Req_fuel & VE table

[Damonfg]

Greetings.
I have just installed a MS2 and it fired up on the first crank. It's running rather rich, and I'm a little confused after reading the manual.

This is a naturally aspirated 86 Fiat, 92ci, and I am reusing the four factory bosch low impedance injectors, rated at 18lb/hour.

I used MT's Req_fuel calculator, 92cubic inch, 18lbs/hour, AFR of 13. It said my Req_fuel was 15.2.
Then I stepped over to the VE table generator. Idle on the car is roughly 900 RPM at 40kpa. 75ft/lb at 3500RPM, 75HP at 5500RPM, and a redline of 7000. It generated a table with values from the 46 up to 71.

Started it and got it idling, and went to adjust the injector PWM parameters. I set PWM threshold to 1ms and set the PWM current limit to 30% and kept dialing it back. I worked my way down to 16% and had no noticeable change in idle quality.... So I just set it to 20% and hope that is safe.

It ran fine, but it was quite rich. Idle was around 10.5:1. I started to decrease req_fuel down from 15.2 to about 12, and that brought the AFR up closer to 13.5:1. (this was without any enrichment nor EGO correction)

1) is 20% current limit reasonable? How far can I go? If it appears unresponsive to adjusting, is something wrong ?
2) is it proper to adjust the req_fuel to get in the ballpark, then tune the VE table around it?
3) I was figuring some values on the VE table would be near 100, but this wasn't close - why is that?

Thanks guys !!

[devastator]

I can't answer the first question you have as I have high impedance injectors, but I'll take a shot at the other 2:

2) is it proper to adjust the req_fuel to get in the ballpark, then tune the VE table around it?

Yes, that should work fine. If you find your VE table requires values that are out of range, (numbers higher than 255 or lower than 1), you might have to increase/decrease your req_fuel value to get yourself back in the ballpark.

3) I was figuring some values on the VE table would be near 100, but this wasn't close - why is that?

I think of the VE table numbers as "modifiers" to the req_fuel value. The manual has the calculations that MS uses to figure the pulsewidth,(PW), if you want to review them. Suffice it to say, the VE values modify the PW as the RPM and kPa values change. They modify the PW based on your original req_fuel value. You could change the req_fuel value to give VE numbers of 100 in just about any area you like, because as you increase the req_fuel, the VE numbers will decrease, and vise-versa. So, to answer your question, the values in your VE tables aren't close to 100 because of your req_fuel value, but this will only be a problem if you find you require values lower than 1 or higher than 255 in your VE table to get the AFR you are shooting for.

[Hjulen]

Is this a Fiat X1/9?

From my own experience with my Fiat 124 I just left the PWM at 30% and everything worked.

I initially reused my Fiat Injectors as well, though I found they were dirty after almost thirty years of driving and didn't give very consistent fueling.

[Damonfg]

Thanks guys.
It is a X1/9 and I have added a turbo for a little extra fun. I have lowered the PWM down to 10% and have not noticed any adverse effects.

I was a little confused about the whole req_fuel versus the table - and they just didn't look right. I ended up lowering req_fuel down to 12.2 for a fair idle, and then made a few drives with it. With EGO correction and MLV's VE analyzer, it is shaping up quite nicely.

The new VE map peaks at 108, so I think that looks reasonable.

My plan is shaping up to include a rough tune to get the VE map to match the AFR map, then start refning for a solid idle (had a little hunt and seek briefly last night) then refine it for power and cruise. What a great system!

After 4 rides, it's already better than the OEM ECU. Took it up to 6# of boost last night, what a blast!