1980 Buick Extremely Poor Performance When Cold

(insert name here)

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I have an old beater 1980 Buick Riviera with a 4-barrel 5.7L Oldsmobile engine. It has served me well as a backup/winter vehicle for the last decade. The car has a number of problems, so trying to diagnose the cause of my specific issue here may be difficult/impossible. I'll start by listing known drivetrain problems:
- Transmission slips between gears
- Exhaust needs replaced. Currently it's two pipes that end halfway under the car. Catalytic converter is gone; mufflers are glasspacks, so no backpressure. I can feel a leak where the driver's side pipe connects to the exhaust manifold.
- Gas mileage is quite bad. Less than 10mpg (I'm thinking it's at about 8mpg). Car got 16mpg ten years ago (with no exhaust backpressure).

These problems were all annoying, but no big deal for a backup car. However, I've noticed recently that the car has an extreme lack of power when it's cold. Like, takes over a quarter mile to get up to the speed limit of 45mph in front of my house...and that's if you floor it. The car feels like it's missing, and also starts to bog down once you get up into third gear. It idles fine, and does fine in first and the bottom of second, but once you get up to 15-20mph it really starts to struggle. Once the car is warmed up, the issue goes away. The solution of "let the car warm up" before driving isn't terribly practical either, it takes a good 10-15 minutes of idling before it's warm enough that the problem goes away.

Any thoughts on where to start? I figure it's not plugs or wires because the issue disappears once warm. I figure it's not the distributer cap because (if I recall) a crack generally causes problem when the car is warm, not the reverse. The car has no points, so it can't be that. Maybe the exhaust leak is causing the feeling of the engine missing? But surely it wouldn't cause such a massive lack of power. A failing transmission could perform poorly when cold, but the bogging to me says it's an engine issue. As it stands now, I'm inclined to think carburetor, which is unfortunate because Quadrajets are ridiculously expensive. Any troubleshooting advice is welcome.
 

MelsRegal

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I have an old beater 1980 Buick Riviera with a 4-barrel 5.7L Oldsmobile engine. It has served me well as a backup/winter vehicle for the last decade. The car has a number of problems, so trying to diagnose the cause of my specific issue here may be difficult/impossible. I'll start by listing known drivetrain problems:
- Transmission slips between gears
- Exhaust needs replaced. Currently it's two pipes that end halfway under the car. Catalytic converter is gone; mufflers are glasspacks, so no backpressure. I can feel a leak where the driver's side pipe connects to the exhaust manifold.
- Gas mileage is quite bad. Less than 10mpg (I'm thinking it's at about 8mpg). Car got 16mpg ten years ago (with no exhaust backpressure).

These problems were all annoying, but no big deal for a backup car. However, I've noticed recently that the car has an extreme lack of power when it's cold. Like, takes over a quarter mile to get up to the speed limit of 45mph in front of my house...and that's if you floor it. The car feels like it's missing, and also starts to bog down once you get up into third gear. It idles fine, and does fine in first and the bottom of second, but once you get up to 15-20mph it really starts to struggle. Once the car is warmed up, the issue goes away. The solution of "let the car warm up" before driving isn't terribly practical either, it takes a good 10-15 minutes of idling before it's warm enough that the problem goes away.

Any thoughts on where to start? I figure it's not plugs or wires because the issue disappears once warm. I figure it's not the distributer cap because (if I recall) a crack generally causes problem when the car is warm, not the reverse. The car has no points, so it can't be that. Maybe the exhaust leak is causing the feeling of the engine missing? But surely it wouldn't cause such a massive lack of power. A failing transmission could perform poorly when cold, but the bogging to me says it's an engine issue. As it stands now, I'm inclined to think carburetor, which is unfortunate because Quadrajets are ridiculously expensive. Any troubleshooting advice is welcome.
Have you ever changed the fuel filter located in the inlet of the carburetor?
 

(insert name here)

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I believe I changed it a couple years ago. I recall the inlet being cross-threaded, but I was able to straighten it out and tighten it back down without any leaks. Definitely a cheap enough part that I don't mind doing it again (though I may be pushing my luck with the screwed up threads).
 

MelsRegal

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I believe I changed it a couple years ago. I recall the inlet being cross-threaded, but I was able to straighten it out and tighten it back down without any leaks. Definitely a cheap enough part that I don't mind doing it again (though I may be pushing my luck with the screwed up threads).
Well if not ignition it has to be fuel so a pressure test would be another thing to try if filter is clean.
______________________________
 

2007LucerneCXL

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MelsRegal

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This may be useful, hopefully others can confirm, you may have a electronic Quadrajet if so the mixture control solenoid as part of the problem and choke as another.

