[Mk2] [Turbo] Speedo fail

[dantheman]

I know its quite a common topic but ive searched and read and i still cant work it out.

speedo was working, then i removed the dials, put in a different set (also from rev2 but with a non rev2 speedo). the dials had a clamping delimiter on the back of it. when the engine was started the dials kept fluctuating with the car stationary. it kept doing this with the car moving. i removed the delimiter and that stopped the constant fluctuating, still it fluctuates every now and then when the car is moving and reads 0 the rest of the time. i changed back to the old set of dials both with the new and old speedo's, neither moved when the car did.

clearly the speedo gets power because the clamping delimiter can make the dial fluctuate, and changing dials doesnt do anything.

ive followed the instructions here: http://www.imoc.co.uk/forums/viewtopic. ... edo+sensor

pin1 gets 11.1 volts. resistance of pin 2 was well below 200 ohms

so, whats the likely problem?

[dantheman]

any ideas?

[Rob]

Im having the same issue on my rev2 N/A to Rev3 Turbo conversion.

Swapped speedo sender out - no success.

Swapped clocks out - no success.

[Stef Derner]

The sensor wires can break inside the insulation at the connector for the sensor. Check for 12v pulses on the top left screw of the speedo viewed from behind. Bottom left is 12V, bottom right is ground, top right is 5V pulses to ECU. The sensor is easy to lift out of the gearbox, so you can get someone to spin it while you check for pulses at the speedo. The sensors are common across many models of Toyota so you should find them (and the plugs) in scrapyards. Bear in mind different Toyota models have different drive gears but these can be easily swapped so the gear off your old sensor will fit.

If the wire is broken you can tell by gently but firmly pulling on the individual wires, if one stretches it's broken inside. Change the plug and a short length of the wires. If it's one of my delimiters, you can turn on the test mode by moving the switch to the opposite position and back again with the ingnition on. Next time you turn on the ignition the needle will sweep to 120 then 60 then 0, that will check your speedo. Turn off the test by doing the same thing.

If the speedo bounces all over the place, chances are the screws are loose and the poor connection creates random pulses that the speedo reads as speed pulses.

[dantheman]

ah right, thanks for the info.

it sounds like its one of yours. its a small (~2 inch) square circuit board with a switch from kph to mph and white text that says bits4twos MR2 top on it.

if it is yours i have a few questions for you.

firstly i accidently made it do that test thing. is it always supposed to be 120 then 60? its been 6 weeks since i did this but i seem to recall it did 80, 40, 0. does that mean my dials will not read correctly when i get them working?

also i presume the delimiter is intended to be receiving a kph signal, so it gives the choice of kph->kph or kph>mph. my gearbox has one of those resistance based converters spliced into the gearbox wiring. will this conflict with the delimiter? will running it with the delimiter switched to kph produce a mph reading? or is it just best to remove the converter and rewire it back to stock, then use the delimiter as a converter?

[Stef Derner]

ah right, thanks for the info.

it sounds like its one of yours. its a small (~2 inch) square circuit board with a switch from kph to mph and white text that says bits4twos MR2 top on it.

if it is yours i have a few questions for you.

firstly i accidently made it do that test thing. is it always supposed to be 120 then 60? its been 6 weeks since i did this but i seem to recall it did 80, 40, 0. does that mean my dials will not read correctly when i get them working?

also i presume the delimiter is intended to be receiving a kph signal, so it gives the choice of kph->kph or kph>mph. my gearbox has one of those resistance based converters spliced into the gearbox wiring. will this conflict with the delimiter? will running it with the delimiter switched to kph produce a mph reading? or is it just best to remove the converter and rewire it back to stock, then use the delimiter as a converter?

Yes that's one of mine.
The test mode sends out a frequency equivalent to 120 then 60, it's generated on the board, so your speedo looks to be out.

If a converter is spliced into the gearbox wiring you need to remove it. I wouldn't think it would be resistance based as the system is purely digital.

The result of a converter as well as my delimiter is that you'd be feeding my delimiter with mph pulses, these would be echoed to the ECU, so the limit would be moved to 180 mph and capped there by my delimiter, all the converter does is mess up your power steering. Removing it would be best.

To turn off (or on) the test sweep, toggle the selector switch back and forth with the ignition on, next time you switch on the ignition the change will have been made.

[Shmed]

I think I might have a similar problem, I bought my dials from somene on here as I had the original 110mph ones and trip was reading in kph.

After I fitted it, it always did the sweep test, but I didn't know that was a test mode. Now I get nothing on the speedo when driving, could I have broken the device by having it permanently in test mode?

I've done no investigation work as yet, but it used to work, and I've done nothing in or around the dash recently.

Cheers

[Rogue]

Im having the same issue on my rev2 N/A to Rev3 Turbo conversion.

Swapped speedo sender out - no success.

Swapped clocks out - no success.

That's because you have a wiring issue... Contrary to popular belief, turbo engine swaps are often not plug and play, even if you swap the loom down to the passenger footwell.

To point you in the right direction, the break will be at the point where the passenger loom passes into the cabin. There's a small breakout connector there that will have some of the aircon functions as well as the speedo signals. Look particularly for a brown wire (signal ground from dashboard) and a purple wire with a white stripe (speed signal).

[Rob]

Im having the same issue on my rev2 N/A to Rev3 Turbo conversion.

