Fixed a Secondary System Vacuum Leak - ZR-1 Net Registry Forums

QB93Z · 07-19-2009

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.

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

Aurora40 · 07-19-2009

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?

QB93Z · 07-19-2009

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

FU · 07-19-2009

Way to go Jim

secondchance · 07-19-2009

"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.

Aurora40 · 07-20-2009

Ahh, I see that hose you mean. Yeah, on a '90 that comes out on the driver's side. Interesting about the throttle cables. The windshield is what I lean on though, when I'm standing on a tire and the alternator and trying to reach whatever the heck had me pulling it off in the first place.

If our cars didn't have clamshell hoods, I'd really have a hard time of it.

XfireZ51 · 07-20-2009

Jim,

I rest the plenum up by the front of the wheel well. Like Bob I use the windshield for support. Also, I disconnect that hard line at the throttle body and then just slip it on fitting as one of the last things before I button things up. I put some sillicone sealer at bottom
of that hardline and the one next to it. In fact, I put a small coating of clear silicone gasket around all vacuum line junctions that usually have a tendency to pop out. Just a thin film to seal and hold in position.

RICKYRJ1 · 07-20-2009

Great Job guys, Now that you mastered the plenum pull, time to step up to doing some P&P work.

QB93Z · 07-19-2009

Quote:

Originally Posted by Kb7tif

Most of the time its surprisingly simple to get the secondary on line isn't it.
that permagrin will wear off soon enough. next plenum pull will be porting ect.

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

LT5-1935 · 07-19-2009

Thanks again for all your HELP today Jim & Dave

really appreciate your help and the way the car runs now.

Thanks Again

George

07-19-2009	#1
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,684	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. 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

07-19-2009	#2
Aurora40 Join Date: May 2005 Location: Leesburg, VA Posts: 2,704	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?

07-19-2009	#3
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,684	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

07-19-2009	#4
FU Join Date: Mar 2004 Location: Found Member Posts: 4,327	Re: Fixed a Secondary System Vacuum Leak Way to go Jim

07-19-2009	#5
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,730	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.

07-20-2009	#6
Aurora40 Join Date: May 2005 Location: Leesburg, VA Posts: 2,704	Re: Fixed a Secondary System Vacuum Leak Ahh, I see that hose you mean. Yeah, on a '90 that comes out on the driver's side. Interesting about the throttle cables. The windshield is what I lean on though, when I'm standing on a tire and the alternator and trying to reach whatever the heck had me pulling it off in the first place. If our cars didn't have clamshell hoods, I'd really have a hard time of it.

07-20-2009	#7
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,685	Re: Fixed a Secondary System Vacuum Leak Jim, I rest the plenum up by the front of the wheel well. Like Bob I use the windshield for support. Also, I disconnect that hard line at the throttle body and then just slip it on fitting as one of the last things before I button things up. I put some sillicone sealer at bottom of that hardline and the one next to it. In fact, I put a small coating of clear silicone gasket around all vacuum line junctions that usually have a tendency to pop out. Just a thin film to seal and hold in position.

07-20-2009	#8
RICKYRJ1 Join Date: Dec 2005 Location: Tinton Falls, NJ Posts: 1,169	Re: Fixed a Secondary System Vacuum Leak Great Job guys, Now that you mastered the plenum pull, time to step up to doing some P&P work.

07-19-2009	#10
LT5-1935 Join Date: Jan 2009 Location: KINGSVILLE, MD Posts: 65	Re: Fixed a Secondary System Vacuum Leak Thanks again for all your HELP today Jim & Dave really appreciate your help and the way the car runs now. Thanks Again George Last edited by LT5-1935; 07-20-2009 at 05:38 PM.