I recently installed a Holley Terminator EFI system on the 360 in the '73 Sportabout.  Right away the ECU couldn't get the idle speed down below 900 RPM and the IAC valve stayed at 0%.  I can close both primary and secondary butterflies and put my thumb over the IAC hole and the car still runs at 900-1100 RPM.  I've plugged off vacuum lines and ensured the throttle body gaskets are sealing - no change.  SO... air must be getting in at the intake to head mating surfaces.

I'm going to have to pull this manifold and seal everything back up.  Any advice?  I usually use indian head or aviation form-a-gasket around the intake ports and a thin bead of Right Stuff or UltraBlack around the water ports.  I also use Edelbrock fiber gaskets.  My valley pan has the mating surfaces cut off and it's tek screwed to the bottom of the manifold.  Crazy, yes, but it works for me.

Start watching at 4:20. This may be a problem for you, it was for me.  I put a FAST EZ-EFI on an El Camino and struggled with the exact issue you describe.  It started out fine, but what I wasn't seeing was that there was so little contact between the intake mounting flange and the TB in one spot and enough vacuum to slowly pull the gasket into the intake and create a leak.  I didn't have room for an adapter, so I went with a new intake, but I should have done a little more homework before getting the Air Gap I did get. Apparently TBI systems prefer single plane intakes to smooth out the manifold pressure signal that the MAP sensor sees.  A fully divided dual plane intake will pulse the MAP sensor.  The Air Gap I have has a 1" cut out of the divider which helps, but not as good as a single plane intake.

Could just try running an open spacer under the throttle body to test this theory.

I remember on Engine Masters, they had some issue when they tried to run the Terminator on a dual plane manifold as well.

Red20, does the 360 in the Sportabout have the factory intake manifold or aftermarket?

Is this just the Holley system that acts like this? Or all aftermarket throttle body EFI ?

This doesn't sound good at all.

I have an MSD EFI system that is planned for install on the White70 with an Edelbrock performer intake. Which (correct me if I'm wrong) is a dual plane intake.

I suppose I should remove the wall between the two sides before I install the manifold?  Anyone have the MSD EFI on a Performer intake? Does it function correctly?

I had all kinds of issues with the MSD that turned out to be ignition based and not the EFI itself.

An additional reason for the switch was the amazingly POOR support from MSD that I experienced at that time. Now that Holley and MSD are one company I would hope the MSD support has improved.

I heard of the dual plane vs single argument but if the Sniper is any indication the MSD will run like a champ on the Performer so long as the ignition system is not an issue. My car did fantastic on the chassis dyno without modifying the Performer but keep in mind that was with the ignition system sorted out and with the Sniper. Results may vary and all those other disclaimers.

pit crew wrote: Now that Holley and MSD are one company I would hope the MSD support has improved.

Don't bet on it.  I have two friends with Holley systems and they both claim that tech support is non-existent.

Red20,

I was thinking....maybe you should try placing small balls of clay or something similar against the sealing surfaces on the heads where they mate to the intake manifold and set the manifold in place to verify that the mating surfaces are actually somewhat parallel. You could check how much each ball of clay got squashed. If all of them are the same, or nearly so, at least you'll know the surfaces are parallel.

I have an MSD Pro Billet RTR distributor, IIRC the MSD EFI and this distributor are supposed to interface in a good way. I have a 6A box and MSD Blaster coil as well. Hopefully all these parts will  play together nicely. You'd think so anyway for what they cost.

 I didn't buy the 6A box, it came free with the MSD Atomic EFI. Not sure how good of a box the 6A is ?? Or how versatile.  I'm not even sure I want to use it. It must be one of their early versions that they wanted to get rid of cuz the lot of them were taking up too much warehouse space. LOL  I believe the 6AL is a more versatile unit. 

As for issues with EFI and dual plane, for sure a single plane is better, but not all EFI TBs will be the same.  The Terminator is particularly difficult because the MAP sensor is on the bottom surface and to the side, so with a plenum divider, it’s only seeing signal from one bank.  Other systems, QFI for example, have the MAP sensor in the ECU and you run a vacuum source to it. 

Dad used to do this all the time. It worked and he never did fry a vehicle, lucky???

I use carburetor cleaner, much less volatile - no engines catching fire! Do this outside and always have a fire extinguisher handy. Just short bursts - NOT a steady spray!

The RPM will jump at a leak point. Repeat at the same RPM jump point to confirm.

I haven’t sprayed ether looking for a leak, but I sprayed brake cleaner.  Didn’t find anything.  I’m at Disneyland with the wife and kids, so I’ll pull the intake, maybe machine the plenum spacer down a little, and reseal it when I get back. 

Red20,

Use extreme care with brake cleaner, it's very bad nasty stuff when burned. It really shouldn't be burned at all. The by product of burning brake clean is phosgene gas, lethal as can be. 

Here's a testimonial

http://www.brewracingframes.com/safety-alert-brake-cleaner--phosgene-gas.html" rel="nofollow - http://www.brewracingframes.com/safety-alert-brake-cleaner--phosgene-gas.html

Use extreme caution with shop chemicals everyone.

Well I’m back from Disneyland.  It rained the entire time, lol.  I hope to get time to work on the car this weekend.  I originally wanted to have a LOT more done and be heading to the Zip-Tie Drags in Tucson this evening, but that plan was shot weeks ago. 

At any rate, I’m going to pull the throttle body and spacer and check the gasket imprint for proper sealing and mic the aluminum spacer for trueness.  Then I’m going to seal up all of the ports on the intake and see if I’m getting a significant vacuum at the breather tube, which I’m sure I will be.  I’ll likely be pulling the intake manifold and resealing it.  

In order to not have the intake off again in the near future, I may go ahead and install the Summit 8600 cam I have waiting to go in.  The risk is the EFI not running well enough to break in the cam as well as the general rule of thumb that you should only do one thing at a time.  I’m pretty confident it’ll fire up and run at 2500 RPM for at least 20 minutes for me though.  

A bolt clamping directly on aluminum alloys tends to pick up/deform some softer metal before full clamping force, giving a false torque. Steel on steel will slide and provide a much more even torque/clamping.  

I got everything buttoned up last night.  I just need to put the plugs back in and break in the cam.  After that, I’ll let it settle into an idle and learn for a bit.  Hopefully I’ll be able to get some response from the IAC valve and everything will be solid.  I’m ready to start driving and tuning this thing and get back to enjoying my car.  

Yessir, that’s what I use.  Do you use it around the intake runners as well as the water jackets?  I’ve always been under the impression that it could soften and deteriorate exposed to the fuel/air at the intake ports.  

of an intake to see if it is machined at 90 ?

On the Block between the heads to check 90 the Carpenters Square won't work though, right?