FiTech GoEFI 400 vac advance question

[Mikesimp70]

My engine builder installed a Fitech go efi 400 after breaking my engine in with a carb. During the runoff, he told me not to hook up the vacuum line to the distrubitor. That was so long ago I forgot why he said this and if he meant forever or just until the Fitech had some learning miles.

While putting everything together my buddy convinced me to hook it up. It ran like crap until we disconnected the vac again then it settled back down and ran well.

Any idea?

 

[DirtDonk]

There's no normal reason I can think of for leaving the vacuum advance disconnected.
Now, there's a big difference in how an engine is tuned when you choose ported vacuum vs full vacuum, but either should be able to work with the EFI.
It might just take the computer longer to figure out the reason it's trying to idle higher with full vacuum though. Not sure about that, but it's possible.

In what way did it run poorly though? Hunting for idle? Rough running and won't accelerate? Something else?

Which port did you use for the advance?
What is your base timing set at now?

Paul

 

[Mikesimp70]

We had it hooked to ported vacuum

It ran rough, hard to start and even backfired. Temp reached 220 and vacuum was low. Removed the vacuum connection to the distributor, it smoothed out, runs 185-190 and has plenty of vacuum for brakes.

Not sure on base timing it was set at the builders shop

 

[DirtDonk]

I wonder if the advance diaphragm is leaking? Seems like it would have to be a pretty big leak for it to run that bad with EFI, but I've seen stranger things.
Be nice if you could remember what the guy told you originally.

It certainly changes the timing in a "when and how much" kind of way. But you'd think the computer could figure it all out.
Are there settings in the setup that you're supposed to change if it's running vacuum advance?

Paul

 

[Mikesimp70]

Ill call him on Monday. Doesnt make sense to me now just thought someone here would have an idea

 

[Broncobowsher]

Did you connect it to manifold vacuum or ported vacuum?

 

[DirtDonk]

He said ported in this case.
I would also try full manifold though, just in case.

Maybe the guy said to leave it off simply because he had the same issue as you're having now, but didn't actually figure out why. Which is normal sometimes, because the hunting expedition might have cost a ton of extra money.

Paul

 

[Mikesimp70]

We tried the 3/16 nipple (ported vacuum) indicated in the Fitech instructions.

 

[Mikesimp70]

Initial timing was 18, I dropped it to 8. Idle dropped to 750rpm. Full mechanical advance is now 28

Tomorrow I am Going to connect vac advance to full vac and decrease idle AFR target to 12.7, reset fitech learning and drive it a bit.

Thoughts?

 

[Broncobowsher]

Put the vacuum advance on ported instead of full. That usually works better.

18° of initial is a lot. I generally aim for about 10°. I see what they did. Aiming for a high total advance (38°) they dialed that in and base timing turned out to be 18°. Instead of adjusting the centrifical total number like they should have they just took the easy way out and closed the hood. The 38° is a bit aggressive. If you really wanted to cheat it, 14° initial will give a decent 34° total.

I can see why it ran like crap with the vacuum advance hooked up, timing overly advanced and the vacuum pulling it even further ahead.

 

[DirtDonk]

Initial timing was 18, I dropped it to 8. Idle dropped to 750rpm. Full mechanical advance is now 28

Tomorrow I am Going to connect vac advance to full vac and decrease idle AFR target to 12.7, reset fitech learning and drive it a bit.

Thoughts?

Yeah. Don't!
Well, do one or the other, but not both at the same time. Change one to see what it does.
I'm with bowsher and like to try ported vacuum first. You may already have done that, but if your advance was set to 18 initial you were already at a disadvantage.
Set it to whatever, then attach the vacuum hose and see what you get. Just do NOT mess with the mixture until you've messed with the other stuff. Changing two things at the same time to fix one problem rarely works until you've had oodles of experience with both and know what to expect.

And a target of 12.7 is kind of crazy sounding unless that's what they ask for. I don't know why these companies (Edelbrock, MSD, FiTech) keep telling people to richen things up so much. Unless it's to cover up lots of weaknesses in an engine or fuel system, or just to cover their butts if someone races around with their system on and burns out an engine from running to lean?

Don't know, but please only change one parameter at a time while tracking down this issue.

Paul