I have a TB that came with my Holley ProJection system. I am definitely NOT using the ProJection, but the TB looks like it will work with the rest of the GM electronics...except for the fact that it is missing the IAC. I have seen several posts that talk about not using the IAC on a TBI engine. So...could I use the 670cfm TB with the 1228746 ECM I got today or is that a dead end deal?
TIA...

 

well you could tap a vacum fitting and use a IAC housing from g/n or another buick v6 or get one of the universal housings from somebody like accel.

 

If it's just missing the IAC then I believe the GM ones just bolt in, If it doesn't have the provisions for on, then you can run without one, but, it might be more trouble then it's worth.
The FWD Vin3's, just to name one, starting in 87 have a removeable IAC housing, so with a small AL plate or some Epoxy you can easily make one.

 

The IAC bore isn't even there. Maybe I should post a pic of it so you can see what I am talking about. The problem isn't with the IAC and a vacuum leak. I am wondering how the ECM would react to sudeenly learning that it doesn't have an IAC. Can't the IAC steps be zeroed out in the BIN to basically cause the ECM to not do anything with the IAC?

 

Jeepguy,
You may want to do a search, or ask around on the TBI board. I know there are some guys over there doing without the IAC.

Personally, I would want a functional IAC for stuff like cold starting and A/C rpm compensation, but I'm sure things will work without one.

Another question to throw in here, would the Idle motor off a Mopar TBI engine work on a GM ECM? I know they used one on the Dakota 3.9 (Only application I'm sure of!) it bolts to the TB, and opens the throttle blades, instead of a bypass setup like GM uses. Maybe an older Cadillac motor if you wanted to keep it all GM (although Mopar would be closer to what Jeepguy already has! )

 

Yes, there is an IAC malfunction code, but off hand I don't remember it setting a bunch of default stuff. But, disabling the code gives the ecm anesia about it anyway.
But you might double check a hac on that info..

 

That's what some of the projects had, lots of carbby applics had them for A/C load compensation, and for overrun.

Usually called a Throttle Kicker, FWIW.

 

Nah, I'm talking about the stepper motor that they used on the Cad's, and Mopar's. I would think it would work exactly like an IAC, I'm just wondering if the IAC driver would be strong enough, I think they are a bigger motor.

I'm very familiar with the throttle kicker solenoid, my car has one (until I get the EFI on it!)

 

I may disconnect it and see how the ECM reacts. If it doesn't cause any problems, I may put the Holley TB on the engine and see what happens.

 

Oh, the ISC?.
Now that's real garbage, IMO.
Use the Throttle Kicker, it's much less prone to failure, or erratic idling.

 

I could put a kicker solenoid on it. In fact, there already is one on the Holley TB. I could use that solenoid for kicking the idle up a few rpms when the A/C is on or I am using the on-board air system.

 

my set up uses two IAC. one is non functional(broken). so my warm up and AC is 1/2 of what it should be on rpm. i ran with it disconnected(plugged bleed lines) for a while and set min idle in constants at 650 rpms. since i have a manual trans i could live without it as high speed idle was foot controlled. with air on idle was a bit too low but never died.

 

The only reason I mentioned it was because it would maintain a variable control of the idle speed. I never really like them either, just mentioned as a possible alternative!

 

I took one of the holley TB and just drilled the hole for the IAC. The outer was like 13/16 and the inner was 3/8. Then you have to have the hole threaded. Most machine shops have the right tap.
It's an easy surgery!! All the TB's I have seen have the casting for the IAC, it's just not drilled and tapped.
If it has the back facing TPS then just put your GM one on it.

HTH

 

I think I am gonna put that TB on there in a few days and see what happens. I may go poking thru the BIN and try to neutralize any IAC related stuff in there before I do it.

 

You know, Bill, you're right. That casting IS there. Doesn't that inner hole need to be tapered for the IAC?
It does have the back facing TPS too. Hmmm...this is getting better and better as it goes.

 

I used a 5/16 IIRC then finished it with a tapered stone. But to tell the truth. The IAC pintle is tapered so it would seat well enough on a standard hole. Sort of like a valve seat. Think about it. Does the IAC go to zero very often?
Not on mine.
Just verify the measurements. It's been a while since I did mine!!

HTH

 

How far down into the TB does that hole go? Is there a passage cast into the TB for the IAC bleed?

 

It goes to 0 every time you key off and depending on code at the MPH reset.

A straight cut hole is fine. It's not really critical is there is a slight air leak there.

The pintle has to be talered other wise it would be just an on/off devise.

