Lateral-g Forums - FAST XFI tuning question

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67rag --

Jody / Frank ....

This is the same motor - with the dyno sheet posted earlier in the thread - that has (IMHO) VERY lean conditions - especially at peak torque and WOT... they were in the high 13's and low 14's at peak torque....

So if he's 'running' lean - it could be a lean miss - even with low load conditions - and he said he's observing A/F's on the dashboard at 14.5's and even as high as 15. I'm ASSuming that they observed these readings while cruising at the "trouble" point. I'm thinking if he's seeing 15 A/F readings -- he's feeling a lean miss...

If his VE's are close -- I wonder if he couldn't change the "BLOCK" of A/F at his trouble spot -- to something like 13.4 or 13.6 etc -- while driving === and see if the miss/hiccup goes away. If it does - then it's just a matter of finding the leanest A/F ratio he can run at that Map point... and run with it. If it's still there -- then we know it's not a lean miss -- and he can start working on more "complicated" solutions?

OOOPPPPSSSSS ----

Wrong - my bad -- one guys is 61 Ragtop and this guy is 67Rag ---- so sorry --- I was going to reference the post with the dyno sheet -- and realized I had the wrong car.

However..... I'll stand by my statement of trying to fatten the fuel a bit and see if there is a lean miss - given his observed 15 A/F readings

Quote:

Originally Posted by GregWeld (Post 237007)

true, but at a cruise MOST combos can be leaner than 14.7:1, however not all so it's a legitimate thing to test. Of course, if the pressure is fluttering you can try changing the a/f or v/e tables and cannot cure it as the pressure is moving all around.

Jody

Jody,

Ah ha -- Got it.

So how steady should the needle in the gauge be when running? With the pump pulsing - my gauge vibrates a lot - but my gauge is in the line not in the regulator.

I was reading my install instructions for my XFI and you can connect a sensor directly to the ECU . It has wires for sensors built in.
I don't know squat I'm just learning but I hope this helps . Wayne

This connector houses the 8 analog inputs that can be used for things such as fuel pressure sensor, oil pressure sensor, EGT probes, etc. An Analog Auxiliary input harness kit (part # 30-1402) is available from FASTä.

Pin A – AAUX1, blue/gray (C12)

Pin B – AAUX2, gray (C13)

Pin C – AAUX3, purple (C14)

Pin D – AAUX4, light green (C15)

Pin E – AAUX5, yellow/black (C16)

Pin F – AAUX6, blue (C17)

Pin G – AAUX7, brown/white (C18)

Pin H – AAUX8, white (C19)

Pin K – Analog return, black (C11)

2.1.20 AUX SHAFT

This connector is for the auxiliary shaft sensor input circuit. The FASTä VSS and auxiliary shaft harness kit (part # 30-1403)will supply you with the harness, sensor, and magnets to monitor things such as turbo speed and torque converter/clutch slippage.

Thanks guys, I guess I will pick up the FAST fuel pressure sender kit(301408), this way I can dat log the pressure and A/F ratio while it occurs.

If the pressure is fluctuating, any Idea what the solution would be, should I move the regulator to the firewall?

Thanks Rich

Quote:

Originally Posted by 67ragtp (Post 237091)

relocating the regulator may be an option, wait and see if the fuel pressure is steady or not. Did you try richening the tuning in the area that it occured in?

Jody

Well we bumped up those areas in the v/e table by 2 numbers and brought the a/f ratio map in those areas from 14.7 to 14.3 and it didnt seem to help. That should have added a bit more fuel(I think). I was a bit nervous about making a big number change in the v/e table. If I raise the v/e table numbers will the air fuel ratio automatically richen up or does the A/f map while closed loop automatically compensate to hold that A/F ratio. Should I really change the numbers alot?

I hope Jody will add to this -- but VE's are the efficiency of the engine at a particular MAP point... once the VE is "on" -- then you should leave that alone and just change the A/F ratio that you want to run at that spot. Check your O2 sensor readings -- and if the motor is 'putting out' the A/F ratio that you've set and it's not adding/subtracting more than say 5% -- then I'd just leave the VE where it is.

I have Accel -- so it's hard for me to tell you what your screens are... but the Accel has a 'screen' that is similar (I think) to the Fast system - where you can see a scale of what the O2 sensor is doing.... and if the VE is on the money - the O2 sensor is doing 'little'. That would mean the VE would be right on... If the O2 sensor is adding and subtracting 10 or more % - then that should be corrected first. Once the VE is on - then you should be able to change the A/F ratio and the ECU will just simply figure that ratio out and that's what the engine will get.

Does that make sense? Ideally -- you'd want the VE table so well set - that the O2 sensor is just along for the ride. That is not always possible of course... but if the VE tables were perfect - you wouldn't even need an O2 sensor.

Quote:

Originally Posted by GregWeld (Post 237213)

getting the VE's right with the O2's working as little as possible is the goal. But if you change the a/f desired at a particular range the VE will also change to keep it ideal. I treat the VE table like jet sizes, larger numbers are richer and smaller are leaner, so if you change your a/f table you'll want to dial in the VE table as well.

In closed loop the computer will compensate by adding or subracting fuel to reach you desired a/f. You can limit how much it adds or subtracts in the tuning software, usually most aftermarket systems have a max limit of 25% +/-. That means if your VE table is within 25% of the ideal number to reach your desired a/f number, then the computer will automatically add/subtract to get you there. Your job as the tuner is to get you there without a lot of computer intervention, so it still has room to add/subtract fuel due to varying conditions like temps, baro changes, etc.

Jody