[Mk4 Golf] Compression down in cyl. 3 - Engine, Tuning and Performance - uk-mkivs

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Compression down in cyl. 3



Best Answer DerPanzerWagen , 05 August 2020 - 06:47 AM

:funky:

 

The compression is definitely back! 9 bar across all cylinders! I had to pinch myself, so we tested it again and it is definitely there. 

 

What was wrong? Evap system is bunged up and can't deal with the gases until it's forced through.  We thought it was the ignition coils sparking it was so loud and frantic when it clicked. The valve on the charcoal canister went in the garage and it now sounds like a kettle whistling. Took the valve off and everything calmed down inside the engine. 

 

Got a few more things to do to the car:

 

Change sparks 2, 4 & 6

Fit new plug on the MAF sensor as plastic has cracked due to age

Do an engine flush and another oil change

Put in some proper ignition coils instead of the emergency ones from ECP I'm running

Clean up the negative and positive connection points on the car

Check the noisy cooling fan on the front as the extra heat from the engine over the last few months has put a bit of strain on it ( :Y: warranty job)

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Poll: b0rked! (3 member(s) have cast votes)

What to do?

  1. Take the head off and investigate further? (1 votes [33.33%] - View)

    Percentage of vote: 33.33%

  2. Just stick another block in with recon head? (2 votes [66.67%] - View)

    Percentage of vote: 66.67%

  3. Sell car with or without engine? (0 votes [0.00%])

    Percentage of vote: 0.00%

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#1 DerPanzerWagen

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Posted 21 July 2020 - 08:04 AM

Big job has happened... Found out that my vacuum leak isn't a vacuum leak. 

 

All other cylinders are great but number 3 is down on compression causing lumpy running at low speeds and slight misfires. Enough to trigger an engine light. When the engine light comes on though, car runs like nothing has happened. (HOW?!) 

 

So what to do?

 

- Take the head off and investigate further down the rabbit hole? 

- Just stick another block in and recon the head?

- Sell car with or without engine?

 

The last option is a shame really and not something I want to do as all suspension is only 2 months old. It has had various new sensors and new oil sump in the past few months. Just had a major service, which is very annoying as I asked original mechanic who looks at my car about the various issues it has been having over the last 6 months. (There's one place I wont be visiting again ever.... I've learnt my lesson that this car wants someone good with a set of tools and not reliant on the error code reader.)

 

Anyhow, what to do? It's less scary to just get on with option 2 as the work has been done and everything has been changed. Also saves opening it up again in the near future. Option 1 is on another level as it could go either way.




#2 northpole

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Posted 21 July 2020 - 09:01 AM

IMO if you go and open up the block you'll find that compression problems usually are the bottom block... meaning it needs to be honed,new piston rings etc etc etc ... buying another engine would be the simplest course of action and with it being a V6 4 motion with an engine problem, what i would do is go R32 or R36 engine (last one is from a Passat R36 and kinda hard to find but if you do find it and can afford it go for it, R36 = 296BHP/350NM) but i would deffo go for the more powerfull r32 engine... but that is me... if you can't find one in your budget make sure you get the same engine code V6 as that will be a fit and forget option... 

 

so it's the best course of action..as you can see by the votes...  



#3 Neutron

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Posted 21 July 2020 - 10:57 AM

I'd try and find out where the compression is going, valves, bottom end or gasket (do you get blowing with the oil filler cap off?) and hope that it's a sticky ring. I've had some success improving compression by engine braking on the overrun to free up/reseat rings, or maybe running some misted water through one of the vacuum lines in the inlet to loosen any carbon build up



#4 DerPanzerWagen

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Posted 21 July 2020 - 01:23 PM

buying another engine would be the simplest course of action and with it being a V6 4 motion with an engine problem, what i would do is go R32 or R36 engine (last one is from a Passat R36 and kinda hard to find but if you do find it and can afford it go for it, R36 = 296BHP/350NM) but i would deffo go for the more powerfull r32 engine...

