Seat of the pants tuning for FAST efi help?

C

corvettedave01

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Nov 23, 2008
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I'm going to try to retune my motor since I got the new wideband installed and need some basic help.

Timing: Approximately what should my timing map look like? Total advance in at 2500 rpm, 36*? What should it look like below that and at idle?

Fuel: I installed the 48 # high impedance injectors and I think I'm going to turn the fuel pressure down to about 43-45 psi before I start because I can't get the motor to idle above 12 on the A/F reading. Shouldn't it idle at 14 ish?

Any other help would be great.
 
YES it should idle at 14-15 to one easy...just like it was running,...

in fact except for emissions bullshit, you can idle at something like 17 to one....so I"m told....the target for EPA crap on a normal car is 14.7 for idle and light load running...

:quote:
 
corvettedave01 said:
Timing: Approximately what should my timing map look like? Total advance in at 2500 rpm, 36*? What should it look like below that and at idle?
Click to expand...

With a 20* stop bushing, it should idle about 16*, then linear increase from there to 2500-2800RPM. (Vacuum disconnected)
 
OK thanks Bigbird. I think I"m going to bump the fuel pressure down to 43 psi and see if I can get the thing to lean out at idle.
 
corvettedave01 said:
OK thanks Bigbird. I think I"m going to bump the fuel pressure down to 43 psi and see if I can get the thing to lean out at idle.
Click to expand...

Depending on your cam spec, it is sometimes necessary to have a slightly rich mixture...(13-13.5:1). You might use the provided fuel map for starters. On timing...run as much initial as the starter will allow...usually 18 20 degrees at idle. Then add timing as quickly as the engine can take it without pinging. Good to hear you have the FAST up and running again. Any thing on why no power above 5,000 rpm yet?
 
Last edited:
no results yet, still configuring the base timing table. I'll try to download it to see what u think.
 

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Yeah, sorry about the pic. I tried for 3 hours to figure out a way to print that thing. I need some decent photo editing software...

I do have a pretty big cam, maybe too big, so maybe it won't idle at 14:1? It is a solid roller 671/671 and 250/258 @ .050, 111* LS. Hopefully this weekend I can do some work on it. I found the old tune with the 48# injectors, so I think I can get a starting point.
 
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