R34 RB25DE to DET conversion

[Scottyp]

Hey all

new to the forum, just wanted to see if anyone had had a similar issue when doing this conversion, i have put an RB25DET into an R34 GT,  it was a complete motor loom and computer.. only thing thats the same is the car itself..completed it last september, car runs drives fine no issues with boost or any driveability issues however i have lost my speedo and odometer. Everything else on the cluster works fuel, temp, oil pressure etc but no speedo or Kms

 

has anyone got any insight on this?

i have been using a temporary GPS speedometer in the mean time but i would really like to get the original speedo working again 

Appreciate any help i can get! 

Cheers

 

[Rusty Nuts]

Is it auto or manual ????

[Scottyp]

Sorry probably should of mentioned that

 

its factory manual has RB20 box in it 

[Rusty Nuts]

check your speed sensor plug is CLEAN and tight and check the body loom wiring for cuts or crushing. The raw signal from the speed sensor is modified by the cluster to run the speedo and odometer. Good luck electrical gremlins are PITA

[Scottyp]

Yeah had the loom out and checked it, all looks okay put it back in and ran it back through the car and all seems fine. Sensor seems fine. All clean inside pins are all straight sprayed electrical cleaner and all seems well there... 

I envy good auto elecs  

mechanic by trade but this stuff just baffles me! 

[Rusty Nuts]

2 hours ago, Scottyp said:

I envy good auto elecs

Special animals auto elecs, but the designers of some auto elec systems need a booting and rooting.

[DatsunBanana]

Someone else had a similar problem here though no solution was ever posted ...

http://www.skylineowners.com/forum/21-tuning-technical-questions/144927-help-r34-speedo-not-working-after-rb25det-neo-conversion.html

Bit of a different situation than yours but I've bolted a turbo and supporting mods on to my auto GT and now running a GTT manual ecu in there. Speedo works fine. I don't know why yours doesn't after swapping the whole engine.

[Scottyp]

Thats the strangest thing

the only thing existing is the Chasis 

everything else supports the motor

has had me stumped for months

[GTSBoy]

Might have broken the drive gear on the sender.

Electrically, the sender sends a +/-1V AC/sawtooth signal out - exactly what you'd expect from a rotating coil/magnet arrangement.  The dash works with that signal.  The dash converts it to a 0-5V square wave signal for the ECU.  There's nothing that could have happened from changing the ECU (because it's at the tail end of the signal chain) that could have caused the speedo to stop working.  The only possibility is that you damaged the wiring from the speed sensor up to the speedo, but you say that you've checked it and it's OK.  We have to trust you on that.

But there's a couple of other points to suggest/query.  The RB25DET gearbox's speed sender is on the gearbox.  I thought that the R34 N/A manuals had the speed sender on the diff nose.  In which case....if you've been looking at wiring plugs on the gearbox, you may have been looking at the neutral or reverse switch and not the speed sender.  Perhaps worth another look and a rethink.  The speed sender is down low on the RHS, towards the rear end of the box.  The other two elect connectors on that side of the box are the neutral and reverse switches.

If you do not have a working speedo, then there a number of ECU functions that will not work properly.  You really need the speed signal to the ECU or it won't run things completely properly.  Things like having the idle sit higher when the vehicle is rolling with clutch in or in neutral won't happen without it.

And lastly, drive it gently.  Those skinny little RB20 gearboxes do not last very long if you give them RB25 torque.  I killed 2 of them just with a boosted RB20.  Wore out the input shaft bearings.

[Scottyp]

Thanks heaps for the information ! Appreciate it

I might have another look today and double check. I do recall a small plug on the diff,  but maybe i am looking at the incorrect sensor on the box. There are a few sensors on the loom in the engine bay that dont match up to anything but im sure they are unrelated to the speedo as nothing runs into the engine bay for the speedo function. And ABS has nothing to do with the Speedo on these do they? I mean im sure the ABS is all plugged in as it was before. But that doesnt seem like my issue

sounds like a cluster or speed sensor problem

its still on standard boost and i drive it like a baby. Box still feels great! 

again appreciate the help! Probably the most help i have had with the issue. I was willing to pay someone to fix it as im terrible at electrical faults but i cant seem to find anyone in Melbourne that can pin point the issue 

i will have another look underneath this afternoon and give that another go

 

Cheers! 

