RPM Cycling Situation & Vacuum Switch Location Query

[4wdchico]

Everything was left connected except the line from the VSV which was just left open & hanging there.

Called my 'yota parts connection and the canister is discontinued. Tried the Calif. Air Resources Board parts locater hot line. The vendors I was referred to are just pulling used stuff, charging huge bucks and selling the canisters with a 6 month warranty. Such a deal.

What I'm going to do now: hit the u-pull JY and hopefully find a canister that does not draw air very quickly/easily out the purge pipe. If that is not happening I'll find a Terc w/ a dead vac advance and just break off the extra vac nipple that is only used on the FED versions with the HAC. That nipple has a restriction in it. Then I'll just insert it in the line that I currently have disconnected (between evap VSV and the ported vac nipple on the carb). The system will still purge like it was designed to but I should not have too large of an effective air leak to cause the cycling.

Of course, while I'm there I'm going to harvest a fat handful of that fine 'yota specific vac line and a couple of those reaally high quality 1157 tail light bulbs from the newest 'yota I can find. Aftermarket bulbs are such trash these days that used 'yota bulbs easily outlast them.

Time to get'r done...

[m1marty]

[quote="4wdchico"] If that is not happening I'll find a Terc w/ a dead vac advance and just break off the extra vac nipple that is only used on the FED versions with the HAC. That nipple has a restriction in it. Then I'll just insert it in the line that I currently have disconnected (between evap VSV and the ported vac nipple on the carb). The system will still purge like it was designed to but I should not have too large of an effective air leak to cause the cycling.
quote]
Why not use a piece of the plastic hard lines? Might be the right size restriction and theres a good bit of it under the hood.

[4wdchico]

Well the slight restriction from the vac advance bit, as mentioned before, does not fully cure the cycling issue. Lots better for sure, you have to be trying to get the tach needle to climb as slowly as possible for it to cycle. If it does cycle, it now does so in a much smaller RPM range and most often will only cycle once before the tach needle will continue climbing.

I checked four tercels at the JY and they all had evap canisters that pull lots of air just like mine does. I wonder why this problem is not more widespread.

Since I don't expect an old evap system to not contaminate my nice tight engine with particulate matter I looked into using a small in-line fuel filter to clean up the purge air before it enters the carb. Turns out that the best fit for this application is from fuel filters intended for hydrocarbon fueled remote controlled stuff. Possibly one of those mini fuel filters would add enough additional restriction (thinking that the sintered bronze units might be the best bet) that the cycling will fully go away.

[m1marty]

Mine was doing this with partial throttle input as well and I've been having a heck of a time trying to figure it out- until I read this thread. I have the line blocked right now and was able to dial the mixture back a bit. No more pinging! I have some RC fuel filters left over from my RC days so I'll try one of those tomorrow. Will I hurt anything to run it blocked for the time being?

[4wdchico]

Will I hurt anything to run it blocked for the time being?

Glad to hear that the info helped. No, having it blocked will do no damage. At least to your car. The car will pollute a bit more as he evap won't be recycled. I'm trying to get my system working correctly by adjusting for too much flow from the evap canister so that it can burn off evap but not stumble badly.

I'd like to hear about the results you get from a R-C fuel filter in the purge line. Might not slow the flow down enough by itself, but who knows.

[ARCHINSTL]

4wdchico & m1marty -
Anything new on your endeavors in this situation? I have not yet bestirred myself to do anything...
Tom M.

[4wdchico]

4wdchico & m1marty -
Anything new on your endeavors in this situation? I have not yet bestirred myself to do anything...
Tom M.

I have not changed anything since my last report on the subject. I did buy a nice dark blue ano R/C car fuel filter with a super fine ss screen inside. My car will surge a bit at very small throttle openings when in that specific rpm band but it is not too bad. Hoping that the small amount of extra restriction it will add to the system when it is purging will make it a bit better.

[warbstrd]

Damn, you guys went through a lot of trouble shooting and still not fully cured. personally i think i would have bought a weber.

[4wdchico]

Damn, you guys went through a lot of trouble shooting and still not fully cured. personally i think i would have bought a weber.

Not going to happen if you want to pass the California smog check like I have to. Besides, I like the fact that my car runs uber clean.

[ARCHINSTL]

Another Resurrection of a Mature Thread.....
I have been once again been attempting to discover the source of my RPM-cyling from 2300 to 1900 to 2300 to...ad infinitum.
I have (again) used a multimeter to check the "A" and "B" switches, the EBCV, the O2 sensor, the canister's VSV and OVCV and both solenoid valves. I again renewed all the various canister lines with new fuel/emission hose, cleaned and blew out the canister and the steel line to the tank, and also installed a new gas cap (the 3 year-old one "didn't rattle any more" as it should).

Like 4wdchico stated back in April, I am convinced that it is a vacuum leak through the vapor canister, as when the carb port for the purge line is plugged and the line itself is left unplugged, the cycling stops.
Note that this occurs when the "A" switch is connected, both electrically and to its vacuum line - I had previously only left the switch's vac line plugged to stop the cycling. So with this latter method, "A" did not signal the ECU, which did not signal the canister's VSV - and no purging ever occurred - the tank and float bowl vapors went - where?

The VSV purges the canister at 2300 RPM, and when the deceleration fuel cut system opens at 1900, the purge ceases and the VSV is off.
So - it would appear that the purging introduces "air" plus the vapors and then knocks the RPMs down to 1900, at which point the VSV closes and there is no "air/vapor" introduced and the RPMs can build back up. And so forth.

So - it seems that despite electrical and compressor checks to the contrary, the vapor canister is bad.
As 4wdchico mentioned, the canister is not available new anywhere, and I'm dubious of salvage canisters.
While I could just leave the purge line hang, I thought I might put it in some sort of small canister to prevent the fumes from smelling up the place (I would not think there is much, if any, of a fire risk?). I thought I could use the small "plastic" canister from the MityVac kit (I had to buy another kit last year, so have two of the canisters), and stuff it with cotton balls to absorb the fumes.
Or - add a fitting to the air cleaner to attach the purge hose - what are those effects? The Canadian MTs' canisters apparently feed into the carb continuously, with no VSV, but it seems like I read somewhere that some purge lines go into the air cleaner instead of the carb, and that this can lead to hard starting and a ragged initial idle...

At least with either of the above methods, "A" would again be activated and able to do its tasks, among which is cueing the first fuel cut solenoid. The loss would be fuel vapors, whether to an "auxiliary canister" or to the air cleaner (the latter would involve their burning, so maybe that would be a plus - so long as the cleaner did not explode , which would seem unlikely? ...).
I wonder just what is the quantity of vapors which make their tortuous way from the tank and float bowl to the canister? ? ? An ounce a day - or ...?
Pre-1996 cars no longer have to be emissions-tested here in MO.

Any thoughts on these proposals - or anecdotal experience?
Thanks,
Tom M.

[Neu]

I would assume that maybe the line going back into the engine would hit your mpg a lil bit, but it may not. I'd just have a canister and hook the hose up to an empty canister.

Really i dont think it matters all too much

[takza]

The EGR runs off that same R port I think. You can hit the ports in the canister with a little WD40...there are check valves in there that might get stuck. But not too much WD40...since the oil and so forth can contaminate the charcoal.

Not sure if you've tested it...but I had cycling that was related to the vac modulator that controls the EGR...I also hit the ports on this with a little WD40.

[ARCHINSTL]

I have not yet tested the EGR vac modulator, as that was NEW three years ago when I replaced an inoperative one - at the same time I scoured the clogged-SOLID EGR valve itself. I am going to remove the valve today and check it out - curious to see what 8K miles have done to it.
The 2300/1900 RPM cycling, however, was present before and after the cleaning/modulator replacement...
Tom M.

[sdoan]

Tom,
I did not read the whole thread so apologies if I've stated the obvious or repeated others.

I like putting the vapor line into the air cleaner because it burns any vapors that are emitted while running. I think the charcoal can is designed to store vapors emitted while sitting e.g., after shut down of a hot engine or on a warming day - so the vapor line to the air cleaner won't help that. The vapors will be so few and so diluted with incoming air there is no way I can imagine the vapors actually reaching a flammable concentration - and there is no ignition source in the air cleaner. OTOH, older motorcycle carbs have vent tubes that just drain to the ground.

RPM cycling is often a symptom of an air leak. If the idle mixture screw is unsealed on your car you could richen the mix to see if that puts an end to the cycling. Or you can often find the leak by spraying carb cleaner around the suspected leak. (Starting fluid is too volatile to pinpoint the leak and I don't trust WD40 to burn in the engine).

ONe other thought. Doesn't the charcoal canister have a line going to the gas tank? Could a leak in that line lead you to think the canister had failed?

Good luck. Let us know what you find.

Shawn

[ARCHINSTL]

Thanks, Shawn -
I don't blame you for not reading the whole thing - it is lengthy, dating to late 2005, revived this Spring, and again resuscitating, now being one up on Lazarus...it also has over 3K hits - amazing!

I just removed the EGR valve for cleaning. I did it three years and 8K ago, when it had a SOLID block of carbon inside. Now, it is just quite sooty but no lumps/chunks, etc.

I had blown out the canister-to-tank tube and also attempted to draw a vac on it, until I remembered that it should be open at the tank. I had not considered a leak in this tube. I had renewed all three of the fuel hoses at the tank three years ago - guess I'll try to remove a hose and plug the steel tube and try to draw a vac at the front.
Frankly, since none of the steel tubes were the least bit rusty at the time nor are they rusty now, I had not considered a leak there.
It did cycle both before and after I installed the hoses back in '95, so I guess this is a possibility that I certainly had not considered before. Wouldn't it be funny if this tube were the cause? I can only wish...
Tom M.