey guys just wondering can a tuner correct the issue of exhaust popping when letting off the throttle? I here it has something to do with fuel? I do have a chip on my '93 mustang but I might just see another tuner to correct this and to add timing since I will now be running with methanol.

[cgrey8]

The way I got rid of it was to activate DFSO which cuts off fuel on decel.

However an alternative to that if you don't want DFSO for some reason is to make decels lean instead of rich. There's a number of ways to do that, but I found (before I activated DFSO) that it was easiest done via the low slope. Although making decels lean can have its own set of disadvantages if you aren't careful...such as leanout/bucking on tip-out. You don't realize how much you take a smooth tip-out for granted until you try driving in traffic with a tune that leans the engine out which causes you to loose all power on tip-out.

[bx4525]

Awesome thanks CGrey8. Hopefully my tuner knows what to do but I will definitely mention to him what you just wrote and see what he thinks and prefers. Point is it can be fixed in a dyno tune correct?

[cgrey8]

With DFSO turned on, there's no exhaust popping/bubbling/gurgling...whatever you want to call that decel noise for me. In fact, I sped up the rate at which DFSO turns on as well as lowered the RPMs that it can be active at so that I get activation of DFSO quicker and more often. But I remember back when I was still using the stock settings. DFSO took a second or two to activate once you went Closed Throttle and during that time, I could still hear the popping, then as soon as DFSO kicked in, it went away.

If your tuner uses the X3Z (93 Cobra tune) as a basis of comparison to setup DFSO, just keep in mind stock setting on X3Z tune is to allow DFSO at 1600RPMs or above. If the engine is lower than that, you won't get DFSO and so you'll still have the popping at decel. I dropped that down to where DFSO is active to about 1100RPMs. With that, I never have decel pop.

[bx4525]

Great explanation I really appreciate it. Thanks

[Chucko]

Check the closed throttle timing curve FN111. The 'pop' is because the fuel didn't finish burning in the cylinder. Adding timing at higher RPM helps.

[decipha]

be careful though, lots of timing at high load can do bad things

on all boosted cars i always set fn111 to 25 degrees of timing above 1500rpm

[cgrey8]

FN111 is only active at Closed Throttle...so it should never be actively commanding spark at high load.

[firemanwill28]

Is DFSO a stock setting for an A9P and if not can it be added?

[EDS50]

Is DFSO a stock setting for an A9P and if not can it be added?

It should be disabled by default if it is available in the guf1 strategy. DFSO first became available on the 93 cobra x3z to my knowledge. For some reason or another it is now set to enabled on all the gufx strats which in my oppinion for a stock.bin should be disabled as the it was from the factory but thats another discussion.

[firemanwill28]

So will it work in the GUFx stragtegies or is it ignored?

[EDS50]

So will it work in the GUFx stragtegies or is it ignored?

Works perfectly fine in the gufx strats. It will work just as fine in the guf1/a9p since Chris added it as a Z_hack-scaler to the guf1 strategy as well as the gufx. Feel free to use it just the way you have things. What you are looking for is the scaler Z_DFSW. It is probably already enabled in your tune and you dont know it. If not, enable it.

[Chucko]

be careful though, lots of timing at high load can do bad things

on all boosted cars i always set fn111 to 25 degrees of timing above 1500rpm

I wouldn't be surprised to learn that some boosted engines can keep a fair bit of pressure in the intake manifold with the throttle closed.

[cgrey8]

The ability to use DFSO in GUFx tunes was always there. In fact, it didn't have its own enable/disable feature from Ford. Z_DFSW was added to explicitly disable it. The Ford way of disabling it was to set the Max Load scalar (DFLOD) to something below what the engine would ever see at any running condition. I think the stock setting for DFLOD on A9P and A9L was ~1%. Even at decel conditions, Load is going to be above that so DFSO was effectively disabled on these tunes. Increase that max load scalar and you should be able to get DFSO working on any GUFx tune. Set it to a value just a tad above what your decel load is.

Once enabled, the main factors that SHOULD affect DFSO's activation and deactivation should be TPS, RPM, ECT, and MPH. Although I set my minimum ECT value really low so I get DFSO even before the engine is warmed up. There's a steep hill coming out of my subdivision, and I go DFSO before the engine's above 120 almost every day and haven't had any problems with it. I did up my minimum MPH from 5 to 20 just so I didn't get DFSO while in 1st gear.

The min RPM for DFSO (DSFRPM) is the only confusing scalar in the bunch. It is not a fixed RPM value. It is an RPM above DSDRPM. So in order to set it intelligently, you need to know what your DSDRPM value is while at decel. This is a dataloggable status value. So if you don't know what it is, datalog it, and then add it to DSFRPM. That will be your effective minimum RPM for DFSO. I have DSFRPM set to 550. With a DSDRPM of ~600, I get DFSO active all the way down to ~1150RPMs...not ~1600 RPMs which is about where X3Z deactivated DFSO.