Engine: 2.5: Strange engine...

[Streethawk]

Well, my 2.5 non-turbo auto has been running ok since its last service about 1k ago which included new sparkplugs, but started running a little rough last week. It got worse this morning and ran rough all through a 5-10 mile run into town with several stops but was only runing a little rough by my return up the hill.
(ATS didn't charge me for fixing a big puncture - kudos to them as ever)
After lunch we delved in to try to see if this is a simple problem and found something that (to us) appears really odd...

To try to determine if any of the cyliders aren't firing, I disconnected the lead to the coil of each cylinder hoping to find one that didn't make it run any worse when disconnected, thus hopefully identifying a potential culprit. 5,4 & 3 all made it run worse, but disconnecting 2 made no difference. Diconnecting 1 made it rougher once more.

We've run through further diagnosis on 2 - the spark plug looks like it's been burning fuel without any obvious mixture or oil issues. We checked for a spark, no problem. Swapped the coil with number 1 made no difference, likwewise swapping plug didn't either.

So I didn't really get anywhere, it's running okayish when warm so i figured I'd try again tomorrow from cold.
HOWEVER, before stopping I tried disconnecting each lead again and found the same rough running without one of 5,4 or 3, no change when disconnecting 2 and now no change either when disconnecting 1!
I must have got it wrong so I double checked and Ms. S watched me to ensure I'm not just being an idiot.
I even disconnected 1 & 2 simultaneously and it makes no difference to its running at all

Is there something about Volvo engines different to anything else so these two cylinders don't need a lead but the others all do?!?
Or have I been running on 3-4 cylinders for aaages in blissful ignorance.
The engine light has gone on and off for years apparently at random without noticeable effect on mpg or performance by the way - it's currently illuminated.

Totally baffled - any pointers anyone please?

[Clan]

Originally Posted by Streethawk

Well, my 2.5 non-turbo auto has been running ok since its last service about 1k ago which included new sparkplugs, but started running a little rough last week. It got worse this morning and ran rough all through a 5-10 mile run into town with several stops but was only runing a little rough by my return up the hill.
(ATS didn't charge me for fixing a big puncture - kudos to them as ever)
After lunch we delved in to try to see if this is a simple problem and found something that (to us) appears really odd...

To try to determine if any of the cyliders aren't firing, I disconnected the lead to the coil of each cylinder hoping to find one that didn't make it run any worse when disconnected, thus hopefully identifying a potential culprit. 5,4 & 3 all made it run worse, but disconnecting 2 made no difference. Diconnecting 1 made it rougher once more.

We've run through further diagnosis on 2 - the spark plug looks like it's been burning fuel without any obvious mixture or oil issues. We checked for a spark, no problem. Swapped the coil with number 1 made no difference, likwewise swapping plug didn't either.

So I didn't really get anywhere, it's running okayish when warm so i figured I'd try again tomorrow from cold.
HOWEVER, before stopping I tried disconnecting each lead again and found the same rough running without one of 5,4 or 3, no change when disconnecting 2 and now no change either when disconnecting 1!
I must have got it wrong so I double checked and Ms. S watched me to ensure I'm not just being an idiot.
I even disconnected 1 & 2 simultaneously and it makes no difference to its running at all

Is there something about Volvo engines different to anything else so these two cylinders don't need a lead but the others all do?!?
Or have I been running on 3-4 cylinders for aaages in blissful ignorance.
The engine light has gone on and off for years apparently at random without noticeable effect on mpg or performance by the way - it's currently illuminated.

Totally baffled - any pointers anyone please?

why have you been changing so many head gaskets ? It could be blowing between cylinders 1 and 2 .... or an air leak into 1 and or 2 ... or tight valve clearances .

[Streethawk]

Originally Posted by Clan

why have you been changing so many head gaskets ? It could be blowing between cylinders 1 and 2 .... or an air leak into 1 and or 2 ... or tight valve clearances .

I had it changed at 86k and again about 115k, probably because the first one was never done at all (i.e. by using additive) or maybe just done badly without a skim.

Do you think this is anything to do with the odditty reported?

[Clan]

Originally Posted by Streethawk

I had it changed at 86k and again about 115k, probably because the first one was never done at all (i.e. by using additive) or maybe just done badly without a skim.

Do you think this is anything to do with the odditty reported?

you had the gasket changed for no reason ? They are not a service item ... what additive do you mean ? Did you have a skim ? And has it ever overheated ? If so blocks can warp as well as heads ..

[chelle_belle]

Might be worth doing a compression test.

Craig.

[Streethawk]

Originally Posted by chelle_belle

Might be worth doing a compression test.

Craig.

Spot-on craig, losing compression on 3 cylinders. This one's done for (considering all the electric and suspension work it needs).

[Streethawk]

Originally Posted by Clan

why have you been changing so many head gaskets ? It could be blowing between cylinders 1 and 2 .... or an air leak into 1 and or 2 ... or tight valve clearances .

I finally got back to this after 9-months solid of contract work.
Took it to the best local old-school garage and had feedback from the mechanics that compression on the first two cylinders are nil/low and the third slightly low.
Any further investigation & remedy was to see the head lifted so I am going to let this one go under 'uneconomical repair'

Good news is I'm after a v50