Drivability mystery problem - ignition timing

General discussion about our beloved Tercel 4WD cars
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Drivability mystery problem - ignition timing

Post by eightyfive4WD »

I have a 1985 Tercel DLX 4WD with automatic transmission, with unknown exact mileage but estimated ~170k miles, and it has begun to develop a strange problem. Sometime between 2nd and 3rd gear, before I can hear the 3rd gear begin to spin up and engage/whine inside the transmission, the car will drop its RPM's briefly, and act like a brake is being applied. It jerks once, twice, sometimes a few times, then it accelerates as normal. It does not have difficulty in shifting 1st to 2nd, nor 2nd to 3rd gear. This erratic behavior occurs between 2nd and 3rd gear, around 20-25 MPH usually and is accompanied by a clunking noise, audible from inside the cab. Transmission fluid is only 5k miles old; the fluid pan was cleaned and inspected at the same time. The magnets were nearly particle free, and the old fluid in the transmission had plenty of life prior to my drain and fill. I filled with Dex VI which I have since learned some people have doubts in, but I figured in this case it's a suitable replacement for the specified Dex III (it says so right on the bottle label). Even doubting that, I don't think running Dex VI in a dinosaur automatic transmission would cause this kind of behavior.

I have so far added about half of a bottle of Lucas ATF Transmission Fix with some margin of success. It has improved overall transmission characteristics but I still have this mystery clunk and ...shuddering, for lack of a better term, occurring at 20-25 MPH. But only when the transmission is cold. Once it warms up after a few miles of driving and shifts, no trouble. It starts to shift as expected and the noise and shudder goes away.

I didn't think it was torque converter related at first, but that is what I'm beginning to suspect. I don't think it could be worn clutch packs because there is no RPM spike with lack of acceleration that usually accompanies slipping with transmissions. I'm kind of stumped on it. I may just continue to add more and more of the Lucas Stop Slip product to the existing fluid and see what happens.

Any thoughts or insight?
Last edited by eightyfive4WD on Tue Mar 08, 2022 7:08 am, edited 10 times in total.
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Automatic Transmission mystery problem

Post by eightyfive4WD »

I have a complete rebuild kit in my possession but I don't think the drivability has been compromised enough to warrant its use just yet.
I will happily take the time to do so eventually, but I'm really just looking for a temporary band-aid to help me bide my time right now.
I figure at this stage of the behavior, this isn't a problem that some additive won't help solve yet.
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
Petros
Highest Ranking Member
Posts: 11930
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Automatic Transmission mystery problem

Post by Petros »

the shudder could be clutch chatter when it shifts. it can do this for a long time, but generally this action is not good for long life. typically it occurs when it is worn unevenly, or if for some reason it has bad fluid on the clutch packs. usually it improves with an ATF change. you might try out several different additives for the trans fluid, they do not cost much, and you may be able to make it go away. this will give you more time to get another transmission for it.

good luck.
'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)
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Automatic Transmission mystery problem

Post by eightyfive4WD »

Petros wrote: Wed Jan 19, 2022 1:37 am the shudder could be clutch chatter when it shifts. it can do this for a long time, but generally this action is not good for long life. typically it occurs when it is worn unevenly, or if for some reason it has bad fluid on the clutch packs. usually it improves with an ATF change. you might try out several different additives for the trans fluid, they do not cost much, and you may be able to make it go away. this will give you more time to get another transmission for it.

good luck.
Thanks Peter.
It really has been difficult for me to diagnose this, as it usually only behaves this way for the first bit of my driving of the day. Usually around the same location each day, and goes away after the first time it shudders or jerks. Once the fluid starts to warm up it clears itself up.
I have done a bit of research on other additives like you said, and I think I'm going to give Lubegard 19610 Instant Shudder Fixx a try. It is a friction modifier meant for use as a diagnostic tool. If the shudder goes away instantly, it claims this indicates a fluid problem. If the shudder persists, they say this indicates a mechanical failure.
https://www.amazon.com/Lubegard-19610-T ... JMLQU?th=1
I'll pick some up soon and give it a shot. Hopefully I'll find something to clear up these symptoms while they are mild and just beginning.
If, say, the Lubegard product takes care of it for me, I'll just be sure to add another 2 oz. bottle when I drain & fill the transmission next.
Last edited by eightyfive4WD on Thu Jan 20, 2022 2:59 pm, edited 1 time in total.
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Automatic Transmission mystery problem

Post by eightyfive4WD »

So... I've added the LubeGard Instant Shudder fixx. The transmission shudder I felt before is gone, but I am still having a jerking & noise occur when I am between 20-25 MPH and applying medium acceleration. RPM's momentarily drop while the noise occurs. The noise is more of a what I would call a dull "pop" now.

The noise doesn't sound like marbles in a pan or metal-on-metal. I had a 5 speed '81 pickup whose transmission grenaded on the highway, I remember what that sounded like. This is nothing like that, it's definitely not a gear-grinding sound or anything like that.

Now that I've listened to this noise more over this many-day period, it doesn't sound like my transmission per se. It almost feels as though the engine is backfiring? Not from the tailpipe, but like a popping/backfiring from the carburetor. The noise is not coming from the rear of the vehicle, which is why I initially still suspected my transmission was to blame for the noise.

For the last several days the jerk & pop has only happened when the engine is cold. But today, it also did it a bit after several miles of highway speeds.
And then later in the evening, only made a single small pop once during the 25 miles home.

I really don't know what to make of the situation any more. I've now added a couple different additives, and the transmission no longer shudders but now there is this strange jerking & popping occurring. Doesn't sound or feel like metal-on-metal. It sounds much closer to a popping/backfire in the carb, followed by the immediate drop in RPM, and the jerking motion. I can't make sense out of why that would only happen in the very specific circumstances I have outlined here, though.


I'm sort of taking my attention away from the transmission and considering the fuel & spark systems now. That being said, I really can't make heads or tails out of why my relatively happy Weber 32/36 carburetor would randomly develop a problem like this. Additionally, I have just been through the entire fuel system on the car (minus the fuel pump which I did not check) and everything looks great. I have noticed that while my fuel pressure gauge typically reads between 2-3 PSI, and on some occasions I have seen it as low as ~ 1 PSI. Is there any possibility that a failing fuel pump would cause intermittent low fuel pressure & improper air-fuel mixture, leading to the situation and noise that I have outlined here?
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
Petros
Highest Ranking Member
Posts: 11930
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Drivability mystery problem

Post by Petros »

Sounds like you have a fuel metering problem (sometimes if you have more than one issue at the same time, trying to find it can be an extra head ache). there is a mixture control device in the fuel system that activates about 2500 rpm or there about. it leans the mixture to control the fuel air ratio better to reduce emissions. As I recall it is one of the devices on teh right fender next to the strut tower. It sounds like one of these devices is malfunctioning or has a vac leak.

I do not recall what it is called, but if you go though the FSM (available for free down load from this site), in the fuel system chapter (or might be in the emissions control chapter) and see what devices are actuated in the mid rpm range, and do a functional test on them (per the FSM). the tests are usually simple, like pull and cap the vac line and than rev the engine to see how it responds. the FSM in the fuel system chapter has a good diagnostic table, listing the symptom or behavior,and than gives you the section to go to so you can check and test the system and the probable cause.

Often when you have a mid rpm range hick-up it can be traced to that system. might be a simple fix, like get the vac lines routed correctly, or replace any leaky vac lines. other times you have to replace the device, which in NLA so you will have to get one from someones parts car or the wrecking yard. I believe these devices may also come in the carburated corolla from the same year. it also may be possible to by pass it, rig is so it runs at the same mixture at all rpms. I knew of one T4wd owner who traced it to a device about the size of a baby food jar on the right fender (right behind the coolant over flow tank), it is a black metal can. He could not find a good one so he tried to bypass it. it ran good, smooth, but the fuel economy suffered.

Good luck.
'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)
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Drivability mystery problem

Post by eightyfive4WD »

Petros wrote: Thu Jan 20, 2022 10:49 pm Sounds like you have a fuel metering problem (sometimes if you have more than one issue at the same time, trying to find it can be an extra head ache). there is a mixture control device in the fuel system that activates about 2500 rpm or there about. it leans the mixture to control the fuel air ratio better to reduce emissions. As I recall it is one of the devices on teh right fender next to the strut tower. It sounds like one of these devices is malfunctioning or has a vac leak.

I do not recall what it is called, but if you go though the FSM (available for free down load from this site), in the fuel system chapter (or might be in the emissions control chapter) and see what devices are actuated in the mid rpm range, and do a functional test on them (per the FSM). the tests are usually simple, like pull and cap the vac line and than rev the engine to see how it responds. the FSM in the fuel system chapter has a good diagnostic table, listing the symptom or behavior,and than gives you the section to go to so you can check and test the system and the probable cause.

Often when you have a mid rpm range hick-up it can be traced to that system. might be a simple fix, like get the vac lines routed correctly, or replace any leaky vac lines. other times you have to replace the device, which in NLA so you will have to get one from someones parts car or the wrecking yard. I believe these devices may also come in the carburated corolla from the same year. it also may be possible to by pass it, rig is so it runs at the same mixture at all rpms. I knew of one T4wd owner who traced it to a device about the size of a baby food jar on the right fender (right behind the coolant over flow tank), it is a black metal can. He could not find a good one so he tried to bypass it. it ran good, smooth, but the fuel economy suffered.

Good luck.
The problem with that is, I am not running any of the factory emissions equipment any longer. I've swapped to a Weber 32/36 carburetor. Unless I am not understanding something, I believe I've removed all of any emissions equipment like that already, so I don't think that's my problem in this case. As for the vacuum lines & routing, I can certainly have a look over my lines and see if they aren't damaged but again, since I am running a Weber setup, I am suspicious about that sort of problem at the moment.
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
BaileySims
Highest Ranking Member
Posts: 626
Joined: Sat Aug 30, 2014 6:52 pm
My tercel:: 1983 Tercel SR5 4WD
Location: Texas
Contact:

Re: Drivability mystery problem

Post by BaileySims »

I can't quite recall what exactly happened to my car when it started acting up, but I had a Weber setup as well. On the back of the Weber, there is a little adjustment bolt/screw for the secondary throttle plate. That became loose on my setup and I remember it not running correctly. Might be worth a look.
WAGON MAFIA.
Blood, sweat and beers.
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Drivability mystery problem

Post by eightyfive4WD »

BaileySims wrote: Fri Jan 21, 2022 2:00 pm I can't quite recall what exactly happened to my car when it started acting up, but I had a Weber setup as well. On the back of the Weber, there is a little adjustment bolt/screw for the secondary throttle plate. That became loose on my setup and I remember it not running correctly. Might be worth a look.
Thanks, I'll have to take a look at that as well. Anything's possible - I'm really stumped because I've been through everything just recently. It's even got a brand new fuel pump now, and the popcorn-style backfiring is much worse now than previously. The new fuel pump made no difference in the engine idle, and the erratic acceleration behavior is too bad for me to realistically drive the Tercel further than down the street until I figure out what's going on.
Another idea I have is to check ignition timing. Could possibly be off, I've never checked timing before but I have recently purchased a timing gun. What better time to learn than now?
From what I've read in the FSM, lots of my symptomatic abnormalities can be attributed to improper ignition timing (dieseling on shut-off on occasion, rough and erratic idle at times, sputtering/backfiring through the carb, etc.)
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Drivability mystery problem

Post by eightyfive4WD »

BaileySims wrote: Fri Jan 21, 2022 2:00 pm I can't quite recall what exactly happened to my car when it started acting up, but I had a Weber setup as well. On the back of the Weber, there is a little adjustment bolt/screw for the secondary throttle plate. That became loose on my setup and I remember it not running correctly. Might be worth a look.
Okay, it's been quite a while since I've messed with anything on the car. It started right up today while it was idling, I took a look at the back of my Weber, and jiggled the throttle plate shafts, didn't feel any looseness or anything unusual there.

