Ms tacho issues

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Richard P6
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Ms tacho issues

Post by Richard P6 » Sat Oct 14, 2017 12:44 pm

Hi all, I have a P6 with Megasquirt 1 V3, running fuel and ignition on a 4L Rover V8. Most things working now except the tacho. To try and get it working, I contacted a company who sells a device called a 'tachfix.' After conducting a few tests, like attaching the IDM to the tacho, where it made the tacho jump a little when engine turned on, and again when it turned off, nothing when running. I then disconnected the orange wire on the EDIS and brushed it against a ground with the ignition on, and the tacho jumped to 500 - 1,000rpm every time I did it. I then connected the SAW to the tacho and that worked but was reading 100rpm low.

He gave me two options, the one I chose was to send him the ECU and he fitted a tacho output, which connected up to the Tachfix. It arrived back and I connected it up, red to ignition live, black to earth, orange to new tacho output wire and yellow to tacho. Fired the car up, the tacho burst into life but the needle just bounced up and down.

As I have a wire fitted to the ECU as a tacho output, a tachfix, and a Tacho which 1/. Worked with the coil set up, and 2/. a spare Tacho I have does the same and jumps, I can only assume that something is wrong with either the output wire or the tachfix. I was hoping that there is something in Tunerstudio was pointing in the wrong direction and that I could just hit a few keys and get it to work - now there's optimism for you

Is there any way, with the help of a multi meter that I can check the output wire and the tachfix?

I have made up a small electronic board from the manual which takes the feed from the –ve side of the coils. This contained 4 x 1N4004 diodes and an 18V zener diode. This works up to 1,300RPM but above that, the needle just drops to nothing. On advice from a google search I changed the zener to a 1000 ohm resistor - then it didn't work at all. I have been given another type of circuit from a non MS source and will be making one of these up as well.

I would however prefer to use the output from the ECU because it would just be neater, so I tried another type which worked from the installed output wire and consisted of a 1000 ohm resistor, a transistor and an old relay. Nothing, not a sausage

This, along with the fact that the tachfix doesn't work from this wire either, and that the tacho works with coils, does make me suspect the installed wire. I took the top off the ECU and found that the person who added the wire, also added this circuit :-

Seems I can't add pictures :shock:

Any ideas anyone?



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Post by DaveEFI » Sat Oct 14, 2017 3:46 pm

I feel your pain. :D

Mate has an SD1 same as mine with EDIS too. And the diodes circuit worked just fine on his car- but I've heard tales of it not working with other similar tachs.
Because of the complexity of the wiring involved for the diodes, I decide the relay coil voltage booster would be neater. Could be fixed beside the EDIS module with easy access to the existing tach wiring. That worked - but stopped reading above about 4000 rpm...

Because the SD1 has an open frame tach, it's easy to get at the electronics. So I removed them and replaced with a custom rev counter chip - driving the same meter (dial) That gets its feed from IDM on the EDIS8 module.

The relay coil thingie should have worked at least after a fashion, though. Are you sure you used the correct transistor and connections - 2N2222 seem to have more than one set of pinouts, depending on make. And I don't suppose the relay you used had by any chance a diode fitted?
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Richard P6
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Post by Richard P6 » Sat Oct 14, 2017 7:11 pm

I am not an electronics expert by any means, quite a novice in fact, so I checked the circuit many times before and after fitting. I am 100% sure that it is correct. The transistor used in the circuit is a 2N5551 - third one down on here.

http://www.msextra.com/doc/ms2extra/MS2 ... m#tachoout

Forth one down is the one with the diodes, which worked to 1,300rpm.

It's very difficult to explain without pictures, but they are all on here ( I hope I can put a link on to another forum :? )

https://forums.lr4x4.com/topic/101792-tacho-issues/

Is there a way I can check the output of the wire added to the ECU?

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Post by DaveEFI » Sun Oct 15, 2017 8:30 am

The only way to check a pulse properly is with 'scope. But you may get a reading of sorts from a DVM set to AC volts. If you have a posh DVM that also reads frequency, you may get a reading with that too.

