Vacuum pump

[zig]

Still trying to learn the differences in the ZR-1 from the 96 LT-1 I have. When I turn the ignition on I hear the vacuum pump run and then shut off. How long should iut remain off before it kicks back on? Mine shuts off for a couple seconds then turns back on for about a second. The cycle repeats until I start it up. Is this normal or do I have a vacuum leak?

[Dynomite]

Originally Posted by zig

Still trying to learn the differences in the ZR-1 from the 96 LT-1 I have. When I turn the ignition on I hear the vacuum pump run and then shut off. How long should iut remain off before it kicks back on? Mine shuts off for a couple seconds then turns back on for about a second. The cycle repeats until I start it up. Is this normal or do I have a vacuum leak?

I think you have a vacuum leak....once you start it up, plenum vacuum takes over. The faster the vacuum pump cycles (engine off) the greater the leak. The fact it does shut off even for a couple seconds means the leak is not extreme....but often kind of normal for vacuum lines that have become hardened with age. I think everyone has some vacuum leak more or less without knowing it. Plenum vacuum can easily compensate for small vacuum leaks such as that I think once the engine is running.

The Plenum vacuum source is that little connection center of Plenum on Drivers side. The other side of Plenum vacuum connection is Cruize and HVAC Vacuum.

If the vacuum pump does not cycle once the engine is running, that is an indication the Plenum vacuum can keep up with any small leaks. Now when Plenum vacuum drops at wide open throttle you still have sufficient vacuum with the vacuum pump keeping up with the leaks.

But I will check this out tomorrow when I fire the 91' up again
OOPS...that will have to wait until I fire up the 90'....I have no vacuum pump on the 91'

[Paul Workman]

Yep. Like Cliff said, the fact that it shut off indicates the leak isn't severe, And, aside from knowing it won't get better by itself, that much of a leak won't affect the operation of the Secondary Port Throttles (SPT as it is referred to).

The "Right of Passage" for any ZR-1 pilot is a plenum pull. So much stuff is under the plenum that sooner or later you'll want to do a "walkabout" under there. When you do, a Mitivac (hand-held vacuum pump from Harbor Freight (or the like) will come in handy to isolate the source(s).

P.

[scottfab]

That cycle time is way too short. The leak is too fast.

Here is some background on the secondary system on LT5s where the system is still in tack.
http://www.zr1netregistry.com/Inform...Diagnosis.aspx

First try checking that the pump itself is not the problem.
Do that by disconnecting the hose (be carful) and using your thumb plug
the side that runs to the pump. You can find a fitting on the
hose to do this where it goes over the two oil lines that
run to the radiator stack. The pump should run for a short time then
stop for as long as you plug the line.

If the pump runs again even with the line plugged then the diaphram on the pump has a hole in it.
Here is a pic of mine after I fixed it and fasioned a bracket to fit around it instead of glueing it back together.

[zig]

Thanks for all the input. A plenum pull is definitely in my near future. It only has 12,000 miles and pretty sure the original injectors so they are on the list also. I have had the plenum off my 91 Z28 w/L98 for just about the same work and had the plenum off a 96 LT1 for cleaning and gasket replacement. Every coolant hose and vacuum line on the 96 was bad and needed replace.

Paul - Got a MityVac a while back. Sure was handy replaceing the rear end lube.

Scott - I'll check the pump today. Thanks.

Mike

[zig]

Vacuum pump diaphram checks out good. Guess I'll order a gasket set and pull the plenum. It needed to come off for a good cleaning anyhow. It may not be bad but it goes against my grain when it's not right.

[zig]

Gaskets and new fuel injectors ordered. Guess I know what my weekend plans are now.

[scottfab]

Originally Posted by zig

Gaskets and new fuel injectors ordered. Guess I know what my weekend plans are now.

You might want to read up a bit:
http://www.zr1netregistry.com/Inform...m-Removal.aspx

[zig]

Scott - Thanks for the link. I have all the tools but the long T40. Also have a FSM. Off to a couple of my favorite shops to find a long T40. Maybe I'll luck out and find a tool truck.

[zig]

Got the vacuum leak diagnosed. Bad solenoid. I ordered one for a C2500 truck. Looks like the same solenoid but different mount. I'll try to swap the mounting bracket and see if it works. No other vacuum leaks and all the hard lines were in good shape. Not brittle like I'm used to.

Got all the way down to the starter moter and found a rats nest... literally. He chewed the insulation off the purlpe wire (starter relay?) The drain hole was clear though. He stayed to the forward end of the cavity and none of his "furnishings" made it to the back. I guess he didn't stay long though because I cant find any other chewed wires and no evidence of bones.

Last night I pulled the radiator and did the clean and inspect. Pretty bad but it didn't have any overheating issues. Better safe than sorry though.

Got a 6" T40 Torx from Amazon and it was delivered today. Worked great getting the two bolts off the plenum. Thanks again Scott.

Clean and reinstall everything with new injectors, o-rings and gaskets tomorrow. Hopefully I'll have it back together for a test drive tomorrow sometime.