Can't say if they are the problem or if you have it but they were available during that era. This is out of my area again maybe someone else knows about these in detail.

Parts source
I know on Corvettes the electronic solenoid started in 81.
 
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2007LucerneCXL

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My 79 Eldo had EFI so not sure what the 80 Rivera had, but looking at the top of the carb and if it has two wires coming out could confirm I guess.
 

(insert name here)

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Small breakthrough: Went out to take a couple pictures of the carb and started it up with the air cleaner pulled back. Noticed the vacuum-operated choke pull-off wasn't doing anything. Pulled the line off and there was no vacuum. Propped open the choke and took the car for a quick spin before it warmed up and my performance issue was almost completely gone (lost a tiny bit of power going into third, but nothing too bad). Got back and checked the vacuum line for the choke pull-off again and now there was vacuum (not that it mattered at this point). So whatever controls the vacuum pull-off isn't working correctly.

On older cars, I thought these pull-offs plugged straight into the intake manifold so they'd work as soon as the engine started, but on this car it goes to a hopelessly convoluted mess of vacuum lines. This is one of the newest cars I own, so I'm pretty out of my element when it comes to the vacuum system; there's a lot more to it than my other cars.

An additional note: In the past as this car was warming up, after it ran for a minute or two it would have very distinct moment where the idle would increase and the exhaust would quiet down, like someone flipped a switch. Always found this odd, but never really gave it too much thought. This year I'm noticing it does the opposite. After it runs a minute or two the idle suddenly drops and the car runs a bit rough (had it bog and die on me just now when I pressed the gas to raise the idle back up, which has never happened before). And this happened before I propped the choke open, so me fiddling with the choke wasn't a factor. Not my main issue here, but I'm curious what's controlling this behavior since it appears to be automatic.

To answer the question about the electronic carburetor, as far as I'm aware, mine is all mechanical. The only electrical component I'm aware of is an anti-dieseling solenoid, which doesn't work and was previously adjusted by someone else to never contact the throttle linkage. I have a carburetor from an '81 Riviera, and it on the contrary does have a couple spots for electrical connections (I assumed this carb would not work on my '80). Pictures of the carb on the '80 if they are of any use to anyone:
Picture 1
Picture 2


So I guess my main question now is: What controls the vacuum to the choke pull-off? I'm inclined to find an "always active" vacuum source and just reroute to that, but I'm also curious how the system is supposed to work.
______________________________
 
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2007LucerneCXL

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As a reference, again this series is out of my wheelhouse, but this is where it should be and I am not familiar with the area in red if it's plugged.

Screenshot_20221119-162829_Google PDF Viewer.jpg hY8EmXM_d.jpg
 

2007LucerneCXL

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Yep that's one with it. GM like all the others were doing all kinds of things for emissions so who knows what was winding on which vehicles.
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(insert name here)

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It shows the choke pulloff hose going to the carburetor airhorn. Is your 80 different?

Oh, I probably should have specified that I was referring to the front two barrels. Those were the ones I propped open. I didn't fiddle with the back two at all. Here's a picture indicating the pull-off I was referring to: Picture

I'd go out and get a picture of all the vacuum lines, but it's now nighttime and the arctic winds are strong tonight. I have a busy day tomorrow, but I can try to find some time to pull the lines up where they're visible and get a picture.
 

CorvairGeek

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The Buick 350 was available with the electronic control in '80 with California emissions, but it looks like we've determined that is not the case here.
The differences seen in the carburetor with the '81 is likely because it is from an Olds 307. The Olds engine retained a hot air choke through the end of production. No Buick 350 after '80, but the 252 V6 became available. No sure if the quadrajet was still configured like the Buick V8.
 

(insert name here)

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I was under the impression that the 350 in my '80 was an Oldsmobile engine.

Upon further review, the vacuum line for the choke pull-off goes to a little doodad on the air cleaner, which connects to several other vacuum lines. I took a few pictures of the nest of vacuum lines, but I'm not sure they're that useful. It's just such a massive tangled mess, and there's no good angle to see it all or enough slack to pull things up into view (since they're all twisted around each other).
Picture 1
Picture 2
Picture 3
Picture 4

The car's cruise control doesn't work, but I noticed it had a vacuum line that ran straight into the intake. Swapped it with the choke pull-off so the pull-off would get suction as soon as the car started. Tried to take it for a test drive this morning, but there was some weird traffic jam about a half block from my house, so I didn't get a chance to get up to speed before having to sit and wait (allowing the car to warm up, ruining the test).


(As an aside, this all may be an exercise in futility. I noticed this morning that the framerail on the driver's side looks like it may be rusted through in a few spots. There's too much snow/slush on the ground to get the car in the air and do a proper investigation without getting soaked, but things will be melted in a couple days and I'll be able to check and see if the car has reached the end of its useful life.)
 
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2007LucerneCXL

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Buick got the Olds engines.
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BuickGirlFromMars

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1999 Buick Park Avenue Ultra (Supercharged) , 1977 Buick Electra Limited (350 SBB)
I have an old beater 1980 Buick Riviera with a 4-barrel 5.7L Oldsmobile engine. It has served me well as a backup/winter vehicle for the last decade. The car has a number of problems, so trying to diagnose the cause of my specific issue here may be difficult/impossible. I'll start by listing known drivetrain problems:
- Transmission slips between gears
- Exhaust needs replaced. Currently it's two pipes that end halfway under the car. Catalytic converter is gone; mufflers are glasspacks, so no backpressure. I can feel a leak where the driver's side pipe connects to the exhaust manifold.
- Gas mileage is quite bad. Less than 10mpg (I'm thinking it's at about 8mpg). Car got 16mpg ten years ago (with no exhaust backpressure).

These problems were all annoying, but no big deal for a backup car. However, I've noticed recently that the car has an extreme lack of power when it's cold. Like, takes over a quarter mile to get up to the speed limit of 45mph in front of my house...and that's if you floor it. The car feels like it's missing, and also starts to bog down once you get up into third gear. It idles fine, and does fine in first and the bottom of second, but once you get up to 15-20mph it really starts to struggle. Once the car is warmed up, the issue goes away. The solution of "let the car warm up" before driving isn't terribly practical either, it takes a good 10-15 minutes of idling before it's warm enough that the problem goes away.

Any thoughts on where to start? I figure it's not plugs or wires because the issue disappears once warm. I figure it's not the distributer cap because (if I recall) a crack generally causes problem when the car is warm, not the reverse. The car has no points, so it can't be that. Maybe the exhaust leak is causing the feeling of the engine missing? But surely it wouldn't cause such a massive lack of power. A failing transmission could perform poorly when cold, but the bogging to me says it's an engine issue. As it stands now, I'm inclined to think carburetor, which is unfortunate because Quadrajets are ridiculously expensive. Any troubleshooting advice is welcome.
do you have a THERMAC on your intake air cleaner or a flapper in the exhaust manifold? (that sends heat back up to the intake, TFE I think it may be called I cant remember)

is your throttle cable stretched, and have you had the distributor cap off and the rotor off? take a pic for me of that?
Do you have vacuum lines bad

DO you have a feed back 4 barrel? I dont think a 1980 riviera would have a 350 olds but more like a 307 but I could be wrong. Is the qjet new or renewed at all?
Does it have a 4 speed or a 3 speed , maybe a 3 speed with lockup? Fix your exhaust leak that will not do well for flow which will hurt atomization.
Have a plug in for the car?
 

BuickGirlFromMars

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this is a 1980 260 oldsmobile with a dualjet so its likely different, but i am showing it in case we are having an ID issue or if components are similar if things stand out at all. non feedback, 1981 was for sure feedback, but this is in a g body cutlass not a riviera (b body? g?)
 

(insert name here)

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Sorry about not responding to the last few posts. I didn't get an e-mail that there were replies waiting for some reason.

I'll start by saying that, after further inspection, the rust damage to the frame I found is pretty severe. Bad enough that I stopped daily driving the car. Quotes for repairs are in the thousands of dollars, so this car is likely done. Deciding what I want to do with it since I may still save the engine (though realistically I don't ever see myself using such a low-powered and inefficient engine).

I did take it for a short test drive up the road this morning and the issue I made this thread about is completely gone. Outside temperature is 30 degrees right now, started the car up and immediately pulled out onto the road without giving it any time to warm up at all. Ran fine, no stuttering or falling on its face in higher gears. So the issue was the choke pull-off not working (which I corrected by connecting it to a different "always on" vacuum line).

Obviously there's some sort of vacuum issue since the hose going to the pull-off does suck, but only after the car is warm. I'd be interested in a diagram of the vacuum system on this car, but it's certainly not necessary given the circumstances. Mainly just for learning purposes.

Any tips on storing and preserving the Quadrajet off this car? If I end up scraping the whole thing due to the frame, I want to save that at the very least. I have a few cars that use that carb, and with how stupidly expensive they've become, it'd be nice to have an extra sitting around.
 
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