missfire or bad sync

**UrS4boy** · 14 April 2009, 14:26

Link to the Engine Bay Device Map (and its links)

Originally posted by GazzaG60

1. it looks like the 2 plug POS is not firing or not firing correctly as when we unlplug it no difference to engine runnning. have tried a known good POS from the AAN and no change.
2. when we unplug a crank sensor it stalls.
3. when i unplug the cam sensor no change at all.
is there a way to check the cam sensor?
how do the triggers work? does one crank sensor do one bank and one the other?
im pretty sure i can isolate the issue to 2 down plugs but what makes the POS fire in the first place? many thanks

Here is a link to an AAN engine bay device map. Follow the hyperlinks below the diagram to learn more about the POSs, cam sensor and cranks sensor.

http://forums.audiworld.com/showthread.php?p=18945405

Drill down through the POS link and it's sublinks.

One thing you should check is your spark plugs.

**GazzaG60** · 14 April 2009, 14:52

thanks for the link. looks good.

swapped in new plugs first, no change. im pretty sure that the pos is not getting a trigger signal so there is no feed in also. how is it triggered to fire the plugs.

this is the issue i had when i thought i bent a rod ikm sure it was last year and it has reappeared again. after pistons skimmed, rods, changed plugs, cam sensor i had no issues but never found a broken part.

the car starts with the cam sensor just about with throttle but wont when unplugged so maybe not that?

**UrS4boy** · 14 April 2009, 15:02

The car starts with the cam sensor and then runs on the crank position sensor. If the cam sensor fails after starting, the engine will still run - off the crank position sensor. However, if you shut the engine off, and the cam sensor has failed, it will not restart because the cam sensor signal tells the ECU where the No.1 piston is. More importantly, with a good cam sensor signal, the ECU will trigger the J17 Fuel pump relay which controls a lot of things, as shown here:

http://forums.audiworld.com/showthread.php?p=18856859

You might want to pull the crank position sensor and check the end for debris, as shown here:

http://forums.audiworld.com/showthread.php?p=23763331

Paul Nugent should chime in with info on checking the cam sensor signal.

**GazzaG60** · 14 April 2009, 15:10

i have had the 2 crank sensors out and swapped in know good ones. the problems still the same.

im gonna do some more pos chesks later and see whast what. any other sensors cause misfire. im using VEMS and so no maf.

**UrS4boy** · 14 April 2009, 15:42

Originally posted by GazzaG60

im using VEMS and so no maf.

Not Motronic? You should have mentioned in your first post. Suggest you contact a VEMS guru or VEMS website.

**GazzaG60** · 15 April 2009, 08:04

the sensors are the same as is the wiring. im gonnqa give vems a check over after and see what i can see.

what i did find is that the change when i pull injector wires to test it is bearly audiable. that may be just the difference between injector and not injector hard to tell.

gotta say vems seems mega reliable but thats the next job to give it a proper checkover.

is it possible that the cam sensor would pick the incorrect position in the cycle therefore messing the order up?

**GazzaG60** · 27 April 2009, 08:43

well following lots of tests the problem has been found. its a snapped 7a cam.

the cam has snapped between the lobes of no 4. basically i had the valves of 5 stuck open and one of 4 stuck closed.

no engine damage so thats ok but it has been detting a little as i got pitting on the pistons. not sure if some of the det resistance has been removed by skimming the pistons?

anybody need a cam for a 3 and a half cylinder?

**S2central.net** · 27 April 2009, 12:32

STROOOOOOOOOOOTH - thats a close escape... Gotta be unusual to snap a camshaft !

**s2avant** · 27 April 2009, 13:11

I've seen it before with an 1.8T Passat. Car wouldn't start and was throwing a hall sender fault. Hall sender was replaced and still nothing. When they pulled the cam cover it had snapped the cam under the last cap before the hall sender.

Ben

**GazzaG60** · 27 April 2009, 14:47

not had chance to refit the head yet.

i thought unusual. seen many a melted piston damaged bores ruined crank but not snapped cam. i reckon it had took a small crack by whoever took it out. it was black and oxidised across around 4/5 of the cam where it had broken. i tweaked the cam timing a 2 days before it broke. it had been going a lot better so maybe the extra did the job. when i popped the head after finding no compression on no 5 i had a sinking feeling as last year when the running symptoms were the same i found no damage. thought maybe i got a car that likes a few weeks off each year.

glad i got spare cams.

**Acidburn** · 27 April 2009, 14:51

I've not heard of the cam's snapping in the middle before but there has been a few people reporting the gear on the end that drives the dizzy becoming detatched from the cam.

**GazzaG60** · 27 April 2009, 15:05

it snapped in the middle between the 2 lobes for pot 4. so opposite end really. eitehr way i was glad not to find a chewed up bore.

**Jonnybravo** · 30 April 2009, 23:54

Originally posted by UrS4boy

The car starts with the cam sensor and then runs on the crank position sensor. If the cam sensor fails after starting, the engine will still run - off the crank position sensor. However, if you shut the engine off, and the cam sensor has failed, it will not restart because the cam sensor signal tells the ECU where the No.1 piston is. More importantly, with a good cam sensor signal, the ECU will trigger the J17 Fuel pump relay which controls a lot of things, as shown here:

http://forums.audiworld.com/showthread.php?p=18856859

You might want to pull the crank position sensor and check the end for debris, as shown here:

http://forums.audiworld.com/showthread.php?p=23763331

Paul Nugent should chime in with info on checking the cam sensor signal.

Brilliant link, that has basically confirmed my thoughts on a potential cam sensor fault on my S2

**GazzaG60** · 11 May 2009, 11:28

well the issue is fixed. engine is runnnig sweet again.

shame the brand new behr radiator lasted about 20 minutes.

missfire or bad sync

missfire or bad sync

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment