At my wits end with this crank trigger - the saga continues!!

[Valver.]

Hi there,

I purchased a 2nd hand PnP VEMS v3.3 and have installed it on my Mk1 VW Golf 2.0 ABF 16v Turbo. The former owner has written a lot of info about the assembly here: http://www.vems.hu/wiki/index.php?page=MembersPage%2FBasilDaham%2FCordobaSX so this should fill most of you in. The car runs wastespark Bosch VW coil with the factory ignitors removed.

As you'll see in the link above, it uses a multitooth 60-2 trigger wheel, which is standard on this engine and located inside the engine on the crankshaft.

When we first installed the computer, the car ran ok, but with a weak spark. After a few starts, the crank signal started to become intermittent: it would appear and then disappear and the car would run and then fail to run without the signal. Eventually, the RPM signal disappeared entirely and "trigger errors" showed up on Megatune. After checking all the grounds (all fine) and everything else, we decided it must be a hardware problem, so sent the ECU back to Hungary where said it showed signs of damage and replaced the board.

To cut a long story short, I now have the ECU back and at first had no crank signal. I decided to pull the harness out of the car and redo all of the grounds to make entirely sure they were ok. After doing this and replacing the crank angle sensor (just to make extra sure) the RPM signal returned. However, the ECU had come back with the 1.0.73 firmware installed and this resulted in no spark. Not being entirely sure how to fix it with all the config. stuff (I'm not used to ECUs that are so DIY), I reloaded the 1.0.53 which the VEMS was previously running. I rebooted the ECU and then the car almost started.

Since this point, the RPM signal has become intermittent again:
- It jumps to 250rpm under cranking and back to 0rpm all the time: signal, no signal, signal, no signal. Sometimes cranking, it'll only register a signal once, the rest of the time nothing shows up on the RPM gauge and the trigger errors symbol appears again on the Megatune.

I have a new mainboard, new crank sensor, perfect grounds and a car that was running fine - WHAT THE HECK IS GOING IN?! Is it a firmware problem, perhaps? And if so, how I do fix it as I really don't understand the firmware side of things at all!!

I've been trying to get this car running properly for months. My next to step is to pull the ECU and vit an Autronic, but I want them VEMS to work out of principle - plus it seems like a good, user-friendly unit.

Please help!!! 



 

[rob@vems.co.uk]

What sort of voltage are you getting during cranking?  If you put your meter onto ACV and measure across the sensor's pin you should see a sustained value.

[Valver.]

It has about 3.5-3.85v coming out under cranking and a 12v supply going in  Thanks

[GintsK]

ABF use Hall type sensor for 60-2 wheel.

I am not sure about OE supply voltage for this sensor (if 12V, it goes through protection inside digifant unit), but I never use  12V supply because it is not free from transient voltage spikes which can easily kill sensor.

3.85V looks like voltage from VEMS unit. Every teeth must pull down this voltage close to 0V. When cranking voltmeter must read about half of 3.85.

Gints

[rob@vems.co.uk]

So perhaps we're wanting to use the 5V supply from the VEMS to drive this?  Or some form of controlled supply.

[Valver.]

Thanks for your replies. I'll test the voltage again when I have time at the end of the week and report back with the findings. In the standard ABF engine, the sensor gets a 12v supply as well so I'm assuming this isn't the problem, but you never know.

The car did run ok when I first installed the VEMS, but there was a very weak spark.

What is the quickest and easiest way to change the sensor supply back to 5v? The 5v supply pin on my vems currently isn't used, shall I just go this way?

Thanks again 

[GintsK]

My suggestion is check both new and replaced sensor first.

Easiest way to do is move some piece of steel against sensor and during this watch what do voltage in signal wire (igntion ON, sensor attached). It must drop close to 0V from reference value (voltage when sensor is not attached - >3V).

If both sensors are OK, then this is not the reason.

BTW inside VEMS exist from spikes and noise protected 12V. But no 12V pin to outside normally.

Gints

[Valver.]

Thankyou for the sensor testing idea, we hadn't thought of that! I'll have a good look at the car again tomorrow and report back

Also, the Megatune ALS light has been on from the first install of the unit... how do I disable it?

[s14nismo]

Also, the Megatune ALS light has been on from the first install of the unit... how do I disable it?

In Megatune   "extras"-"advanced ALS", input channel used must be disabled.(in the dropdown menu)

[Valver.]

Just for the record, I've connected the sensor to the VEMS 5v supply (rather than 12v) and also sent the signal wire direct to the primary trigger pin. Now the only crank sensor wiring going through the PnP harness is the ground wire.

I haven't had to time to remove the current sensor to test its operation (as described in the process above) but will do so asap.

For now, the problem still exists: The car gets a crank signal and tries to start (gets spark), but then the RPM gauge drops back to 0rpm and the spark is obviously cut. A few seconds later the RPM gauges registers a signal whilst still cranking and the car tries to start again, before the signal again disappears!!!!!!!!!! It is so frustrating 

[rob@vems.co.uk]

It sounds like the spark is causing the signal to drop out.  It may be possible that the ground voltage rises enough to 'deafen' the trigger.
What happens with the spark disconnected?  Does the cranking RPM remain consistant?  Can you datalog these experiments so that we can get an idea of what the ECU is doing?

Thanks

Rob

[Valver.]

It sounds like the spark is causing the signal to drop out.  It may be possible that the ground voltage rises enough to 'deafen' the trigger.
What happens with the spark disconnected?  Does the cranking RPM remain consistant?  Can you datalog these experiments so that we can get an idea of what the ECU is doing?

Thanks

Rob

You may well be right - I'll try this tonight One other suggestion I've had is to disconnect the alternator which I'll also try out.

What I don't understand is why the signal is sometimes perfect, sometimes intermittent and sometimes non-existent. It is an absolute mystery to me!

[rob@vems.co.uk]

What I don't understand is why the signal is sometimes perfect, sometimes intermittent and sometimes non-existent. It is an absolute mystery to me!

Its a mistery to me too Intermittent faults are a pig to solve, it could be anything from the condition of the: wires, sensor, battery, ecu location.  The fact that the ECU showed signs of damage when it was sent back to Hungary is of concern, did they actually tell you what was wrong?

[Valver.]

What I don't understand is why the signal is sometimes perfect, sometimes intermittent and sometimes non-existent. It is an absolute mystery to me!

Its a mistery to me too Intermittent faults are a pig to solve, it could be anything from the condition of the: wires, sensor, battery, ecu location.  The fact that the ECU showed signs of damage when it was sent back to Hungary is of concern, did they actually tell you what was wrong?

Good question, Rob! In effect, all they said was board replacement is necessary to guarantee troublefree operation and so that's the way I went. They did seem to think it showed signs of damage, but didn't elaborate more than that - perhaps I'll ask Katalin for more info (?)

I just cranked the engine with the alternator disconnected and then with the coil unplugged and it made no difference (same problems with the signal). I've tested one of the sensors and it appears to be working fine as well. Whilst waving the steel past it, the fuel pump was running as it should too.

It makes no sense at all. I've asked some of the best ECU contacts we have in Australia and all of them are baffled. All I can do now is reinstall the distributor and try and start the car that way, bypassing the crank trigger altogether... Surely, it'll work then!?

[GintsK]

But what settings you use? Firmware? Megatune version?

Yesterday I put VEMS on car where 36-1 was installed, but my settings was for 60-2. symptoms was about similar a s yours.

Gints.