The gearbox has developed an interesting issue over the last few weeks.

 

If I drive conservatively the gear change is as per normal but if I give it some beans it doesn't change gear unless i lift the throttle a bit and it changes OK. Most of the time this is when going from a standstill but one when going along and had to escape a numpty from crashing into the back of me as they weren't paying attention.

 

I have had the gearbox fluid replaced and the gear changes are a lot better but this problem persists.

 

For some reason my Datascan will not connect to do a diagnostic.

 

Is this something simple like TPS or kick down switch?

Take a look here >>

 

https://www.300zx.co.uk/forums/showthread.php?175920-Pesky-targa-drains-and-electrical-issues&highlight=auto+gearbox

 

Jeff

Thanks Jeff

 

I had taken the kick plate off to check for water but was all dry. I didn't look at the connectors at the side though. Will try and take a look tomorrow and see .

Checked the connectors etc around the footwell and all clean and dry, pins look like new.

 

Checked the TPS plug and that was a bit green so cleaned that up.

 

Took it for a run and still not changing from 1st when i give it beans but if I lift slightly it changes and is OK for the other gears.

Too bad the diagnostic isn't running for you.

 

You can get a couple of dressmaker pins and push them into the back of the TPS plug, follow the wire, you want to make contact with the internal crimp or back of the contacts

 

Then use a multimeter/volts and adjust the TPS voltage while the engine is in PARK / idle.

 

I have found that lower value allows changes a bit easier.

it could be a number of things but from my personal auto headaches ive had in the past 12 years i think the auto ecu is the weak link in the whole system. my z has had probably the exact same issue as you describe not wanting to shift from 1st into second gear and ive even gone up to the rev limiter at low speed and the auto just wont shift. i found info last year pointing to the auto ecu failing and needing resoldering so i decided to swap out my na auto ecu to a tt one and since the the shifts are back to normal. i still want to service the auto with new fluid soon but i think the auto ecu may need servicing to help fix your issue.

Spent all day working on the Zed, trying sort out this issue...

 

Replaced the ATCU (Thanks JaiKai for the replacement) Didn't solve problem but did allow me to do the Auto Box diagnostics it flashed up error 3 - Throttle Sensor Circuit Short Circuited or Disconnected.

 

Checked the TPS voltage a little high but within specs so adjusted a little lower, just in case.

 

Checked the voltage across pins 34 and 35 on the ATCU and was a little low about .3v rising when the throttle was pressed.

 

Still doing the same running at 3.5k rpm at 70ish mph and still wont change when given the beans...

 

ideas ??

Working on the Zed again and realised i hadn't reset the ECU's so disconnected battery and left for half an hour. Took car for a run and changed from 1st to 2nd without giving it beans but cruised at 70mph at 3.5k revs, is this normal ? Still felt like it wanted to race all the time..

 

Got home and ran the AT diagnostics and came back with no errors.

 

I then got the meter out to check the TPS again and noticed that with ignition on but not turning the engine over, voltages all correct (0.42v rising when throttle pressed) but as soon as i gave any throttle there was a buzzing from the back of the engine...

 

Is there an electronic solonoid on the gearbox that may be on its way out ?

Mmm... 1st and second are mechanically operated gears with the electronics taking over for the rest, which is why so many autoboxes with faults will still change 1st to 2nd.

 

The buzzing is not to do with the box but another issue at with the aiv solenoids when the closed throttle switch opens.

 

You really need to go to the next level of testing now as your box does not seem to be going into third gear.

 

Now this will need a Conzult, lap top and an assistant, basically set up the ConZult, select the auto box screen, with the engine running you will see line pressure ( around 30 psi )and gear, don`t worry if it showing 1st gear when your stationary that us default if in drive.

 

 

Go through the gear selection with your foot on the brake pedal, check to see the gear indication also changes on the lap top, then in drive again with foot on the brake pedal apply some accelerator, see if the line pressure raises.

 

 

Then with an assistant manning the lap top go for a drive and allow the box and electronics to do its thing, the assistant can watch the lap top for gear changes, if it is showing gear changes into third and overdrive that suggests the electronics is trying to command the box to change, if the box is still stuck in lower gears then its a mechanical fault in the box. That said the wiring loom from the inner wing to the box should be checked, seen a few touch down on the exhaust and melt through.

 

 

The above can be done without an assistant, by raising the wheels off the floor, but a lot of care is needed and sometimes is less accurate as there is no load on the drive train.

 

 

Jeff

Edited January 27, 20196 yr by JeffTT