fast ?'s

[blown96w]

i am new to fast and i have a couple of ?'s my system is on a ford 408 with a 77# injector, and a mondo xxwith a 34 tooth pulley,

1. on a log taken at a dragway fast said that i spiked my rpms at 7700, but the system config is set at 6600 and 6900 rpms, ?

2. my injector duty cycle at its peaks is 110 and up, how can this be right if the greatest % is 100%

3. i have been told the car should idel around 1500 rpms but after mine warms up it idels around 700 -875 rpms which is fine but i have to hold the pedel down until i reach 120 degrees.

4. and lastly stock timing on a 351w is 10 degrees, the shop i had set up my system set my timing at 40 degrees until i stat to see boost, i dont know but i think that this is too high

thanks for your time

 

[bobc455]

Originally posted by blown96w
i am new to fast and i have a couple of ?'s my system is on a ford 408 with a 77# injector, and a mondo xxwith a 34 tooth pulley,

>>1. on a log taken at a dragway fast said that i spiked my rpms at 7700, but the system config is set at 6600 and 6900 rpms, ?

Is it possible you actually hit 7700? The ECM will just "extend" the last values of the tables if you run off the edge.

>>2. my injector duty cycle at its peaks is 110 and up, how can this be right if the greatest % is 100%

Shows that you are not getting enough fuel!!! Fix it now!!! Either your injectors are too small or your fuel pressure isn't high enough. Do you reference fuel pressure to boost? 110% means that the ECM is calling for more fuel than your injectors can pump in. What is your O2 correction when that happens?

>>3. i have been told the car should idel around 1500 rpms but after mine warms up it idels around 700 -875 rpms which is fine but i have to hold the pedel down until i reach 120 degrees.

Who said 1500? You can set the idle speed vs. CTS table to hold idle a bit higher if you like. Then set idle speed wherever you like. Maybe you also want to adjust the throttle blades to stay a bit more open as well.

>>4. and lastly stock timing on a 351w is 10 degrees, the shop i had set up my system set my timing at 40 degrees until i stat to see boost, i dont know but i think that this is too high

Well it's not really emmissions friendly, but it will make the engine idle smoothly. 40 does sound high- have you verified that it matches what's actually in the engine (with a timing light)?

-Bob Cunningham

 

[blown96w]

i have verified the 40 degrees with a timing light, any ideas were a good starting point would be?

i dont have the wide band option could this be why the duty cycle is so high, in combination with the fact the my ve table in some areas is as high as 150 , any ideas

thanks for your original post and any others that you send thanks again

 

[bobc455]

Well in the old days, a lot of cars had 6-10 degrees initial timing (at idle). Raising the timing seems to help idle a bit, as long as you aren't trying to pass an emmissions test. My idle timing is in the low 20's, but whatever the car likes.

The injector duty cycle is controlled by a formula that looks something like this:
pulse width = Target A/F ratio X Volumetric Efficiency / Injector Size. Well it actually looks nothing like that, but the idea is that the higher your VE value, and the richer your target A/F ratio, the higher the pulsewidth will try to be.

If everything is set up right, you shouldn't have to have any VE values over 100 (right tyrfryer?), so if you have VE values over 100 then you might want to double check some stuff. I bet that is why your injector duty cycle is so high (and that you are probably running very rich).

If you don't have a wide-band sensor, do you have any other idea of how the car is running? Without the wideband option, I would get one of those cheeseball O2 sensors and gauges (to control to 14.7:1 for driving around, idling, etc.) and take the car to a dyno with a wideband and calibrate your VE values for WOT. Otherwise you are working totally blind. Any chance you can save up for the wide-band option? It makes things a LOT easier...

-Bob Cunningham