Shifting questions

[DRoc81]

Hi all, coming to you from the USA,

My son purchased a 93 Skyline GTS25 NA.  I will be honest..... it's slow..... it seems to have decent top end, but there's no punch when flooring the gas pedal.  Also, I have noticed that I can't really feel the transmission shifting while driving it, and I don't feel a definitive downshift when punching it while driving at speeds.  Is this a normal thing?  What are the normal characteristics of this transmission?

 

My sons question: How can I make it faster?

 

Thanks all.

[r32-25t]

Sell it and buy a turbo version will make it a lot faster 

[GTSBoy]

The NA 2.5 has very little torque. You won't feel much.

Those trannies are also a million years old now and it could well be f**ked. First generation electronically controlled autos will often refuse to kick down, ete, etc, depending on what's wrong with them.

[DRoc81]

5 hours ago, r32-25t said:

Sell it and buy a turbo version will make it a lot faster 

Well thats probably not gonna happen right away. LOL

[DRoc81]

4 hours ago, GTSBoy said:

The NA 2.5 has very little torque. You won't feel much.

Those trannies are also a million years old now and it could well be f**ked. First generation electronically controlled autos will often refuse to kick down, ete, etc, depending on what's wrong with them.

Gotcha, I mean that is at least good to hear. Are there signs, or troubleshooting tips to make sure the transmission is operating properly?

[GTSBoy]

Perhaps just get a proper mechanic who is good with Nissan autos (they were more or less the same across all the RWD, FWD, 4WD cars at that time, even if they were actually different boxes) to give it a good going over. He might be able to plug in a Consult or other scan tool and find out if it's got some fault codes.

Otherwise, my approach to the problem if not liking the way the auto was workign behind my RB20 turbo, was to drop it on the workshop floor and put in the manual box that it really needed. That solved all the auto problems.

[joshuaho96]

8 hours ago, DRoc81 said:

Gotcha, I mean that is at least good to hear. Are there signs, or troubleshooting tips to make sure the transmission is operating properly?

Verify it's going into each of the 4 gears in normal acceleration, make sure the torque converter locks up over ~65-70 kph or so at low throttle opening. If you ease into the throttle at those speeds eventually you should get a "gear" between 3rd unlocked and 4th locked. It should downshift eventually if you floor it at 65 kph too. Get some Matic D ATF and drain the pan, check for signs of sadness in fluid and drain plug magnet. Top off to the correct level afterwards. If the transmission is worth saving you can drop the pan on a second drain and change the filter while you're at it.

These are not complicated transmissions, at least compared to modern stuff.

[dbm7]

From the OP's description, sounds to me like the TCU is in 'limp home' mode --- that is, no actuation power to shift solenoids, and the EPC valve is shut (full line pressure). This effectively sticks the box in 3rd gear, with as much line pressure as possible, to try hold the high clutch clamped shut....and so you get woeful acceleration and don't feel any shifts (because they're not happening).

If you don't have Consult or some other scanner to interrogate the TCU itself, you can test with a multimeter to see if it's in limp home mode....ie; stick it in D with engine at idle (hold vehicle with hand/foot brake), and measure the voltage at the TCU feeding shift solenoids A & B -- both should be ON (battery voltage). If they are energized at the TCU, you can unplug the harness from the TCU, and check resistance down through the wiring to the solenoids themselves -- you should see about 20ohms on each coil --- if you do, you can presume the wiring to shift solenoids is OK -- if both measure open circuit, you have to check intermediate connectors in the loom down to the gearbox (and the gearbox connector itself), and check the shift solenoid resistance at the gearbox connector itself --- if the shift solenoids test open circuit here, problem is in the box (ether the solenoids or wiring to them is bad).

If you get no voltage at TCU connector for the shift solenoids (and the solenoids/wiring test OK), check powers/grounds to the TCU itself --- if they're ok, it suggests the TCU is the culprit (and you'd need to interrogate it if possible, to find out why it's behaving badly)... 

[Dose Pipe Sutututu]

Could put in a ZF8HP, the short gearing would make it more tolerable until a a 500kW motor package goes in. 

[DRoc81]

8 hours ago, dbm7 said:

From the OP's description, sounds to me like the TCU is in 'limp home' mode --- that is, no actuation power to shift solenoids, and the EPC valve is shut (full line pressure). This effectively sticks the box in 3rd gear, with as much line pressure as possible, to try hold the high clutch clamped shut....and so you get woeful acceleration and don't feel any shifts (because they're not happening).

