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Lean Burn Computer with HEI conversion Help?
https://www.slantsix.org/forum/viewtopic.php?t=34738		 Page 3 of 3
Author:  Ed Mullen [ Fri Apr 24, 2009 6:28 am ]
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Quote:
Whatever the Holley book and your underhood sticker says, the computer needs a manifold vacuum source, not a ported vacuum source.
OK. So Chrysler Corp. put the wrong sticker under the hood, and it's been set up wrong since my father drove it home from the dealer in 1987. sure...why not. I'll go with that for the moment...

The fact remains that BlueBandit has a lean burn with a 1945 Holly and asked about hooking up a distributor to it.

That OSAC era 1945 in the picture has the same port as my last-year-they-ever-put-a-slant-in-anything 1945. BlueBandit's 1945 is from some time in between.

It is not unreasonable to speculate that his 1945 may have that same port. If he does, why can he not use it for his vac advance?
Author:  Reed [ Fri Apr 24, 2009 8:56 am ]
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These are scans from a 1984 Dodge Truck FSM-

Here is for a Holley 6145 (electronically controlled 1945):

Image

Here is a Holley 1945:

Image

As you can see, both the 6145 and the 1945 have an "ESA signal tube". This tube provides full manifold vacuum at all times. Next to the PCV tube, the 1945 has a "Ported Spark Tube" which will provided a ported signal for vacuum advance. Note that the 6145 does not have this tube.

In the 30 years since these vehicle have been manufactured, who knows what has been done with the hoses under the hood, and who knows whether or not the carb is still original, and, if not, if the replacement carb was hooked up right.

My point is that the spark computer needs a manifold vacuum source, not a ported vacuum source. And yes, it is possible that someone hooked it up wrong on the assembly line.

Ed- it looks like your ESA is hooked up to the EGR port on the carb. This is wrong. You should put it on a port that gives full vacuum signal all the time, preferably the port designed to provide vacuum to the ESA computer.
Author:  Ed Mullen [ Fri Apr 24, 2009 2:22 pm ]
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I explained before that the first photo I posted is wrong (in the sense that it has an arrow pointing to the EGR port) and that my ESA is hooked up to the one to the left and rear of the EGR port (i.e. the "ported spark tube")

I know what has been done under my hood because I am the second owner--the first owner being my father who never let anyone else's hands touch it, apart from the guys who mounted his tires, and a transmission rebuilder.

I know that the carb had not been removed or disconnected until I had inherited it 10+ years ago. I have, myself, had it off and on again to replace a broken exhaust manifold, replace the manifold gaskets, and a few carb rebuilds.

Many vacuum lines had been destroyed by exhaust/cat heat and I had to scour the internet to find advice on how to properly hook up the EGR amplifier, etc, but the ESA line remained untouched and original (one of two remaining original vacuum lines when I replaced all--mostly with 600+degree semi-rigid industrial tubing--this past summer) loomed with a wiring harness running along the firewall safe from the ridiculous heat that the pre-cat gave off.

Mine is a 1945, not a 6145, and what BlueBandit describes is a 1945 as well.

I'm switching th HEI, and if I come to find that I don't need to change carbs to do so, then I will do it sooner rather than later.

Next time I'm under the hood anyway, I'll give direct manifold to the ESA a shot. (I strongly suspect that the lean burn setups vary more than anyone seems to know--the guy w/the OBD-I whom everyone thought was nuts, for example.)
Author:  oldblue [ Tue Apr 28, 2009 3:30 pm ]
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I have a 1982 D150 with the 1945 carb.When I hooked the advance to the port for the choke pull off[the one in above post that says to "heated air fitting"}I got the best vacuum.Tried the port next to pcv and had very little vacuum.
Author:  Reed [ Tue Apr 28, 2009 3:40 pm ]
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Look, what I have been saying all along is that the ESA needs a manifold vacuum source and a distributor for street use needs a ported vacuum port. I don't care where you put the hose so long as the type of vacuum signal is correct.
Author:  tyb525 [ Thu Jun 28, 2012 7:34 pm ]
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A street car/truck distributor needs ported vacuum so there is no spark advance at idle. Manifold vacuum would cause the spark to advance when you don't want it to.

On a different note, my '85 D100 has Lean Burn and the 6145 carb. It is original.
Author:  SlantSixDan [ Fri Jun 29, 2012 1:38 pm ]
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Quote:
]OK. So Chrysler Corp. put the wrong sticker under the hood
They almost certainly did not.
Quote:
and it's been set up wrong since my father drove it home from the dealer in 1987
It almost certainly has not.

This has been covered before (here and here)—it is not correct to say that slant-6 distributor vacuum advance nipples always only ever have vacuum above idle, not at idle.

Keep in mind that vacuum nipples in the same position on two different examples of the same kind of carburetor are not necessarily routed the same way inside the carburetor. Some carburetors' distributor vacuum advance nipple (or whatever of the several other names it has been called over the years) have "ported" vacuum, that is, vacuum only once the throttle plate is open above idle speed. Other carburetors have manifold vacuum to this connection, though in either case there is a restriction to smooth out the vacuum signal to whatever is connected to that nipple—that's an important thing to keep in mind, is that not all vacuum connections of any given kind (manifold, venturi, "ported") are the same; sometimes you need a restrictor or a delay valve or a check valve or some other modifier in the vacuum path so whatever is hooked up operates the way it's supposed to.

Quote:
When I hooked the advance to the port for the choke pull off[the one in above post that says to "heated air fitting"}I got the best vacuum.
Messing with hookups until you get what you think is the "best" vacuum is not the right way to do it (whatever "it" might be).
Quote:
Tried the port next to pcv and had very little vacuum
Hooking up hoses to random vacuum connections is also the wrong way to do it. So is guessing and assuming what's supposed to go where, and why, when the correct information is readily available.
Author:  Sam Powell [ Sat Jul 07, 2012 7:08 am ]
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Reed, I looked your specs on the van in the linked thread. Very interesting. Refresh my memory here, it is too long since I worked with a distributor. Does an 8.5 vacuum advance canister add 8.5 or 17 at the crank? Is that number crank or distributor degrees? If I read your specs right you are at getting 22 advanced plus initial, which you stated was 6 advanced. This puts you at 28 WOT plus whatever your vacuum canister adds at various loads. If the vacuum canister adds 17 total at the crank this makes for 45 total at high vacuum cruise. If you double the canister number. Am I thinking correctly here?

Sam
Author:  emsvitil [ Sat Jul 07, 2012 2:05 pm ]
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Yes, you double the canister number to get crank degrees.
Author:  Sam Powell [ Sat Jul 07, 2012 7:55 pm ]
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Thanks Ed.
Sam
Author:  Reed [ Sun Jul 08, 2012 9:12 am ]
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I was out of town and not online this weekend. Yes, you got it right.
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