EGR, EFE, TVS. 1978 L48 350 ci

[Corvetteville]

Acronyms ehh?
OK, my EGR is connected to the top port of the TVS on the manifold, but the vacuum hose from the lower port goes to the upper port of the EFE TVS & not to the carb??. I have tested the EGR & TVS with vac pump & they work & hold vacuum ( TVS cold & closed)
Has this been done to improve performance?
Also, I can't find an EFE actuator or hoses to & from the stat housing TVS??
So in effect they're both non operational & the fuel cannister as well?
Car seems to run fine, ( slightly reluctant starting from cold) auto choke works. Needs a few pumps, which works, also have the heat riser built into the air pan snorkel, which is connected & seems ok on vac test.
Please let me know what you think, should I leave alone? Thanks in advance, ( pun, LOL ).Steve

 

[johng]

Where is the lower port of the EFE TVS connected to? If it goes to a ported vacuum then the EGR will probably work much as intended, although it would be simpler just to connect the EGR TVS straight to the ported vacuum as it's supposed to be.

 

[Corvetteville]

Where is the lower port of the EFE TVS connected to? If it goes to a ported vacuum then the EGR will probably work much as intended, although it would be simpler just to connect the EGR TVS straight to the ported vacuum as it's supposed to be.


View attachment 4349

Hi John, Nowhere! There's NO hose on the lower TVS port. There are 2 spare carb ports which are blocked of with what look like "factory" caps. Not a bodge bung.

 

[Oneball]

Can’t help with most of it but the auto choke is adjustable, so might not be set right, hence the cold start issue.

 

[Corvetteville]

Can’t help with most of it but the auto choke is adjustable, so might not be set right, hence the cold start issue.

Hi One Ball, Thank you for your reply.I will look into that next. Seems to operate Ok, 2 presses of the loud pedal & the rpm is fast, and can be knocked down by tapping the pedal. Then seems to reset to normal RPM after a few minutes driving. It's not a big problem but will have a look. Thank you.

 

[Oneball]

Hi One Ball, Thank you for your reply.I will look into that next. Seems to operate Ok, 2 presses of the loud pedal & the rpm is fast, and can be knocked down by tapping the pedal. Then seems to reset to normal RPM after a few minutes driving. It's not a big problem but will have a look. Thank you.

That doesn’t sound like it’s quite right, just blipping the throttle shouldn’t really change the idle speed, whether it’s warm or cold.

 

[Corvetteville]

That doesn’t sound like it’s quite right, just blipping the throttle shouldn’t really change the idle speed, whether it’s warm or cold.

I'll have to read up on it, I only know what I read, not much actual experience! LOL I've got an owner's handbook which hopefully should tell me.

 

[johng]

Sounds like your EGR is doing nothing then, as it's got no vacuum connected to it. My hoses weren't all plumbed up correctly either, but the red arrow shows where I think the bottom of your EGR TVS should be connected. The green arrow shows a cap I put on, if this is the sort of thing on your carb then they are readily available, so aren't necessarily "factory" items.

 

[Corvetteville]

Sounds like your EGR is doing nothing then, as it's got no vacuum connected to it. My hoses weren't all plumbed up correctly either, but the red arrow shows where I think the bottom of your EGR TVS should be connected. The green arrow shows a cap I put on, if this is the sort of thing on your carb then they are readily available, so aren't necessarily "factory" items.

View attachment 4350

Yes, I'm sure you're correct having looked at the diagram

 

[Corvetteville]

Yes, I'm sure you're correct having looked at the diagram which you posted before. I think currently the distributor advance is on that ported vacuum. Looks like the dizzy should be on the manifold vacuum? I'm thinking one or both the TVS's are duff, the ERG one may be stuck, I haven't tested it at hot yet. but why put dizzy on ported?

 

[kentvette]

Unfortunately, the removal or "butchering" of the EGR/EFE/TVS system is not uncommon - a typical "bubba" trick when it was thought the system robbed power. My '78 is in a similar situation with disabled TVS and no connections to EGR EFE etc. And, I have plugged ports on the carb that, like yours, look like factory items, even though I know they are not.
I'm fortunate in knowing a chap who was the "go-to-guy" for performance tuning in LA for 30 odd years who had a good "go" at ours when he was staying with us. The fact that all that stuff was missing didnt phase him, but he did spend a lot of time setting up the carb and was happy with the result!

Re your starting and idle speed; when cold, it is normal to give two full "pumps" on the throttle. Ours will fire after exactly 5 seconds of cranking and the "fast idle" facility will let it idle at about 1300-1400 rpm for some minutes. "Blipping" the throttle when the engine has warmed through enough will knock off the fast idle and the car should then tick over at about 1000 rpm in N, going to 900 in D.

If you have the Haynes manual the section on the '78 carb is actually pretty good and details the setting up of the choke. It's tricky to get just right, but it should be shut tight when cold. On ours the Choke Pull Off diaphragm had failed and that caused all sorts of issues, but once replaced all was OK. Check that works.

