Check Engine Light / Misfires / Start Stop Errors at Random

afropelican said:

24th May:

Same symptoms: sufficient enough this time to trigger the check engine light again. Any suggestions for next steps?

Thinking about hard resetting the car by unplugging the battery for 30 mins and touching the leads (disconnected from batteries together as per humblemechanic)- would I need radio codes etc? What sort of settings will I lose?

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Hope u get it sorted mate. Hopefully turns out something small

Thanks mikey. Fingers crossed as I like this car otherwise!

I've since ran some more spray cleaners through the intake and went on 4 x 35 mile drives at 3000rpm where I could but if it is a carbon build up likely only manual cleaning will help.

My local vw dealer offered only diagnostics and said they'll charge me whether they find a fault or not and would prefer if I replicate the fault which I can't do. Besides that another specialist said they've seen this fault before and the fix is to rebuild the engine for £1200 which seems a bit extreme...

After playing around with live data on obd11 and doing some other checks 2 things caught my eye:
1. Charge pressure actual stays pretty much at 1000hpa even if I rev the car.
At idle the specified value is just 355hpa.
And in an example of revs it specified 450hpa and still measured actual at 1000hpa
Is this an issue, what does this mean if so?
Could this be a faulty map sensor and would that cause my symptoms?

2. I checked the voltage of my battery after leaving it for a day its dropped to 12.2v is this normal? Also got the battery tested at another garage it measure 463cca. Could this cause the cold start misfire?

With all due respect I think the observation you are making is very much looking for a pattern that's not there.

It didn't completely surprise me that the battery drops to 12.2 under load just before a start, there's a lot of heavy circuits kick in, but once the engine is turning voltages should recover very quickly as the alternator comes in so I wouldn't expect any symptoms of a weak battery to hang over into full engine on unless the battery was so bad it's barely starting the car at all.

If you had a bad map sensor its own reading would be nonsensical, so go look at that before considering it as a fault.


...if it creaks, it's probably made by VAG

I completely agree that the battery is a longshot. Just I've heard that the electronics on the golf are quite complex and sensitive so I thought just in case.


In terms of where the 12.2V came from its the no load voltage of the car measured directly across the battery terminals with a volt meter. The reason I thought it might be amiss is that other cars (2013 Hyundai, 2009 Toyota) measured at >12.5V when I left them sitting for a similar period. But again... a long shot.


In terms of the MAP sensor I have attached a plot of the specificed charge pressure vs actual pressure. I blipped the throttle a few times when I generated this plot.
Would this suggest a faulty MAP sensor? Or, perhaps indicate another problem? Again no codes (other than the generic misfire codes when the car does misfire)

Sticky wastegate servo linkage.....these engines across many types of servos & turbos have badly designed linkages which seize...just look in my how to guides for this...

https://www.golfmk7.com/forums/showthread.php?t=28690

2nd June Update:
Ran more fuel cleaners as a last ditch effort - and went on another couple of spirited drives.

Fixed Battery Drain (although this was unlikely to solve the problem anyway).
Reset car by joining battery leads together for 2 hours.
Symptoms still exist.

With respect to MAP sensor it still reads 1000 hpa even if the sensor is physically removed from the pipe. The pressure at the sensor hole is definitely changing as if I plug the hole with a cloth and rev the engine, it will shoot out at higher engine RPMs. Further to that diagnosis – unplugging the MAP sensor does cause the pressure reading to change. I suspect the MAP sensor to be faulty. I have already tried cleaning it so I will replace this before looking into wastegate servo linkage.

I should mention that I have consulted garages / specialists – most state they can not offer me a solution unless I can replicate the fault – and would luck have it – it did not happen for them! They said that the steps I’ve followed so far is exactly what they suggest. Bar that I’ve been offered an engine rebuild – with the scare tactic saying that my engine will destroy itself if not fixed.
Assuming the symptoms remain as is – the car cold start misfires once a fortnight for 20 seconds – what is the worst that can happen to the engine – IMO the misfires do not feel violent or last long enough for the car to kill itself – I may just live with it and treat it as an ECU glitch.
If it escalates to the point that it occurs more often I will get it checked out, then.

