Can You Test A Crank Angle Sensor?

[Capn. Pugwash 0]

I had a really productive afternoon yesterday- changed the oil, fixed a leak from the oil cooler, new filter.... then decided to put my nice clean refurbished SAD in to replace the dicky one. It was a mammoth mission considering I didn't want to drain the coolant to remove the little elbow hose from the thermostat, but eventually I got it in. I took the time to clean the brown multiplug and the CAS plug, plus get rid of lots of gunk from the area around top of the gearbox. I put everything back together, whipped the HT lead off the coil and spun up some oil pressure, then put it back on again and voila, no go!

 

Car is (as mentioned) a 1991 205 GTI 1.9L 8v DKZ with motronic ignition (Australian spec series 3). It was running well beforehand, except for the idle on cold mornings, but now it just cranks and cranks and won't fire at all. The Haynes Workshop manual doesn't really show much on the wiring diagram for the car as far as I can see- it has the Ducellier coil mounted on the intake manifold and the distributor has no low tension leads going to it. I checked the 4 LT wires to the coil and they all have 12v- is this normal? No reason to really suspect the ignition module- I didn't touch it, it was fine before and the car is now stone cold so no chance it overheated. The distributor rotor looks a bit worn, but I would have expected it was still a goer. All this makes me think it's the crank angle (position) sensor. Is there any way I can test it?

 

This is sooooo frustrating! I thought I'd done a great job too!

[pugdamo 111 2 Cars]

Are you sure theres no wires on the dizzy?When you was fiddling about with the sad,you didnt happen to knock a connector coming out of the dizzy?if it is still connected maybe poor connection??

I hate it when things like that happen,you try and do the car a favour and it comes back and kicks you in the balls.

[petert 554]

Depends on what resources you have. Easiest way is to pull out the fuel rail and crank it over. If the injectors fire you know the CAS and ECU are fine.

 

There are no low tension wires to the dizzy because all ignition advance is controlled by the ECU. Same as Mi6.

 

After that, a test light or multimeter is required to test supply voltage to the coil and ignition module.

Edited October 31, 2009 by petert

[Capn. Pugwash 0]

I've rechecked the coil supply- my $4 multimeter was lying. There is 12v at connection number 4, 0v at 3 and 2 and about 0.5v at connection 1. The ignition module is getting power. I just tried a known good CAS and module, still no go :'(

Dead coil? Seems surprising for it to fail so suddenly after fiddling with the SAD...

[sub205 5]

I've rechecked the coil supply- my $4 multimeter was lying. There is 12v at connection number 4, 0v at 3 and 2 and about 0.5v at connection 1. The ignition module is getting power. I just tried a known good CAS and module, still no go :'(

Dead coil? Seems surprising for it to fail so suddenly after fiddling with the SAD...

 

you can test a cas with an oscilloscope of course. just quickly move some metal part at the cas and look if there is a signal.

normally these sensors never fail. the only reason to fail is a dead magnet inside.

 

check some other things: are the injectors firing? is the fuelpump running? is there a spark?

alll this things can be checked without great equipment. all this things (despite of the spark) can be tested by a generic led-based polarity tester.

[Capn. Pugwash 0]

The fuel pump is running and there is pressure at the rail. What is the best way to get an injector pulse reading? Check for continuity between one of the injector terminals and earth? There is no spark...

[DrSarty 90 1 Cars]

The fuel pump is running and there is pressure at the rail. What is the best way to get an injector pulse reading? Check for continuity between one of the injector terminals and earth? There is no spark...

 

Just pull the fuel rail out, hold it over some plastic cups and crank. There's no need to measure anything if you can see they're firing.

 

If they are firing, as said before, you know your CAS is working, which means we can look elsewhere for the fault.

[Capn. Pugwash 0]

OK- I tried that, they aren't firing! There is pressure at the fuel rail, and there is 12v at the pump when cranking, but the injectors aren't squirting. I even tried cranking with the rail in and it's not wetting the plugs. This is with a known good CAS and module...... Now what?!

[DrSarty 90 1 Cars]

OK- I tried that, they aren't firing! There is pressure at the fuel rail, and there is 12v at the pump when cranking, but the injectors aren't squirting. I even tried cranking with the rail in and it's not wetting the plugs. This is with a known good CAS and module...... Now what?!

