Why they are expensive

[JohnRoberts]

  That ECU sucks! (sorry, I had to...)

Modern ECU are pretty remarkable compared to the very old ways when ignition timing was a lever on the dashboard, etc.

I had one hot rod back in the 60's that was hard to start cold due to too much ignition advance, so I connected the old choke cable I wasn't using to the distributor so I could retard it, just to start, then return the advance once it was running. That worked like a charm.  ;D

  Now some use fuel sensors and knocking detectors to adjust the timing even with different fuel qualities to be right before knocking. I was surprised no one did electromechanical valves (solenoids) and take the timing belt out but that started last year.

JS

Yup mass air flow sensors, etc... I could have used a knock detector for my '93 after I put the supercharger on it.  If denser fuel mixes support faster flame fronts, with increasing RPM my increasing positive manifold pressure resulted in faster and faster burning, too much of a good thing. Ping (detonation) at 7500 RPM doesn't sound much like ping, it sounds like pistons melting.    I added a special ignition that would sense the manifold pressure and retard the timing as appropriate.

I think I have a bad temperature sensor feeding the ECU on my current ride. When cold it feels like the engine is running lean (lags or bogs from low RPM). After the engine is warmed up it runs strong. The trouble with modern ECUs is bad data causes bad results.  The old mechanical controls were pretty robust.

JR 

 

[joaquins]

...
The trouble with modern ECUs is bad data causes bad results. [...]

JR 

  I agree but that's not the only problem. I've also seen problems with vacuum lines in older engines, once in the shop I asked the mechanic, what's that noise, seems something is blowing... After looking a bit I found an unplugged vacuum line, it was pretty clear where it went, but plugging it back would make the engine idle awfully  let's let it where it was...

JS

 

[JohnRoberts]

  I agree but that's not the only problem. I've also seen problems with vacuum lines in older engines, once in the shop I asked the mechanic, what's that noise, seems something is blowing... After looking a bit I found an unplugged vacuum line, it was pretty clear where it went, but plugging it back would make the engine idle awfully  let's let it where it was...

JS

A small vacuum leak will not dramatically alter engine performance, (might run a touch leaner). Imagine if the vacuum line that was left unattached was for the ignition advance (timing advance for low suction, retard for high vacuum), but... they then  adjusted the fixed timing (distributor angle) to be ballpark correct with the disconnected vacuum line. 

Connecting the vacuum line back up, on top of that fixed mechanical timing would then screw up the idle timing (when vacuum is high) big time...

Connect the vacuum line, and readjust the fixed timing back to what it should be. Engine will probably run a ton better.

Sounds like typical shade tree (don't have a clue) mechanics... "Gee this works sort of"  :..

JR 

 

[PRR]

My very basic Willys had a vacuum booster as the back-side of the fuel pump diaphragm.

Didn't work when I got it, didn't bother to fix, but it was supposed to keep wiping at full pedal.

Canister makes little sense for a long-term load. Couple my Fords had a #6 soup can as vacuum canister for the short-term loads of heater door operation and Thunderbird headlight covers. (OK, the covers were really a long-term load. After a week of not running, the lids would "wink" as the vacuum leaked out and the failsafe spring pulled them open.) 

 

[Gene Pink]

(timing advance for low suction, retard for high vacuum)

John, ya got that backwards. Has it really been that long since you turned a wrench?  ;D

A "vacuum advance" is called that, because that is what it does. At light throttle cruising down the highway with high vacuum, the lower compression pressures can deal with, and benefit, from a lot of advance They burn more thoroughly, better economy, lower HC emissions. Then you romp on the skinny pedal, in come much denser charges that don't need that much advance to fully burn, and with that much advance, the extreme pressures would set off local detonation pockets of charge that would cause spark-knock, ringing like a telephone. So full throttle retards the timing.

At idle, it is a different story. Somewhere in the late ,60's instead of distributor vacuum coming from the manifold, they started drilling a hole in the side of the carburetor, just above the side of the throttle plate that lifts on opening. Similar curve as manifold vacuum, the difference being no vacuum at idle. Ported vacuum, as in a port on the carburetor..

This is too far of topic, anyone interested can DuckDuckGo "Ported vacuum"

Gene

 

[joaquins]

A small vacuum leak will not dramatically alter engine performance, (might run a touch leaner). Imagine if the vacuum line that was left unattached was for the ignition advance (timing advance for low suction, retard for high vacuum), but... they then  adjusted the fixed timing (distributor angle) to be ballpark correct with the disconnected vacuum line. 

Connecting the vacuum line back up, on top of that fixed mechanical timing would then screw up the idle timing (when vacuum is high) big time...

Connect the vacuum line, and readjust the fixed timing back to what it should be. Engine will probably run a ton better.

Sounds like typical shade tree (don't have a clue) mechanics... "Gee this works sort of"  :..

JR

  I know some other correction would put the vacuum line to be useful, it just wasn't related with the problem was in for. The mechanic in question did knew what he was doing, the guy before I don't know...

JS

 

[JohnRoberts]

John, ya got that backwards. Has it really been that long since you turned a wrench?  ;D

A "vacuum advance" is called that, because that is what it does. At light throttle cruising down the highway with high vacuum, the lower compression pressures can deal with, and benefit, from a lot of advance They burn more thoroughly, better economy, lower HC emissions. Then you romp on the skinny pedal, in come much denser charges that don't need that much advance to fully burn, and with that much advance, the extreme pressures would set off local detonation pockets of charge that would cause spark-knock, ringing like a telephone. So full throttle retards the timing.

At idle, it is a different story. Somewhere in the late ,60's instead of distributor vacuum coming from the manifold, they started drilling a hole in the side of the carburetor, just above the side of the throttle plate that lifts on opening. Similar curve as manifold vacuum, the difference being no vacuum at idle. Ported vacuum, as in a port on the carburetor..

This is too far of topic, anyone interested can DuckDuckGo "Ported vacuum"

Gene

The server ate my long answer (http 500 error)  but short answer yes, I wrote it wrong... "vacuum advance" is clearly vacuum advance.

I may try again later... included a picture

JR

 

[Gene Pink]

I may try again later... included a picture

That'd be cool, always interested in what you have to say.

Gene

 

[JohnRoberts]

That'd be cool, always interested in what you have to say.

Gene

I tried twice but the forum software rejected my pictures and me...  :'(

My brother recently replaced the 4 barrel Holley on one of his old vettes because ethanol had turned it into a leaking fire hazard.  I have a picture of the bottom of the old holley showing the vacuum passages.

JR