Hopefully the MAP sensor replacement fixes the issue. If not my last thought, before accepting this to be an ECU glitch for the car:

After researching my issue since it first happened - carbon build up on intake valves keeps cropping up as a potential to cause similar issues to mines. Recently I discovered that another member on golf forums, previously experiencing the same issue with their mk7 1.2 tsi resolved it by getting carbon build up removed from their intake valves.

So as for dealing with this as a potential issue:
Seafoam spray (and various other intake fed sprays) did not work for me. Neither did driving on the motorway at higher sustained revs.

I know that walnut blasting (or even manual cleaning) would be best, but I haven't found a specialist garage local to me that offers walnut blasting. - Unless anyone has any suggestions for ones they have good experience with. Or... I might even consider doing it myself if anyone else has done this before successfully?

What are your thoughts on Hydrogen Carbon Cleaning services in the UK? There are a few local to me who bring the machine round and do the treatment for circa £60. They pump hydrogen through the intake as opposed to terraclean which is run through the fuel system so in theory it should hit the valves

How does carbon build up on the inlet valves when there's no fuel in the air until it's been injected into the cylinder?


...if it creaks, it's probably made by VAG

Most of the information is covered in these videos made by ShopDAP and Humble Mechanic:


https://www.youtube.com/watch?v=PS8riAae_bM
https://www.youtube.com/watch?v=RnhUJsZXzmga


From what I've read the crud can be introduced by the PCV (or via some form Exhaust Gas Recirculation system). On port injected cars the fuels wash over the valves and can keep them clean. Whereas on direct injection cars it can develop into carbon build up.
Thats the theory anyway.

Update:



Got a hydrogen clean done a few days ago and immediately took it for another blast up the motorway in 3rd gear 50mph and 4th gear 70mph to keep the revs up and 2nd gear when in my local streets. Unfortunately issue still persists.


I can't say for certain if this is the case, but the other driver who uses this car has never experienced this issue. Yet I have multiple times. The only difference I see is I start the car by switching ignition on, letting most lights go out and then cranking the car as this is a habit I'm in as I used to do this to let the glow plugs warm up for the diesel vehicles I owned previously. Whereas they turn the key and start the car in one motion. - NVM - I now start the car in one motion and it still happens - they must drive the car when its still warmish.



Perhaps this points towards leaking fuel injectors? - as @dr_mat suggested previously. - What is the best way to test this theory on this engine? I dont think the High Pressure Fuel Pump is broken as the actual and specified values logged by OBD11 are quite close.Although the fact that the misfire is across multiple cylinders mean this may not be the case?

Also had the battery retested since fixing the drain and its good.

For completeness: I've also just replaced my MAP sensor (before throttle body) and Fuel Door lock today.

To update the thread for all, in case someone else experiences similar issues to me. About a year and 5k miles down the line I lost power (speed dropped from 70 to 40 mph on the motorway) one day halfway through an 80 mile trip without warning. The car was misfiring badly with lot of smoke coming out the CAT, unless I kept it in a low gear high RPM (no hard shoulder on that stretch). I managed to reach a safe place and pull over safely. Garage diagnosed that 2 injectors had stuck fully open, and the spark plugs were heavily fouled as a result. I got all 4 injectors and spark plugs replaced. I ended up selling the car shortly after but the light never came back in the short while I kept it after so perhaps there was a slow leak in the injectors originally.

afropelican said:

To update the thread for all, in case someone else experiences similar issues to me. About a year and 5k miles down the line I lost power (speed dropped from 70 to 40 mph on the motorway) one day halfway through an 80 mile trip without warning. The car was misfiring badly with lot of smoke coming out the CAT, unless I kept it in a low gear high RPM (no hard shoulder on that stretch). I managed to reach a safe place and pull over safely. Garage diagnosed that 2 injectors had stuck fully open, and the spark plugs were heavily fouled as a result. I got all 4 injectors and spark plugs replaced. I ended up selling the car shortly after but the light never came back in the short while I kept it after so perhaps there was a slow leak in the injectors originally.

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Better late than never.