 

Edited May 10, 2018 by Scottyp

[Scottyp]

So i have had another look underneath and found the second plug you are talking about

i was looking at the first one closest to the engine... 

further back i noticed the second one with a green dust cover over it unplugged it and gave it a clean, re connected it and the only thing i can find with it, is the sensor doesnt click in i can just pull it out theres no release tab for it? However it still seems to plug in fine

just thinking back to what you’re saying about the dash, is it worth trying another cluster? Or even another loom? Maybe its something so simple ? Is it possible the clocks on the back in the cluster have gone? and how about ABS side of things? Like i said The loom seems okay no crushing or cuts breaks etc but if there was a short somewhere?

I get motivated to fix it and then give up to easily  and then try again and repeat haha. And this has been going on since september 2016.. ( i was wrong on my time since the conversion)

Would be a great accomplishment to find the problem after all this time but i dont think my skill level is enough. Yet not many places out there that could do it either.. 

 

 

 

Edited May 11, 2018 by Scottyp

[GTSBoy]

If you get a wiring diagram for the R34, you will find the wire identification for the connection from sensor to the dash.  Pull the dash out and continuity check each wire of the pair from top to bottom.  If that's all good, take the speed sensor out, connect its terminals to an analog multimeter (or better, an oscilloscope) and spin the drive.  See if it makes an AC signal.  Don't try it with a digital multimeter.  Waste of time.

See this photo.  It's an RB20DET box.  Same box as RB25DE.  Small details may be different.  But note the following.  The reverse and neutral switches are 1. towards the front of the box, just behind where the bellhousing starts to swell and 2. at the rear of the box, up high, with the yellow wire visible.  The speedo drive is below that, at the bottom just a bit rearward.  You can see the speedo drive cable cut off to about 3" length and sticking out downward at ~45°.  That same spot is where an electronic drive would be if the gearbox had one.  If you have nothing there, then the speedo sender must be on the diff.

 

 

Edited May 11, 2018 by GTSBoy

[Scottyp]

So i have been trying to study the wiring diagrams,

im thinking of starting from scratch... as i think i have gone in guns blazing and missed vital checks.. so i will start again this week . Obviousy firstly checking the power to the speed sensor itself, and checking for continuity on pin 29 ( Vehicle speed signal ) ? Followed by checking the wires in the back of the cluster.

Could the fault be caused by a malfunctioning ABS System?, or is my ABS system malfunctioning because of the Speedo fault.. One thing i have noticed just today is there is ABS light on the dash when the vehicle does its normal self check, after noticing this i went for a slow drive down and road to see if the ABS was still functional, and the wheels indeed locked up, pedal doesnt pulse at all. So theres no ABS either 

is there an easier way of starting the diagnostic process over again? As i now have to work out if the ABS issue is related

 

 

Edited May 13, 2018 by Scottyp

[Scottyp]

i dont have this module in the photo (E) TCS/ABS module...or any wires under the glove box leading to a module other than the ECU

seems like it is something i should have...

that would explain the no ABS

 

Edited May 13, 2018 by Scottyp

[GTSBoy]

There is no power supply to the speed sensor.  It generates the +/-1V signal when it turns.  Follow my advice ref cont checking the wiring from there to the dash first.

The VSS signal at the ECU is a product of the speed sensor and the speedo working.  No point in looking for that signal until the speedo is working.

The lack of ABS shouldn't affect it.  The ABS uses the speed signal after it is produced.  But does the car even have ABS?  Does it have sensor rings at the front hubs?  Does it have the ABS rig in the engine bay?  The missing ABS modulw would be explained by the car never having it.

[Scottyp]

So basically i need to continuity check the speed input signal from the connector in the back of the cluster, to the speed  sensor on the transmission? If that all checks out then pull the sensor with the green dust cover out in (the photo attached) and check with a multimeter while spinning it? 

Looking in the R34 Manual I cant seem to find a pin number or wire colour for the speed signal input into the cluster connector or any wiring info On the speed sensor on the box? There is a small earth strap looking connector on my Diff nose

is this the signal wire on the diff you were refering to?  

Its likely ABS was never working then ... i do have the module/pump under the bonnet which is all plugged in. But dont seem to have any ABS function 

i honestly cant remember using my brakes enough to trigger ABS when the car was NA, nor can i recall an ABS light in the self test on start up. 

 

 

 

 

[6BANGER]

I have the same issue and been losing hair everytime I take another look into it. I can understand the frustration 

Here is what I have tried so far...

1. Run a wire from the speed sensor in the gearbox to the cluster and ECU

2. tested for continuity between ABS computer and cluster (speed signal wire) - all ok

3. tried a second hand cluster that was working at the time

4. used self diagnostics and got the following codes  (26 - 44 - 46 )