Does anyone know what the computer uses for inputs to control overdrive and the lockup converter?

Reason I ask is I have a 90 ranger with a4ld transmission that doesn't shift properly. If I start off in D then everything works great until I stop then the converter will not unlock until it slows down enough to downshift into second gear (about 15 mph) caushing a shutter. If I start off in OD then every thing works properly under slow acceleration - 2nd gear at < 15mph 3rd gear at 25 and 4th at 30mph, but I still have the same problem with the TCC not unlocking until 2nd gear downshift. Accelerating harder causes the shift points to go up like normal except for the shift to 4th gear. I still wants to shift at 30mph so I get a double shift into 3rd follow immediately by a shift into 4th. It acts like the computer wants to shift into overdrive and unlock the converter at the same speed reguardless of engine load and stay in overdrive and lockup reguardless of engine load. Stomping the accelerator will not cause the tcc to unlock of the trans to shift out of 4th.

I think I read somewhere that the computer uses the speed sensor and the map sensor to determine when to activate the solenoids but I'm not sure. Any help would be greatly appreciated. This thing is driving me nuts. I just put a new motor in and it runs great but I can't drive the thing with the transmission problems. Is it possible that I hooked some vacumn lines up wrong so the computer is getting the wrong input?? I can run a computer diagnostic but I need to know what to look for.

 

When you installed the new engine, did you hookup the kickdown cable properly?

RP
Zach

 

Didn't remove the kickdown cable. On the 90 ranger it goes from the accellerator thtough the firewall to the trans. I thought the kickdown cable on this model was just a kickdown cable and not a tv cable. Am I wrong? If so then I will look into adjusting.

 

Just for a little background info... The shift pattern on this is as follows... 1-2, 2-3, 3-4 (OD) and then after it has shifted into OD, the TC will lockup.

Here is a little info on the operation of this transmission from my Ford Bible...

Operation

The transmission operations, provided by seven operator-selected positions of the selector lever, are as follows:

P, R and N -- same as other Ford automatic transmissions.

(D) (overdrive) -- Normal driving position. Selection of this position provides all automatic shifts including the application and release of the converter clutch. The transmission may also be shifted manually between all forward ranges.

D (drive) -- Selection of this position provides all automatic shifts, including the application and release of the converter clutch, except the shift into overdrive. This position can be used when overdrive is not wanted such as hilly or mountainous terrain or when towing a trailer.

2 (manual second) -- Selection of this position provides only second gear operation regardless of vehicle speed. It is useful for start-up on slippery surfaces or to provide engine braking on downgrades.

1 (manual low) -- Selection of this position at start-up or when selected at lower speeds provides only low (first) gear operation. Selection of this position at higher speeds results in a downshift to second gear. An automatic downshift to low will occur when vehicle speed decreases to approximately 48 km/h (30 mph), depending on axle ratio and tire size. Once in low, the transmission will stay in low until the selector lever is moved to another position.

When operating in the overdrive (D) position, the transmission will automatically shift gears from first to second and from second to third and third to fourth gear overdrive. The shift into overdrive decreases engine rpm by 25 percent and occurs when the vehicle approaches the desired cruising speed and the driver eases up on the accelerator pedal. The converter clutch is applied after the shift into overdrive. The converter clutch and overdrive applications are based on both engine speed and vehicle speed by combined transmission hydraulics and on-board computer electronic controls (EEC-IV). The converter clutch can be applied in third gear in the D position, and in fourth in the (D) position. Because of this feature, the transmission may be sensed as executing as many "shifts" (in the overdrive (D) position) as would a five-speed transmission.

Two functions have been incorporated in the A4LD transmission for times when the driver requires acceleration or more power for negotiating grades or driving into very strong headwinds. They are:

l Disengagement of the converter clutch to achieve added acceleration from the resultant increase in engine speed.

l A part throttle 4-3 (overdrive to direct drive) downshift for further acceleration.

These events can also occur during cruise control operation when more power is required to maintain the selected speed.

While driving at highway speeds, four different engine speeds can be obtained by transmission operation in:

1. Overdrive with the converter clutch engaged (lowest engine speed for best fuel economy).

2. Overdrive with the converter clutch disengaged (slightly higher engine speed for improved acceleration).

3. Third gear (direct drive).

Now if that didn't help you, here is a little information on the description of the trans, and a little bit how the TCC works...

Description

The A4LD is a four-speed automatic overdrive transmission with a lockup torque converter.

The 3-4/4-3 shift functions and converter clutch lock/unlock are controlled by the EEC-IV processor through a 3-4 shift solenoid and a converter clutch solenoid.

The EEC-IV electronically controls the converter clutch solenoid, which hydraulically operates the piston-plate clutch in the torque converter that provides lockup (solid drive) and unlock functions. The electronics also prevent clutch application in engine modes where noise, vibration or harshness concerns would be most evident in a solid-drive transmission. These modes are:

l Tip-in/tip-out

l Application of brakes

l Closed throttle

l Cold engine

l Very heavy/wide open throttle

l Low engine speed to minimize lugging boom

l 23.5 inches of mercury absolute barometric pressure or below in the intake manifold


4. Full throttle in second gear for maximum acceleration.


So as far as the torque converter giving you troubles, either the solenoid for the converter is bad, or it could even be a dirty wiring harness. Let me know if you have any more questions.

 

Oh and another thing, it looks as if it is possible for you to manually control the lockup of the converter. I did it with my 95 F-150, which also has the electronically controlled transmission.

How this system works, is there are several leads (wires) leading to the transmission. When those wires a connected to a ground (by the computer), it will engage them. So if you find the TCC lockup solenoid wire, cut it in two, and hook it to a toggle switch inside your truck, you can control when you want to let the computer lock up the converter. If you also ground out that wire manually, it will lock it up.

 

I understand when the tcc is supposed to engage and unengage and when overdrive is supposed toapply and doesn't. What I don't understand is why the computer that controls the tcc and overdrive solenoids doesn't apply the different input signals it gets as to braking engine load and such to control the trans properly. The solenoids are working because the tcc locks up and unlocks and it goes into overdrive and out but not when it should. Its acting like it's just ignpring the signals. That's why I was wondering what sensor inputs the computer uses to apply and unapply the solenoids so I can check them for proper operation.

 

The TCC and 3-4 and 4-3 shifts are controlled by the computer. They are based on throttle position, engine RPM, vehicle speed, the MAP sensor, and many others that I'm forgetting.

 

Handyman...just a thought. Locking up the torque converter when the vehicle was parked would serve as a good theft preventative I do believe, correct?

So if the shifts are computer controlled...something's up with the tranny or PCM, correct?

RP
Zach

 

Theoretically.... it's possible. It's like having a standard transmission with a broken clutch switch. It would be like trying to start it in gear. So basically, if they didn't have a key, they would have to unlock the converter somehow, break the column to steer, and also rig up a way to pull it out of gear without hitting the brake, if the vehicle is equipped with the switch that doesn't allow it to be pulled out of gear without the brake.