VR6 - Sporadic Starting Problem

[Wullie 1]

Have you checked the output from the alternator? Looked back through the thread and don't see it mentioned. The symptoms you describe in the last post hint in that direction.

[mattwelcer 0]

No not as yet, however that was rebuilt last summer but I guess it could still fail or have been rebuilt incorrectly (its a 120A alternator)...

[dr_mat 0]

See, you keep saying that when it "doesn't start" it is cranking the engine over but not firing .. that's really unlikely to be a battery issue if it can turn the engine over at all..

You really need a VAGCOM scan.

If it is slow at firing after being left standing but the engine is turning over fine then you might have fuel or spark issues.. or an intermittent crank sensor problem.

[mattwelcer 0]

I have VAGCOM, i said at the beginning but there are no stored faults or anything!

There are no faults stored in memory (checked with VCDS/VAG-COM)

Unless someone can tell me what needs to be scanned/monitored/logged during start up i don't see how VAGCOM can help at the moment as there are NO stored faults!

[dr_mat 0]

On VAGCOM I think I'd go to the measuring blocks and start looking at the readouts from the various temp sensors and other things like the throttle sensor.

You can also check the battery voltage in there!

[mattwelcer 0]

Ok a little update on this, i managed to log various measuring blocks. I just need to "tidy" up the data so it makes sense.

 

Additionally i have now found that if i switch everything off before i start the car i.e. radio, interior light, air-con/blower then the car starts straight away. If any of these are on then at the first start attempt the car takes a while until it springs into life. I'll post later the readouts from VAG-COM/VCDS

[dr_mat 0]

You could have an ignition switch / starting relay problem .. the ignition switch should cut off the supply to "non essential" electrics such as the air con and radio when the starter is engaged, so they should literally make no difference.

[mattwelcer 0]

Well the ignition switch is brand new so i guess it could be the relay.

 

Is there any way of testing them or just try and swap for one that works from another car?

[dr_mat 0]

I'm not sure, tbh. What do you observe? does the radio stay on while you're cranking the starter over for example? It should go off as soon as you push the ignition key to the starting position.

 

And, obvious question, did you buy a genuine ignition switch? There's been a lot of issues with pattern parts.

[mattwelcer 0]

Yes this time I learnt my lesson and bought a genuine VAG ignition switch :) I'll need to check and see what the radio and Climatronic do when I turn the ignition to the starting position.

 

I think the relay your on about is Relay No. 18 "Load Reduction"

 

---------- Post added at 1:26 PM ---------- Previous post was at 1:25 PM ----------

 

[dr_mat 0]

Yes, that's probably the one. If there's another identical relay, swap them over ...

[mattwelcer 0]

Ok it seems it was the Fuel Pressure Regulator and that 4bar is too much, with the 3bar it starts fine every time.

 

Guess i'll have to see if a remap can solve it as i know it runs lean and runs better with the 4bar but doesn't start as well :(

[dr_mat 0]

Ok, interesting result!

When did you change the FPR? Is it possible one of them is just plain faulty?

[mattwelcer 0]

OK a year has gone by and i haven't managed to solve this problem.

 

I checked the Fuel Pump relay (Postion 12, No. 67) and it is receiving no switched earth from the ECU which comes from PIN 6. If i put an earth to this PIN on the ECU directly from the negative terminal of the battery then you can hear the relay click and the fuel pump primes as normal. So to me this rules out a problem with the wiring. However this has had no affect on the start issue.

 

I checked the Crank Sensor today as per ELSA. The crank sensor has a value of 900ohms which is within the tolerance (480-1000ohms). I checked how much resistance is between the white connector and the ECU PIN1 & PIN67 ECU, PIN2 & PIN68 ECU, PIN3 & PIN56 ECU and all had very low resistance 0.3, max. tolerance is supposed to be 1.5ohms and none of the wires are shorting to each other.

 

I have replaced the MAF with a brand new one and a 2nd hand ECU with the same BOSCH/VAG number but that too has the same problems.

 

Therefore what should be the next step, check all the earth points? Or recheck the spark plugs?

 

Once the car starts it runs fine, seems to have ample power and never goes out or stalls.