 

Heard that the r36 one is a bit of a pain in the bumflaps to get right in a mk4 but the r32 one would be a quick n easy option. :) 



#5 northpole

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Posted 21 July 2020 - 02:18 PM

reason why i would ust drop in an R32 is because of the extra power... and basically you have almost the same running gear so if the engine has a problem like this, instead of fixing it i would just replace it... R32 would be my first point of call... and yes the power hike is nice but all in all the r32 engine is better than the v6 engine...  and they use the same amount of fuel on average so why not? 

 

What engine code do you have now as if you have the BDE engine you need less stuff... but here's a quick summery: 

 

4mo exhaust bolts straight up as the cast manifolds are the same though the down pipe has smaller flanges at the cat end
The 4mo cat is about a foot shorter so if you plan to fit a r32 exhaust you will need to bear that in mind

you can use the 4mo gearbox clutch/flywheel you can use either but don't mix parts as the r32 flywheel depth is different
Probably best to use the clutch and flywheel for the gearbox you intend to use

you should be able to pull the immo pin from the r32 ecu you can then log into the ecu to code it to the existing clocks or if can't be bothered you can just get a immo defeat done
try get a complete engine as things like injectors and fuel rail are different as obviously is the inlet manifold Throttle body and pipe to the airbox as is the MAF
vac pipes you can use the 4mo ones though it will foul the aircon inlet slightly the r32 one has a bend to clear it
you can use the 4mo fuel pump but the r32 one is better
also you won't have the exhaust flapper or the wiring you will get a fault code for that


the more you get with the engine the better i'd say



#6 DerPanzerWagen

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Posted 22 July 2020 - 02:27 PM

Quick update:

 

Cyl 3 is down by 40-45%.

 

Cyl 1, 2, 4, 5 & 6 have full compression.

 

I thought it would have been cyl 5 to cause the most grief as that is where I keep having to stick new ignition coils on.


Edited by DerPanzerWagen, 22 July 2020 - 02:29 PM.


#7 DerPanzerWagen

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Posted 24 July 2020 - 12:44 AM

Well I've taken the car out twice since getting it back from the garage. Strangely noticeable things are the car:

 

  • still goes like stink and gives locals a run for their money on a roundabout or at the lights.
  • even in the middle of nowhere, up a big hill a farmer driving a tatty mk1 Ford Focus will pass by leaning out the window saying 'Nice car!'  

 

The first trip, I just drove it as normal and headed for the hills. Drove fine for 45 miles util I got about 1100ft up where the engine made a complain and engine light came on. Didn't have the reader with me but discovered the car ran better than it just did. Drove car back home on the A roads without issue. 

 

Tonight though I decided to drive it in a more normal environment and see what it does and doesn't like. I cleared the engine light as you shouldn't bother reading it the first time round.

 

If you do the following, you can feel the power come back on all 6 cylinders:

 

  1. Change gear between 2.8k and 3.4k revs until you can hold the car at 3k for any speed. 
  2. For driving around town, use 2nd at 25mph.
  3. You can keep the compression up by not coming fully off the accelerator pedal when changing gears.

Driving like that, you don't notice any problems and feels like the car is just driving itself, with very little accelerator input. The mpg remains good. However, once the engine warms up and if you do any of the below, it reduces the mpg somewhat and now triggers the engine light to come on:

  1. Driving the car under 2.4k revs for any more than a few minutes makes the car complain and it loses the compression. This gives very lumpy running when warmed up but not while warming up. For instance, driving it at 30mph in 3rd gear around town
  2. Sitting with the engine idling for more than a few minutes. This also gives very lumpy running when warmed up but not while warming up.

BTW, the engine light is: p0420 and I've managed to trigger it a few times this evening. Once it comes on, the car drives like none of the above has ever happened. (Recently all 4 O2 sensors replaced and wiring checked, ECT sensor replaced and wiring checked, coolant refresh, spark plugs new and rechecked, coils checked. No funky smells from the exhaust outside, no fumes leaking into the car and no exhaust leaks.) 

 

So is the code related to the lack of compression in cyl. 3 or in addition to it? As I don't want to replace the engine and find the cat is fubar'd. I just want to get the whole job done and costed up once rather than in stages as I know I'll have to replace a few hoses once the engine is out too.



