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Discussion Starter #1
This spring I ventured into the brave new world of EFI, and installed a FAST EZ-EFI 2.0 system on my Camaro. I also installed a new Tanks, Inc. fuel tank and an in-tank fuel pump. After diagnosing and replacing a bad ECU module, I’ve been driving the car for the past few weeks and allowing the FAST system to learn. I’m pretty happy with it – throttle response is outstanding, cold start is much easier, and the fuel economy has improved. My car doesn’t have gauges, so the handheld monitor’s ability to display coolant temperature and battery voltage is also a plus.

I’ve left all of the FAST AFR settings at the factory default values and given the computer some time to learn. As I’ve become more familiar with how the system is operating, I’ve noticed a few gremlins that I’d like to try and correct by tuning the system. Trouble is – I don’t know where to start.

Here’s what I’ve noticed so far:

The IAC calibration is a little tough to get right. The indicator is usually to the left of the preferred target when the car is idling in Park, and to the right of the target when the car is in gear.

The system seems to hunt for the correct idle speed for quite a while before finally settling down at the idle speed I’ve selected (870 RPM). This problem occurs frequently when the car is restarted after it’s come up to full operating temperature.

I’ve also noticed a small off-idle stumble when the car is up to full temperature. The system has an Accel Fuel adjustment available, but I haven’t messed with it yet.

I’m hoping there are a few folks on this site who have ventured down this path already, and can give me some advice to tune the system. Thanks!
 

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Can't speak for your system but here's what I've found with my system....

First, does your system have timing control and if so are you using it?

Hot start idle
Yours may be like mine and only have a single IAC position for starting. If so, then it'll go to that value every start regardless of temperature. What that does often is on hot starts it's really too far open so it idles way up, then there is a preset decay time for it to come back to the RPM controller where it drops so many IAC steps for so many revolutions. On my system, the decay time is adjustable so I have it set to decay very fast. They came out with a new ECU that has starting IAC temperature adjustments and timing control as well that will install on my unit but I never did buy one.

Also on mine, there is an RPM and TPS (throttle position) window that you set to allow the IAC to control RPM. You have that so the IAC isn't working during cruise or shifting etc. My TPS setting is of course 0 but the RPM window is tricky. Reason being the hot start thing....since I only have one IAC setting for all starts, hot starts sometimes "flare up" to a high RPM. If that RPM goes higher than the RPM controller window setting, then the IAC will not activate at all and it'll just hang there. I have mine set at 2000 RPM which has cured that problem.

One other thing that caused an idle issue was when my TPS sensor went bad. It would not hold its calibration and when it should've been reading at most 1 step (100 for wide open) it was fluctuating up to 2-3 which made the ECU add more fuel like I was pressing the throttle.

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The way I set my idle was to get the car HOT, then put in my idle RPM target BUT set it about 50 RPM BELOW what I really wanted, i.e. my desired idle is 850 but my target is 800.
Then I adjusted the throttle plates down to my desired RPM (50 RPM above target), then did a TPS calibration.
In this manner, the IAC is almost always fully closed at idle because it's trying to get 50 RPM lower than the system can go, and because it can no longer work on both sides of the actual RPM there is no hunting.
This does not affect cold idle since my table is set up to idle at 1200 RPM cold and dropping from there to 800 (target) when hot. That is the IAC can take the idle higher when it needs to but can't do much of anything once the car is hot because it goes full closed and the throttle plate position is what is truly setting the hot idle now. Since I'm only at 1000 ft altitude and frequently drive through the mountains it's not an issue (less air up higher) as it can open up to get up to 800 target if my throttle plates are not allowing enough air for higher altitude. As you're in TX it would be the same.
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Off idle stumble
I fought this for a while on my car AFTER I fixed my timing. Bear with me, this is going to be a round about story and I hope it's easy to follow.....

I ran ported vac for a while because I was using an HEI can with way too much vac advance in it to use full manifold advance. I also had my accel enrichments jacked way up and it ran good like this. When I changed out my distributor to a unit with a vac can that would let me run full manifold vac (14 initial plus 10 vac in my case), I first had to reset my throttle as would be expected since the extra timing caused the idle to raise.

Then I had a problem with very light throttle movements, i.e. it would buck really bad. What I found is that my ported vacuum in the old setup was actually not pulling vacuum at light throttle so I was running low timing at light throttle (no vac advance) and so my rich acceleration enrichments did good because a rich mix needs less timing to fire. Once I had that extra timing it was TOO rich with the extra shot and a lean mix needs more timing to fire. So, I was basically rich misfiring at light throttle movements now that I had more timing.

Anyway, once I had my timing right I had to go back and lean all of my low throttle angle accel enrichments back out to get rid of the light throttle movement bucking.

Now, yours may actually need more fuel and the best way to find out would be to watch the AFR when you start out. If it goes really rich it may actually be lean as a lean misfire will often read rich. There can also be an issue right off idle because you are transferring from an idle cell in the fuel table to the main map, so you might be jumping from your fairly lean cell into a cell that is too rich right off idle. On mine the fix for that is setting the RPM cells that are a few hundred RPM above idle down at the same fueling level as the idle cell. I'm sure you can't do that with your system but at least it gives you an idea of what to look for.

Adjusting accel enrichment at least is easy to trial and error with. Bump it up and if you get worse just go the other way ha ha.
 

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Have you tried the Fast forums? I had good luck with them and there are some very knowledgable people there who eat, breath and live this stuff.
 

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i had a stumble and i put my accel to -4 made a big difference car runs great,i am running a 350 crate motor with a standard trany rpm set at 800
 

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Discussion Starter #5
Thanks for the information and suggestions guys. I'll take it one step at a time and hopefully learn a little along the way.

FYI - I'm not using the FAST system to control timing. The car has an Accel HEI distributor set at 12 degrees initial, 34 total - all in around 2800 RPM, and it also has vacuum advance.
 

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Mark,
First USE the ECU to control timing, just bite the bullet and it very worth it.
secondly the target IAC you refer to is the set point the fact that its hunting to either side shows its working...Open up your throttle blades till your IAC count is about 10 in park ( this works better on my combo than the 20 on the set point screen ) just put it on Master screen and with it fully warmed up just open throttle angle till IAC count settles around 10, its going to hunt thats what its job is to modulate itself to try to attain your desired rpm set point....

Your off idle stumble could be timing or accel enrichment or both and a vacuum leak...the EZ unit is easy to play with...watch your AFR whats it doing? Going rich during the stumble? IF its longer and rattier then negative accel...usually quick blips are lean so positive accel...

You can also play around with that your engine likes to idle at and THAT ratio from idle AFR to cruise will affect drive off too....

The EZ efi unit is very capable but has many set in stone curves so YOU have to learn what your engine likes and modulate its settings to attain the best compromises......
Personally I lean the idle AFR out till the engine stumbles then add till its drops vacuum back up a hair and leave it there, in other words dont care what the display tells me the AFR is but what the engine wants ( I also have a ton of overlap )...
 
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