Issues with 4AC swap in a 1981 DLX

How-to's and repair secrets for your 4WD can be found here. Have a question? Ask it in here!
ErickC
Newbie
Posts: 23
Joined: Fri Nov 28, 2014 7:36 am
My tercel:: 1981 DLX, 1982 STD

Re: Issues with 4AC swap in a 1981 DLX

Post by ErickC » Sun Aug 25, 2019 11:01 am

On the 3AC, the bolt is located just under the upper timing sprocket, and I'm pretty sure it went into the head. It doesn't really matter, though. I was looking at photos of AE86 4ACs and it looks like their upper covers lack that bolt entirely, so I'm just going to bjork it off with a Dremel one of these days, when I have time to get the balancer off and swap out the lower covers.

The car is drivable, but I'm still working out the bugs. I set the idle, initial timing, and TP the other day, but I'm still having a couple of weird issues:

1. The engine wants to stumble with the throttle open in two very specific positions, I'd say about 20% and 50%, roughly. Engine speed doesn't seem to be a factor, just throttle position at any RPM under any load (cruise, acceleration, et cetera). If I go below or above those positions, it runs great! I can floor it with no issues. Just those two weird spots.

2. I'm not getting any vacuum to a lot of accessories - the distributor being the main one of concern. Way back before the old engine blew, I just sort of figured I had a faulty TVSV, since that's what Toyota TVSVs do, they go bad, and the VSV never really seemed to be getting any vacuum. So I bypassed the TVSV and set up the lines to fool the car into thinking it was always warm (which the car didn't really seem to mind, not even when it was 35 below out). The distributor still wasn't getting any vacuum, and I tested all of the check valves, switching valves, and so on - they were all in perfect working order. Fast forward to today, and nothing's changed, and I checked all of the vacuum components again. Well, I hooked the distributor up to an unused port on the carburettor, and that one isn't giving any vacuum, either. So, basically, I'm pretty sure some of these ports are dummies and I need to map them out or buy a Weber... which I'm loathe to do. I'm a commuter, not a drift racer. Also, I'm broke.

User avatar
Petros
Highest Ranking Member
Posts: 11038
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Issues with 4AC swap in a 1981 DLX

Post by Petros » Mon Aug 26, 2019 7:54 pm

the distributor should run off straight manifold vacuum, not from ported vac on the carb. some of the vac ports on the carb draw from specific parts of the throttle (above, below, at the venturi, etc) and do not always have vac, and as speculated, some might be inactive for your model of car.

there are a couple of vac operated accessories that are affected at certain rpms, I do not recall which. you might look in the FSM on fuel system and emission controls and see what changes, switches or transitions at that 20 percent and 50 percent throttle position, as a good place to start looking.

there are no components that operate on throttle position in this car (unlike modern EFI cars), there is not even a throttle position sensor. There is a push rod that opens a closed choke above a certain throttle position, but that does nothing after it is warm and choke is open.

OTOH, this could also be caused by a vac leak, I would double check for vac leaks. consider it might be leaking at the manifold gasket or carb gasket, not just at the vac lines.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

ErickC
Newbie
Posts: 23
Joined: Fri Nov 28, 2014 7:36 am
My tercel:: 1981 DLX, 1982 STD

Re: Issues with 4AC swap in a 1981 DLX

Post by ErickC » Tue Aug 27, 2019 6:06 am

I've been driving the car more the last few days, and it seems now like it's more of a load problem, because it wants to occur in certain combinations of throttle position and engine speed. It's basically the low-midrange slump that every carburetted A engine I've dealt with has, but way more severe. It happens intermittently during cruise as well, mostly during small throttle adjustments. I wonder if it might have something to do with the secondary throttle plate. Maybe the actuator is sticking a bit?

Bear in mind that this carb is from an AE82, so I'm really making this all up as I go along. Are there any 4AC carbs with comparable plug/vacuum arrangements? Maybe from an E70 Corolla? I'm tempted to throw the 3AC carb back on it, but I don't know enough to know if it can handle the 4AC. Should it be capable?

About the distributor - I hooked it up to the nearest available vacuum line temporarily to see if maybe getting any vacuum on it at all might solve the first problem. It's ultimately fed by the VSV and I suspect that the VSV may not be getting vacuum, since it's been tested and is otherwise working properly. I'm going to have to yank some hoses and find out.

User avatar
NWMO
Highest Ranking Member
Posts: 609
Joined: Wed May 20, 2015 1:08 pm

Re: Issues with 4AC swap in a 1981 DLX

Post by NWMO » Tue Aug 27, 2019 1:39 pm

I'm tempted to throw the 3AC carb back on it, but I don't know enough to know if it can handle the 4AC. Should it be capable?
I simply moved the carb from my old 3a when I purchased and rebuilt the 4a engine (to include the 272 grind cam upgrade from Delta) and the carb does fine.

