Help with engine tune problem

[Belsy]

Hello to everyone I'm back, this time with a 95 Blk/ Blk with 82,000 miles which I just picked up and need some opinions please. The car starts & idles fine but on slight acceleration seems to have slight miss but when it reaches 3,000 rpm in any gear it simply cuts in & out as if the key was being turned off & on!! No matter how you approach it wont increase past 3,000. There is a check engine lite on but I have not pulled any info yet. Could it be in some limp mode? car has been well maintained by the one owner but the ZR1 knowledge in the area is questionable.
As always any advice or direction on this will be greatly appreciated!!

Look forward to getting with everyone thru the mails and future gatherings,

Gene in Fl.:dontknow:

[LGAFF]

Could be a plugged CAT or 2ndry MAP.....key is to pull the code....autozone or other auto parts store will do it for free

[XfireZ51]

Secondary cutoff?

[tomtom72]

Those sound like the symptoms for a DTC 61 I forget the FSM name for the DTC. It involves the 2* system. The limp home mode for that DTC is a 3k rpm limit....or at least in the 90 FSM it is outlined that way.

[Belsy]

Thanks for the responses, so far I have tracked to the vacuum pump will not shut off unless I place finger over the hose from plenum area!
The previous owner had some local work done???? Can I stop any leaks to at least see the area of needed repair? Would running in low power help? Where is the best gasket supplier? I remember White Racing here in Fl., are they still involved? Would cutting power to vac. pump allow better diagnosis?
Thanks in advance for any advice,
Gene=D>

[XfireZ51]

Thanks for the responses, so far I have tracked to the vacuum pump will not shut off unless I place finger over the hose from plenum area!
The previous owner had some local work done???? Can I stop any leaks to at least see the area of needed repair? Would running in low power help? Where is the best gasket supplier? I remember White Racing here in Fl., are they still involved? Would cutting power to vac. pump allow better diagnosis?
Thanks in advance for any advice,
Gene=D>

You have a vacuum leak to the secondary throttle system. When you get to 3k rpm, the ECM sees you have insufficient vacuum to open the secondaries and therefore the secondary injectors don't fire. System goes lean if you push it. Plenum pull to determine source of leak.

[tomtom72]

I was thinking to just try a check valve at the disconnect point as a diagnostic tool short of pulling the plenum? I know it's kind of a shot in the dark that the check valve is the source of the leak.:o

I use this store for gaskets.
http://jerrysgaskets.com/store2/root/

You could try pulling a vacuum using the secondary MAP line, as that on is T-ee'ed off of the left bank actuator?.....Or just pull the plenum.

:cheers:
Tom

http://www.corvetteactioncenter.com/forums/c4-corvette-zr-1/14272-1990-1995-zr-1-secondary-port-vacuum-diagnosis.html Try looking this link over as it might help visualize what you are checking.

[Hammer]

I was thinking to just try a check valve at the disconnect point as a diagnostic tool short of pulling the plenum? I know it's kind of a shot in the dark that the check valve is the source of the leak.:o

I would agree with Tom. Make a little loop with a check valve from the auto store. This should tell you if the car is sound and then a plenum pull will probably be in order to fix the leak (probably the check valve under there). Disconnect battery for 10-15 seconds to clear codes before restarting.

[Belsy]

Gentlemen,
I certainly appreciate the advice on this and will go as far as I can. New to some of this I must ask where to add the check valve (are there various styles and sizes), and the loop referred to as I attempt to check vacuum system?

I noticed the pump runs until finger is placed over open end then it stops, but when engine is running the pump is not running unless I pull the hose off from under plenum to pump then pump runs, put hose back on and pump stops. Hope this helps you guys determine anything new as I am on my way to get a vacuum pump and have ordered plenum gaskets in case.

Are there any similar articles w/pics on the art of pulling the plenum? I watched them do it in '07 at Van Dorn's shop during the BG ZR1 gathering but have never done one.
Again thanks to all for all your helpful direction,:worship:
Gene