I've still got a backfire through the carb. It will sputter if I quickly apply throttle when idling in park, and under medium acceleration when driving. Hesitation & carb backfiring is something that I've read can be due to a lean carb mixture. Maybe there's a possibility that I just never quite got the carb tuned right before, and it's off enough now to cause these issues?

I’m not really convinced of this being a fuel mixture problem. I’ve been getting ~24.5 avg. MPG. Not terrible for a 3 speed automatic, with roof bars and no emissions & Weber carb. Up until this popcorning thing started happening, haha.

Still haven't adjusted my timing like I mentioned, so I guess there's the possibility the timing still isn't quite right. Those are about the only two things I can think of right now.
Last edited by eightyfive4WD on Tue Feb 08, 2022 11:07 pm, edited 2 times in total.
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Drivability mystery problem

Post by eightyfive4WD »

While I was letting the car idle, I blipped the throttle to see if it would backfire like it did before, and I noticed a couple times the idle would shoot up after backfiring. This makes me think that for some reason my electric choke may not be operating properly? I guess I'll confirm that my power wire is making good contact on the Weber and also on the green plug in the engine bay. Definitely not trying to shotgun parts here, I just feel like I'm grasping at straws with this now.
Last edited by eightyfive4WD on Wed Feb 09, 2022 12:18 am, edited 1 time in total.
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
NWMO
Highest Ranking Member
Posts: 1615
Joined: Wed May 20, 2015 1:08 pm

Re: Drivability mystery problem

Post by NWMO »

eightyfive,

I'm not a Weber guy, little to no experience with them. However, regardless of what carb you are tuning/trouble shooting, I would suggest getting the timing set properly before proceeding. Factory spec is 5 degrees BTDC, most of us are running 10-15 degrees BTDC and prefer.

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
rer233
Highest Ranking Member
Posts: 1013
Joined: Sat Jan 01, 2011 1:49 pm
My tercel:: Multiple

Re: Drivability mystery problem

Post by rer233 »

Couldn't agree more...
if it aint there, there's a good chance it won't break!
83 SR5 Silver/Blue (Snowmobile/work beater)-totaled but drivable
85 SR5 Blue
88 SR5 White (the 'good' one)-not anymore-totaled
87 fwd silver wagon a/t
87 4wd dx Cream (a/t- not anymore- now m/t)
User avatar
eightyfive4WD
Advanced Member
Posts: 85
Joined: Mon Jan 25, 2021 9:59 pm
My tercel:: 1985 Tercel 4WD 5 speed wagon
Location: Arizona

Re: Drivability mystery problem

Post by eightyfive4WD »

NWMO & rer233,

Thank you both for chiming in. To touch on my previous comments, I confirmed there's no funny business with the electric choke. The power wire is making sound contact on both ends. Fuel pressure appears good with the new fuel pump still, although I have not tossed the OEM fuel pump as I'd like to do a little cleaning and test it further before I decide to toss it. I did see very little fuel pressure at my gauge before I removed the factory pump, but I'm still not sure I want to trust my gauge over the OEM part just yet. I won't toss the old pump until I'm positive it's bad.

I agree that checking for proper timing is certainly a good starting point, before I tear into anything further at this point. Will have to start familiarizing myself with my timing gun. Is there anything unusual about setting timing on the Tercel specifically I should be aware of?

Thanks,
Erik
1985 Toyota Tercel DLX 4WD 5 spd wagon (manual swapped, daily driver)
2007 Toyota Tacoma TRD 4WD access cab long bed (road trip/adventure-mobile)
User avatar
NWMO
Highest Ranking Member
Posts: 1615
Joined: Wed May 20, 2015 1:08 pm

Re: Drivability mystery problem

Post by NWMO »

From the Service Manual,

Your timing light should have a positive and negative clamp to receive power from the battery and a single “clamp” that gets placed around the #1 (front on our cars) plug wire.
You do not have the required permissions to view the files attached to this post.
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
Post Reply