You can post pics here - but has be done via a hosting site. Photobucket now want you to pay for this, so I use
https://imgbb.com/signup

I have most test gear here, and will happily check anything you want at no cost other than the return postage.
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Post by Richard P6 » Sun Oct 15, 2017 9:50 am

Cheers for you help Dave, Good ol' photobucket, I'm sending them a basket of fruit 8)

I was advised to make up a small circuit like this -

Image

Which didn't work. So I had a good rummage around in the ECU and found that the person who added the output wire, had added this circuit as well -

Image

Please let me know if I am talking nonsense (I really am a complete novice at electronics and circuit wizardry), but is this part of the circuit that I should have made? i.e. can I just add the relay?

I did make up a circuit (This is my first ever circuit board :D ) which takes the feed from the coils. This worked up to 1,300rpm.

Image

I would rather use the one fed from the ECU as it will keep my wiring a lot neater, but I have found on google, that I can change the zener to a 12V one and it often works, or add a resistor between the diodes and the zener which runs to earth. I will try this, but would appreciate any opinions on the installed output wire.
Last edited by Richard P6 on Sun Oct 15, 2017 10:16 am, edited 1 time in total.

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Post by DaveEFI » Sun Oct 15, 2017 10:16 am

If you want to check that circuit (the one which uses the relay) is working, rig it up to a 12v supply. With no input, you should see 12v on both ends of the coil. If you apply 12v to the input too, you should see 12v and ground across the coil. That will show the transistor is good.
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Post by Richard P6 » Sun Oct 15, 2017 3:37 pm

When I started this morning, I checked the circuit and got 12.6V on the +ve side of relay and 0V on the -ve.

I googled to 2n5551 and managed to convince myself that I had the wrong way round, so built a circuit board with it the other way round.

Now if I put a 12V supply across the circuit, I get 12.6V on the +ve side of the coil (85) and 8.15V at the -ve (86).

If I then put the supply on the added wire from the ECU as well, I get 12.6 +ve and 7.3 at the -ve

Wired onto the car, the relay didn't buzz like it should, the transistor got hot, and nothing on the tacho. With the original and I suspect the correct way round transistor, the relay did not buzz.

I have also made up three more little fixes from my googling, i.e. One with the 4 x 1n4004's with a 12V zener which only worked to 1,200 rpm. One with a 1K resistor between the diodes and the zener running to earth which worked at 1/4 speed (2,400 rpm showed 600 on the tacho), and one with a 1K resistor over one of the diodes, which again worked at 1/4 rate.

Image
Last edited by Richard P6 on Sun Oct 15, 2017 6:35 pm, edited 1 time in total.

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Post by DaveEFI » Sun Oct 15, 2017 5:48 pm

Assuming the relay coil has a resistance of about 80 ohms

That would suggest to me either a faulty transistor or you've mixed up the connections to it.

You can check them here:-

http://www.el-component.com/bipolar-transistors/2n5551

Just in case you're not familiar with transistor connection names, the top one on your diagram is the collector, the bottom one the emitter and the middle the base - sorry if you already know this. :D
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Post by Richard P6 » Sun Oct 15, 2017 6:54 pm

I must stop editing posts when you are answering them :oops:

I used this diagram

Image

I have a spare transistor, so can make up another one tomorrow. Is there any way I can test the transistor before starting, in case I have some from a bad batch?

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Post by Richard P6 » Mon Oct 16, 2017 6:22 pm

I've added a relay and now have this

Image

I took the switching gear out of the relay as it wasn't needed but this meant I couldn't listen to it to check it was working correctly, so I went out and bought a new one.

Started the car and the tacho sat at 750-800 rpm which was right :D but only for a few seconds and then it dropped, then started again, then stopped, and started again, etc.

I got out of the car and listened to the relay, and it buzzed, then stopped etc in line with the tacho, so if it buzzes, the tacho works.

I can only conclude that the signal switching the relay, from the ECU, is not switching it reliably.

I take it from the diagram, that the transistor is like a switch which is turned on and off by JS3 after going through a 1K resistor, and this then allows the current to pass through to earth, thereby firing the relay.

