help please for a new member

[richard sanderson]

Hi Everyone, I would like some advice if that would be possible. Especially as I live in the south of Spain, so I am obliged to do all my own mechanics - nobody round here has even heard of a ZR-1! (Mind you, if someone feels insulted by this comment, please get in touch and I will give a grovelling apology, and be very grateful for any help they might be able offer). Anyway, the first problem I had to fix was that the Src light had been taken out, so although the suspension was naz, no codes were set. But after having to pull the dic and rearrange the lights in the proper place, I now have got that bit sorted and can get on with fixing the ride. Next the secondary vacuum doesn't seem to behave correctly. When the ignition is on but the engine is not running, the pump runs continuously. If I unplug the pipe from the pump, and block it off with my finger, it runs in little bursts, say 1 second on then 3 second off. I assume something is wrong under the plenum. So I have printed out the Big Country Corvettes instuction sheet, and am preparing to assemble all the bits I will need for a plenum pull. Item 5 in the removal procedure says remove the vacuum hose with a flat blade screwdriver. But idly fiddling around with things while going over these instructions on the car, I gave a very slight tug on this pipe, it came off the rubber tubing that goes into the plenum. Should this rubber tube be removed from the plenum, or could this be the cause of my leak anyway? Also, looking through other posts, I am unsure whether this secondary vacuum system is actually necessary to get into full power. Can full power mode be acheived without this part of the system working? I dont want to tie the secondaries open. I am too much of a purist to want to cheat on something like that. Any comments welcome! Richard - 1990 #231

[xlr8nflorida]

Originally Posted by richard sanderson

Hi Everyone, I would like some advice if that would be possible. Especially as I live in the south of Spain, so I am obliged to do all my own mechanics - nobody round here has even heard of a ZR-1! (Mind you, if someone feels insulted by this comment, please get in touch and I will give a grovelling apology, and be very grateful for any help they might be able offer). Anyway, the first problem I had to fix was that the Src light had been taken out, so although the suspension was naz, no codes were set. But after having to pull the dic and rearrange the lights in the proper place, I now have got that bit sorted and can get on with fixing the ride. Next the secondary vacuum doesn't seem to behave correctly. When the ignition is on but the engine is not running, the pump runs continuously. If I unplug the pipe from the pump, and block it off with my finger, it runs in little bursts, say 1 second on then 3 second off. I assume something is wrong under the plenum. So I have printed out the Big Country Corvettes instuction sheet, and am preparing to assemble all the bits I will need for a plenum pull. Item 5 in the removal procedure says remove the vacuum hose with a flat blade screwdriver. But idly fiddling around with things while going over these instructions on the car, I gave a very slight tug on this pipe, it came off the rubber tubing that goes into the plenum. Should this rubber tube be removed from the plenum, or could this be the cause of my leak anyway? Also, looking through other posts, I am unsure whether this secondary vacuum system is actually necessary to get into full power. Can full power mode be acheived without this part of the system working? I dont want to tie the secondaries open. I am too much of a purist to want to cheat on something like that. Any comments welcome! Richard - 1990 #231

The pump is at the bottom right hand side of the car near the reserve coolant tank. I would unplug it first to see if your noise stops. If so, its your pump and you can get a new one from http://whiteracingproducts.com. You can also check ebay as they pop up from time to time. Also, they can be repaired - contact TomTom72 and Tom told me there is another fix by buying another brand of car pump which would probably be $100. I'm sure he will come in here and give feedback.

The same thing happened to my car. It's one small hose but they can come apart. Make sure yours are securely pushed in together.

You could probably get full power but if you are balls to the wall with the accelerator all the way down, there may not be enough vacuum.

I hope this helps.

Hi Richard,

Welcome to the family and I don't know about SIR, but will share this that I found most helpful with the same vacuum issue when I got my 90:

http://www.corvetteactioncenter.com/...cuum+Diagnosis

In addition, here is where you can save $ with all those outrageous prices out there for the replacement pump. There are folks here that are buying them and making a big profit for those that don't know or have taken the time to research the details by selling them on Ebay, etc.