Swapped speedo sender out - no success.

Swapped clocks out - no success.

That's because you have a wiring issue... Contrary to popular belief, turbo engine swaps are often not plug and play, even if you swap the loom down to the passenger footwell.

To point you in the right direction, the break will be at the point where the passenger loom passes into the cabin. There's a small breakout connector there that will have some of the aircon functions as well as the speedo signals. Look particularly for a brown wire (signal ground from dashboard) and a purple wire with a white stripe (speed signal).

Thanks very much for your input - I appreciate it especially considering you did not do the work so are not obliged to help!

[dantheman]

The sensor wires can break inside the insulation at the connector for the sensor. Check for 12v pulses on the top left screw of the speedo viewed from behind. Bottom left is 12V, bottom right is ground, top right is 5V pulses to ECU. The sensor is easy to lift out of the gearbox, so you can get someone to spin it while you check for pulses at the speedo.

i had a check of this today. removed the sensor and it looked intact. should the cog on the end have longitudinal play in it? i measured the voltages at the speedo. here are the results:

with no sensor connected:
8.6V, 4.7V
10.3V, 0.05V

with sensor connected
9.5, 4.7
10.5, 0.05

readings were the same when the sensor was being turned by hand too.

so does this mean i need to get a new speedo sensor or is the problem somethwere else?

also if its reading 10.5V for the 12V slot, and the result of measuring my cig lighter was 9.5V not 12V, is that a good indication my battery needs replacing?

[dantheman]

ive now changed the speedo sensor and its made no difference. the random fluctuations seem to have gone but ive only done about 1 mile so far. also ive removed the converter at the gearbox end.

so if its not the sensor, the plug is fine, the wires arent broken, the dials have power, the converter is gone and i dont think ive dont anything to any other wiring, what on earth is causing the problem? i just cant work it out.

[Stef Derner]

When you removed the converter, did you re-connect the speed pulse line to the speedo?

Do you have access to an oscilloscope so you could check the pulses coming into the speedo head?

If your measurements are the voltages at each of the screws then yes, your battery is low, but it might only need charging.

If you measure the top left and rotate the sensor while watching the reading, it should vary from approx 12V to almost zero volts. You can pretty much ignore the top right screw as the 5v comes from the ECU and is grounded by the speedo, but if the speedo doesn't get any pulses it won't give any out. You should get 4 pulses per rev of the sensor. Bottom left is 12v Ign and the bottom right is ground.

If you take a wire from the bottom left and dab it rapidly on the top left the speedo should move. Be careful not to dab it on anything else. If this works then there's definitely a break in the purple and white wire.

Like Rogue says you have an open circuit between the sensor and the speedo.

[dantheman]

the converter had been spliced into the original wiring, so when i removed it i reconnected the loom end of each wire to the clip end with crimped connectors, ie from black/yellow to black/yellow, brown to brown etc.

ill have another look at rotating the sensor. i dont have access to an oscilloscope unfortunately. ill post the results afterwards

thanks for the info.

[dantheman]

If you take a wire from the bottom left and dab it rapidly on the top left the speedo should move. Be careful not to dab it on anything else. If this works then there's definitely a break in the purple and white wire.

did you definitely mean bottom and top left? when i bridged those nothing happened. when i bridged top left and bottom right (ie pulse and ground) the needle fluctuated.

so i tested the theory that the purple wire was broken. i ran a wire from the speedo plug to the purple and silver dotted wire at the speedo, and it made no difference. i still didnt get any pulses when turning the sensor. it just stayed static at about 11 volts.

so is there anything left in the system to check if its not the sensor, the purple wire, probably not the clocks themselves as ive tried with 2 different ones.

am i right in saying the brown wire from the sensor goes to ground and the green and black goes to the power steering via an ECU somewhere? so green and black is not the cause. is it worth chopping the brown wire and running it directly to a ground point?

also when i removed the clocks the first time i noticed that the puple and silver dotted wire, and the purple with white line wire had been cut, with a small amount of extra wiring put in. i recall i wondered why it was there as the wires still ended up in the same place, and i cut out the extra wiring in favour of crimping. could there be any reason why these were cut in the first place, by a previous owner or whatever?

the only other factor i can think of is when i installed a charge cooler i took the live feed from a green and black wire in the smaller clip in the fuse box. there are g/b 2 wires in this clip, one small one with a lighter green highlight, which appears to be the one from the speed sensor. the other is thicker, with a duller green, and its this one i used. i cant find out what this wire is, but would taking a live from it have any affect on the speedo?

[Stef Derner]

The extra wiring was almost certainly put in to replace a previous speed converter.

The brown wire is ground, the purple wire is pulses out to the speedo and the green and black is the ign 12V. The purple wire carries pulses from the sensor to the speedo head, the speedo then grounds the signal from the ECU giving pulses to the ECU which controls the fuel cut at speed limit and also relays on to power steering control. The speed wire is purple with a white or silver stripe. Trace the wire from the speedo top left screw via the sixth connector from the left on the middle plug, it should be purple with a stripe not dots.

Run your test wire from the purple at the sensor directly to the top left screw on the speedo, use a ring crimp under the screw head.

Get rid of the inline crimps and solder the ends together, insulate with heat shrink sleeving, crimps are notoriously bad connections.