 

I'm glad you've eventually done this simple test. I bet lots of people assume if there's fuel in the rail and the pump's pumping then all is well. Ultimately you have to go right back to basics and think 'I want compression, fuel, air and spark in the cylinder at the correct time'.

 

That's not meant to be patronising, but it's the best way to look at things IMO.

 

So with no fuel injecting, but it's in the rail, then we have to ask are the injectors getting power? That's an easy test. They need to receive 12v whilst cranking and on run. You can even test that with a light bulb and 2 bits of wire.

 

Injectors normally have a relay; they do on an Mi16, so perhaps if you have no power at the injs then your relay's pooped.

 

Then we can check for the injector trigger signal from the ECU, which is purely a switching ground; again an easy test that can be done with a bulb.

 

I was thinking it would just be the power to the injectors, but you say you have no spark too; so this is slowly leaning towards either two problems happening at once (unlikely) or the CAS (still) or the ECU.

 

Try that lot. We'll get there.

[Capn. Pugwash 0]

No patronising taken I tested voltage across the two injector wires in each plug with the engine cranking, no voltage present. I also whipped out every relay I could find and hosed it and it's plug off with electrical contact cleaner in case it was just something simple like that, but it didn't help. Obviously it wouldn't if the relay's dead! Looking at the Mi wiring diagram (the Motronic 8v isn't in haynes!), it seems the injector relay is a simple 4 pin jobbie- just a green one I take it? I'm guessing it's either in the box near the left hand strut tower or behind the left headlight, unless it's hiding somewhere else...

 

First things first though- my dinner is on the table and I'll cop a bollocking if I don't sit down and eat it!

 

Many thanks for everyone's help so far- I do feel like I'm getting somewhere even though it's still not running

Edited October 31, 2009 by Capn. Pugwash

[DrSarty 90 1 Cars]

Yes, just a normal 4 pole relay.

 

There's a green relay usually screwed to the lip by the expansion tank on UK models (i.e. RHD like yours). Is that it?

 

But, beyond that, also check 12v is getting TO the relay in the first place. If it is, then you know the ECU is not triggering the relay as it should.

 

What baffles me though, is that if you find a duff relay, then what was causing no spark? Starting to point to an ECU fault OR, perhaps the ECU is getting no power? I'd check the latter too, but if the FP's working then it means the ECU must be working.

 

Most odd.

 

What did you have for dinner? Hope you washed it down with an icy cold VB.

[Capn. Pugwash 0]

Yep, there is a green relay there. I tried replacing it with a known good one from a wreck, no change. I did the same with the two in the black box right next door, still nothing! Just about to probe for voltage, I'll let you know!

 

Nothing like a couple of snags from the barbie for tea, none of this VB rubbish though- it's Cascade Lager all the way!

[petert 554]

Cascade. That's obviously your problem. Try switching to Corona and see what happens. I bet you run a lot smoother......... but seriously, you won't be able to measure a voltage across the injector clip, as the injector is only earthed out by the ECU for approx. 3-7ms. There is +12V on one lead all the time however. So with ignition on, test from the clip to earth. Do you want me to send you the manual? If so, email me.

[Capn. Pugwash 0]

Measuring voltage between battery negative and the injector leads gives 12v on BOTH wires...... This is on injector 2, didn't check any others.

 

Another thing to mention is I've just discovered a black aftermarket relay and ceramic ballast resistor hiding up under the bonnet slam panel. At first glance, it looks to be a starter relay, as there are 5 pins, one is a direct + from the battery, two disappear under the inlet manifold (one is joined to a light blue or grey wire and disappears back into the loom, the other goes onto the starter solenoid), solenoid lead goes back onto the relay centre pin and another pin goes to earth. The ballast resistor is earthed at one end, but has no connector at the other. Probably totally unrelated, but thought I better mention in case it has something to do with it!

 

Corona and VB are both Mexican beers...I should give it a try and report back hehe!

