Ignition problems?

[biggie_]

Hi m8s,

Somedays ago happened something when i was driving my Q4, i was driving slowly, just having a "walk" through the town, and suddenly i heard a BIG explosion and the car turns off... after that inmediatenly the car start without any problem...

I asked to my mechanisc and he said me that it can be a problem with the ignition leads or the coil ignition leads... what do you think? can be another thing?

P.S. apologies for my english level.

[wrinx]

Perhaps overfuelling???

wrinx

[juamin]

crankshaft sensor/cable failure?

[arjunior45]

Most likely your mechanic is right.
Do you have any other problems? Do you start the engine easily or does it take some time?

[biggie_]

Perhaps overfuelling???

wrinx

I have a pressure fuel gauge and i have set my fuel pressure at 2.5 bar "OEM condition".


crankshaft sensor/cable failure?

Crankshaft sensor was changed last year i think, i have to ask to the mechanisc to confirm, but i'm 99% sure.


Most likely your mechanic is right.
Do you have any other problems? Do you start the engine easily or does it take some time?

Sometimes... doesn't matters if the engine is cold or hot, it takes two or three times to start, and another days, it starts normal, the engine turns on at the first time all day.

Many thanks m8s ;)

[AlfaJack]

Check the mechanic ran the cable for the crank sensor away from the cam belt. Some years back I used to get a huge jolt from the car as the cable was being worn away by the belt.

[kepsus]

It could also be the Cam sensor.

[Juan AR155Q4]

Any rare explosion when starting the engine?

[AlfaJack]

Any rare explosion when starting the engine?

On mine I sometimes get a backfire on starting. Do you know what it could be?

[Juan AR155Q4]

I have had all this symptoms once when a cable from the cam sensor was chopped off.
Also gives an ignition cut @4000.
So from my experience, a faulty (1 wire less) cam sensor gives:
- backfire when starting (not allways)
- suddenly backfires and engine off while driven (not to often)
- ignition cut @4000 (always)

[AlfaJack]

I only have the backfire when starting sometimes. Non of the others...could be something to do with the cam phase sensor then..

[wrinx]

I've also got the backfiring, but only when starting :roll:

wrinx

[biggie_]

Any rare explosion when starting the engine?

Hi, yes, very few times (just three or four times), sometimes more strong than others

I think I have to take sometime to check all the possibilities and will see :)

[wrinx]

I've also got the backfiring, but only when starting :roll:

wrinx

Thinking about it, I also had one big backfire a few weeks ago whilst driving at about 15mph.....crank sensor eh?

wrinx

[juamin]

I've also got the backfiring, but only when starting :roll:

wrinx

Wrinx, my car does the same when i disconnect the camshaft sensor .

[wrinx]

Ahhh,will have a look for it :D

wrinx

[kepsus]

Normaly it would be the cam sensor. The car need the sensor to tell whre the cylinder 1 tdc is. But as soon it have the signal it, then it can run without the signal from the cam sensor because it then calculate where signal should be.

[Juan AR155Q4]

Are you sure?
Normally both signals are used to trigger.

[AlfaJack]

Are you sure?
Normally both signals are used to trigger.

As in crank and cam phase sensors?

Is there a way to test the cam phase sensor?

[wrinx]

Now having problems with the JTD not starting when hot :roll:

A way of testing would perhaps save me ?50, but otherwise I'll replace cam and crank sensors to be safe :D

wrinx

[Juan AR155Q4]

Best way is with a oscilloscope.

Just to know if the cam sensor is working, you can measure frequency with a multimeter.

[wrinx]

Now having problems with the JTD not starting when hot :roll:

A way of testing would perhaps save me ?50, but otherwise I'll replace cam and crank sensors to be safe :D

wrinx

Unidiag reckons Crank Sensor (and MAF!) so I'll go with that first :D

wrinx

[biggie_]

Hi mates, here i'm again

I decided to check myself the different things that can cause this problems on my car, and firstly i'm trying to change the ignition coils and ignition leads...

Here's my first question... does anybody changed the ignition coils without taking off the air intake box? I have followed all the steps to change the ignition coils that are on the Q4 Workshop Suplemment "ignition" but I'm not able to change the ignition coils because i think that there isn't space enough to do that job.

Anybody have any experience about that?

Many thanks in advance ;)

[biggie_]

Nobody has changed the ignition coils? :frown:

[arjunior45]

As far as I can tell, to change the ignition coils you need :
a} disconnect all the small hoses, and the one that goes to the APS.
b} disconnect the gas cable and free the throttle body from it's hose.
and
c} remove the inlet plenum, which is the difficult part .
There are two bolts from beneath that fix {support} the inlet plenum to the inlet manifold and you must rise the car to get access to this bolt{see 1st picture}. Then there are the 2 bolts at the tops {see 2nd picture}. And of coarse the plenum - inlet manifold hoses must be loosen.

once the inlet plenum is out you can reach the ignition coils.

This 'difficulty' is the only reason I'm going to go for this mod :

http://forum.berlinasportivo.org/showthread.php?t=1401

or you can just move the ignition coils to another place as many people here have done {search a little to 'readers cars' and engine reassembly from Jim Nielsen

[biggie_]

Big thanks arjunior45, that's some help, i was in the doubt if i was doing something wrong, now i know that's necessary to lift up the car to change the ignition coils ;)

Will inform here about my progress, currently only have time to do this...