 

You know, I have a set of pipe thread taps. I bet I have the right one...and I do have a drill press with a vise so I could chuck the TB up on the press and do the drilling that way to keep everything in line.

 

I'll put two shiny pennies on a wager that the IAC is a straight thread, ie not pipe. The sholder is the seal, so it'd be doubtful it'd be pipe.

 

I had my Holley Pro-jection TBI drilled and tapped for an IAC and the threads on the IAC were metric, 18 mm fine thread if I remember correctly, but I am sure they are metric.

 

I don't think I have that one, but I bet I can get it easy enough.

 

It's definately not pipe. I do have an IAC that is threaded with pipe threads. Now how do you suppose I know that!!!
And why would I have an IAC with pipe threads???

DOHHHHHH

If you look at the TB you will see exactly how it works.
Drill the outside hole for the threads. the IAC screws in and seals this hole back up.
drill the inner hole. Air comes down from the top of the TB inside the air cleaner, through the hole, the IAC is positioned to control the amount of air passing the pintle, then into the intake.:lala:

IIRC mine was more like 24mm, almost 1 in. My plugs and O2 bung are 18MM.

 

I just made my O2 bung out of a 18-mm plug non-fouler. I also just got (Sunday) a nice, shiny new Lincoln MIG welder. I wonder what kind of projects I can think up to put THAT to work on...
I better go look at that Holley TB. I really don't think that there is a passage from there to the intake meaning it would probably have to be drilled into the TB itself.

 

I use the anti fouler also. i just cut the threads off.

"I really don't think that there is a passage from there to the intake meaning it would probably have to be drilled into the TB itself."

I'll bet you that new shiny welder!!!

 

Not a bet I think I have good odds on. BRB...gotta go look and take a few pics.

 

You would have won, Bill...here it is...this is the side view. I will definitely have to put the GM TPS on it if I do this.

 

Here's the top where you can see the cast IAC passage into the side of the TB

 

Oops...wrong button

 

Please let it be a 170 or a 210 please please......
I have another spring over to do!

 

...and the bottom...

 

Nope...only a little 100...but you could do a SOA in ultiple passes with it I think.
Here's a pic of the TBI AMC 360

 

How bout a dana 300??

 

I only have one of those and it is currently in use...

 

Better mount that est on a small metal plate for some heat transfer.

 

Now that I have THIS...clicky clicky I can do just that.

 

Here is the holley TB with the 350 inj pod on it.

 

Maybe we should take this to the TBI forum...why put the GM injector pod on it?

 

Lemme see if I can sound like Crocodile Dundee...
That's not an ignition coil....now THAT'S an ignition coil:

 

Cause the old Holley inj's suck!!
You already know the GM inj's are fine for your motor so just make the adjustments for the increase in air volume when you add the 2" TB.

 

I see...and you get the GM FPR too...

 

I would take one if someone gave it to me.
I now have a JY ford TFI coil. very cheap and supposed to out do the GM HEI coil by a bunch

 

I agree...I really like the TFI coils...that Accel coil I posted is just a TFI on steroids.

 

I make it adjustable also.

Just twist the round bottom until it spins then run the indicator tab to the top of the slot. Then check with a FP guage. Should be around 15psi!

 

NOW you got me thinking!!! Heh heh heh...:lala:

 

It's a SCOUT thing. Some day you will understand.

SCOUT
The
Official J@@P recovery vehicle!!!!!

 

Okay...let's not get started bashing Jeeps... I get enough of that from my wife...really. She hates it.
How much tweaking did you have to do to make the ECM like the 2" bores?
Oh yeah...did I mention the 727 tranny under the Jeep? And the LARGER AMC 360? I found a set of Dana 60s this weekend...now I have to get my friend's dad (they own a junkyard...Jeep parts gold mine) to let me take em off his hands. He did GIVE me another 360 engine...complete...in trade for an old TH400 tranny I have.

 

It didn't take much to change at all.
These old IH's are low rpm motors. so the 2" bores really only affect the top end and a little AE!
The motors are governed by the valve springs at 4000rpm.
Just got a set of LS6 BBC springs for it so I should see 5000 shortly.

Find me a D300!!
I just picked up a jeep 727 tailshaft and housing to bolt up a J@@p 300.

Are you logging with the new 8746 yet?

 

Nope...long story there...offline.
If you need a few pointers on opening up that 727, let me know. I rebuilt mine almost 3 years ago and it hasn't even burped yet. I did it for less than $200 in the backyard shop at my in-laws' place in the middle of February...new converter and all.