It would be nice to have things like the charcoal canister connected up (it deals with fuel vapour odour), but if the car is running OK and starting as described, I'd be tempted not to fiddle too much! What I would say is to ensure that the PCV system is connected as it should be.

 

[Corvetteville]

Unfortunately, the removal or "butchering" of the EGR/EFE/TVS system is not uncommon - a typical "bubba" trick when it was thought the system robbed power. My '78 is in a similar situation with disabled TVS and no connections to EGR EFE etc. And, I have plugged ports on the carb that, like yours, look like factory items, even though I know they are not.
I'm fortunate in knowing a chap who was the "go-to-guy" for performance tuning in LA for 30 odd years who had a good "go" at ours when he was staying with us. The fact that all that stuff was missing didnt phase him, but he did spend a lot of time setting up the carb and was happy with the result!

Re your starting and idle speed; when cold, it is normal to give two full "pumps" on the throttle. Ours will fire after exactly 5 seconds of cranking and the "fast idle" facility will let it idle at about 1300-1400 rpm for some minutes. "Blipping" the throttle when the engine has warmed through enough will knock off the fast idle and the car should then tick over at about 1000 rpm in N, going to 900 in D.

If you have the Haynes manual the section on the '78 carb is actually pretty good and details the setting up of the choke. It's tricky to get just right, but it should be shut tight when cold. On ours the Choke Pull Off diaphragm had failed and that caused all sorts of issues, but once replaced all was OK. Check that works.

It would be nice to have things like the charcoal canister connected up (it deals with fuel vapour odour), but if the car is running OK and starting as described, I'd be tempted not to fiddle too much! What I would say is to ensure that the PCV system is connected as it should be.

Hi Stephen, as all ways great to hear from you. Your description of the starting & choke operation is spot on.Mines the same. Maybe a little more than 5 seconds, always seems so long after starting a new car, which goes on the button! I get tempted to give it a few more pumps, which does squirt fuel in, I've checked.
The PCV is all connected, renewed it recently. I will check the choke operation, as I do have a Haynes. Might get a timing light to check the advancement? is that the way? Rev up & the white line moves.?
As my new daily is " Saving the planet" I think I'll just stick with the Vette as is. Anyway at 42 years old, it must be more carbon neutral that renewing your car every 5 years LOL !!

 

[kentvette]

Hi Stephen, as all ways great to hear from you. Your description of the starting & choke operation is spot on.Mines the same. Maybe a little more than 5 seconds, always seems so long after starting a new car, which goes on the button! I get tempted to give it a few more pumps, which does squirt fuel in, I've checked.
The PCV is all connected, renewed it recently. I will check the choke operation, as I do have a Haynes. Might get a timing light to check the advancement? is that the way? Rev up & the white line moves.?
As my new daily is " Saving the planet" I think I'll just stick with the Vette as is. Anyway at 42 years old, it must be more carbon neutral that renewing your car every 5 years LOL !!

Ha! And with the new car, I don't even need to hang on to the key, just a flick and it'll start when it's ready!

I've tried an extra pump - didn't seem to make any difference, and "my man" seemed to think two was what was required. But it sounds like yours is more or less doing what it's supposed to!

I set my initial timing to what's in the Haynes manual (I think its 6 or 8 BTDC from memory). There is a chap in the US called Lars who recommends setting the initial much higher. I'm not 100% convinced..... But, I have slightly "llighter" springs in the distributor which allow it to go to full advance a bit quicker. It's worth putting a timing light on the car just to check that the centrifugal advance/retard is working as it should. We had an issue some years ago now and I discovered that the mechanism had seized! Took a bit of freeing up, given that I didn't want to remove the distributor! I put new weights and springs in at that time. Don't forget to disconnect the hose to the vacuu advance on the "dissy" before you check the initial setting.

 

[Corvetteville]

Ha! And with the new car, I don't even need to hang on to the key, just a flick and it'll start when it's ready!

I've tried an extra pump - didn't seem to make any difference, and "my man" seemed to think two was what was required. But it sounds like yours is more or less doing what it's supposed to!

I set my initial timing to what's in the Haynes manual (I think its 6 or 8 BTDC from memory). There is a chap in the US called Lars who recommends setting the initial much higher. I'm not 100% convinced..... But, I have slightly "llighter" springs in the distributor which allow it to go to full advance a bit quicker. It's worth putting a timing light on the car just to check that the centrifugal advance/retard is working as it should. We had an issue some years ago now and I discovered that the mechanism had seized! Took a bit of freeing up, given that I didn't want to remove the distributor! I put new weights and springs in at that time. Don't forget to disconnect the hose to the vacuu advance on the "dissy" before you check the initial setting.

Thank you Stephen, excellent advice, all ways a pleasure to read your posts. I shall do as you advise. Also the choke maybe slightly open after depressing the throttle, will check. Lars, yes read his stuff on US forums. Talk about mediation LOL !
As for the new car, yes don't even take the keys out of my pocket! Cheers thanks again. Steve