Chris
Psalm 37:4 "Delight yourself in the Lord and he will give you the desires of your heart"

In remembrance of my friend ARCHINSTL:

T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"

"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
Mark Twain

User avatar
Petros
Highest Ranking Member
Posts: 11038
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Issues with 4AC swap in a 1981 DLX

Post by Petros » Tue Aug 27, 2019 1:56 pm

do you think you might be getting fuel starvation at those power settings? check you fuel lines are all good (no cracks or leaks), and replace the fuel filter. a leak in the fuel line up stream of the fuel pump will not leak much fuel, under vacuum it will suck in air instead of fuel, starving the engine at high demand conditions.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

ErickC
Newbie
Posts: 23
Joined: Fri Nov 28, 2014 7:36 am
My tercel:: 1981 DLX, 1982 STD

Re: Issues with 4AC swap in a 1981 DLX

Post by ErickC » Sun Sep 01, 2019 5:17 pm

I think the fact that this carb sat in the trunk of a Corolla in a ditch behind a garage at a farm for two years is probably a larger component of the problem, though a fuel filter is cheap and I'm going to replace it when I get a chance real quick here. Anyway, I ran some tests to diagnose the vacuum advance problem:

1.) Checked hose from intake manifold to VSV to ensure VSV was getting vacuum. It was. This eliminates a lack of vacuum to the VSV. Possibilities: VSV not functioning correctly (despite having been tested off-vehicle), TVSV not getting vacuum, TVSV not functioning properly.

2.) Checked hose from manifold to TVSV to ensure it was getting vacuum. It was. Possibilities: VSV is not functioning correctly, TVSV is not functioning correctly.

3.) Sent intake manifold vacuum directly to VSV (bypassing TVSV) - the distributor receives vacuum. This means that the VSV is functioning correctly, so the TVSV is the problem.

I have three options:

1.) Bypass the TVSV. Since winter lasts like 11 months up here, this is a bad idea.

2.) Find a functional replacement. Of course, it makes just as much sense to ask Sofia Vergara on a date, because the odds of success are about the same (actually, I think the odds of the latter are better).

3.) Jury rig a compromise

If I can find a functional thermal vacuum switch that has the right size and threading, and at least does "on/off" correctly, then I can very easily rig up something that will work. Does anyone have any suggestions? I found a unit for a mid-90s Corolla, and I wonder if it will fit. I also need to find a heater valve that can be retrofitted to work, because the only way to move the current one is with vice grips.
Last edited by ErickC on Mon Sep 02, 2019 7:56 pm, edited 1 time in total.

User avatar
Petros
Highest Ranking Member
Posts: 11038
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Issues with 4AC swap in a 1981 DLX

Post by Petros » Mon Sep 02, 2019 5:40 pm

it seems to me it would not be difficult to by pass it, and perhaps rig a manual shut off valve that you can switch from the driver's seat. that should be simple, and a good solution until you can find a working VSV, or get a date with Sofia Vergara.

If your odds are better, why not just go for Sofia Vergara. After that, who needs a functional VSV anyway?
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

ErickC
Newbie
Posts: 23
Joined: Fri Nov 28, 2014 7:36 am
My tercel:: 1981 DLX, 1982 STD

Re: Issues with 4AC swap in a 1981 DLX

Post by ErickC » Mon Sep 02, 2019 8:00 pm

I've considered that possibility. The Camry 2-pipe valve is only $20, though, so I'm tempted to try it and see if it'll screw in, since that's all I really need. I already have the basic schematic for the modified system percolating in my head. I also thought of the possibility of slaving the identical VSV from my other car (I mean, I'm going to be using some seatbelts and the fuel sender from it anyway) to the Camry valve and using that to perform the TVSV functions... but it seems a little over-complex when solution one (basically the automated version of your solution) will do it just as well.

EDIT: and this exact part is in my brother's 4AFE Corolla... so I can probably determine if it will fit tomorrow.

ErickC
Newbie
Posts: 23
Joined: Fri Nov 28, 2014 7:36 am
My tercel:: 1981 DLX, 1982 STD

Re: Issues with 4AC swap in a 1981 DLX

Post by ErickC » Wed Sep 04, 2019 7:21 pm

Success! Today's work:

1.) Reinstalled original nonoriginal carburettor

2.) Deleted BVSV vac lines to distributor

3.) Routed K line to BVSV, installed a junction to bind L and M lines, and piped this junction to the BVSV

In other words, I am using the BVSV as a TVSV, and it works just fine. For the first time ever, the choke and fast idle engage and disengage properly. The stuttering problems are also gone, though I'm still going to change my fuel filter as soon as I empty this tank.