If you don't have Consult or some other scanner to interrogate the TCU itself, you can test with a multimeter to see if it's in limp home mode....ie; stick it in D with engine at idle (hold vehicle with hand/foot brake), and measure the voltage at the TCU feeding shift solenoids A & B -- both should be ON (battery voltage). If they are energized at the TCU, you can unplug the harness from the TCU, and check resistance down through the wiring to the solenoids themselves -- you should see about 20ohms on each coil --- if you do, you can presume the wiring to shift solenoids is OK -- if both measure open circuit, you have to check intermediate connectors in the loom down to the gearbox (and the gearbox connector itself), and check the shift solenoid resistance at the gearbox connector itself --- if the shift solenoids test open circuit here, problem is in the box (ether the solenoids or wiring to them is bad).

If you get no voltage at TCU connector for the shift solenoids (and the solenoids/wiring test OK), check powers/grounds to the TCU itself --- if they're ok, it suggests the TCU is the culprit (and you'd need to interrogate it if possible, to find out why it's behaving badly)... 

Thank you, this will keep me busy for a bit.  I will update progression.

[dbm7]

Yeah...I always start at the shift solenoids, because there's only a few reasons these will spook into limp mode, and bad shift solenoids is one ~ the other can be the shift control module (if you have steering wheel shift buttons)...it's easier to eliminate the solenoids first.

[DRoc81]

Are there any indicators that the vehicle is in limp mode?  Any dash light, or something.  Or is it just lack of acceleration?

[joshuaho96]

8 hours ago, DRoc81 said:

Are there any indicators that the vehicle is in limp mode?  Any dash light, or something.  Or is it just lack of acceleration?

 

Power light apparently functions as a transmission error light, you can try the power sequence to read any codes from the transmission control unit.

 

[dbm7]

18 minutes ago, joshuaho96 said:

 

Power light apparently functions as a transmission error light, you can try the power sequence to read any codes from the transmission control unit.

 

Yeah, they're pretty dumb though...ie; they'll throw a solenoid error if the solenoid is dead, shorted, wiring is open circuit, or even if the driver transistor has failed (they can't self-diagnose much, they can only test inputs/outputs)... but if you wanted to try, I believe it's this protocol....(uses a long pulse indicator with short pulse counter)...

 

 

[MBS206]

Put a camera facing your dashboard so you can film the gauges.

Head out to a straight but of road, and filming it as you go from a stand still at wide open throttle to as fast as you can/feel comfortable doing.

Then film the dash board as you for example accelerate like normal onto a freeway.

This will give us an indicator from Speedo of your expectation of slow, and will give us the rpm reading too to see if it's shifting. (Auto still has tacho from memory)

[DRoc81]

14 hours ago, dbm7 said:

Yeah, they're pretty dumb though...ie; they'll throw a solenoid error if the solenoid is dead, shorted, wiring is open circuit, or even if the driver transistor has failed (they can't self-diagnose much, they can only test inputs/outputs)... but if you wanted to try, I believe it's this protocol....(uses a long pulse indicator with short pulse counter)...

 

 

This was a huge help.  We followed the steps,  although shifting into 2nd was actually into 3rd for us,  and 1st was into 2nd ( steps 9 and 11) .  The long flash was the 4th flash.  So shift solenoid A is possibly the culprit.  Is this inside the transmission itself? Or is it accessible by just front the pan? Or is it bolted to the outside of the transmission? 

Thanos for your help everyone

[dbm7]

If shift solenoid A is bad, that explains limp mode --- now you're in the same position as I mentioned previously, in that the next step is to confirm loom/wiring integrity from TCU to gearbox connector with a multimeter (the TCU cannot detect a broken wire, which can happen ..ie; rodent damage, loom rubbed through)...and then finally measure resistance (at the gearbox connector) for shift solenoid A ...

...once you confirm shift solenoid A is bad (open circuit, really low or greater than 40ohm resistance), then it's a job ; you have buy a complete solenoid set, get under the car and drop transmission oil pan, and remove valvebody assembly (the solenoids sit on top), replace solenoid set, and reassemble....it's not exactly a fun task, but readily doable.

[dbm7]

...gearbox connector...

CD06 -- solenoid A

 

[dbm7]

...oops. forgot the TCU end...

[dbm7]

...just a note of warning, you shouldn't drive it about with the TCU in limp mode with only 3rd gear available ~ apart from the fact you end up sheering the ATF at the torque converter interface, the high clutch in these isn't especially the strongest, particularly bolted to the RB25DE mill...which is likely a 4AX01 box with lighter duty high clutch (the RB25DET got the bigger high clutch)...be careful out there...