BC GTA

The stock plenum in my 1989 GTA has two large runners on the driver and passenger sides, but also has a smaller “runner” on the passenger side. Is this for a cold start injector? I thought cold start injectors would discontinued in 1989. I am the original owner so I know this is the set up that came with car when it was built in early 1989. If this is not a cold start injector please advise what this small runner on the passenger side of the plenum is? Thanks.

jackballs529

89 does not have cold start. I have an 87 so Im not sure about what the runner is...

okfoz

EGR

From 85 - 88 as we all know came with the cold start injector. There was a small tube on both sides of the runners, one for the EGR (passenger side) and the IAC/cold start injector (Drivers side)

Starting in 1989 they droped the cold start injector, and therefore the IAC tube on the drivers side went away. So they had to find a new route for the IAC, which now instead of running through the plenum, was now delevered at the back side of the Throttle body.

My bet would be that they did this to save money, it would be cheeper to make the runner, and it would be cheeper without the 9th injector...

Interestingly enough, if you have an 86-88 TPI with the 89 chip like I have you can use a 89-92 throttlebody...

That is exactly what I have now...

John

thebruce

If you convert to the '89 program (I'm converting an '85 Corvette to a '165 ECM with the '89 bin), what do you do about the idle air passages? Do I leave everything hooked up normally on the '85 plenum and throttle body? I'm using an EGR blockoff plate and cold start injector plug, but I'm not sure what to do about IAC.

Thanks.

okfoz

89 Bin will not work on the 85 computer unless you upgraded the system.

Leave the intake alone, and you will be fine. I am using the ARAP bin from 1989, and have no problems with the 87 intake & runners.

John

TraviZ

iTrader: (2)

that one little runner does nothing, when in contacts the base manifold, its blocked off.

thebruce

okfoz-

I just finished the harness conversion so I can use the '165 ECM. I'm trying to sort out the plumbing issues, and my final concern is what to do about what I think is called the air intake tube on the throttle body. Do I need to plug it? If I need to hook it up, where do I connect the other end of the tube? This will be on a '74 non-emissions (EGR, AIR, etc) vehicle with headers, so I can't hook up stock '85 Corvette exhausts to keep all the proper TPI plumbing.

Thanks.

okfoz

without looking at the intake, I think your talking about the vacuum tube that goes into the right valve cover from the Throttle Body. THere is also a port on the drivers side between the runners that goes into the left valve cover.

There are water ports that do NOT need to be hooked up on the throttle body, I just took a piece of pipe, I want to think it was 3/8" copper or 1/2" copper I forget, it worked perfect tho to bypass the throttle body.

As for your Throttle body, all throttle bodies from 85-92 are the same, the only difference is on the 89-92 models they cut out a section in the back of the throttle body that allows the EGR to work.

JOhn