Custom EGR System with Weber Carb

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deejay1272
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Custom EGR System with Weber Carb

Post by deejay1272 » Tue Sep 03, 2013 1:22 pm

Hi Everyone,

I've been busy working up a solution that will allow me to run a WEBER 32/36 carb WITH the existing EGR system in order to help me pass smog tests. So far I'm really close to a complete solution (with big thanks to DLB for his support over PM).

I've hooked up my EGR system in line with page 108 of the FSM. I've tested that the EGR vacuum modulator closes and opens appropriately in low pressure and high pressure scenarios, AND I've confirmed that the EGR valve itself does in fact hold vacuum.

The EGR valve is supposed to stay closed when the coolant is still cool (which it does). But here's my problem: Once the car is warmed up, the exhaust gas is constantly recirculated whether the car is at idle or under load. It's all fine and good when I'm giving her gas, but at idle it runs rough. Does anyone have any ideas for how I can prevent vacuum from being pulled to the EGR valve at idle?
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dlb
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Re: Custom EGR System with Weber Carb

Post by dlb » Tue Sep 03, 2013 2:51 pm

i'm looking at page 108 and it says when the throttle valve is below the carb's EGR port, there is no vacuum applied from there to port P of the modulator. this should be the case at idle since the throttle is at complete rest then, so if you are getting vacuum applied to the modulator at idle that means the throttle valve is always above the carb's EGR port. that seems like a dumb design on weber's part but i don't know how EGR systems work on other cars so maybe the tercel's EGR system is the dumb one. anyway, i know the weber only has 2 or 3 vac ports on it so i would just confirm that you are connected to the one marked EGR in this diagram.

Image

failing that, i would cap that port and instead, add a 'T' to the vac advance port and try running the EGR off of that. that seems to make sense since both ported vac advance and the EGR operate at moderate throttle, aka cruising speeds. keeping the manifold vac line connected to the EGR system via the TVSV will keep the system from engaging while the engine is cold, so i think that should work. hopefully, anyway!

deejay1272
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Re: Custom EGR System with Weber Carb

Post by deejay1272 » Wed Sep 04, 2013 9:55 am

Thanks for the thoughts, DLB.

Ok - I've completed my custom EGR solution and my Terc seems to be running pretty well near perfectly.

Here are the images from page 108 of the FSM that show you how to hook up your EGR system with a WEBER carb. It's really quite easy to do. There are a few checks that you're supposed to do (on page 109 and 110 of the FSM), so be sure you confirm that the EGR valve holds vacuum, the vacuum modulator does what it's supposed to do and that your check valve operates properly (TVSV needs to be functional as well, but that's obvious).

Image

Image

I ended up having some difficulty with my idle speed when I hooked up my EGR system, so be sure that you reset idle as per the WEBER recommendations (http://www.carburetion.com/Weber/adjust.htm) before you get frustrated like I did. Pay special attention to the mixture screw. You need to have a slightly richer mix in order for things to run smoothly. Aslo, your timing may need to be adjusted slightly to really smooth out any hiccups (I'm runing at about 10* BTDC on my timing before my smog test. I'll be changing this to ~15* BTDC after the test to reduce risk of exhaust valve failure).

I'm going to take the car in today or tomorrow to get it smog tested. I'll follow up on this post to complete the loop and let you all know if it worked or not. I expect that it will since the exhaust went from smelling like toxic death to normal carbureted motor exhaust. Onward to a cleaner future!
Last edited by deejay1272 on Sun Sep 08, 2013 7:14 pm, edited 2 times in total.
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dlb
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Re: Custom EGR System with Weber Carb

Post by dlb » Wed Sep 04, 2013 10:04 am

did you get the EGR to stop opening on idle while still connected to the EGR port?

and pics!! i'm very excited about this.

deejay1272
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Re: Custom EGR System with Weber Carb

Post by deejay1272 » Wed Sep 04, 2013 10:11 am

dlb wrote:did you get the EGR to stop opening on idle while still connected to the EGR port?
Turns out that the idle was set all weird so that was causing improper vacuum all over the place. Once I smoothed it out by resetting idle, things cleared up nicely!
dlb wrote:and pics!! i'm very excited about this.
I thought about posting pics (and I'm still happy to do that), but the diagram is the most clear for sure. I didn't want to confuse things too much...
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deejay1272
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Re: Custom EGR System with Weber Carb

Post by deejay1272 » Sun Sep 08, 2013 3:31 pm

deejay1272 wrote:I'm going to take the car in today or tomorrow to get it smog tested. I'll follow up on this post to complete the loop and let you all know if it worked or not.
Boom. Passed the emissions test. It may be a good idea to sticky this thread for others that pursue the Weber carb solution to simplify fuel deliver/emissions systems.
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dlb
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Re: Custom EGR System with Weber Carb

Post by dlb » Sun Sep 08, 2013 7:17 pm

deejay1272 wrote:
deejay1272 wrote:I'm going to take the car in today or tomorrow to get it smog tested. I'll follow up on this post to complete the loop and let you all know if it worked or not.
Boom. Passed the emissions test. It may be a good idea to sticky this thread for others that pursue the Weber carb solution to simplify fuel deliver/emissions systems.
unreal, congrats! this is a real game changer for a lot of folks! good for you for figuring it out and making it work.

