At Holding Gears Too Long, Tps/wiring Problem... Help

[Talej]

Howdy,

I'm having a problem where my stagea is holding on to gears a lot longer than it should, particularly from 2nd gear to 3rd it won't shift up until at least 5500rpm which means I'm basically driving around in 2nd gear a lot of the time.

I'm at the point where I'm running out of ideas, rego is due and I really need some help...

A bit of background

Just before christmas I was pottering along and suddenly snapped a con rod. Found a cheap replacement engine locally and swapped it out with a mate. It's got a piggyback adaptronic ecu in there so I had it retuned and since I got it back from the workshop I've been having the gear changing issues - they say it's nothing they did so I'm on my own.

The gearbox diagnostics is saying there's a TPS fault. I've had it looked at by an auto transmission place and their conclusion was "it's an electrical problem". I have swapped out the TPS with the one from my original engine without any change and have tried taking it to local auto elecs who have been reluctant to even look at it.

My guess is that one of the wires related to the TPS has been damaged somewhere along the line but I'm just not sure how/where to start with diagnosing that. Although the adaptronic ecu still seems to be getting TPS signal correctly so it is likely somewhere between TPS and standard ECU or standard ECU and gearbox???

Does anyone have any suggestions?

Cheers.

[shaund]

Hi,

If your getting no fault codes from the ECU for TPS, but a fault code from gearbox diagnostic, I'd guess that the TPS signal to the gearbox isn't getting there, or is dodgy.

Its possible you've got a damaged wire, plug or socket somewhere along the way. This may have been damaged with the engine failure you've had and easily with the remove/install of the replacement engine. Its easy to stretch/crush wires in a wiring harness when you're hauling the engine in/out.

Without seeing the wiring diagrams/manual, I'd guess that the TPS signal to the gearbox would be used to help figure out when to kickdown, and how long to hold gears under different levels of throttle. In the old days it used to be done with vacuum.

Check the workshop manual for the skyline with the same engine as yours and look for the expected signal from the TPS and measure to confirm. I'd suggest measuring this at the TPS, and at the pin on the ECU to confirm good signal, and then see if you can find where the gearbox computer is, the pinout for it, and then confirm the signal there too.

To measure signal at the ECU, use a fine piece of wire and shove it into the back of the ecu connector, following the wire. If you get lucky you'll make contact with the bare end of the crimp connector. Alternatively, you can use a sewing pin and puncture through the insulation of the wire near the ECU plug and use a crocodile clip on your multimeter to attach. A small dab of a rubbery glue over the pinhole is a good way to re-seal the insulation of the wire if you feel its necessary.

Good luck!

[Talej]

Thanks, that certainly gives me a good place to start - will have to try and track down a wiring diagram for the gearbox side of things. I haven't actually managed to get the ECU diagnostics working yet so that should probably be my first test.