Hello, I'm new to posting on the forum, but have been reading for a while. There seems to be quite a few knowledgeable people on here concerning DFI. I'm hoping someone can offer some help. Here is what I have... 67 Camaro (I know not a 3rd gen). 350 engine with Vortec heads, Comp roller cam 294/300 duration, .540/.562 lift, Weiand Stealth Ram intake, DFI gen 7 ecu, 6 spd trans. I was running a carb setup and just switched to the stealth ram and efi. I have a little experience in tuning with a Motec efi, but I'm not familiar with the DFI's Tau vs. Map/ECT table for transient fueling. I follow the math model in the instructions, but I'm still unsure of how I should go about tuning it. My main concern is at low speed, especially idle, the MAP signal is moving around quite a bit, so when I'm trying to dial in the steady state fueling with the VE table, I'm afraid that the Tau table is adding fuel due to the fluctuations in MAP. Is there a way that I can disable the Tau based transient fueling? I really appreciate any and all help.

So, yes, you could have some fueling issues. So there are a few things you can do. First is, you DO need to use the Tau table if you want any form of accel. pump feature; i.e. transient fueling. Using just the base fuel map, you'll go lean whenever you tip into the throttle. Last thing you want to happen.

What you can do, though, is change the MAP points so that the range is more appropriate for you; ie. set a wider area between the points near your idle.

What I'd suggest, though, is to talk to your Accel EMIC that you purchased the system from and get a baseline tune from them. I had some strange Tau issues as well, and their tune fixed 99.9% of them. The rest are due to my unusual configuration.

Jay

Jay,

Thanks for the response. I meant I just wanted to suppress the Tau map just until I get the idle tuned, but realistically, can't I just use the TPS rate of change for the pump shot?

When you say "change the MAP points so that the range is more appropriate for you; ie. set a wider area between the points near your idle." are you talking about the manifold pressure axis numbers or the actual Tau numbers? I don't realy understand what direction to go with the Tau numbers meaning I really don't have a feel for how the Tau numbers affect the AE. It's my understanding that the difference between the tau numbers from cell to cell is what affects the AE more so than the acutal Tau number itself.?>?
Thanks again.
Joe

Does anyone know for certain if the Tau table is inactive without the use of manifold surface temp sensor (MST)?

Yes,realistically you could set the top ones all at 100, the next row down at 99, next row at 98, etc. and it'll have virtually no impact on fueling at that point. Again, I strongly disagree with this point, but yes, you can do it. No, TPS rate of change is NOT as effective as Tau fueling. Tau fueling is all about the liquid fuel clinging to the intake wall (yes, there is always some) and that when there is an instant need, it can pull from this "extra" fuel and put it in the cylinders. You can never accurately get 100% of the needed fuel in the cyl for each individual filing event. So this fuel comes in handy for tip-in and other immediate-draw events. So, what you are setting is basically at idle there is X amount of fuel on the intake. When you tip in, then there is X-Y amount on the intake, and when you let off the throttle, there is some Z amount that builds up (if all is perfect) to our previous X level; i.e. Z+Y=X. Make sense?

Now on the other point, what I'm referring to is changing your default MAP range; i.e. instead of having 16 equally spaced steps, I change mine so that I have less spacing where I don't need it; i.e. 0-20 is only 1 point, and more at key areas for better resolution; i.e. 20-30 has 4 points, 80-105 has 5 points, then a smattering in between those for transition. You can then scale the manifold pressure as needed and desired for your motor. Does that make sense?

It is NOT inactive just because you don't have a MST.

Jay, I'm down with what you are saying about the fuel film in the intake and how it changes with throttle. I guess I just don't have a feel for what the actual tau numbers should be.

When you talk about scaling the MAP axis to get more resolution are you still talking about on the Tau table or are you talking about the VE table? Because I can play with the axis numbers on the VE and A/F tables, but not on the tau table. Also I only have 8 MAP rows in the Tau table vs. 16 in the A/F and VE tables.
Thanks

Ahhh, good point on the VE table. I forgot that it was fixed. But do use it to help you smooth out the other tables (VE / Timing / A:F). What level key do you have?

Ya, I really don't fully understand the Tau table, because it's kinda like black magic. I can tell you the #'s that mine has in it.

Tau..jpg

Jay, That helps. Unfortunately, I just have the Sportsman key. Where is a good place to buy the Pro key? I don't need the cable, just the key.

What engine/cam are you running?

Give Doug Herzog a call at (636) 456-9006 and he'll be able to get you one at a decent price. Got quite a few things from him in the past. If you look on ebay he's on there, but doesn't usually list individual parts.

Ford 351c stroked to 408c, Accel Gen 7 DFI, cam is hyd roller unit with .62 lift for intake and .63 lift exhaust. Around 525 hp at the crank, 425 at rear wheels.

Jay