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Re: Custom EGR System with Weber Carb

Post by teranfirbt » Tue Sep 10, 2013 7:22 am

I notice you're from the Portland area. Were you having trouble passing the Portland emissions test before? I've gone through twice with a Weber and no EGR and have not had trouble. The idle test doesn't check for NOx at all, which is what the EGR reduces...
It would be interesting to hear if it improves mileage at all, since EGR should help with that.

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Re: Custom EGR System with Weber Carb

Post by Petros » Tue Sep 10, 2013 7:25 pm

The EGR reduces compustion pressures and peak temperatures when it is in operation, that can not improve economy. It reduces efficiency, reduces fuel economy. It dilutes the incoming air with exhaust by lowering the O2 concentration, reducing the max amount of fuel that can be burned in the combustion cycle. The basic Otto cycle efficiency if reduced when peak temps are lower.

This is one of my complaints with the EGR, it may reduce parts per million (a percent, or ppm), but it will cause the car to burn more fuel to drive the same distance. So I suspect it may actually increase the parts per mile. the original proposal was to reduce NOx and CO by parts per mile, but the Big Three (who make all their money on big gas hog cars) lobbied to have it changed to PPM, and hence we get the ERG. I had followed this regulatory "compromise" when I was in high school, I always like smaller cars and parts per mile would favor smaller, lighter, and more fun to drive cars. But it would not favor the land yachts that Detroit was always peddling, so Detroit got its way and we got crap EGR in our small engines.
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teranfirbt
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Re: Custom EGR System with Weber Carb

Post by teranfirbt » Tue Sep 10, 2013 8:39 pm

If it's working properly the EGR system significantly reduces pumping losses by increasing the pressure in the intake plenum with non-combustible gas. Since pumping losses are generally the second biggest mechanical loss in the system (after friction...) EGR usually improves economy slightly.. On an engine like the 3AC it's probably not more than 1 mpg or so... Of course, it requires a properly designed and working system.

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Re: Custom EGR System with Weber Carb

Post by Petros » Wed Sep 11, 2013 10:59 pm

that might be true of the modern cars with electronic controls, I doubt it is true of of the older carburated cars. The engine management systems of the modern cars controls EGR and fuel air ratio according to feed back sensors, and can optimize the operation of the engine with the EGR engaged (which only occurs at part throttle cruise conditions). When the EGR was first introduced it had a profound detrimental effect on fuel economy of the older carburated cars. there was a "cottage" industry of back yard mechanics disabling them. At what point the EGR was optimized to improve economy is the question. I think in most conditions at best it as little effect on it, only in the more modern cars (OBD 2 and newer) does it help. I searched the internet to see if there was a correct answer to this question and it was no help (a lot of bad information). Though it does appears it is important for the modern computer controlled cars (these cars also control the shifting of the trans with the same ECU, spark advance, as well as mixture), but on earlier cars I do not see how it can help at all. Reducing the basic Otto cycle efficiency does more harm than reducing some minor part throttle pumping losses, with the 16-valve induction system there are not a lot of pumping losses anyway.

Consider the corolla all-trac ('88-92?) that uses almost the same engine as the FWD corolla. Both engines are identical in all ways EXCEPT, for some reason, the all-trac does not have an EGR. I do not know why, but the all-trac gets excellent fuel economy.
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Re: Custom EGR System with Weber Carb

Post by dlb » Wed Sep 11, 2013 11:31 pm

Petros wrote:Consider the corolla all-trac ('88-92?) that uses almost the same engine as the FWD corolla. Both engines are identical in all ways EXCEPT, for some reason, the all-trac does not have an EGR. I do not know why, but the all-trac gets excellent fuel economy.
my all trac has an EGR. however, the 2wd corolla wagon i had did not, even though both have the same 4afe engine. pretty curious.

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Re: Custom EGR System with Weber Carb

Post by SynthDesign » Tue Jan 26, 2016 3:24 am

I have gotten significantly better gas mileage on a stock carb'd 3AC without the ERG system. Even better with a tuned emissions system. For my weber setup, it's worked great w/o the egr and baseplate heater.
Also I've had no problem just leaning out and advancing a weber setup to pass emissions in both Washington State and Canada.
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