Engine limited to 5000 rpm 1990 ZR1 LT5

[DPZR1]

Here's a thought and question. In that the vacuum pressure drops to zero instantly, doesn't that mean there has to be an electronic dump valve of some sort?

What in the ZR1 system could release all the vacuum pressure instantly?

[Dynomite]

Originally Posted by DPZR1

Here's a thought and question. In that the vacuum pressure drops to zero instantly, doesn't that mean there has to be an electronic dump valve of some sort?

What in the ZR1 system could release all the vacuum pressure instantly?

Lets suppose when the Secondary Port Throttle Valve Solenoid opens it dumps vacuum into a completely failed Vacuum Canister (or vacuum lines between Secondary Port Throttle Valve Solenoid and Vacuum Canisters are completely disconnected/failed).....vacuum goes to zero. Once the Secondary Port Throttle Valve Solenoid valve closes vacuum builds up to normal.

[tccrab]

Originally Posted by Dynomite

Lets suppose when the Secondary Port Throttle Solenoid opens it dumps vacuum into a completely failed canister.....vacuum goes to zero. Once the Secondary Port Throttle Solenoid valve closes vacuum builds up to normal.

I think Cliff is onto something here.
I'm pretty sure the vacuum pump is only used for low RPMS, once the engine revs it doesn't need the additional vacuum.
If the canister has failed or a secondary vacuum line is out of place then when the solenoid opens, no more vacuum.
No more vacuum, no more secondaries.

Really good write up of the secondary port vacuum system at the Corvette Action Center, you should keep this link handy:
http://www.corvetteactioncenter.com/...diagnosis.html

'Crabs

[Pete]

Bingo,what Todd said (tpepmeie)

Ok it does not just drop vacuum the secondary MAP sensor (under ECM)
Has to see above 3.00 volts if it sees less the secondaries shut down and feels like you hit a rev limiter,sounds like your running out of vacuum.

Pete

Originally Posted by tpepmeie

I would surmise vacuum pump. in the low gears, there is probably enough vacuum in the reservoir to keep the SPT's open. by third gear, that's probably exhausted, so you would need the pump to provide the vacuum.

I've never had these problems, but just giving another idea.

[Paul Workman]

Nothing to add on the secondaries - The GURUs of LT5 have spoken!

As for dying after idling, that is not secondary port throttle (SPT) related. But, perhaps the most efficient way to get to that is to look at the plugs - easy enough to do, and if there's any doubt you can replace them cheaply with the AC Delco 41-602s (copper, no less) work very well, and for about $25 for 8 (much less than a tank of 93 octane) you can have a fresh set every season, if you are anal-retentive, or every 9k-11k miles (about 2-4 seasons for me). (Pete put me onto these plugs and they've been perfect in my "FBI 500+" package.)

OBD-I will not reveal plug issues when scanning the ECM, but they will look at the pair of O2 sensors. Are the cross points approximately equal for both sensors, or is one only a fraction of the other? (A lazy sensor can result in improper fueling commanded by the ECM, and also result in the spark plugs on the side of the failing O2 sensor to be sooty or even fouled (first-had experience)).

Q: Did you purchase new stainless injectors from FIC, or "rebuilt" injectors? (Actually, either new or "rebuilt" can have problems, but the reason I ask is because the failure rate of the "rebuilt" injectors - according to the # of posts on this and other forums - is noteworthy in comparison to new stainless steel injectors.) In either case, a static pressure test* is in order to be sure a leaky injector(s) is not the problem. (In one case, Bob G had a new injector that would not close and leaking to the point of hydro-locking a cylinder with fuel!)

but I would want to do a static fuel pressure test to make sure one or more is not leaking (which also would usually show signs of trouble (wet, sooty, etc) on the respective spark plug(s).

And, BTW, if there are any codes being thrown, the secondaries will be switched off by the ECM. So if there is a service engine soon (SES) light on, the secondaries will be shut off, or will not open in the first place.

