again with FN348 Cranking Pw ECT questions

[canuck1]

My injector size and engine displacement are accounted for, but I had to keep bumping up the higher temp values (above 160) to where its beginning to make me nervous:
-65536 5.70
-40 5.70
0 5.22
40 2.50
80 1.21
120 0.82
160 0.49
200 0.49
65534 .0.49

[decipha]

yeah thats a bit higher than id expect could be some vapor lock issues

try reducing the crank pw and increasing the pump prime time to test

[canuck1]

Thanks. It was at .42ms for 200+ ECT but when I switched the injector data to the stuff Chris at PAS pointed to, it was only provided for 43.5 psi (dropped from the 55 I was running).
I think you’re pointing to the key element. Main issue is restarting after getting fuel (embarrassing when it doesn’t go vroom!). I’ll report back after increasing pump prime time & dropping PW.
Sean

[canuck1]

Nope, no luck. Increased pump prime time (from 3 seconds) to 6 seconds after lowering higher temp cranking pw from .49 back down to .42 ms.

Parked warm car, left it for 10 min to let it heat soak sitting in my garage, would not fire. 2nd attempt it sputtered once during cranking, but no start. Pushed the pedal to the floor for third attempt to make sure I didn't flood it, no difference.
Anyone else dealt with this???

In my case, .42ms of pw amounts to 25% more than calculated requirement.

Sean

[decipha]

That verifies she wants more then.

Yeah its not uncommon for some engines to want more fuel on crank especially when warmed up.

[canuck1]

Obviously my goal is to use the lowest ms value I can to work at warmer temps, but I’m trying to calculate the upper limit.

I was running the same injectors at 55psi in my first tune (using different data). The new data works vastly better in every respect, but I didn’t want to alter any of the manufacturer’s values to start, so I reduced pressure to 43.5 psi to match what was provided.

Since pressure impacts injector flow, if I had a working FN348 (.42) ms value at 55psi, doesn’t it mathematically calculate that at 43.5psi that same volume of fuel would require something approaching .47ms?

Am I on the right track?

Sean

[decipha]

you have to factor in offset difference too

[canuck1]

Is offset a time (ms) multiplier? There is a measurable difference in offset between the injector data I have swapped. I’ll see if I can figure it out. Does a % value difference between the old/new offset equate to a percentage change in ms of pw?

Sean

[decipha]

no

offset is the actual msec time that injector takes to open once its powered on

if you've reduced the offset by .25 msec then you need to increase cranking pw by .25 msec to get back to where you were for a given voltage

[canuck1]

Awesome. Thanks for making it understandable!

Sean