Buy GM part number 94669091 ($113.66) and GM connector part number 12102747 ($19.54). I bought mine from www.partszoneonline.com a few years ago but the prices have not gone up much so get it while you can. I even bought a spare for later years.

I'm sure you will get many more replies from all the smart folks out there. I am just one to share what I find and don't know enough to help you further with your problem.

[xlr8nflorida]

This morning I could not find the information, the pump is from a Kodiak truck.

It fits 91-95 so if you have 90 you need to change the connector.

https://www.partszoneonline.com/part...=&srch4=&srch5

Also if you need GM original, I noticed Kurt white just put up 2 used take outs that are low mileage for $200 a piece.

Good Luck

[Dynomite]

Originally Posted by richard sanderson

When the ignition is on but the engine is not running, the pump runs continuously. If I unplug the pipe from the pump, and block it off with my finger, it runs in little bursts, say 1 second on then 3 second off. Can full power mode be acheived without this part of the system working?

I just tested my old vacuum pump as well as a new vacuum pump and neither vacuum pump recycled when vacuum was held for about a minute using a long vacuum line attached but blocked off. So.....your vacuum pump should hold a vacuum longer than 3 seconds I would think if in fact you had it blocked completely off with your finger.

You have a vacuum leak somewhere on the way to the plenum or under the plenum also (remove the plenum). Keep blocking off the vacuum ports further under the plenum untill the pump runs continously indicating you just passed the leak.

Without a vacuum your secondary actuator canisters will not function opening your secondaries......full power mode cannot be achieved without vacuum and secondaries functioning

The passenger side secondary actuator canister and attached vacuum line is shown here.

[xlr8nflorida]

Disconnect the pump all together, it is down by the coolant bottle and has a L connector. It will then stop running all together.

If you dig deep enough there is a post that says that someone was talking to Graham B. and he said that the yanks made them put the pump on that in reality unless it was extended high RPM runs, you could get by without one.

Perhaps its hearsay, I'd want mine fixed and for $140, you can have a new pump.

That being said, it might not be your pump but it seems likely it could be if it keeps running.

[tomtom72]

Okay, two more cents from the peanut gallery......

Rich,

If you separate the vacuum line that goes up from the pump at it's factory connection, just near the right water outlet tube on the right I/H, you can do some tests at that location.

If you plug the side of the line from the pump, the pump should stop, period. The pump's vacuum switch will detect full vacuum and not come on again as long as the plug is air tight. Make sure that you have a good seal when you do that part of the diagnostic. If you are certain you had an air tight seal and the pump behaved as you say, then the pump has a slight leak. It may not be all of the issue as you say the pump runs continuously in KOEO mode.

Next take a hand vacuum pump and attach it to the part of the line that goes under the plenum. It should hold vacuum until you use the release lever on the hand vacuum pump. If it does not hold vacuum at all, or leaks down rapidly then there is an issue under the plenum. You are on your way with that so I will not belabor the point, unless you are having doubts about what could be leaking under the plenum. If so just post up & we will take you thru it.

I just want to be sure you know that if the pump is sealed off and allowed to run, it should stop when a vacuum is achieved. If not then the pump has an issue.


Tom

[ZR1Vette]

Here is the vacuum line/connector Tom is referencing>>>



And it goes to a rather complicated 'plumbing' system under the plenum>>

[richard sanderson]

Thanks guys, My problem is that with everything connected up, the pump runs continuously, and with the pump disconnected and blocked off at the arrow in the above photo, the pump runs intermittently. So that tells us there is something wrong with the pump (can it be repaired?), and something wrong under the plenum, I guess. Maybe that is why the engine seem so strong although it has already done 125000! Nobody has managed to stress it for quite a long time! I live in hope. cheers Dick

[WB9MCW]

something wrong under the plenum

Until you do the Tom Tom Test (Below) you may be OK under there

Next take a hand vacuum pump and attach it to the part of the line that goes under the plenum. It should hold vacuum until you use the release lever on the hand vacuum pump. If it does not hold vacuum at all, or leaks down rapidly then there is an issue under the plenum. You are on your way with that so I will not belabor the point, unless you are having doubts about what could be leaking under the plenum. If so just post up & we will take you thru it.