So any ideas why this intermittent feed is happening?

Thanks in advance :)

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Post by DaveEFI » Tue Oct 17, 2017 8:09 am

Firstly, a 2N2222 may not survive the high voltage flyback pulse, hence a 2N5551 being specified for this purpose. If you look at circuits where you use a 2N2222 to drive a relay, it includes a diode across the relay to remove this pulse safely. But of course in this application it's the pulse we actually want.

I'm not that familiar with MS1 as I started off with MS2. But you select the tach output in software. I'd try changing it, saving, then changing back to JS3 and saving again. If it is still intermittent, use a different port?

Also, are you using the latest version of the code? Could just be there is a bug in your version.

If the relay buzzing annoys, you could remove the coil from the relay and just use that on its own. Also takes up less space.
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Post by Richard P6 » Wed Oct 18, 2017 9:07 am

Hi Dave

hmmm... So I can try to remove the 2N222 and replace it with the 2N5551 in the ECU - I am not good enough at soldering to do that :(

Or.. cut both the red and orange wires in the ECU and solder them together, to bypass the circuit in there, and then have a wire direct from the JS3. Then run that through my circuit.

Image

I'll try changing the tacho output over and back - cheers. How do I use a different port (Lost me there :) )

It asks me every now and then to upgrade to the new code, and I always do so I should have the latest.

I have a relay with the switch taken out, I only bought a new one so I could listen to it working for checking purposes :)

I have googled the output system and found that I may have the settings wrong.

Image

I have changed the figures in the boxes from 7, 1, and 0 to 5, 2, and 55, which should apparently start the feed from JS3 at 500rpm, stop it if it gets down to 300rpm and give it a higher limit of 5,500rpm.

This made no difference at all :evil:

After much messing about yesterday, the car stopped and refused to start again. I checked every relay, every joint, every plug and socket, every wire, everything, nothing wrong anywhere. So after scratching my head for a while went and bought some petrol :oops: I know I am getting fed up with this as I am starting to make silly mistakes now :)

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Post by Richard P6 » Thu Oct 19, 2017 8:47 pm

Out with the multi meter - right with this circuit the relay buzzes intermittently. With the engine running, the voltages are +ve side of coil (85)- 14.3V, -ve (86) - jumped from 0.5V to 9V and all points in between. Voltage at JS3 jumped around from 1V to 4.5V.

Image

I disconnected the orange wire, and then connected a patch wire to it, then clipped the other end directly to JS3 with a crocodile clip. This basically bypassed the circuit in the ECU without me having to remove/cut anything :). I then connected this to my circuit board like this

Image

Now, the voltages are (85) - 14.3V, (86) - 5.4V (pretty much constant), JS3 4.5V, base of 2N5551 0.7V, resistor in 4.5V, resistor out 0.7V. All of these voltages are fairly constant.

The tacho does now point in the right general direction but still waves around a fair bit. It's better, but not yet right, and not accurate enough to use. There is not enough voltage to fire the relay, so no buzzing at all. All the above readings are at tickover (750-800rpm).

So, more from intuition than electronic knowledge, I would say there's something amiss within the added circuit in the ECU - although any opinions would be greatly received :)

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Post by DaveEFI » Fri Oct 20, 2017 8:30 am

Adding a second circuit in parallel with the first may not be ideal, as you'll be drawing twice the current from the port. (I've not got figures on how much current the port can deliver)

Measuring the voltages in a circuit where they are actually pulses really needs a 'scope. But you could check your circuit is operating correctly by moving your crock clip to 5v DC. The relay should then make and you should see more like 0.6v on the emitter of the transistor.

Just when you hear the rely buzzing may depend on the actual RPM.

If you get totally stuck, post the ECU to me. I'm cheap. :D
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Post by Quagmire » Fri Oct 20, 2017 8:04 pm

On mine, the relay buzzed all the time with the engine running, but I guess what the relay does is a factor of the spec and brand it is...
1974 Rover 3500s
1984 3.5 90
1959 2.25 series 2

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