Fixed a Secondary System Vacuum Leak
 

We just got done with a plenum pull to locate a secondary vacuum system leak on George's (LT5-1935) recently purchased, 1990 ZR-1. Everything under the plenum was in excellent condition. All the tubing and fittings were tight. The leak was from the Secondary Actuator Valve. We repalced it with a new one and he was on the road in under an hour and a half.

He returned from the test drive with a big grin. :dancing :-D :razz: It was the first time he had really experienced the LT5 in full power mode.

BTW, the 1990 plenum pull is easier than the 1993, 1994 plenums I have done. There are less vacuum connections and electrical connections under the plenum.

Jim

Re: Fixed a Secondary System Vacuum Leak
 

You are turning into a regular ZR-1 shop! Nice work on the troubleshoot and repair. :) That's interesting about the ease of plenum pulling. Other than EGR, I thought the later ones had done away with that TB extension vacuum hose. And the ASR cars only have one throttle cable to disconnect.

What are the extra cables and such that the later cars have?

Re: Fixed a Secondary System Vacuum Leak
 

I should clarify. The plenums are easy to remove, but the 93-95 plenum is more of a pain to re-install because there are two more electrical connectors (one is for the Secondary Vacuum Sensor which on the 90-92 is over by the battery), and there is a hard plastic vacuum tubing that has to be plugged into a double connector deep in the valley. It pops out if you raise the plenum too high. The EGR line on the later LT5's is not too much of a problem since it is on the "outside" of the plenum.

I am practicing for Corvettes at Carlisle. I will pull the plenum on Darrin's 1990 ZR-1 and replace the plug wires, in the ZR-1 area of the Fun Field. I hope lots people attend so that we can have a good Q&A session and share under-the-plenum knowledge.

Jim

Re: Fixed a Secondary System Vacuum Leak
 

Way to go Jim :thumbsup:

Re: Fixed a Secondary System Vacuum Leak
 

"And there is a hard plastic vacuum tubing that has to be plugged into a double connector deep in the valley. It pops out if you raise the plenum too high."

I know which line you are talking about. I think it's actually PCV line.
When it pops out of the rubber boot best way I found is to crazy glue back into rubber boot deep in the valley first. Then after putting the plenum down, lift up the front, slide rubber hose back on to connection attached to the plenum and finally use a needle nosed plier to slip the metal clamp over the connection.
Another tip is to have replacement weather pack connectors on hand just in case you crack them while unplugging. Those things go real brittle sandwiched between the plenum and valley.:hello:

Re: Fixed a Secondary System Vacuum Leak
 

Yes, when you first look under the plenum, it is very confusing, but after using the diagram and tracing it out, the Secondary Vacuum System is very straight forward.

I just wonder what the GM/Lotus engineering reasons were to put so many vacuum connections on the plenum and in so many different places. I would love to know if was just random or if there is really a purpose.

Jim

Re: Fixed a Secondary System Vacuum Leak
 

Thanks again for all your HELP today Jim & Dave:worship: really appreciate your help and the way the car runs now.

Thanks Again :handshak: :cheers:

George

Re: Fixed a Secondary System Vacuum Leak
 

You are welcome my friend!

Jim

Re: Fixed a Secondary System Vacuum Leak
 

Anytime!

It was lots of fun and always great to help another Z brother!

:cheers:

David

Re: Fixed a Secondary System Vacuum Leak
 

Darn, you guys have all the fun!:mrgreen:

Way to be Jim & Co.:thumbsup: