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Converter Lockup problem ?

evariste

Active member
Joined
Jul 20, 2002
Messages
40
Location
Paris, Ile de France, France
Corvette
1981 Silver & Dark Blue
Since last week, I have no more speedometer, because the cruise control regulator is out.

I have noticed that speed changes are smoother at high revolving ranges (while overpassing for instance). Before it, the motor stayed one second at about 5000 t/mn in the second gear, maintaining the speed desperatly constant, and suddenly, the tranny selected the third gear and it was like a booster light on.

I think that the ECM gets its speed information from the speedo, and drives the converter lockup. I intend to put a new regulator when I receive it, but I would like to keep the smooth and efficient speed changes and save gas with the lockup converter...

I believe that something was going wrong, but what ? Throttle position sensor ? Wich way should I search ?
Does anybody know the logic of the ECM for the converter lockup ?

Evariste
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
lock up

I am having problems with my lockup too, it goes on to early and stays on and I cannot get it off without going wide open... If anyone has any information on this, it would be greatly appreciated... I was reading something about the detent switch? Just a thought, thanks again for any help.

-Tatortot
 

Nut

Well-known member
Joined
Oct 15, 2000
Messages
890
Location
Bowie, MD
Corvette
Vette-less for now
Guys..... I put in a manual override switch that locks in/out the TCC. I tapped into the disconnect circuit at the brake pedal switch. I used a 12V lighted switch that just happened to fit perfeectly into the rear window defogger switch opening (which I don't use). Switch on (light comes on) TCC is locked on. It will not jump out for any reason. I can downshift to second gear (I have a TH350 tranny) and the TCC stays locked on. Switch off..... TCC is off. It is a sweet set up and took me only a couple hours to set up. I'll have to dig around and see if I can find the schematic diagram that I used to tie it in. I hooked this up years ago and have never had a problem.

........... Nut
 

Stingray6974

Well-known member
Joined
Oct 12, 2000
Messages
494
Location
Garland,Texas
Evariste,
The ECM recieves info from the VSS(vehicle speed sensor) on the back of the speedometer. Without the speedo working the ECM is not recieving a signal. You should have a code 24 set.

Tatortot,
The ECM recieves info from the Map sensor and the TCC vac switch to engage the lock-up. It should not engage below 45 mph and should disengage when accelerating, deaccelerating or touching the brake pedal. The TCC soleniod has an internal diode which usually fails causing erratic and early lockup.

Mike
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
lockup

Stingray6974,

So this could all be the cause of the not being able to upshift unless wide open throttle? It wont leave the current gear im in unless I floor it... Thanks for any help you can give me.

-Tatortot
 

Stingray6974

Well-known member
Joined
Oct 12, 2000
Messages
494
Location
Garland,Texas
Tatortot,
No, the ecm only controls converter lock-up, not normal shifting. Normal shifts are determined by the vac modulator and the detent(throttle pressure)cable with the govenor acting as a referee between the two. The govenor can override the modulator and detent or can prevent any shifting.
I'm assuming you have a 350C trans. You're saying it won't shift at all unless you floor it. Please explain in a little more detail.
With it in drive, will it 1 - 2 shift normally or do you have to hit hi rpm's? What about 2 -3? If it won't 1 -2 shift what happens when you let off the gas? Does it feel like it's still in gear or feel like it went to neutral?

Mike
 

evariste

Active member
Joined
Jul 20, 2002
Messages
40
Location
Paris, Ile de France, France
Corvette
1981 Silver & Dark Blue
Stingray6974 said:
Evariste,
The ECM recieves info from the VSS(vehicle speed sensor) on the back of the speedometer. Without the speedo working the ECM is not recieving a signal. You should have a code 24 set.
Mike
Exact. I checked the codes, and I sure have a 24 code.
Before this speedo cable failure, speeds were'nt passing normally. For instance, at wide open throttle, the 2nd gear could stay engaged although the motor went up to 5000 rpm. After about one second, it passed in 3rd, giving a violent push.
Since there is no more speed information, the transmission behavior is much more friendly. It seems it is because the ECM doesn't know my speed, and doesn't energize the Converter Lockup Relay.
Today, I opened the carburetor. The throttle position sensor itself seems to work perfectly : if I push on it with a screwdriver, it gives a "full throttle information", but if I push the throttle itself, it will tell 3/4 open. It looks like the plunger was too short. It is green and not adjustable.

Evariste
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
th-350

Stingray6974,

Yes I have the th-350. What happens is it seems to prematurely go into gear under any acceleration, it also seems to shift rougher. and when in second gear, accelerating normally, at about 35 mph or 2600 rpm the lockup seems to go on (mechanic verified it) and loses about 300 rpm. It is also very hard to leave the current gear I am in, for example, cruising at 35 mph.. I have to depress the accerlerator pedal to almost wide open to get it to shift back to second, and when in second at very low speeds it will not shift to first at all unless I completely stop or floor the pedal. Ive had to resort to manually shifting gears at times. The lockup doesnt not seem to imediatly come off anymore. At wide open throttle, when it shifts to second gear at around 50mph it seems to sort of stall for a second, then pick up power, it never used to do this. Also, my fuel gauge started reading a quarter of a tank more then it should at this same time all this started happening.. could it all be relatated? (just a thought) Thanks for any help you can give me.

