TVSV repair attempt

[xirdneh]

I started by testing three TVSV’s according to the FSM (page EC-20). There are three temperature stages to test. All TVSV’s did OK in stages 1 & 2 and failed in stage 3. (Air would pass on “N”)
I used a Dremel tool with a super thin cutting wheel to cut away the brass crimp that holds the black plastic looking portion of the TVSV to the brass nut portion of the TVSV.
I disassembled the TVSV and took a picture of the parts.
There is a hole about 1/8” diameter in the brass nut portion of the TVSV that receives the steel drive pin. I inserted the steel pin into the hole and pushed it down as far as it would go. I heated up some water in a pan just about to the boiling point and one by one held them in the water using a pair of pliers. As the sensor end absorbed the heat the steel pin began to rise out of the brass. I measured the maximum distance the pin protruded from the brass.
I also had a TVSP that was busted so I dipped four of them. The distance varied from .43 to .595. The pin needs to protrude at least .64 for the TVSV to work properly.
I found a nail with a diameter that closely matched the drive pin and cut off a 0.10 - 0.125” length for use as a spacer. I dropped it into the plastic part that fits to the end of the drive pin. The hole in this part is about 0.20” deep.
I cleaned out the seating area in the brass nut for the black plastic part. Then I polished the brass nut for a clean place for the glue to stick. The base of the black plastic part was cleaned up also. I wiped both off with Acetone.
I carefully smeared some Permatex non-hardening gasket compound into the black plastic seating area of the brass nut. Then I assembled the TVSV. The spring is now trying to undo everything so I held it together as I slipped it into the vise (see picture). While in the vise I spread JB WELD around the joint and left it overnight to dry.
I wired it up making sure the wire was tight enough to hold the thing together should the glue decide to fail in the future. I put a dab of glue on top to keep it in place.
I put three together and all tested OK.
Note: On one of them I cut shallow grooves around the top of the brass nut with the thin cutting wheel figuring the glue would grip better. I also cut the spring making it 1/8” shorter to slightly decrease the spring’s power.
The exploded TVSV photo shows the small nail spacer (abt 1/8" long) and a full length and cut down spring.

http://farm5.static.flickr.com/4031/433 ... 7a3a_m.jpg
http://farm5.static.flickr.com/4014/433 ... 6d0c_m.jpg
http://farm5.static.flickr.com/4052/433 ... 6980_m.jpg

[takza]

You got pretty deep into it! You should qualify for a job at Toyota in quality control? That spring is really strong...it's wonder the top stays on the base.

[xirdneh]

That spring is really strong...it's wonder the top stays on the base.

Thats part of the reason why I shortened the spring.
The TVSV "N" port is for the AAP and only works the AAP until the car is warmed up.
I'm guessing that the malfunctioning TVSV, allowing the "N" port to work when the car is warm, might affect gas mileage.
The malfunctioning TVSV's were not closing off the "N" port so i figured weakening the spring might help along with adding the spacer, so far it seems to be working fine on the car i'm driving.
After the AAP the only other things the TVSV seems to control are the "choke breaker" on top aft side of carb and the "choke opener" on the front driverside of carb.
I'm sure i could get by without the "choke breaker".
The "choke opener" is needed to hole the choke open when car is warm otherwise the choke blade is free to float around.
The choke automatic choke only holds it closed and sets it free when car is warm.

[takza]

Since I run a manual choke...I could probably do without a TVSV?

* Probably don't need the AAP since I can control the cold mix manually? Might buck a little for a block or two.

* I could route the choke opener to straight manifold vac to keep the plate from moving around

* Same for the choke breaker? I still have both of these hooked up....since the choke plate does move around.

But it did seem to me that at least one of the TVSV ports went to a common vac line....?? Looks like one diaphram on the dist and the EGR also connect to the TVSV?

All 3 of the above could affect mpg if they didn't work right? So might the dist/EGR?

When looking at the FSM...looks like the TVSV sources vac from the manifold (full) and also from above the choke plate (light vac)...or could be this is just a "relief opening" to allow pressures to equalize?

[xirdneh]

i'm wondering if the automatic choke could be modified to hold the choke open.
as it is now the choke spring rests against the choke shaft lever holding the choke closed.
when the coiled choke spring heats up it moves away from the lever and is no longer touching it
why could'nt i connect the spring to the lever permanently so it holds it open when hot? (maybee bend the end of the spring into a small loop that would fit loosley over the lever)
then i could rig up the vac lines to eliminate the TVSV (assuming i could live without the AAP)
the vac lines to the distributor would be direct

[takza]

A couple of people on this forum... including myself.... have tried bypassing most of the vac lines...but there is some part of the system or the carb that needs vac and when it doesn't get it...it won't run right. I didn't stick with it very too long...cause my car already ran OK.

Might find out if you made one change at a time?

I think the choke plate moves around so that when starting the air flow moves it where it needs to be for easy starting...then the two vac thingies do their thing? I do know that with the manual choke...how you position it is critical in getting it to run right after starting....OEM auto choke worked perfectly on my car before I messed with it...just needed light oil now and then.

[dlb]

xirdneh, i've been unsuccessful in attempting to repair a TVSV. the one i had would not get to the third (hot) stage so i took it apart and measured it. my findings were similar to yours, so i added a tiny 2 mm spacer. with the spacer it got to the hot stage fine but this messes up the cold stage because the cylinder that slides up and down the plastic body of the TVSV to direct vacuum through the different ports sits too high when cold. did yours work on all three stages after you repaired them?

i think i've figured out why the TVSV wears out, at least. there is no spring at the bottom of the steel drive pin so my guess is that there is a small amount of air and as it is heated, it expands. this expanding air pressure is what pushes the drive pin up. in order for this to work though, there must be a good seal between the brass and the drive pin. this seems to be accomplished with very precise tolerances and a tiny amount of grease. each time the TVSV heats up and cools down though, the pin slides against the soft brass and slowly wears it down. this would most likely occur at the exit point of the brass since, once heated, the majority of the pin sits outside of the brass and can wobble around a bit. once this wear around the outer part of the brass occurs, the seal is only good part way up and out of the brass. once the pin reaches that point, the air escapes around the pin, through the worn spots and no longer pushes the pin any further.

so to me, the best idea seems to just replace the damn thing since the brass can't be restored. used ones from cars with low miles should be fine for a while but new ones would be great, if they can be found. the next best thing i can think of is coating the drive pin with a heavy grease to help maintain the seal. i'm going to give this a try and see how it goes. wish me luck.