It's broken - now fixed - or so I thought

[Reggit 0]

Just tried to start the car and it's been lazy and can't be bothered to go! :cry:

 

Found out that there is no spark, it has been running perfectly until tonight. Ideas please!

 

VAGCOM shows engine speed sensor fault only, which I assume it would as engine isn't running.

 

I don't fance changing random parts on the ignition system but fancy tackling it in a logical order (but don't know what that logical order should be!)

 

Car is '93 VR6.

 

Any help or ideas gratefully accepted.

[Reggit 0]

If I connect a voltmeter or oscilloscope between each of the 3 middle connections and earth on the coil pack connector I should see an oscillating 12v waveform whilst the engine is cranking. Am I right in thinking this?

 

If true it should be an easy way of checking the electrics prior to coil pack.

[Reggit 0]

I can also hear a relay clicking rapidly whilst engine is turning over, I don't know if this is a symptom of the fault.

[Funkster 0]

You won't get 12V oscillating on the coil pack wires unless you provide a pull-up to 12V (e.g. coil connected) - coil outputs are open drain outputs so can only pull down to earth. You'll need a 'scope to see the pulses, I shouldn't think they'll be longer than 10ms.

 

Check your crank sensor with the scope while you're there - I have no idea where it is or what type it is though :)

 

hth,

--

Olly

[Scruffythefirst 0]

Relay clacking?

 

Is your fuel pump dead?

[Reggit 0]

Relay clacking?

 

Is your fuel pump dead?

 

It's not been showing signs of dying, even if it had I'd still have a spark wouldn't I?

 

 

Just realised that I have no fuel either, plugs are dry after loads of cranking. Starting to think G28 sensor. Where abouts on the engine does it live, I want to clean it and check signal cables before shelling out on a replacement.

[Henny 0]

ignition switch.... ;)

[Kevin Bacon 5]

If the crank sensor dies, you don't get fuel or ignition...so that's a good place to start your investigations....

 

£140 from the dealer if it's dead.

 

It's on the front block face, adjacent to the the clutch bell housing. Follow the wires on the front engine mount if in doubt. 5mm allen bolt.

[Reggit 0]

Have tested G28 according to bentley check, it appears to be in order. 500 Ohms across 67-68, all other combinations are open circuit.

 

I've also found out that it is the fuel pump relay that is switching when engine is turned over. Pump primes normally when ignition is first turned on.

 

Need to do more head scratching!

[Henny 0]

One of the classic signs of a dead ignition switch is the pump relay going mad while cranking the engine over as the switch fails/makes the contacts it's supposed to... ;)

 

Stick the car onto stage 2 of the ignition (ignition lights on) and put a wire between the solenoid's +ve connection and the battery (MAKE SURE THE CAR IS NOT IN GEAR!) This'll fire the starter motor as long as you hold the wire onto the battery. If it fires up doing this, then you need to spend £20 and 30 mins fitting a new switch. 8) If it doesn't, then it's something else... :|

[Reggit 0]

Henny,

Cheers for that info, I've just bought a new switch from GSF on Trafford Park this morning, will be fitting it tonight. Will let you know how it goes, that little screw looks a bugger to get to!

[Henny 0]

bend a cheap watch makers screwdriver slightly... ;)

[Reggit 0]

New switch didn't make any difference. :cry:

[Kevin Bacon 5]

There's a load induction relay you change on the fuseboard too, can't remember what number it is though!

 

Another thing could also be the fuel pump itself, maybe it's dead and causing the pump relay to pulse? 2CC & Roddy both had sudden and total pump failures.

 

If not the pump, then I reckon it's the crank sensor still, given you've said you've lost fuel AND ignition. They also just die completely. What did the VAG-COM codes say about it? No signal or Implausible signal? No signal is normal (engine off) but Implausible signal is bad news.

 

Or yet another long shot is you've got an immobiliser issue that's knocked out the ignition and also a pump failure, but that would be seriously bad luck - and unlikely!

[Reggit 0]

I really don't understand this blooming car! (other than it being a 'rado). Was fearing the worst of having to change the engine speed sensor, decided to turn engine over one last time, and the thing starts normally.

 

There is obviously something starting to fail, but it's gone away for now!

[CoxyLaad 0]

quality!

 

Put the whole episode behind you and pretend it never happened :wink:

[Reggit 0]

Unfortunatley the fault has just returned :cry:

 

When it starts it performs faultlessly, but when it doesn't start ther is no fuel to cylinders and no spark to plugs.

 

Have ruled out fuel pump, load reduction relay, ignition switch, vagcom is clear (other than speed sensor-no signal). Think I'm going to have to bite the bullet and get the stupidly expensive speed sensor from the stealer.

[Kevin Bacon 5]

I hate to say it bud, but that is the classic sign of a dying crank sensor. They either work or they don't, there's no inbetween. Have you taken it out and inspected it for swarf and dirt etc?

 

Ask CrazyMarcel.... he had EXACTLY the same symptoms and he had to replace the sensor....so dust off your credit card mate, you're gonna need it :(

[Reggit 0]

Just been the stealer and ordered the sensor £126 + vat.

 

Removed old one and cleaned + replaced (no swarf on it, which is good), hey presto, car starts up. Looks like the sensor definately at fault.

 

Got to wait til tuesday until new one arrives, so in the meantime I'll be crossing my fingers that it keeps going!

 

Cheers for the help guys :thumb right:

[jonrb 0]

Did you get it sorted in the end?

 

Sounds like EXACTLY the symptoms my VR6 is currently exhibiting so I'd be particularly keen on learning what your fault turned out to be. :)

[Jim 1]

I'm guessing (hoping?) by the lack of further posts that this might have done the job Jon :)

[jonrb 0]

Indeed. Unfortunately I've already cleaned mine (quite how cleaning a sealed solid-state electronic device can cure anything is beyond me though).

 

I'm hoping that Ady_G still has the one he bought in error (or the old one if the new one is on his car) and am hoping to try that.

[GB_SEAN 0]

Had this problem before, turned out to be the wiring connection for the engine, (the big black one next to the aux water pump) disconnected it, cleaned up the terminals sprayed in WD40 and has been ok since. I hope!

[Reggit 0]

Sorry, I forgot to update the post.

 

Ended up removing the sensor and cleaning crud off the end of it, after refitting the car started and ran fine. Whether this was due to cleaning the sensor or if it had a fractured wire and removing it remade the connection, I don't know.

 

Anyway I fitted a new one as mentioned above and it has been faultless since.

 

The interesting thing was that it wasn't coded by the ECU.

 

jonrb I still have the one I took out, if you want it you can have it although it may be intermittent.

[jonrb 0]

jonrb I still have the one I took out, if you want it you can have it although it may be intermittent.

That would be great. Even if it only gets the car running intermittently then it will a) prove it is the sensor and b) enable me to drive to teh car's appointment with my indie on Monday rather than having to have it recovered there.

I'll PM you with my address.

 

Cheers!

Jon