Fitech tuning assistance

[Mikesimp70]

Got it running Saturday. Initial timing 10degrees, full mechanical advance 32 and vac advance is not connected.

302 w mild cam

Screen shots below are at idle. These are settings put in by my engine builder.

Issue is that if I am cruising at speed and roll out of the throttle, I experience a “stumble” when I start to press the throttle again. Its like the engine cuts out and there are some pops. AFR numbers climb. It recovers without stall but I have to believe the fix is simple.

Thoughts?

 

[Mikesimp70]

Last two screen shots

 

[KyddsPly]

I’m running a Holley terminator and previously the MSD atomic, but I had this issue with both and the IAC adjustment correct most of it, the rest was higher initial timing.

I don’t know if this helps, as stated not the FiTech but worth a shot as most throttle bodies incorporate the same principle. Both simple and quick to test. My initial is set to 15* at 800rpm and total at 36*


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[Hazegray]

I have the same problem! I was trying to tune it out, but got caught up with other projects at home and forgot what changes I previously made. Yea, CRS kicked in and I had to reload the factory settings...

If you look on the FITech website, they address this issue as a possible lean condition upon returning to throttle after let off. I would recommend making one change at a time, documenting every change on paper, and keeping track of the results. My goal is to try tuning this weekend...

 

[Mikesimp70]

Added a bunch of Accel pump across the temp range and lower AFR at idle and 1100. Big improvement but not quite there yet. Considering a degree of timing.

 

[Eoth]

I've got the same stumble but no "popping". However I didn't want to fiddle with things while it is still "learning". I did notice that it became real pronounced when I reduced the "return to idle" (so I put it back to its original value). I have found myself driving it a little differently to avoid the hesitation so I am not even sure if it is still doing it (it probably is).
It is still light years better than my carb, but I do want this last little bug dealt with.

 

[Mikesimp70]

I've got the same stumble but no "popping". However I didn't want to fiddle with things while it is still "learning". I did notice that it became real pronounced when I reduced the "return to idle" (so I put it back to its original value). I have found myself driving it a little differently to avoid the hesitation so I am not even sure if it is still doing it (it probably is).
It is still light years better than my carb, but I do want this last little bug dealt with.

Assume you mean the DFCO return fuel? I was eyeing this as well. Considering increasing the value. Did you try this direction?

 

[Eoth]

No... Decel open IAC: This is the information I adjusted it with:
This number should be at zero as a base setting, by going negative you are reducing the amount of time it takes to return to Idle, and by going positive you are increasing the time it takes. Normal procedure of adjustment is to add or subtract 10 to start with and then adjust it to your liking or what the engine needs.

HOWEVER I think you are on the right track based on the following:

Decel Fuel Cut Off:
When you let off throttle and decel with your vehicle the EFI will reduce fueling to prevent popping and an over rich condition that would occur if the fueling continued as it normally would. Depending on the size of your engine, camshaft specs, engine temp, gearing, and several other factors like environmental conditions, you may have either too much or too little fuel cut on decel.
In order to change the amount of fuel it applies you must go to Go EFI Tuning and then find Fuel Cut Control. Inside this menu you will see an option called DFCO Return fuel, this number represents the amount of fuel the system will inject when it you start to give the vehicle throttle again. If you are having a hesitation when getting back in the throttle then add to the DFCO Return fuel to give the engine more fuel when transitioning back to acceleration. You may also need to adjust your accel pump settings to help with this transition as well.

 

[airman]

How sure on that initial timing are you? How many miles have you put on it? You need to put some learn miles on (200 of them). It will do some weird stuff while it learns. Mine would almost die around a corner getting on it the first few times.

 

[Mikesimp70]

I am not at all sure on timing!! A friend told me to dial in timing until the. Vacuum at idle read max, back off 7-10% and lock it down. I dialed in timing until Vacuum climbed to 17.6. I backed it to 15.8

I did that and the result initial timing is 31 degrees. I have to say it is running much better and has a lot more power.

I am now doubting the scale on the balancer. Time to check TDC on cylinder 1

I reset all learn and drove quite a few miles tonight. Cannot get IAC steps to come off 0 at idle and idle is running 1200 despite setting of 730i have backed screw nearly all the way out

So confused at this point

 

[Mikesimp70]

Ok so not being sure, I used my light and backed timing down to builders settings. Idle is back at 730 and I dialed IAC steps to 8. Initial 10 and final 36

Driving her to work tomorrow. Time to build miles.

 

[Muddypony]

I struggled with a stumble and intake backfire problem. Tried to tune it out with no luck. Turned out I had low fuel pressure. Wasn’t the pump or the plumbing. It was a bad regulator. Popped a new one in and all was fixed. Definitely worth investing in a fuel pressure gauge. Good luck.

 

[Mikesimp70]

Update. Turns out he timing was the issue. It wanted more timing because it needed it. Apparently when I stabbed the distributor, I was a tooth retarded! Pulled and adjusted today. Timing is now 11 and 36!! Linkage adjustment to bring idle down. Fitech is now doing its thing!