3A-C Mystery Carb/Vacuum Problem

[ÜberDööber]

What a great place to find to chat about our little cars. I hope you don't mind but I don't have a 4WD. I do have an '83 Tercel SR5 and have found all the info and tech docs here to be very helpful.

My car is kind of an ongoing project. She got a new 5-speed two years ago and a brand new crate motor in January of this year. Once broken in, the car has run great up until about four weeks ago when it started to not idle at all. I nursed it back and forth to work with some fancy heel/toe pedal action for a week before I could take a look at it.

Looking down the carb working the throttle with my fingers, I could see a dribble of raw fuel from the primary main nozzle in the primary small venturi. I discussed it with my mechanic/mentor and we agreed it sounded like the float level was too high and we had set it a little fat in July, so it made sense.

I properly adjusted the float, reassembled and had the same problem. I went back through the carb, replaced a few parts like aux pump diaphram, pump plunger, power valve, gasket and o-rings on the venturis and primary solenoid, put it back together and saw no improvement. I replaced half of the vaccum lines, one at a time, and checked them against a chart. Didn't need them but nothing else was working.

Being sure the carb was okay, I started looking at the vacuum and electrical components. Not sure if mine is CAL or FED, but I started checking at the EBCV gizmo. It has two lines and both go directly to the carb and don't split off to the HAC valve (which I don't think I have). One line comes out at the top of the air horn and the other line goes directly back to the carb on the fitting directly above the idle mixture adjusting screw.

Anyway, I tried blowing and sucking on each line on the EBCV while giving it 12v. I could hear the click and was able pass air with the EBCV on. I seem to hear the air coming out the bottom of the EVCV and don't know what this part is supposed to do?

Long story short, my mechanic spent 3 hours with me and he is completely stumped at what the problem is. After going through everything again and having some question if the EBCV was broken or even what it's supposed to do, it was discovered that if the EVCV is bypassed and the line from the top of the air horn and the fitting above the mixture screw connected directly, the car started magically idling.

It's not right but it is running much better than it was. It's obviously sucking fuel at high vacuum.

So, does the EBCV just open and complete the circuit I have now with the directly connected line or does it provide some other function. Without vacuum to the top nipple on the top of the air horn, the car will not run. This seems wrong somehow?

Any ideas how this works or what else in the system may have failed to create this situation. Vacuum S/W (A) & (B) have a vital function? One final note, both the primary and secondary solenoids are on a manually controlled circuit (don't ask) and are in the off position. Turning them on doesn't make any difference. (I can hear them both click)

Thanks for any wisdom and insight you can share.

...Diane

[keith]

If you are bleeding extra fuel through the venturi, I don't think its anything external to the carburetor. If you didn't replace the needle and seat, I'd recommend that you do that next. The only other thing I can think of would be if you left the main jet out.

[Petros]

In my Chilton manual it gives a sequence of simple tests for each of the various systems in the Carb/ emission control system, you need to get that and work thorough each of the tests. If you know what each of the components do you could also systematically by pass each one and see if that makes a difference. Most of the junk can be by-passed but you need to how that can be done because simply blocking it off may not allow it run correctly.

One thing you might do is check for any undiscovered vacuum leaks. Do this by setting a fast idle and spraying a can of carb cleaner on the various parts of the system. If the speed changes you found your leak. You can also bleed propane gas from a line or torch (unlit) to find a leak in a similar way.

If there is any leaking component, hose or gasket, you will never get it to run properly.

You also might search the archives for similar problems and see how others solved it.

Good luck.

[takza]

My idle went totally kaput when one of the small vac lines came off on the pass side.

The EBCV works with the O2 and ECU to bleed air into the fuel stream in order to control the fuel mixture?

http://www.aircarecolorado.com/repair/toyota.htm

[ÜberDööber]

Thanks for your suggestions, guys. I'll take a look at everything.

I did replace the needle and seat, just forgot to list it as one of the parts I swapped.

On the EBCV with 12v applied to it, I can blow on the "in" hose but don't feel the same amount of air coming out of the out line. It is the same blowing on either line. It does seem like air is escaping out of the bottom of the EVCV but it is hard to tell. It's not like the EBCV is an on/off switch that opens up a direct line of vacuum between the end and out hoses.

I'll keep digging. Thanks again. This place is the best!

...Diane

ps.
Can anybody tell me where the ECU is located?

[Petros]

under the dash above the glove box. If you remove the glove box you will see it. These are pretty reliable and usually do not fail (though it is possible), so I would check everything else out first. They likely run okay in 'fail safe' mode even if they do fail.

[neonsport]

Alright, if you have an 83 SR5, you might be able to answer a question for me. Does it have a rear swaybar? None of the later 2WD Tercels have one, so the 83-84 SR5 hatchbacks seem to be the only possibility.

[takza]

My '83 has one.