Connecting 'vacuum amplifier' causes hesitation off idle

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DodgeLad

DodgeLad

Skipped the Light Fandango
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1980 truck
When I plug the EGR port on the Holley 1945, I have slight hesitation off idle until she warms up. Then everything is acceptable, probably not perfect tho. When I connect the EGR port to the vacuum amplifier, the hesitation is more pronounced and doesn't go away after coming up to operating temp.

I've played with the timing and mixture screw ad nauseum. Right now I just keep the port plugged. But I'm sure that's hurting my emissions. Whatever works off the vacuum amp is now rendered inop.
 
It sounds like you must have a vacuum leak somewhere in the vacuum controls system, because when everything is working right the engine does not get any extra air to cause this.
It is supposed to only draw vacuum until it has a reserve of it in the amplifier, and not get extra constantly.
 
thx
Do you know what is not working now aside from the EGR system? I doubt I'll fix it. There are special connectors at the amplifier and all kinds of proprietary stuff strewn under the hood.
 
Those also had a thermal vacuum switch in the radiator OR intake to keep the EGR off line till warm up.
 
mguner said:
Those also had a thermal vacuum switch in the radiator to keep the EGR off line till warm up.
Click to expand...
thx, I think it's located at the thermostat housing on this one.

Does the venting to the charcoal canister work without the EGR vacuum?
 
DodgeLad said:
thx, I think it's located at the thermostat housing on this one.

Does the venting to the charcoal canister work without the EGR vacuum?
Click to expand...

There needs to be vacuum at the charcoal canister for that to work as designed.
Do you have to have the smog stuff where you live?
 
I would take everything except what's necessary for it to run and throw it all in the ditch.
 
Check out the link below this image for a free diagram emailed to you...


vhrd-75-225.jpg


http://www.mopartruckparts.com/tech/t005.html
 
lol
no smog on vehicles over 35 years old here, so I am golden

I am smelling gas now when I pull into the driveway. Can I grab canister vacuum from the EGR port? Or any other port? I would like the venting to work. But I am not hellbent on it either.

Should I use an EGR blockoff plate or is removing vacuum from the valve just as good?

much thx
 
The charcoal canister may be saturated. You can buy replacement charcoal inserts. I think that would be smart. Leave the canister, crapcan all the rest. A properly working canister system can actually improve mileage.
 
RustyRatRod said:
The charcoal canister may be saturated. You can buy replacement charcoal inserts. I think that would be smart. Leave the canister, crapcan all the rest. A properly working canister system can actually improve mileage.
Click to expand...

Do I need the EGR blockoff plate?

What about the air pump? It's the size of a small alternator and the motor must turn it. But I just bought a 'new' reman' one. :banghead: Pretty easy to delete?
 
Oh forgot. I think the canister may be intact. When it does have vacuum I don't smell the gas.
 
I would run the vacuum advance directly from the sparkport. If there is no spark port, I would make one.This is the most important.
The charcoal canister serves a very useful purpose.I would keep it.
Obviously the PCV has to stay.
The EGR system, can be ditched, but when working correctly, serves a very useful purpose. I would try to keep it. It must be disabled at idle and on a cold engine, and at WOT. It must only work at part throttle; And with the amp on there, EGR is varied proportionly, by the venturi vacuum; very nice.
I would verify that all of the diaphragms, and switches,are working correctly and that every thing is correctly plumbed; and then I would leave it all in there. There is nothing in those systems,that if working correctly, makes trouble. If you ditch any of it,except the EGR, you may have other issues. In rare instanced,disabling the EGR can cause problems.
 
The EGR's main purpose is to lower combustion temperatures and reduce NOx emissions. It tends to have a negative effect on efficiency and smooth engine operation. So deleting that is a positive step forward in engine performance. Using a blockoff plate is best as you don't know if the EGR is stuck in the open position or not; you can test by sucking on a hose to the EGR port and seeing if the valve's shaft moves freely.

The smog pump was made to help burn off leftover hydrocarbons in the exhaust; as such it does not really effect performance but tends to be a good place to have problems from corroded parts.

The canister is a part of the fuel tanks venting system, and is not harmful to performance. The fact that you are smelling vapors with not line to it is what would be expected. IMO, keep it connected in the right places; the carb/intake should only pull from the canister under medium and WOT throttle conditions, so keeping the connections intact is needed. The canister re-fill is a good idea.
 