[Capn. Pugwash 0]

As a pre-emptive strike, I double checked the voltage between the battery negative and the injector wires on the other injectors- same result. I also tried removing the ECU, then checking for voltage at the injectors- no voltage (not surprising!). I thought I'd try being a smart arse and put the multimeter on the VDC Hz setting and cranking it over while measuring between the injector wires and earth- one wire showed nothing, the other showed a value of around 0.7 (hertz I presume). Not sure if this achieved anything, but I'm clutching at straws a bit! There is earth at the pins 14, 19 and 24 on the ECU plug. I just discovered the Tandem Mi build thread so printed out the autodata sheet to have a look at... This is rapidly turning into a nightmare!!

 

edit: for what it's worth, the ECU is a 162 version.

Edited November 1, 2009 by Capn. Pugwash

[Capn. Pugwash 0]

There is also a CAS signal getting to pins 47 and 48

[DrSarty 90 1 Cars]

There is also a CAS signal getting to pins 47 and 48

 

Nightmare yes. Someone also just explained the 'Mexican' joke to me. You Ozzies eh!

 

Based on all of the above now, especially the last point, I can only conclude that you've gayed your ECU somehow. (But read on please).

 

Why do I say that? Well you didn't change anything according to your initial story other than the SAD. You didn't really touch anything 'management' orientated.

 

As you have a signal from the CAS, but have no spark, but also seem to have a thoroughly odd set of results from the injectors (one pin, the same pin on each injector should be 12v live when the ignition switch is in crank and run), but the ECU is obviously activating the fuel pump relay (as it's bringING fuel to the rail), then with the loss of injecting and spark I can only see the ECU being at fault.

 

Why did it go wrong? The only logical conclusion is that it was just its time, i.e. a complete coincidence, or, you shorted a wire whilst fiddling with the SAD, or - a very outside chance - what if the one thing you did change has an electrical short inside which has either messed up the ECU or is just causing a temporary fault?

 

So in short, swap out what you changed; we just want it to start. If it does, even with the old SAD and runs badly, at least we've found the cause.

 

If swapping the SAD doesn't change things, then I'm forced to conclude it's your ECU.

[sub205 5]

checked the coolant temp sensor at the back of the head? this thing usually causes strange behavior.

 

also try to give the ignition amp a signal by hand and check if it fires!

[Capn. Pugwash 0]

Well, that was a mission. After sourcing and fitting a new ECU, it didn't fix the problem. I tried the last remaining component, the coil and......voila! Dead coil. This was pretty interesting considering I had 12v on both injector wires and no fuel getting through!

At least it's fixed now...

[stuart 31 3 Cars]

I think that the injector firing is triggered by earth, had a similar problem with my rally car when trying to get that going. I can't remember how we fixed it now though...

[DrSarty 90 1 Cars]

I think that the injector firing is triggered by earth, had a similar problem with my rally car when trying to get that going. I can't remember how we fixed it now though...

 

Yes injectors are earth triggered. One pin receives a switched live (as in it's live all the time the ignition is turned on) and the other pin just gets grounded (on and off) by the ECU. This makes the injectors fire as the solenoid (coil) inside activates opening a valve.

 

And Cap'n P!! What a run around! I haven't read back through, but surely the coil was an obvious potential culprit that you could've checked/swapped out early doors?

 

P.S. I still don't understand your explanation of the voltage readings you got from the injector pins, but no matter now.

[ade 4wd 11]

To have 12V on both injector pins is normal when the ignition is on and the engine is not running. The ECU supplies 12V to the injector to make sure it is turned off and then switches to ground to turn on the injector.

 

What i dont understand is why the injectors were not working when there was a faulty ignition coil. The injectors would still be squirting fuel into the engine even with the ignition coil disconnected.

[welshpug 1,627]

on Motronic most certainly, but not Jetronic, which is very confusing as it is Motronic

Edited November 12, 2009 by welshpug

[Capn. Pugwash 0]

A spare coil (the transformer type) was the one thing I didn't have access to! Indeed it was a run around but at least it's sorted now

There was positively, definitely, absolutely no fuel getting in the cylinders!!!!

[splant 0]

well i was hoping it would turn out to be the same as my problem ,, still might be but i dont fancy shelling out for a coil if its not that how do you check them i cant tell which terminals are neg and pos ... p.s you probably fried your coil by disconnecting the lead when building your oil pressure up ..