ECM upgrade (1227730) for stock 2.8 (Page 52/107)
Darth Fiero FEB 17, 01:44 PM

quote
Originally posted by mswenson289:

Any ideas or comments welcome. Hope this is the right place to post. I am replacing the 2.8 w/ camaro 3.4 93-95 intend to use DIS and 7730 ECM. Thought I would use the 3.4 lower intake manifold to eliminate the cold start injector and fan sensor. Now my concern the 2.8 lower intake has a fitting that the manual refers to as "Cold start valve air tube" running between the intake and the Throttle body. How is this used and will there be an impact by plugging the port on the TB.



The cold start injector isn't needed with the 7730 ECM. That air tube that runs from the stock Fiero 2.8 TB down to the stock lower intake as far as I know is meant to route air flow past the cold start injector (helps distribute cold start injector fuel to all cylinders). Well if you aren't going to be using the cold start injector then you shouldn't need to worry about this tube. Just plug it if you plan on using the 2.8 upper plenum and you should be fine. But since you are going to be using DIS have you considered just using the stock Camaro 3.4 upper plenum as well? You should be able to turn it around so the throttle body faces the transmission.
mswenson289 FEB 17, 02:57 PM
Thanks for the response. I wasn't sure on the tube I knew the injector is unused but was concerned that it still used the extra air. I have not seen a drawing (breakdown of the TB) to see how that routed air for cold start. No valve on it so you would have to assume it breaths all the time.
On the upper intake I missed a bolt on the fuel rail and damaged it(upper intake) , but also it interferes with the thermostat housing. I like the looks of the original intake and am running a 4T60 no high rev's here. The long runners allow for torque and that is what I was really desiring.
mswenson289 FEB 17, 03:48 PM
I just went to measure the port to make an aluminum plug and was wondering if this is the IAC port? the hole is in front of the throttle plate and looks like it is routed down past IAC valve and out that port, idid not remove the TB from the intake to see if or where the IAC was routed behind the plate. Does this make sense? Is it the IAC port is it still OK to plug?
Mike
Blacktree FEB 17, 04:14 PM
That air tube running from the throttle body to the lower intake is the idle air tube. It's essential to the operation of the Fiero V6.

If you use the Camaro lower intake, then you'll also need to use the Camaro throttle body. (You may need to use the Camaro upper intake, as well. But I'm not sure.) That's because the idle air setup is different on the Camaro engine.

Edit to add: if you use the Fiero lower intake, you can plug the cold start and fan switch holes with 3/8" NPT pipe plugs. Most hardware stores should have these.

(edited to correct the pipe thread size)

[This message has been edited by Blacktree (edited 02-18-2008).]

Darth Fiero FEB 18, 04:19 AM

quote
Originally posted by Blacktree:

That air tube running from the throttle body to the lower intake is the idle air tube.



Hmm, after you said that I had to go look it up in my 85 Fiero Service Manual. On page 6E3-78, Figuire-25 it shows the tube in question labeled as the "cold start valve air tube". A couple of pages earlier I found a description of the cold start injector; GM calls it the "cold start valve" in this service manual.
Hudini FEB 18, 09:06 AM
That tube does supply idle air to the motor with the stock throttle body as the IAC port exits at the lower rear of the throttle body. It's the only one I've run across that works like that. All the other throttle bodies I've seen have the IAC port exit just on the backside of the throttle plate.
Here is a pic of the tube:
Pyrthian FEB 18, 09:18 AM
yes, the IAC path is easy enough to relocate - just a control vacuum leak. it doesnt need to be that big - you see on the throttle body side - it under 1/4". but - I would suggest to NOT use a rubber vacuum line - as it may collapse & stall the motor.

[This message has been edited by Pyrthian (edited 02-18-2008).]

JazzMan FEB 18, 01:46 PM
The air tube IAC design was likely done that way in order to use the cold start injector, sort of merging the two functions. The IAC alone would work just fine metering the air back in just past the throttle body.

JazzMan
Pyrthian FEB 18, 02:01 PM

quote
Originally posted by Will:

With a dual image ROM and a bit of wiring, you can change between tunes at the flip of a switch.



yes, was just thinking since the A/C request is already there, and in fact does change parameters - I was just hoping this would be a simple approach.
Darth Fiero FEB 18, 04:14 PM

quote
Originally posted by JazzMan:

The air tube IAC design was likely done that way in order to use the cold start injector, sort of merging the two functions. The IAC alone would work just fine metering the air back in just past the throttle body.

JazzMan



I'm just going on what the service manual says about its function. You may very well be correct that this tube has to be present and hooked up in order for the OE Fiero 2.8 throttle body and IAC system to function; if so, I stand corrected on my previous statement. I haven't researched the inner workings of the stock 2.8 to the extent of knowing everything possible about this particular design. But assuming what you say is true, and someone wanted to use a later design lower intake manifold, they would also have to use the later style throttle body so the IAC would continue to function.

[This message has been edited by Darth Fiero (edited 02-18-2008).]