#8 northpole

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Posted 24 July 2020 - 02:37 PM

yeah it is related to the unburnt fuel getting dumped into the exhaust from cylinder 3... long story short you know what is up i would start getting a replacement engine asap R32 with ecu and engine loom and all aux bits.. so when it finally goes, you can just swap the engine over with all the parts and after a coding session have an R32



#9 adam-

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Posted 24 July 2020 - 07:20 PM

Figure out why compression is down.

 

Do a leak down.  If it doesn't change, it's a bad valve.  Sniff test for headgasket, although you'd know about that.  Go from there.


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#10 DerPanzerWagen

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Posted 25 July 2020 - 12:32 AM

yeah it is related to the unburnt fuel getting dumped into the exhaust from cylinder 3... 

 

Cool, will add that cat to the list. (I ran over one the other day... Guess this must be payback.)



#11 DerPanzerWagen

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Posted 25 July 2020 - 12:35 AM

Figure out why compression is down.

 

Do a leak down.  If it doesn't change, it's a bad valve.  Sniff test for headgasket, although you'd know about that.  Go from there.

 

HG appears to be fine as and no exhaust leaks. I'm not gonna go to further with this now anyhow. On hunt for another engine before MOT's due in October...



#12 adam-

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Posted 25 July 2020 - 10:43 AM

What is compression?  If you have low compression, there's no point in chasing any other hardware issues.  That engine is toast.


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#13 DerPanzerWagen

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Posted 26 July 2020 - 11:33 AM

What is compression?

 

I've heard of it...



#14 DerPanzerWagen

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Posted 02 August 2020 - 10:39 PM

Oh FFS - this is just brilliant...

 

Had another compression test on Wednesday just to get a 2nd opinion as I needed to see if the car would make it to London and back on Friday. Got told cyl. 3, 4 AND 6 were now nearly dead and was told it probably wouldn't make it there and it had hours to live.

 

So typical me thought Two Veg to that and I took it anyway!

 

Attached File  FullSizeR(4).jpg   79.58KB   0 downloads

 

Turns out Friday in London was the hottest day of the year... The car made it there and back again. Car is also still going and seems to be getting better. I don't think it agreed with lockdown and just needed a good old boot. I imagine I dislodged something from inside.



#15 northpole

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Posted 03 August 2020 - 10:09 AM

well if it actually seems to drive better i would go back for another compression test... but with the results you had it wouldn't surprise me if it's the piston rings that need changing... but if it runs better now well in that case the compression might be restored somehow... but you'll only know when you actually have it tested again.. i suggest you do that as it still is cheaper than buying another engine .. and if compression is restored... you might want to do a engine flush and add fresh oil and filter and see what happens than... 

 

ps about the cat... i wouldn't just replace it without running cataclean first... they should be able to work for a while regardless of unburned fuel being dumped in.  



#16 DerPanzerWagen

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Posted 03 August 2020 - 10:57 AM

well if it actually seems to drive better i would go back for another compression test... but with the results you had it wouldn't surprise me if it's the piston rings that need changing... but if it runs better now well in that case the compression might be restored somehow... but you'll only know when you actually have it tested again.. i suggest you do that as it still is cheaper than buying another engine .. and if compression is restored... you might want to do a engine flush and add fresh oil and filter and see what happens than... 

 

ps about the cat... i wouldn't just replace it without running cataclean first... they should be able to work for a while regardless of unburned fuel being dumped in.  

 

Technically, with the compression I was getting, the engine shouldn't be running as when one cylinder bricks itself, it will shut the whole bank down as the misfiring would damage the cat. (Cyl 3 & 4 are on 2 separate banks and were very near to 0.5 bar.) The better cylinders couldn't have made up for that amount of loss surely as that would be crazy? 

 

Will be getting an oil and filter change this week plus another compression test tomorrow. Engine light has been staying off for longer when it's cleared now too. Took it out yesterday even at various road speeds and up hills no problem. It didn't complain but I still feel a slight misfire at idle. 

 

I'll give the cataclean stuff a go. No harm in it if it keeps the engine light off for a while and improves things a bit more. I can go get an MOT on it and then fix things properly. 


