Compression test - how to disable fuel pump. etc?
Posted: Thu Dec 07, 2023 5:10 pm
Greetings!
Happy to have found a dedicated Scirocco forum… I’ll get straight to the point!
TLDR: Which fuel pump fuses/relays should I remove while doing a compression test?
Detail:
Our 2014 2.0L R line TSI Scirocco (factory standard - unmapped) w only 116k miles recently died on us while on motorway. The Engine symbol (“catalytic”) light came in (but not the EPC light) and car lost power where we managed to coast to an exit. Engine then died and wouldn’t restart - it sounded like it was “trying” to start/sputter, but it didn’t “catch”.... So we called roadside assist and had it towed to a main dealer.
I was convinced this was going to be an ign coil issue as when a coil pack went about a year ago, the symptoms were similar (except then the EPC light came on without the cat light), but the car was still driveable. The mechanic at the time only replaced one coil, so I thought the other 3 couldn’t be too far behind and that another of them may now have gone.
However, after a “basic diagnostic”, the dealer said that cyl 3 was “full of oil”. On a later phone call they also said there was water in it, but that as there is no EPC light or codes stored that it’s not the coils and that to troubleshoot further they’ll need to spend another 4 or 5 hrs taking the engine apart (about £1100!). BTW, cyl 3 was the same cylinder where the coil had been replaced about a year prior…
Not happy with that and not being able to talk directly to a mechanic I had the car towed “home” where it now starts, but is rough as hell - and no error lights. It’s definitely misfiring on at least one cylinder…
I removed the spark plug from cyl 3. It was sooty, but not oily. (I need a larger wrench which I don’t have at the moment to remove the other plugs which are tighter). I didn’t see any signs of water, and both the coolant and engine oil look normal and show no signs of mixing. In short, I’m not convinced of what the dealer told me and amn’t ready to write off this car yet without some more homework.. Per title of this post I want to do a compression test - but have read in several places to remove the high pressure fuel pump relay and / or fuses before doing so.
So my question is, which fuses/relays to remove and where are they?
Also.. I removed each of the coil packs and measured resistance. I noticed that the replaced one (i.e. from the “failed” sooty plug cylinder (3) measures 77k which is significantly lower than the original VW Stock ones that each measure about 97k. I’m not sure if that means the “new” coil has failed or if it was always like that - it doesn’t look like a genuine VW part (has “VMQ” on it), has no covering on the “shaft” and weighs a bit less than the others…
If the compression tests are OK, I’ll spend some money on a new coil to test things. I’m just wondering if anyone had an opinion on the different resistances or on this non-vw replacement coil that was running in the now apparently faulty cyl 3…
Tks!
Happy to have found a dedicated Scirocco forum… I’ll get straight to the point!
TLDR: Which fuel pump fuses/relays should I remove while doing a compression test?
Detail:
Our 2014 2.0L R line TSI Scirocco (factory standard - unmapped) w only 116k miles recently died on us while on motorway. The Engine symbol (“catalytic”) light came in (but not the EPC light) and car lost power where we managed to coast to an exit. Engine then died and wouldn’t restart - it sounded like it was “trying” to start/sputter, but it didn’t “catch”.... So we called roadside assist and had it towed to a main dealer.
I was convinced this was going to be an ign coil issue as when a coil pack went about a year ago, the symptoms were similar (except then the EPC light came on without the cat light), but the car was still driveable. The mechanic at the time only replaced one coil, so I thought the other 3 couldn’t be too far behind and that another of them may now have gone.
However, after a “basic diagnostic”, the dealer said that cyl 3 was “full of oil”. On a later phone call they also said there was water in it, but that as there is no EPC light or codes stored that it’s not the coils and that to troubleshoot further they’ll need to spend another 4 or 5 hrs taking the engine apart (about £1100!). BTW, cyl 3 was the same cylinder where the coil had been replaced about a year prior…
Not happy with that and not being able to talk directly to a mechanic I had the car towed “home” where it now starts, but is rough as hell - and no error lights. It’s definitely misfiring on at least one cylinder…
I removed the spark plug from cyl 3. It was sooty, but not oily. (I need a larger wrench which I don’t have at the moment to remove the other plugs which are tighter). I didn’t see any signs of water, and both the coolant and engine oil look normal and show no signs of mixing. In short, I’m not convinced of what the dealer told me and amn’t ready to write off this car yet without some more homework.. Per title of this post I want to do a compression test - but have read in several places to remove the high pressure fuel pump relay and / or fuses before doing so.
So my question is, which fuses/relays to remove and where are they?
Also.. I removed each of the coil packs and measured resistance. I noticed that the replaced one (i.e. from the “failed” sooty plug cylinder (3) measures 77k which is significantly lower than the original VW Stock ones that each measure about 97k. I’m not sure if that means the “new” coil has failed or if it was always like that - it doesn’t look like a genuine VW part (has “VMQ” on it), has no covering on the “shaft” and weighs a bit less than the others…
If the compression tests are OK, I’ll spend some money on a new coil to test things. I’m just wondering if anyone had an opinion on the different resistances or on this non-vw replacement coil that was running in the now apparently faulty cyl 3…
Tks!