AMC Eagle

[beat_truck]

Originally Posted by MadMan

LeanBurn was really cool in concept. It even worked, too. Unfortunately, it suffered from two things. One, being that computer-ish electronics were still somewhat in their infancy, and two, they put a delicate piece of technology on top of a hot vibrating engine. Not Chrysler's finest moment...

Mine still worked, surprisingly for being ~35 years old when I had the truck.

What was the actual benefit of it supposed to be, though? It basically read the ported engine vacuum and advanced the timing? Didn't a regular vacuum advance distributor do the same exact thing, and according to many people, do a better job of it too?

[old_tv_nut]

Originally Posted by beat_truck

Didn't a regular vacuum advance distributor do the same exact thing, and according to many people, do a better job of it too?

The regular vacuum advance was not precise enough to produce the right setting under all conditions. Plus, spark was deliberately retarded from optimum performance on the early pollution-conscious cars. And with no feedback, the result would deteriorate between tune-ups.

My dad was a Ford mechanic and later service manager. Back before mandatory smog regulations, my dad's car was ready for a tuneup, so he did it and said let's have some fun; and on a fine Saturday we took it to the Lung Association free smog check. The guy running the test did it twice because he thought his instruments had failed. My dad told me that of course, it wouldn't stay that good and would also vary greatly with weather conditions (mainly temperature?).

[beat_truck]

Originally Posted by old_tv_nut

The regular vacuum advance was not precise enough to produce the right setting under all conditions. Plus, spark was deliberately retarded from optimum performance on the early pollution-conscious cars. And with no feedback, the result would deteriorate between tune-ups.

How was that primitive Lean Burn setup any more precise? It didn't monitor any other engine parameters like temperature, exhaust gasses, air flow, or anything else. I'm pretty sure it literally just monitored the vacuum from the same carb port that would have went to the distributor, and nothing else. The Lean Burn "computer" even had a diaphragm that looked very similar to what is mounted on a regular vacuum advance distributor. At least that's how my '83 was.

On paper it might have looked better, but nearly all people that replace it with late '70s electronic (no points) vacuum advance distributors report better performance and usually economy too.

[old_tv_nut]

Originally Posted by beat_truck

How was that primitive Lean Burn setup any more precise? It didn't monitor any other engine parameters like temperature, exhaust gasses, air flow, or anything else. I'm pretty sure it literally just monitored the vacuum from the same carb port that would have went to the distributor, and nothing else. The Lean Burn "computer" even had a diaphragm that looked very similar to what is mounted on a regular vacuum advance distributor. At least that's how my '83 was.

On paper it might have looked better, but nearly all people that replace it with late '70s electronic (no points) vacuum advance distributors report better performance and usually economy too.

I didn't mean to imply anything about the primitive Lean Burn System, which I know nothing about, just pointing out what it was supposed to improve.
All the early smog fixes made performance worse, as far as I know, and I can easily believe that this one made no reliable improvement in smog either.

[MadMan]

Originally Posted by beat_truck

What was the actual benefit of it supposed to be, though? It basically read the ported engine vacuum and advanced the timing? Didn't a regular vacuum advance distributor do the same exact thing, and according to many people, do a better job of it too?

https://www.allpar.com/mopar/lean-burn.html

The short version is that the guys at Chrysler discovered that if they had super precise control over the ignition timing, they could run the carb super lean and still achieve the same performance as a richer mixture with a regular old fashioned vacuum advance distributor. Yes, it was motivated by meeting emissions standards, but in theory that sounds plenty better than the 'old way' and it should improve fuel economy and keep the same performance.

It was a simple system, but not as simple as you might think.

The system measured:
1. Engine speed (r.p.m.).
2. Engine load. [likely the MAP vacuum]
3. Throttle position.
4. Speed of throttle movement.
5. Air temperature entering the engine.
6. Engine coolant temperature.
7. Carburetor throttle open or closed.
8. Engine starting.

As for the old fashioned carburetor and ignition system being 'better' - that sounds entirely typical of all the grumbly old farts in the repair industry. It's not that anything is 'better' it's that they are used to something being a particular way. They all said the same things about fuel injection, front wheel drive, unibody, disc brakes, MacPherson struts, I could go on and on. I'm sure that 'many people' also thought that hand cranking your engine was 'better' than having a starter, and that acetylene lamps were better than those new-fangled electric lights. lol You could probably go even further back and some guy would've said that steam was better than internal combustion.

[beat_truck]

Originally Posted by MadMan

https://www.allpar.com/mopar/lean-burn.html

The short version is that the guys at Chrysler discovered that if they had super precise control over the ignition timing, they could run the carb super lean and still achieve the same performance as a richer mixture with a regular old fashioned vacuum advance distributor. Yes, it was motivated by meeting emissions standards, but in theory that sounds plenty better than the 'old way' and it should improve fuel economy and keep the same performance.

It was a simple system, but not as simple as you might think.

The system measured:
1. Engine speed (r.p.m.).
2. Engine load. [likely the MAP vacuum]
3. Throttle position.
4. Speed of throttle movement.
5. Air temperature entering the engine.
6. Engine coolant temperature.
7. Carburetor throttle open or closed.
8. Engine starting.

As for the old fashioned carburetor and ignition system being 'better' - that sounds entirely typical of all the grumbly old farts in the repair industry. It's not that anything is 'better' it's that they are used to something being a particular way. They all said the same things about fuel injection, front wheel drive, unibody, disc brakes, MacPherson struts, I could go on and on. I'm sure that 'many people' also thought that hand cranking your engine was 'better' than having a starter, and that acetylene lamps were better than those new-fangled electric lights. lol You could probably go even further back and some guy would've said that steam was better than internal combustion.

The v8s might have had all of those sensors, but most slant sixes did not. It seems that only the very last couple years did. My '83 didn't have most of them. As I said, it had the Lean Burn box on the air cleaner, but it had a normal 1bbl carb with no sensors attached. And no, the truck hadn't been altered. It matched up exactly with the emissions tag on the inner fender and the rebuild kit that I bought for the carb, and no wires were cut up.

Like I said, that system might have looked good on paper, but like most of those abortions that were created as a stop gap between regular carbs and fuel injection, they didn't work well in reality. Especially as they aged.

I was eventually going to ditch the Lean Burn setup for a regular vacuum advance distributor, but I sold the truck after hitting a deer with it.

[MadMan]

Originally Posted by beat_truck

The v8s might have had all of those sensors, but most slant sixes did not. It seems that only the very last couple years did.

I mean, I don't have much experience with them, but they kind of need 'all' of those sensors to work. By modern standards, it was very rudimentary, didn't control the carb in any way.

[MIPS]

Aaaand we got oil pressure again.




So it seems that for some reason an 80psi pressure sender is not a common part anymore. The Borg Warner catalog only lists a sender rated for 100PSI for the Eagle and pretty much every other car made by AMC, Jeep and International Harvester going back to the 60's. TSM doesn't specify anything either. It also doesn't list the scale resistance and at the same time I've never seen a factory oil pressure gauge on any car for that matter that was scaled for 100psi. Only the aftermarket stuff.
Anyways, lets assume that the variance in range resistance between the 80 and the 100 is about 12%, so with a reading of 63psi I should be seeing around 50psi which for a hot idle should be excellent and if I compare to other people on the internet, should be fine for quick visual indication and MILES above all these randos seeing stuff like 13psi at idle.