You can imagine the sad day in the engineering dept., the day those boys were told to design the air injection system.

It was bad enough saddling the poor old slanty with super low compression, and power robbing systems, but then they added insult to injury by having to ram fresh air into the manifold, to complete the burn, which shoulda happened in the chambers.
You gotta wonder about the people behind the mandates. Of the people/for the people ....hah.
The good thing is those days are behind us now, and they led to new and better engines, with higher compression again, better year-round driveability,more mpgs, and most importantly MORE power! Or at least more power per cubic inch.
 
If the emissions controls aren't working, you are likely polluting more than without them. They are almost impossible to maintain and you aren't required to so sh**-can those poor designs. The air pump in my 1982 Dodge Aries seized. As I recall, it had a plastic rotor. A check valve (rubber flapper?) was supposed to protect it from hot exhaust gas. Guess how long that claptrap worked?
 
The air pump is a new reman. When it dies I'll be ditching it. The truck is running fine right now with the EGR port plugged. What I would like to know is where to grab vacuum for the canister with the EGR system gone.
 
Venturi vacuum
This port is above the butterflies and protrudes into the venturi, hence its name.Sometimes venturi vacuum is used to trigger a vacuum relay which then opens a larger passage underneath the butterflies. The important thing is that the canister should only be evacuated with a good amount of throttle opening, and absolutely not,at idle, where it will cause idling issues.The relay valve on later canisters was in the top of the canister. I can't recall what year they started that, but it was quite early.
This system operates independently of the EGR system, and there should be no interconnecting of the systems.
 
Im running into this problem on my truck. The EGR system is pretty basic. It takes a small vacuum signal from the port above the butterfly on the carb and routes it to the vacuum amp, sort of a "transistor" design as it takes a small vacuum input and makes a large output by porting straight intake vacuum to the EGR proportional to the velocity of the intake. So at idle, the EGR is closed and at WOT, the EGR is also closed but that uses another system. So the EGR is only operational during cruise and low load. It lets inert gas into the intake to dilute the A/F so as to cool it in the CC, staying under the NOx formation temperature level. When it works, it doesnt do too much for driveability. when it doesnt, its hell on emissions. Either the valve will stick open causing a rough idle or the valve will coke up and NOx levels will rise and your mileage may fall as you are allowing a higher percentage of A/F into your chambers. Also the thermo valves the vacuum sources go through to the EGR are non functional when the car is cold. You can test the EGR by manually pulling a vacuum on the EGR valve itself at idle. If the car stalls, its working. newer cars use an electronic EGR valve, either active PCM or servo, or passive positional reporting or are so good they dont even need it.
 
much thanks
so venturi vacuum is the EGR port I assume
I noticed with the EGR system disabled I don't get tailgated as much
 
Venturi vacuum is the weak signal (ported vacuum?) that the amp uses to open the strong manifold vacuum to the EGR when it senses enough velocity to determine that the motor is off idle. 2500 rpm is the number my mazda manual uses to test EGR function.
 
Go back to the drawing, post#8. The canister port seems to be on the opposite side of the carb to the EGR/Amp ports. It's very important to get the right nipple. I believe the correct nipple has a very tiny orifice. As far as I recall there's only one like it. I may have been wrong about the venturi port on a slanty. The carb may be calibrated for a full-time draw from the canister. If/when you see that small-orifice nipple, and it fits the canister hose,plug it in. Mostly the nipples IIRC are different sizes, and that helps to settle the install.
 
See my new post on EGR as I found a workaround and a repair that seems to work fine. Remember no egr at idle! Look at pintle at idle and pull vacuum line. Did it move? It should not warm and deffinantly not cold as the thermo valve will block vacuum to system under 125F. If it just unseat with idle vacuum, try and adjust pintle height if equipped. If not, reroute egr vacuum off of the bad amplifier onto ported vacuum off carb or T it off ported line to distributor. This won't help wot (amp has wot check valve ), but it will clean up a rough idle with a bad amplifier.
 
pishta said:
See my new post on EGR
Click to expand...
What new post on EGR? I'm not seeing one in your recent history. Maybe go ahead and link to it, eh?

I found a workaround
Click to expand...

Anything like the EGR portion (toward the bottom) of this?

Slant-sixers might also want to put on the updated transducer-type EGR valve, EGV-490, which does a better job matching EGR flow to engine speed/load, thus cleaning up some of the driveability faults the previous-type EGR valves could cause.
 
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