September 21, 2021, 12:40:05 AM

Author Topic: FiTech Startup Tuning - No Prime Shot  (Read 7428 times)

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FiTech Startup Tuning - No Prime Shot
« on: August 17, 2018, 03:02:45 PM »
From FiTech Owners Facebook Group

It is generally accepted that the default Prime Shot value (258) is way too high. This Startup Tuning method completely disables the Prime Shot and relies on Cranking Fuel and Afterstart Fuel to start the engine.

Cold Start Tuning.

Prime Fuel Multiplier:
I personally don't like to use this at all. Out of the box is typically set pretty high and does a better job of flooding the engine than it does starting it. So more than likely it's going to need to be lowered or disabled. Disabling this will make it easier to tune Cranking, Afterstart, and Warm up enrichment. Set to -100 to disable. Yes I'm serious.

Cranking Fuel.
The easiest way I've found to tune this is hold the throttle open about an 1/8th while cranking. If it fires up more easily this way then you need to reduce cranking fuel. Worse, add more. Plug reading is also your best
friend here. Let it crank and if it doesn't fire at all perfect. You can pull a spark plug and let it tell you exactly what you need to do. Obviously this is for an engine that has trouble cranking. Don't confuse this for a start stall condition. I'll get to that next. You'll be focusing mostly on the 20f and 65f breakpoints. But remember that
everything between 20f and 65f is interpolated. So as an example if your coolant temp is 40į you'll need to adjust 20f and 65f. Adjust in increments of 10.

Afterstart Enrichment.
This one's pretty self explanatory. Lets say cranking fuel is good. So you try and start the engine. It fires up perfectly but stalls immediately. That's where this comes in. And it's real easy to tune. Once it stalls don't try starting it again. Pull a spark plug. Rich reduce fuel. Lean add more. Adjust in increments of 10 at a time.

Warm up enrichment.
To be honest in all my years of Efi cold start tuning. I've never needed to touch this. But every engine is different. So you got cranking and after start set but after a minute or 2 of idle time the engine slowly starts to idle rough or eventually even stall. That's where warm up comes in. The o2 has likely warmed up enough at this point that you can use it. Stoichiometric is 14.7 AFR. Lower Rich. Higher Lean. But I'm hoping you
knew that already. See it leaning out simply add fuel. Or vice versa. Try to get the AFR as close the AFR target as possible. Chances are AFR trim is probably doing warm ups job anyway but try to get the trim within
+/- 5%. As close to 0 as possible. Warm up enrichment stays in effect until 170 degree coolant temp.

UPDATE: I never bothered to add Crank IAC here because I have yet to see it be an issue until recently with a few people. So I added it below.

Crank IAC Mult: Let's say cranking fuel and afterstart is set beautifully. Your plugs look amazing, etc etc. But maybe once it does start it idles incredibly low for a few seconds to even minutes. But your AFR is perfect on target. You can increase this multiplier to make the engine spin a tiny bit faster and make it idle higher for a small amount of time after it starts. Or maybe the thing starts perfectly but idles way too high after start up for a small amount of time you could reduce this multiplier.

DISCLAIMER: This instruction is for a good running engine and a properly set up Fitech unit.
If you have no power on the white wire while cranking or are seeing no RPM on the display while cranking this instruction is not for you.
« Last Edit: March 09, 2019, 09:49:45 PM by Wheelman »


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Re: FiTech Startup Tuning - No Prime Shot
« Reply #1 on: March 29, 2021, 12:03:32 PM »
" if you have to open the throttle, you have too much fuel.
Back off prime shot to -100, then increase start fuel until it starts reliably, even if itís a longer crank time.....
 at this point if it starts and then stalls, increase afterstart fuel until is doesnít stall.....

Once this is done, then increase prime shot until it starts instantaneously, increase slowly,
only use as much prime as you need and no more.
Any prime shot before that point will be excess fuel."