Things that still need to be addressed:

1.) I still need to retrofit the 3AC timing belt covers

2.) There's a small exhaust leak, but there's always been a small exhaust leak. At some point, I am going to replace the exhaust manifold and build a new exhaust system, and this will probably go hand-in-hand with a vacuum delete. This is because the California-spec exhaust manifold and pipe is a unique, 3-stud affair. There's no way I'm going to be able to find exhaust components that are going to fit, so it makes sense to grab a different exhaust manifold and use off-the-shelf components where they are available. I'd use the manifold off my other Tercel, but I really don't want to deal with the Rube Goldberg waste of space that sends exhaust gas to the #3 cylinder. I wonder if a stock AE86 manifold might be a good option, since everyone and their grandma is installing headers... might be able to get a factory manifold for cheap or free. Anyway, at that point, the smog pump becomes dead weight, and, if I'm going to get rid of that, I might as well send the EGR with it and free up that entire space. I'll keep the choke, TP, and HAI, I suppose.

User avatar
Petros
Highest Ranking Member
Posts: 11038
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Issues with 4AC swap in a 1981 DLX

Post by Petros » Wed Sep 04, 2019 10:45 pm

as far as exhaust manifolds go, you can find a fairly cheap header for it (about $150) that was intended for a 4ac car (not the tercel). And use that to build one that fits the Tercel4wd.

You can cut off the lower half and weld up a new, longer, collector from the parts. it would be a much easier thing to do than to make an exhaust header from scratch.

I have a RWD corolla 4age header that I intend to adapt to my 4age swap Tercel4wd, the upper half fits, but the lower half will not work, so my intention is to have the local exhaust shop build me up a custom exhaust header/system using the 4age header. The owner of the local muffler shop is a long time hot rod guy and I am reasonably certain he can handle this job.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

ErickC
Newbie
Posts: 23
Joined: Fri Nov 28, 2014 7:36 am
My tercel:: 1981 DLX, 1982 STD

Re: Issues with 4AC swap in a 1981 DLX

Post by ErickC » Thu Sep 05, 2019 2:08 am

I was considering the possibility of using AE86 headers, that is, if the clearances are right (I suspect that they're quite similar). I'd still need to rig up something with off the shelf parts for everything past it, though, so if I can grab a stock AE86 manifold for free or cheap, it's probably the better option given that I don't have a whole lot of cash to spare. The first-gen Tercel exhaust pipe is exactly three pieces - the part that goes from the manifold to the catalytic converter, the catalytic converter, and the integrated pipe/muffler assembly. Unfortunately, it's all rusted together and the first piece is starting to leak. With the California-spec pipe having three studs - one of which is behind and between the tandem pipes leading to the catalytic converter - it's almost impossible to mount it with the engine in the car - and, of course, it has to be mounted with the engine in the car. Whoever designed it was a real sadist, to say the least. The Federal pipe on my other car has two studs, and both of them are super easy to access. Of course, it's also got a single pipe instead of the two pipes on the California-spec unit.

I am thinking that, when the time comes to redo the exhaust, my 4AC might become a 4A... just simplify the whole works as much as possible. Manifold, pipe, muffler - but I suspect that deleting the thermo sensor (which would come with deleting the cat) might cause ECU problems. That said, I'm not certain that I'm going to find a cat with the proper opening for a thermo sensor anyway. At least not in my price range.

I do find it interesting that the Clymer manual that I use as a supplement to the FSM skips the 1981 California emissions because "it's so complex," but, honestly, it's really not. The first-gen Tercel FSM sucks for a lot of things (thus why my car no longer has air conditioning), but its diagrams of the emissions systems are concise and easy to follow with a little common sense and a basic understanding of how manifold vacuum works. There are really only a few systems:

1.) The TVSV, which controls when everything else gets vacuum or atmospheric pressure
2.) The VSV, which is slaved to the TVSV, receives vacuum from a big pipe into the intake manifold, and controls the EGR and vacuum advance, as well as receiving fuel vapor from the canister
3.) The EGR system, which constitutes the bulk of the spaghetti
4.) Several choke breakers, all running off the TVSV
5.) The TP
6.) The smog pump, which is disengaged when cold (TVSV), engaged when warm (TVSV), and controlled by the ECU when at nominal temperature
7.) The MC valve, which receives vacuum from the fidget spinner looking triple vacuum port on the intake manifold, as well as a much larger hose from the VSV
8.) The BVSV, which is basically just another TVSV, but sends atmospheric pressure to one of the distributor ports above a certain temperature

The spaghetti is intimidating, but that's why I colour-coded my hard lines with paint markers.

Post Reply