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Guys,
I am trying to track down a vacuum leak on my '77 that is raising havoc with my idle speed. Amongst the leak possibilities is the diverter valve that is attached to the smog pump. As you may know that part cannot be found anywhere, there are other valves that could work but that would required heroics to mount and plumb them. What are you guys in Calif with '77s doing for this? Here is a photo of my valve, ignore the open supply port on the EFE TVS the hose just happens to be disconnected at the moment and the bottom hose is plugged because the EFE that I am using is not vacuum actuated.
If you have a mighty vac you could check the valve diaphram. It has probably failed. I cant help with a repair of those if it does not hold vacum sorry. We dont have smog inspection here so I just disable them and leave them in place for the look.
I agree, check that the diverter holds a vacuum.
If the diverter holds a vacuum move onto the EFE TVS switch.
You have the switched side of the EFE TVS switch blocked off to the actuator.
You also say you are still sending full manifold vacuum to the top port of the switch.
It is possible that the switch itself has failed internally and is open to the exhaust port causing a vacuum leak.
It does not hold a vacuum. So what I did was block off the hose upstream of the tee cutting off vacuum to both the EFE TVS and the diverter valve, improving both idle and air/fuel ratio. My understanding is the failure mode for the diverter valve will allow air to continually flow into the exhaust manifolds (actually headers). That should lower HC as designed and I should be ok as long as I don't get backfiring on deceleration. I don't see what else I can do and still at least appear legal for smog. I sure don't want to have to take the car to a smog referee come next September when I will be due for a smog check.
Jim, just make sure that both crossover check valves are working correctly blocking any back pressure in case of a possible backfire.
There is a internal relief valve in the diverter that should open and vent through the silencer if a check valve fails, but if the relief fails to open pump damage may accur.
I found a diverter on e-bay with the internal silencer and the part number matches the 77 AIM part number if interested. You might ask seller if they would guarantee it holds vacuum?
LINK:https://www.ebay.com/itm/GM-C3-Origi...8AAOSwyNJfGL3Z
Damn I am definitely slipping. Looking at the AIM, the part on my car does not look right nor does the number match. Taking bmotojoe's advice and I messaged the seller asking if it holds vacuum. I'm not a purist, my car is highly modified but for now I'll shoot for the correct part but will keep the other one in mind as a fallback.
What is the part number per your AIM? I was going to look in GMpartswiki.com but the site won't come up for me......
If you post the AIM part number can keep looking..... and it would be a good thing to have on this record too.
Originally Posted by Jim__H
Damn I am definitely slipping. Looking at the AIM, the part on my car does not look right nor does the number match. Taking bmotojoe's advice and I messaged the seller asking if it holds vacuum. I'm not a purist, my car is highly modified but for now I'll shoot for the correct part but will keep the other one in mind as a fallback.
What is the part number per your AIM? I was going to look in GMpartswiki.com but the site won't come up for me......
If you post the AIM part number can keep looking..... and it would be a good thing to have on this record too.
The part number in both the AIM and the 1983 dated Corvette Parts And Illustration Catalog is 17054984 Gr.3.670.
The parts catalog says 1977-1978 uses same number.
After all these years it is possible the part number has been superseded to a different number.
Yes 17054984 is the callout in my assembly manual. The seller of the ebay part with that number is not able to check the vacuum. Is there any reason why the other one might not work on my car?
Jim, Doing a e-bay search of GM #17084018 (Part Number Of Forum Member Carriljc link) 3 other diverter valves come up by 3 different sellers.
All (IMO to expensive) and advertize fitting 77-78 Corvettes.
One photo actually shows under the 17084018 number a hand written number 17054984 so one would think that the 17084018 number is a new superseded number???
I don't know if Dr.Rebuild is still selling Corvette parts but doing a catalog search I found this.
Catalog Page 88 under Diverter Valves listed as fitting 77-78 at a reasonable price LINK:http://www.docrebuild.com/dr-r-web/EGR-SMOG.PDF
Last edited by bmotojoe; Oct 28, 2020 at 07:40 AM.
I would pull all that smog stuff off and sell on e-bay. All it does is choke the motor. It never worked to our advantage as a consumer. Have you ever seen a cat or a smog pump on a dirty cummings or a jet fighter? How about your heating system (oil) your lucky if you are 70% pollution free! The list goes on wear your mask and labor your breathing and does it choke off your breathing , just like a motor.
Jim, Doing a e-bay search of GM #17084018 (Part Number Of Forum Member Carriljc link) 3 other diverter valves come up by 3 different sellers.
All (IMO to expensive) and advertize fitting 77-78 Corvettes.
One photo actually shows under the 17084018 number a hand written number 17054984 so one would think that the 17084018 number is a new superseded number???
I don't know if Dr.Rebuild is still selling Corvette parts but doing a catalog search I found this.
Catalog Page 88 under Diverter Valves listed as fitting 77-78 at a reasonable price LINK:http://www.docrebuild.com/dr-r-web/EGR-SMOG.PDF
I'm reluctant to buy off ebay and consider it a last resort. Got calls in to Bill Hodel and Dr. Rebuild at the moment.
I would pull all that smog stuff off and sell on e-bay. All it does is choke the motor. It never worked to our advantage as a consumer. Have you ever seen a cat or a smog pump on a dirty cummings or a jet fighter? How about your heating system (oil) your lucky if you are 70% pollution free! The list goes on wear your mask and labor your breathing and does it choke off your breathing , just like a motor.
If I did that the car would not pass smog which is required for registration renewal every two years.
You should be able to find all the stuff or reasonable substitutes. It's a lot easier now than when I bought my 68 in 1984 and nobody knew a dang thing. I even fabricated a thermostatic air cleaner to pass in 1985 ..... then a couple of years later I had to drill and tap my headers for AIR and add the AIR pump. Anyway, as you can see we should be able to plod through and get the necessary parts, even if substitutes.
You'll get a lot of opinions from folks that don't know the law.
Originally Posted by Jim__H
If I did that the car would not pass smog which is required for registration renewal every two years.
Last edited by carriljc; Oct 28, 2020 at 07:39 PM.
Don't toss your old diverter valve. It may be repairable with a fabricated diaphragm..... worse comes to worse it isn't repairable, but otherwise it would be an interesting project to attempt with all the modern adhesives......
It's easier now. You can go online and buy tapped repro exhaust manifolds and AIR injection tubes. Back then the smog guy gave me the name of an approved business' that drilled and tapped my exhaust and installed AIR tubes and a smog pump. Nowadays you can go online and find most of that stuff just bolt it on.....
Originally Posted by Jim__H
Thanks carriljc, good info.
Why did you have to retrofit an AIR system to your car?
I don't know about rebuilding it, if that was feasible someone would be doing it on a large scale. It doesn't look like it comes apart easily.
Diverter valve on a '77
