Rough running engine - Diagnostic help

[ainarssems]

Valve timing issue ??? How do you deal with this, I thought it was all automatic. The timing belt seems fine as i have the covers off a couple of bits.

I mean cambelt timingoff or loose belt, failing shock absorber for belt tensioner or faulty chain tensioner.

Let's not get ahead of ourselves, check measuring blocks for lambda control first.

[ulfilias]

Hi There,

Just had a quick play. Alas i left my net top at work last night and thus didn't charge it up, but going to measure blocks and 001 and there were two lamdas and they were both at zero. Engine was running but the error codes had been cleared less than a minute prior so am guessing it cleared the lamda's too.

Will try again in the morning.

BTW 18265
http://wiki.ross-tech.com/wiki/index...5/P1857/006231

For both the auto and brakes!

Lee

[ulfilias]

Hi there,

Ran it for about 10 mins this morning while having a play with engine measure blocks. I can't say i know much about what i was reading

Group 055 I think is probably what i am looking for

rpm / Lamda / Lamda / Bin bits

800 / 0.4 / 1.8

The 1st Lamda was quite rapid going from -0.4 to about +2 when reving. The second started at 0.6 and over the time rose to 1.8, but did it very very slowly.

At the end i did another error code scan and got.

VAG-COM Version: Release 303.1

Control Module Part Number: 4D0 907 559 C
Component and/or Version: 4.2L V8/5V G 0003
Software Coding: 10753
Work Shop Code: WSC 02314
Additional Info: WAUZZZ4DZ1N006219 AUZ7Z0Y1573840
6 Faults Found:
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 - -
16685 - Cylinder 1 Misfire Detected
P0301 - 35-00 - -
17549 - Load Calculation Cross Check: Implausible Value
P1141 - 35-00 - -
16688 - Cylinder 4 Misfire Detected
P0304 - 35-00 - -
16687 - Cylinder 3 Misfire Detected
P0303 - 35-00 - -
16518 - Oxygen (Lambda) Sensor B1 S1: No Activity
P0134 - 35-10 - - - Intermittent

[richyb66]

You said that you replaced the G40 sensor, presumably the one on bank one (the same side as the misfires)?

If it's also running badly on gas, then like you say it's most likely ignition related but that's not definite. Remember that the lpg injectors wiring is basically piggy backed off the petrol injectors to determine the injector timing so you could still be looking at a petrol injector issue (though all on on bank also seems unlikely).


Is it possible that the faulty G40 has caused damage to the plugs on one bank and consequently it's still logging misfires? I'd be pulling the plugs out for a look at the colour and if necessary compare one from bank one with one from bank 2. Give that time it takes to remove them, maybe a new set of plugs would be worthwhile? Don't bother with lpg specific plugs, stick with OEM.

I've got lpg on my 40V in the S6 and I know these issues can be more noticeable running on gas because it's a bit less forgiving that petrol but if you try and resolve the issue while it's running on petrol, then likely as not it'll then be ok on gas.

[ulfilias]

Hi there,

I cleaned the throttle body earlier (which was gunky and probably did well for a clean) and while checking the running, noticed on goup 001 that the two lamda banks were vastly different minute or so after starting. like -10 and 18. Once the engine light was flashing and missfires detected they went to 0 and 0.

I stopped the car and cleared the codes but it didn't like restarting when warm, so another day done!

[ainarssems]

noticed on goup 001 that the two lamda banks were vastly different minute or so after starting. like -10 and 18. Once the engine light was flashing and missfires detected they went to 0 and 0

That definitively sounds like valve timing problem. One bank is getting 57% of air and other 43% (normal is 49-51%). Lambda control tries to adjust fuelling accordingly giving extra 18% fuel on one side and cutting 10% on the other side. Then after a while it gives up and goes 'open loop' because of excessive adjustment needed, this is when you see it go to '0'. I think threshold for it going 'open loop' is around 16%( acceptable is considered -12.5..+12.5% as long as the difference between banks is not over 4%), as one bank goes over it just gives up and stops any corrections. At this point air to fuel ratio goes out of acceptable range and misfires start.

[ulfilias]

Hi There,

Yup. That sounds about right....How do I fix it though or is it a case of give it to a garage at this point

Lee

[ainarssems]

It depends on your DIY skills and tool availability. Next steps would be checking cambelt timing, belt and chain tensioners.

[ulfilias]

Hi There,

I had some plugs so I swapped the 4 on the missfiring bank and no difference at all, but it took me less than an hour so was worth the try.

I was going to take it to a local garage this afternoon and it wouldn't start. Turning her over gave backfires through the Air Intake ?!?!?!

Oddly she starts from cold no problems, and it had been 3-4 hours, but nope....I'm wondering what can cause that ???

Lee

[ainarssems]

If the timing belt is loose it's possible it jumped couple of teeth and started misfiring, now it might have jumped couple more and therefore not start at all. If it jumps too much it can end in serious engine damage. At this point I would at least get cambelt covers off and check cambelt for tension and tensioner damper for operation before attempting to start engine again.