Stumble at very little throttle; EGR valve related?

[lorkp]

Hi all,

I've got a '79 California E21. I'm getting this stumble when I give just the slightest throttle (like the throttle you give when you want to creep slowly while slipping the clutch). It seems to have something to do with the EGR valve, because when I disconnect it from the red vacuum hose that leads to the thermo valve, which I think defeats it, the problem goes away.

I took the blue cap off the EGR valve to see what the valve was doing when the car stumbles. With just this very small amount of throttle, the valve looks to open all the way. Look at the valve movement in the video.

I'm guessing that it shouldn't be opening this much at such low throttle?

My rudimentary understanding of the valve is that vacuum from the red hose opens the valve and vacuum from the blue hose is supposed to resist it. The blue hose is providing vacuum to the valve; at the pressure converter, I measure 5 inHg supplied, and it doesn't change with throttle. However, perhaps it's not affecting the EGR valve because the blue port on the EGR valve doesn't hold vacuum. I'm guessing it should? (The red port does hold vacuum.)

I'd love to chuck the EGR and other smog equipment, but I'm smogging my car this week and so I need it all to work.

Thanks for your help!

[eseeling]

You probably have a vacuum leak. It takes more of a throttle body opening to overcome the leak and subsequently move the fuel distributor baffle. Shoot a little carb cleaner at the injector sites and see if the idle increases. The injector seals dry out over time, and that is the most likely source of a leak.

[epmedia]

Hi all,

I've got a '79 California E21. I'm getting this stumble when I give just the slightest throttle (like the throttle you give when you want to creep slowly while slipping the clutch). It seems to have something to do with the EGR valve, because when I disconnect it from the red vacuum hose that leads to the thermo valve, which I think defeats it, the problem goes away.

I took the blue cap off the EGR valve to see what the valve was doing when the car stumbles. With just this very small amount of throttle, the valve looks to open all the way. Look at the valve movement in the video.
.....
I'm guessing that it shouldn't be opening this much at such low throttle?

My rudimentary understanding of the valve is that vacuum from the red hose opens the valve and vacuum from the blue hose is supposed to resist it. The blue hose is providing vacuum to the valve; at the pressure converter, I measure 5 inHg supplied, and it doesn't change with throttle. However, perhaps it's not affecting the EGR valve because the blue port on the EGR valve doesn't hold vacuum. I'm guessing it should? (The red port does hold vacuum.)

I'd love to chuck the EGR and other smog equipment, but I'm smogging my car this week and so I need it all to work.

Thanks for your help!

Your understanding is correct. And yes, the blue port on the EGR valve should also hold a vacuum.

Notes for reference:
On the egr valve... red vacuum ((via)ported vacuum) opens the egr valve while opening the throttle. Blue vacuum ((via)intake manifold vacuum) 'opposes' opening of the egr valve.
As exhaust pressure increases, the blue vacuum decreases.

More exhaust pressure = less 'opposing' blue vacuum.

The pressure converter is adjustable.
..........
vacuum diagram, minus 4th gear vac advance..

click to enlarge.
vac-hoses4.jpg

[lorkp]

Thanks for your replies, eseeling and epmedia. It was indeed a faulty EGR valve--I was able to get my hands on another and the stumble is gone. Interestingly, the valve looks to open just as early. So perhaps with the old valve it wasn't a matter of opening too soon but being leaky to atmosphere when it was open. So this new valve may improve performance across the board. Next stop, smog test. Fingers crossed ....

[epmedia]

Thanks for your replies, eseeling and epmedia. It was indeed a faulty EGR valve--I was able to get my hands on another and the stumble is gone. Interestingly, the valve looks to open just as early. So perhaps with the old valve it wasn't a matter of opening too soon but being leaky to atmosphere when it was open. So this new valve may improve performance across the board. Next stop, smog test. Fingers crossed ....

The egr valve is tricky, some hidden dual action happening in there. Glad you found a working egr valve so soon

If you wish to tinker with egr adjustments for smog test, and/or performance ::

just fyi: Proper function of egr system will cool the combustion temperatures, thus lowering nitrogen oxide gasses.

