New to Megasquirt 454 BBC TBI Idle Help

[grantvoorhees]

Hello everyone. I just finished assembling my Megasquirt 2 v3.0. I am running a 1971 Chevy C20 with a 454 BBC out of a 1975 1 ton truck. I pulled a tbi unit off a 1987 1 ton 454 truck. I went through it and rebuilt it and tested everything. I then dropped a fuel pump in the tank behind the seat and wired everything up. I am trying to run fuel only at the moment with plans for ignition later. At first I had a massive vacuum leak because the factory gm adapter didn't line up on an edelbrock carb. I then fabbed up an adapter out of some leftover 1/4" aluminum plate.

After fixing the vacuum leak, it starts right up and stays running, however I know that the IAC stepper isn't setup correctly. I tried playing with the settings, however this is my first time. I did order Tuner Studio, however I am still waiting on a registration key, so right now I only have Tuner Studio Lite. The IAC stepper motor gets warm and I accidently ejected the pintle, while playing with the settings outside the housing. I was looking in the menus, and I don't see much for the IAC stepper motor. How do I get this to operate right and test this? Are he additional settings in the full version of the software?

Also is the tbi unit supposed to sound like it is sucking in massive amounts of air in? It seems much louder than I remember, however I only ever had one on a 4.3. It does idle around 9-10 in of Hg. I read somewhere that because the injectors are large on this unit ( 2 x 81 lb/hr), idle performance will only be so great.

Thanks.

[ChevelleFan]

I'll bet the sucking sound you're hearing is because the IAC is pretty far open, unless you have another vacuum leak. Your idle vacuum will also be affected by the ignition timing.

For the IAC, the relevant screens will be:
*) Startup/Idle --> Idle Control. Make sure you have Stepper IAC as your idle valve type.
*) CANbus/TestModes --> Output Test Mode - Idle Valve
*) Startup/Idle --> Cranking Duty/Steps
*) Startup/Idle --> Warmup Duty/Steps

I'm not sure what the limits are with Tuner Studio Lite, as I have the full version. The small amount of money for the full version is money well spent.

Lastly, for future posts, you'll always get better answers if you attach your MSQ file. The more experienced people will usually open it and can spot erroneous settings quick. Help them help you.. ;-)

-Dave

[turbo conversion]

Is this a stock engine with a stock cam?

If so I would be looking for another vacuum leak, 9-10 in. is a little low for a stock set up.

Retarded timing can also have the same effect causing low vacuum, have you verified timing per the manual?

Also as Dave said post your msq so we can have a look.

David

[grantvoorhees]

Here is the msq file. It starts pretty good, but I do think that the IAC is backwards. It is supposed to open when I try to start the engine. As it is now, it fully extends and closes off the passage way for air to come in.

Oh and vacuum is 19-20 in Hg. Brainfart. Almost exactly what it was with the edelbrock 1411 (750 cfm) carb.

[billr]

The idle control for you is a bit different than my MS3, it look like you are restricted to only "home open". To reverse the stepper motor operation, reverse the wires to just one of its coils. On that TBI you can see the pintle operation fairly well by just looking down the opening to it in the air-horn. Oh, the 160 steps you have for homing may not be enough, I use the max that can be entered to be sure it has found home. Stalling it there (with too many steps) is what you want, that is how it is supposed to work and won't hurt the IAC valve.

[ChevelleFan]

Looks like you're using B&G Code 2.92. This forum is for the MS2/Extra code.

With that being said, if B&G code works anything like Extra in terms of idle-steps, your slope is backwards. You're opening it up more the warmer it gets. I'm running a GM IAC too (but on Extra, not B&G). Try using a slope that looks more like this. Yours is on the left, mine is on the right. If that doesn't work better for you, then you'll probably want to ask over on the msefi.com forums.

-Dave