*Static pressure test: With a fuel pressure gauge hooked to the Schrader valve (at the front of the passenger side fuel rail) the ignition switch is turned to ON, without starting the engine. The pressure should fall in the 44 psi ± 2# range and with the switch then turned OFF, the pressure should hold to within 1 pound for several minutes (mine held for almost 30 minutes when everything was fixed). IF there is a leak, you'll want to eliminate the fuel pumps' check valves by opening the fuel line under the fill cap and repeating the static test there. Otherwise, if the plenum happens to be removed, then check for the leak at the injectors first before going to the fuel lines at the pump coupling - would be my suggestion.

Paul.

[XfireZ51]

I'm w Todd. Solenoid/Canister.

[Dynomite]

Originally Posted by XfireZ51

I'm w Todd. Solenoid/Canister.

Just trying to follow exactly where the problem is (the cause if in fact there is a single cause)

One of the most important Tests of the LT5 is the Secondary Functional Test.
See Secondary Functional Test and Reconditioning the Secondary Actuators

Marc Haibeck has identified a simple test to verify the Secondaries are functional without removing the Plenum SEE Verifying Secondary Operation with Plenum In Place. You only need a paper clip and electrical grounding wire with alligator clips on both ends.

1. This simple test verifies if each/both Secondary Canisters activate the Secondaries equally and smoothly.
2. The complete opening of the secondaries should take only a second if the Canisters are functional.
3. The Vacuum Pump will cycle and then turn off when you turn the Key ON.
4. The Vacuum Pump may cycle every minute (vacuum system in great condition) or cycle every 5-10 seconds (vacuum system leaking which all vacuum systems leak a bit).

5. As the Canister shafts move/function during the grounding of Pin C17, the Vacuum Pump will cycle keeping vacuum as the canister plunger moves.
6. Once the canister is fully stroked, the vacuum pump will turn off for a period of time depending on the condition of the Vacuum System.
7. If there is a major Vacuum Leak between the Secondary Port Throttle Valve Solenoid and either Vacuum Canister, the Vacuum Pump will run continuously once Pin C17 is grounded.
8. The Vacuum Pump will turn off once Pin C17 is Un-Grounded.

With Key On........
Find the Pink Wire which is C17 on the ECM. Insert a Paperclip along side the Pink wire
and attach a ground wire with Alligator Clip on both ends. Pin C17 is located in the Green Connector
second connector on the ECM from the passenger side.



Look down on the Passenger Side in the ...........................Look down on the Drivers Side in the
direction of the screw driver (Use a Flashlight). ..............direction of the screw driver (Use a Flashlight).
You will see the shaft of the canister which will ...............You will see the shaft of the canister which will
move toward the FRONT of the engine when ...................move toward the REAR of the engine when
you ground the Alligator Clip (The Front of the ................you ground the Alligator Clip (The Rear of the
engine is to the Right in the Photo)..................................(engine is to the Right in the Photo).

[DPZR1]

What vacuum pressure should the 1990 ZR1 pull? What should the gauge read if the pump is working properly?

[Dynomite]

Originally Posted by DPZR1

What vacuum pressure should the 1990 ZR1 pull? What should the gauge read if the pump is working properly?

I am not sure what the normal vacuum is but the bigger question is "does the vacuum pump cycle when you turn on the key and how often does the vacuum pump turn on and off".

It is prolly easier to just check the operation of the secondaries as in the post above and look for not only secondary canister shaft movement but also smoothness of movement. And check that both canister shafts (passenger side and drivers side) move equally in stroke and smoothness.

The test above does not require any instrumentation.....the test requires a paper clip and a small gauge test wire with alligator clips on both ends (preferably).

[DPZR1]

Problem solved!!!

Thank you everyone!!

I put new actuators in and tested them!! But under hard acceleration one of the actuators wasn't holding vacuum, so I replaced everything in the secondary port vacuum system.

Runs great again!!!