Throttle Body Secondary Valves

[Gary Yarbrough]

At what point to the secondary throttle valves open?

I wish I didn't have to ask this because I know I've seen this information somewhere, but I can't seem to find it...

[Hammer]

Technically I don't know that answer either. But you should feel them open at around 3000 to 3500 RPM.

[bobbyhi]

I think it depends on the chip that is installed. Some of the tuners have different ranges for opening.

[XfireZ51]

Depends on the RPM and the TPS% Opening set in the calibration. Not just one answer.

[Kb7tif]

http://www.corvetteactioncenter.com/forums/zr-1-general-technical-discussion/14272-1990-1995-zr-1-secondary-port-vacuum-diagnosis.html

[Gary Yarbrough]

Thank you! Figure 7 was exactly what I remembered seeing, I just couldn't remember where.

[Kb7tif]

I wanted to see for myself when the big plates start to open so I pulled the intake hose so I could see right down the airhorn, put a mirror there so i could watch from the drivers position when i stepped on the gas.
The big plates crack open at about 15% throttle and go from there. So they open VERY quickey.

[XfireZ51]

I wanted to see for myself when the big plates start to open so I pulled the intake hose so I could see right down the airhorn, put a mirror there so i could watch from the drivers position when i stepped on the gas.
The big plates crack open at about 15% throttle and go from there. So they open VERY quickey.

You realize those aren't the secondaries we're discussing.

[Gary Yarbrough]

Yeah, I didn't mean injector secondaries. I meant the larger valves on the throttle body. Mine seem to take a long time to open... I'm wondering if this could cause my hesitation...

Kb7tif, are you talking about the throttle body?

[Kb7tif]

You realize those aren't the secondaries we're discussing.

He mentioned picture#7 and that is the throttle body plates.
Another thing you can check is that are the plates on xfire is talking about, as just because the vacuum system is working and all does not mean that all 8 plates are opening. the Seconadry throttle linkage on these are somewhat flimsey and can break off. On My car only 1 of 4 were opening on one side.
To check this there is a wire on he c connector of the pcm you ground out 9I think its a purple one) and open the secondairy system with engine off.
Mark H's site expains this in detail on what wire and what connector.
The secondairy linkage is under the aluminum covers on each side. Kurt Has them. (thank god).
Its not worth pulling the plenum just for this but next time its off be worth a few minutes to check.:handshak:
Marc H has a throttle body service he provides which he will check everything, this cures high idle is some cases and provides peace of mind. he can check if everything is aok. 165$ 3 day turn around send it in.

[Kb7tif]

Yeah, I didn't mean injector secondaries. I meant the larger valves on the throttle body. Mine seem to take a long time to open... I'm wondering if this could cause my hesitation...

Kb7tif, are you talking about the throttle body?

YES mine start opening at 15-20% peddle pressure.

[Aurora40]

The TB secondaries are mechanically linked. I'm not sure how they could take a long time to open unless something is messed up?

If you pull off the TB cable cover, you can see on the side the little cam thing that opens the primary vs the secondaries. You can press the pedal while someone watches that. If you have a scan tool you can see at what throttle % the secondaries start to open.

I can also feel it in the gas pedal, the secondaries have more "spring" than the primary, you can sorta feel when you hit them when pressing the pedal.

[XfireZ51]

Here's what the stock settings on secondary throttle looks like: