HCV Location and Driveability Questions

Post by **ARCHINSTL** » Mon May 23, 2005 9:34 pm

Well, I hope my 3A-C questions are not too naive...
1. Heat Control Valve: The FSM does not indicate that this is NOT on all engines, and I simply cannot find it anywhere on the manifold. Is it concealed by the heat shield - OR - does the Cold Mixture Heater System take its place on (some) engines?
2. I will be removing the EGR valve and attempting to decarbonize it, as the forums have recommended. However, I thought I'd check the EGR vacuum modulator first. The FSM shows it being dismantled and the filters being cleaned. Mine looks different and the top APPARENTLY cannot be lifted/screwed off to permit access to the filters. True? I blew through the two side pipes and a little air exits from under the cap, but not a lot - correct? It is the Federal system type.
3. I replaced the oxygen sensor, theTVSV and all 40+ various vac lines (carefully). There is SOME improvement in acceleration, but only when totally warm, and there is yet a little hesitation. Cold starting is somewhat better, but when revved from the cold idle of 1200 the engine just dies until above 2000, and one either immediately removes the foot from the pedal or revs it above 2000 to keep the engine going; this condition continues until the engine is really warm. Needless to say, this is not conducive to smooth starts.
4. Are a lot of the driveability problems we have common to various Toyotas of that era, or are they peculiar to the Tercel?
Thanks, all.
Tom M.

GTSSportCoupe · Post by **GTSSportCoupe** » Mon May 23, 2005 9:55 pm

ARCHINSTL wrote: Well, I hope my 3A-C questions are not too naive...
1. Heat Control Valve: The FSM does not indicate that this is NOT on all engines, and I simply cannot find it anywhere on the manifold. Is it concealed by the heat shield - OR - does the Cold Mixture Heater System take its place on (some) engines?
4. Are a lot of the driveability problems we have common to various Toyotas of that era, or are they peculiar to the Tercel?
Thanks, all.
Tom M.

I can help with a couple of your questions:

1. The heater valve is located IN the manifold below the carburator. I don't think any of the parts are visible with the manifold installed.

4. The driveability problems seem to be specific to small carb'ed engines from the 80's in my experience. I've had the same sorts of problems with other carbed toyota engines, as well as subaru and a few others.

Post by **ARCHINSTL** » Mon May 23, 2005 10:49 pm

GTS - Thanks - it makes sense - but -
I pasted a passage from the Autozone site following, and the diagram it uses is the same as the FSM, and the other diagram in the FSM shows the weight being on the o/s as well. Wish I could figure out how to scan it and send it along.
A/Z:
"The valve is within the exhaust system and has a counterweight on the outside of the pipe. With the engine cold, check that the counterweight is in the upper position. After the engine has been warmed up, check that the weight has moved to the lower position."
This would seem to indicate that the weight is visible from the o/s, since one is supposed to check it when the engine is warm.
Tom M.

takza · Post by **takza** » Tue May 24, 2005 5:04 am

Yes...there is a counterweight...I've only checked to see if it will move OK.......so far.

The EGR could be the source of your driveability problems...since if it isn't controlled just right it will dump too much exhaust into the intake at the wrong times. Check by temporarily disconnecting & plugging the vac line to it. Can also test the EGR itself to see if it works at all.

I haven't heard of anyone testing the EBCV...including myself...supposed to control the mixture.

Might help to check the torque on the manifold bolts you can get to...mine were loose....saw some improvement.

Post by **ARCHINSTL** » Tue May 24, 2005 2:03 pm

takza - thank you for confirming something I suspected about the EGR valve's effects.
I suspected this because of what happened last year with a new Jasper Mitsu 2.6 engine installed in my '88 Ram 50 by a highly recommended local shop. One of several problems I later had to diagnose and fix myself was that its EGR (called a reed valve) had malfunctioned and was sending exhaust back into the air cleaner instead of sucking air from the cleaner into the exhaust manifold. It wasn't causing much hesitation, per se, but just horrible mileage and no power at all. I just unhooked the hose from the valve and plugged the cleaner hole. Power and mileage back with my Ozark-repair and surprisingly it passed the MO emissions with flying colors.
As to the counterweight - I have not removed the carb/shield, etc., and have yet to find it. I guess my fingers are too thick to explore totally around the manifolds. I would have thought it would be more accessible.
A thought - since the head is a replacement, could the TN mech have replaced the manifolds at the same time and that manifold group did NOT have the valve? Did some 3A/3A-C engines NOT have this?
Thank you all.
Tom M.

takza · Post by **takza** » Wed May 25, 2005 6:13 am

It's visible from up top on the pass side of the carb...there is a diaphram that shows and the rusty EGR is below it. Might have to remove the air cleaner.

Chris · Post by **Chris** » Wed Jun 01, 2005 12:07 am

I find it easy to check the Heat Control Valve from under the car on the passenger side. Jack the car up or use ramps to give yourself plenty of room. Look/reach up to the area under the carb. The counterweight is visible there.

Post by **ARCHINSTL** » Wed Jun 01, 2005 8:10 pm

Chris - Thanks for the tip on finding the HCV. I was just about to give up on it. As many times as I was under/over/around the manifold, with several sizes of mirrors, I still missed it.

Now - how easily is it supposed to move? It DOES move, but kinda "rustily". There does not seem to be much, if any, tension on the spring, in that it does not move the weight smartly. While it is difficult to see at this time, it APPEARS that the external spring may be broken, but I am not certain. The FSM does not give a clear view of what the external spring is supposed to look like. The manual ignores any mention of the spring/HCV when talking about the manifolds, and indeed, the HCV is not present on the drawings in the engine section. This looks like a difficult place to direct carb cleaner spray for loosening the valve; any suggestions?

I guess I will be removing the carb and shield to get at the manifold nuts for retorquing, as takza suggested earlier, so will observe it further. There was a new head installed by the previous owner 800 miles ago, and I would guess that it was never taken back for checking.

Incidentally, I've cleaned the EGR thoroughly (it was totally and completely plugged by carbon-not even a small passage remaining open), and have some tips to add to takza's guide to cleaning it (and small tubes and tight places in general). I'll be (gently) tackling the modulator tonight.

I do have pix to post of my method, but do not want them to turn out so huge and unwieldy as those I posted earlier on the EGR. Any suggestions?

Also, has anyone tried the electrolysis method of removing crud/ corrosion that was suggested to takza in a post last year? I've been on various sites and it looks intriguing and simple and inexpensive. It is apparently used by many types of restorers, particularly with heavy old farm equipment - and also coin collectors.

Thanks, all.
Tom M.