Regarding adjustment to the egr's pressure controller... first make sure the pipe and hose (red) between the exhaust manifold and pressure controller is un-obstructed and sealed good. Same with white and blue hoses, of course.

There's a tiny flat-head screw on the middle of the pressure controller. Dig out the sealant to access this flat-head screw. This is the egr adjustment screw - this adjustment considers both exhaust pressure and intake vacuum, simultaneously.

To adjust egr valve (way cool that it's adjustable )... The adjustment is very sensitive, use 1/32 turn increments and keep track of the adjustments. While engine at operating temp - shim the throttle stop to hold the engine rpm's @ 2000. Turn the pressure controller's adjust screw to obtain highest engine rpm. After adjust screw is set to highest rpm (egr valve closed), turn the adjust screw to lower the engine speed about 100 rpm's (egr valve slightly open).

Edit: I forget which way to turn the screw for more or less egr valve opening. While engine rpm's are at 2000 - cycle the adjustment screw 1/8-1/4 turn in both directions to wear-it-in and get a feel for it's behavior.

Hope I explained that ok...

[lorkp]

That’s a perfect explanation, thank you epmedia!

[Somjuan]

I still have my spare EGR equipment for free if you ever need it

[epmedia]

No problemo, Lorkp. Hang on to those serviceable spare CA emissions components!

Also... a 3.64 LSD coupled with a fine tuned 2.0 decimates all from 0 to 55

[lorkp]

Passed with flying colors! Looks like I can run it a little richer, too.

Scan Jul 6, 2020 at 5.21 PM.JPG

[epmedia]

Excellent readings. If you plan to tweak the '3mm idle mix screw' be aware this adjustment is mostly just for idle and a tad above idle speeds. I've always used the 'finger in the tail pipe' test after a few slow runs around the block: tiny black carbon is just right. If you decide to adjust fuel mix through the whole engine load range, you'll have to tweak the WUR - see the diy/faq thread for this. Be aware that clean fuel system throughout, is key before making any fuel system adjustments.

[Beforehuman]

I would be interested in your EGR valve. I am having some trouble and I haven't figured out if it is the EGR but it seems like it's suspect.

Thanks Somjuan

[kamjosbol]

I have a question along the same line: ive been trying to tackle the vacuum line puzzle and as of now it will idle, sometimes rough. The car doesn't accelerate on the throttle until it is let off or held for a few seconds. I also noticed there is a lot of soot in the exhaust, which makes me think the mixture is off. Would the mixture affect the acceleration speed or it is only an issue with the vacuum leaks?

I figured I'd just ask first before i start messing with the mixture and take steps back.

[epmedia]

I have a question along the same line: ive been trying to tackle the vacuum line puzzle and as of now it will idle, sometimes rough. The car doesn't accelerate on the throttle until it is let off or held for a few seconds. I also noticed there is a lot of soot in the exhaust, which makes me think the mixture is off. Would the mixture affect the acceleration speed or it is only an issue with the vacuum leaks?

I figured I'd just ask first before i start messing with the mixture and take steps back.

What year e21 do you have?

[lorkp]

I have a question along the same line: ive been trying to tackle the vacuum line puzzle and as of now it will idle, sometimes rough. The car doesn't accelerate on the throttle until it is let off or held for a few seconds. I also noticed there is a lot of soot in the exhaust, which makes me think the mixture is off. Would the mixture affect the acceleration speed or it is only an issue with the vacuum leaks?

I figured I'd just ask first before i start messing with the mixture and take steps back.

Sounds like you have a major vacuum leak or leaks. With the engine idling, does taking the oil filler cap cause the engine to run much different? On a well running engine it will run noticeably worse and almost stall. But if there’s already a big leak it won’t make as big of a difference because the mixture screw is most likely cranked up to handle the leak and additional air will make less of an impact. And the cranked up mixture would explain your soot, too.