2009 m139 4.2 Quattroporte misfire

[Philip730i]

Hi all!

I’ve done extensive searching here and internet and found lots of advice on misfires but mostly specific cylinders.

I have a 2009 4.2 m139 project car so have signed up for the problems!

When I first got it there was a misfire on cylinders 4 & 8 which was constant.

Changed all plugs and it ran perfect for about a week although at test emissions were still slightly over legal limits.

Week later it developed a very small misfire only noticeable pulling from low revs and lighting engine light.

Codes say misfire on cylinders 1,2,3 and 5,6,7 plus generic misfires

Changed all coil packs and problem persists

Have found the cats have been cut open, emptied and welded up again

Now occasionally at high revs only have alternator warning light which disappears again at low revs

Would alternator going bad/old battery be a part of the misfire?

Would the cats being empty giving the lambda sensors before and after the cats the same reading be an issue?

Just wondering if anyone has experience in similar issues to point me in the right direction rather than throwing expensive parts at the problem

Thanks in advance

 

[CatmanV2]

Welcome. We need photos

Now occasionally at high revs only have alternator warning light which disappears again at low revs

Constant or flashing? Does your gearbox lock into gear?

Would alternator going bad/old battery be a part of the misfire?

I wouldn't be at all surprised.

Would the cats being empty giving the lambda sensors

See above. I don't think that the same reading from pre and post is likely an issue but I can imagine having no cats and the lambdas in free air may be an issue.

Sadly most of the experts are ****** in a ditch in France, but, in the meantime, what are you using to scan for codes?

C

 

[Philip730i]

Gearbox doesn’t lock and alternator light comes on only at high revs sometimes, then disappears as soon as it drops down again

Misfire is only prominent pulling from low revs but according to the reader is always there

Using a topdon artidiag so can do quite a lot

 

[Philip730i]

Currently camping at Le Mans as only an hour or so from my house and surrounded by friends should an issue occur and I need to go home to get a trailer for it haha

 

[CatmanV2]

So there's deffo something wrong with the charging circuit.

Using a topdon artidiag so can do quite a lot

Does it read the other modules, let you read live data from the lambda and so on?

For me, I'd be looking to get the charging circuit diagnosed and sorted (I imagine the reg / rec has gone and a new alternator will be the solution), then start looking at getting the cats re-instated if there's no improvement after that.

But....

C

 

[CatmanV2]

Currently camping at Le Mans as only an hour or so from my house and surrounded by friends should an issue occur and I need to go home to get a trailer for it haha
View attachment 128040

Oh well, go find @Zep and @conaero who are close by and see what they say

C

 

[Philip730i]

So there's deffo something wrong with the charging circuit.



Does it read the other modules, let you read live data from the lambda and so on?

For me, I'd be looking to get the charging circuit diagnosed and sorted (I imagine the reg / rec has gone and a new alternator will be the solution), then start looking at getting the cats re-instated if there's no improvement after that.

But....

C

Yeah I can read live data

 

[Ebenezer]

Yes the alternator is gone if you get the battery light flashing on at over 3k revs. Ask me how I know...

But shouldn't cause misfires though i would have thought?

Eb

 

[CatmanV2]

Yes the alternator is gone if you get the battery light flashing on at over 3k revs. Ask me how I know...

But shouldn't cause misfires though i would have thought?

Eb

Depends what's happening to the voltage to the ECUs at a guess. But it is a bit of a guess. OTOH if there's a know fault, with a solution, fixing it before looking for less clear faults probably makes sense...

C

 

[Zep]

Had this last year on the Don’t Mention The War trip. Alternator locks the auto into gear. Stevo had to keep resetting it all the way home.

Happy to look at it in Arnage tomorrow.

 

[Philip730i]

I’m staying just outside arnage in spay so that would be amazing

Had this last year on the Don’t Mention The War trip. Alternator locks the auto into gear. Stevo had to keep resetting it all the way home.

Happy to look at it in Arnage tomorrow.

 

[CatmanV2]

Had this last year on the Don’t Mention The War trip. Alternator locks the auto into gear. Stevo had to keep resetting it all the way home.

Happy to look at it in Arnage tomorrow.

Over voltage certainly does. Under voltage not so much I feel

C

 

[Erlingtheyounger]

Am I correct in thinking this is the car featured on the Car Chronicles YouTube channel that @philw696 referenced previously?

 

[philw696]

Am I correct in thinking this is the car featured on the Car Chronicles YouTube channel that @philw696 referenced previously?

Yeah this is the Car that Phil bought in the UK and now has in the Mayenne France.

 

[Philip730i]

Am I correct in thinking this is the car featured on the Car Chronicles YouTube channel

Yes that’s the one I just didn’t mention it as I’d never want to appear to be using an amazing forum such as this for a few views

 

[Zep]

We are heading to Arnage in the next 45 mins. I’ll PM you my number.

 

[Zep]

Nice to meet you, very odd issue you have there. Hopefully it will become more apparent soon!

 

[Erlingtheyounger]

Yes that’s the one I just didn’t mention it as I’d never want to appear to be using an amazing forum such as this for a few views

Well I enjoyed them

 

[Philip730i]

Nice to meet you, very odd issue you have there. Hopefully it will become more apparent soon!

Lovely to meet you all and thanks so much for the help; will keep this thread updated as I go!

 

[philw696]

Nice to meet you, very odd issue you have there. Hopefully it will become more apparent soon!

What did you find Zep ?