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#17 adam-

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Posted 03 August 2020 - 06:14 PM

Never heard of it shutting down banks, I don't think that's correct.  Also 0.5 bar (7psi) is literally no compression whatsoever, there's no way that would idle at all.  Sub 100psi is weak.


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#18 northpole

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Posted 04 August 2020 - 07:50 AM

No the v6 and r32 aren't able to shutdown banks, it's not in the ecu and all mechanical links to the 2 different banks are all solid no gears or links that can be stopped by the ecu ... so nope no shutting down of anything... the readout you got might have been like that  at said time and come to think about it... when is the last time you checked your timing chain, guides, and the tensioner? this could also be a problem that gives weird readings but i've never seen compression that low and the car being able to run properly let alone make a 100 mile round trip... so maybe the oil pickup is part of the problem but that would be addressed when you do an engine flush and replace the oil with new and a fresh oil filter...  (use a flushing oil by the way, the gritty stuff isn't the best and can clog oil channels)  



#19 adam-

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Posted 04 August 2020 - 05:31 PM

How is an oil pickup going to cause localised compression issues?


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#20 DerPanzerWagen

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Posted 05 August 2020 - 06:47 AM   Best Answer

:funky:

 

The compression is definitely back! 9 bar across all cylinders! I had to pinch myself, so we tested it again and it is definitely there. 

 

What was wrong? Evap system is bunged up and can't deal with the gases until it's forced through.  We thought it was the ignition coils sparking it was so loud and frantic when it clicked. The valve on the charcoal canister went in the garage and it now sounds like a kettle whistling. Took the valve off and everything calmed down inside the engine. 

 

Got a few more things to do to the car:

 

Change sparks 2, 4 & 6

Fit new plug on the MAF sensor as plastic has cracked due to age

Do an engine flush and another oil change

Put in some proper ignition coils instead of the emergency ones from ECP I'm running

Clean up the negative and positive connection points on the car

Check the noisy cooling fan on the front as the extra heat from the engine over the last few months has put a bit of strain on it ( :Y: warranty job)


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#21 northpole

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Posted 05 August 2020 - 07:48 AM

Change all the sparkplugs at the same time and if i was you i would go for the NGK R versions... they work really well in the V6 and r32 engines they apparently give a stronger  wider spark and startup faster thus making life easier for the coilpack

 

ps i never had a problem with that charcoal canister so i wouldn't even have thought of it... 


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#22 northpole

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Posted 05 August 2020 - 07:52 AM

How is an oil pickup going to cause localised compression issues?

god knows I didn't think that one through, but if the oil channels were blocked somehow it could have oil in some places... a well he found the problem the evap system... 



#23 DerPanzerWagen

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Posted 05 August 2020 - 06:09 PM

Change all the sparkplugs at the same time and if i was you i would go for the NGK R versions... they work really well in the V6 and r32 engines they apparently give a stronger  wider spark and startup faster thus making life easier for the coilpack

 

Yeah, I use those NGK R's already as it also stops the annoying ground problem with some aftermarket headunits. :wink: 

 

 

No the v6 and r32 aren't able to shutdown banks, it's not in the ecu and all mechanical links to the 2 different banks are all solid no gears or links that can be stopped by the ecu ... so nope no shutting down of anything... the readout you got might have been like that  at said time and come to think about it... when is the last time you checked your timing chain, guides, and the tensioner? 

Ah I thought the engine did do that. Hrmm, either that or I dreamt it.

 

The chain, etc was replaced under warranty when the car had 38K on it. Last checked it in January and this week. All blocks are reading correctly, no chain wobble or funny noises and no slack when probed. 


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#24 Neutron

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Posted 06 August 2020 - 06:49 AM

It all sort of makes sense with the PCV pressure being controlled by the vacuum circuit and that being affected by the screwed up evap - if your crankcase was pressurising then the rings wouldn't be happy and compression would be off. Have you got a catch can or anything like that or is it stock?

 

The only problem I've had with the Evap is the hose split near the valve - causing the classic whistle. The self-amalgamating tape I put on years ago is still doing a top job







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