-Tatortot
 

Stingray6974

Well-known member
Joined
Oct 12, 2000
Messages
494
Location
Garland,Texas
evariste,
You need to find out what the TPS voltage is. Normal voltage at idle is .5 to 1. volt. At wide open it's 4.3 to 4.5. The TPS is adjustable but not by the green plunger.

tatortot,
It sounds like you have a shorted TCC solenoid inside the trans. On the trans left side just above the pan is a 4 wire connector. Unplug it and test drive the car to see if this solves the problem. As for the gas gauge.....????.

evariste,
Try unplugging yours also after you get the speedo working. It sounds like you may have a bad solenoid also.

Mike
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
lock up

Stingray6974,

Thanks for the help, Ill disconnect it as soon as I can, thanks for bearing with me on my lack of mechanical knowledge. Thanks again.

-Tatortot
 

evariste

Active member
Joined
Jul 20, 2002
Messages
40
Location
Paris, Ile de France, France
Corvette
1981 Silver & Dark Blue
Stingray6974 said:
evariste,
You need to find out what the TPS voltage is. Normal voltage at idle is .5 to 1. volt. At wide open it's 4.3 to 4.5. The TPS is adjustable but not by the green plunger.

Stingray6974,
I I could'nt measure the voltage, but I measured the impedance.
The TPS is a 20KOhms potentiometer.
When I push the plunger with a screwdriver, the remaining impedance is 3KOhms, that would give a 4,25 V Voltage.
When I open wide the throttle, the remaining impedance is 7KOhms, that would give a 3,25V Voltage... The ECM would think the throttle is only 65% open !

I looked around the pump lever, but I could'nt find any TPS adjusting screw...

Evariste
 

Stingray6974

Well-known member
Joined
Oct 12, 2000
Messages
494
Location
Garland,Texas
The TPS adjustment is on the left side of the carb just behind the accelerator pump lever. It has an aluminum plug covering it. The plug must be removed and adjusted with a "double d" tool. This adjustment is for closed throttle only. If you have .5 to 1. volt at idle but won't go above 4. at wide open then you have a bad TPS or a weak spring under the TPS. An open or shorted TPS will set code 21.
Mike
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
problem

Well I disconnected the tcc solenoid connector today and it didnt help.. still shifted wrong, I just got a check engine light on, thats all.. It seems to be okay for the first 1 or 2 accelerations, but then all of a sudden, its like it has a 3rd and a half gear... and the mechanic says its the lockup.. any other suggestions?

-Tatortot
 

Stingray6974

Well-known member
Joined
Oct 12, 2000
Messages
494
Location
Garland,Texas
Tatortot,
The next step will be to replace the TCC solenoid. There is always the possibility that you have a bad torque converter.

Mike
 

evariste

Active member
Joined
Jul 20, 2002
Messages
40
Location
Paris, Ile de France, France
Corvette
1981 Silver & Dark Blue
Stingray6974 said:
The TPS adjustment is on the left side of the carb just behind the accelerator pump lever. It has an aluminum plug covering it. The plug must be removed and adjusted with a "double d" tool. This adjustment is for closed throttle only. If you have .5 to 1. volt at idle but won't go above 4. at wide open then you have a bad TPS or a weak spring under the TPS. An open or shorted TPS will set code 21.
Mike

Thank you for your help.
I have no 21 code.
I think my carburetor needs to be opened or replaced.
Is it easy, or should I give this job to a specialist ?
If I can do it, what should I order (rebuild kit, TPS, ...) and where can I find this "double D" tool ?

Evariste
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
lockup

Stingray6974,

When I dissconnected the solenoid nothing changed, was this suppose to happen? Does it still need to be replaced even though it did the same thing when it was connected? Also, is there anyway to test if my torque converter is broken short of just replacing it? Thanks for any help you can give me.

-Tatortot
 

Stingray6974

Well-known member
Joined
Oct 12, 2000
Messages
494
Location
Garland,Texas
Tatortot,
The TCC solenoid is just an electric checkvalve to open or close one passage. It uses full-time 12 volts and is ground activated by the ECM. Sometimes it grounds itself and applies the TCC. By unplugging it we have eliminated that possibility. The valve itself can also fail causing lock-up. Only way to confirm this is to replace the TCC solenoid.
Converter diagnosis: when all else fails...replace the converter.

Mike
 

Stingray6974

Well-known member
Joined
Oct 12, 2000
Messages
494
Location
Garland,Texas
Evariste,
I don't know what to tell you about rebuilding it yourself. These are not simple carbs(as compared to the pre 80 quadrajets) to work on. If you were in the U.S. I'd say ship it to me and I'll fix it but I think the shipping would be expensive from France.
Basic parts you need are: TPS, carb kit, float, and fuel filter. Additionally you may need:choke pull-off,mixture control solenoid, and/or choke coil.
There are four different double d tools needed to rebuild one of these carbs. You will also need a scanner or analog dwell meter to set the mixture.
Does anyone over there have any experience with these carbs? I know less then a dozen people over here that are capable of rebuilding one. And forget about buying a rebuilt one. Rare81 (Bud) has seen that nightmare not to mention the price.
I don't recommend doing this yourself unless you have had lots of Quadrajet experience. Sorry for the bad news, I just don't have a good solution.

Mike
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
torque converter replacement

Thanks for the diagnosis Mike... Do you know of any major corvette parts places I can order a tcc soleniod from? I could not find one on Mid America Corvette parts. Also, I could not find the tcc selonoid in my haynes repair manual, is there anything major I need to know about replacement before I TRY to tackle this job? Any tips or outlines you can give me? If this doesnt work I guess I have to take it into a transmission shop to replace the torque converter, I hope I can find one that will know how to work on my vette and take good care of it. Thanks again for all your help.

-Tatortot
 

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