Only running on two cylinders (I think)

[MidLifeCrisis]

So, engine sounds rough, low on power .... (1.9 DF with Pierburg carb)
When I pull HT leads off one at a time, only 2 of the 4 cause a change in rpm - which leads me to believe that I'm only running on 2 cylinders; (does that sound correct?)

Both of the HT leads that lead to the non-working cylinders will spark a plug - so that part is working.

So I guess my question is - is there a fault that would 'kill' 2 cylinders - the bad cylinders are the 2 cylinders towards the rear of the vehicle.

Aside from compression check (which I haven't be able to do yet) - is there anything else I can do/check??

Cheers for any help

[Aidan]

usually it's the insulation between the lead and the steel shroud has broken down so the spark instead of going to the plug finds path of least resistance shroud to head outside the cylinder, corrosion due to build up of crud around the spark plug on the road side can contribute to it it is adviseable to blow out the crud before removing the spark plugs and if the corrosion on the plug is high then some plusgas/rostoff penetrating fluid is a good idea before trying to remove the plugs if you haven't already
plugs are supposed to be 2 yearly service item (originally 10k+ a year sort of use)
the new leads don't seem to be as good as the originals which could last 20 years but a set of genuine ones from VW is over £150 as opposed to £35 for a beru set from the usual sources; Beru is oem but I think they are now made in china as are the bosch

[kevtherev]

Yes
Remove all the possibilities.
What your left with is the reason.
Cap, arm, leads, plugs (gapped right)

[Ralf85]

Also check the rotor arm first. The insulation can crack causing misfire problems - it happened on my van.

[MidLifeCrisis]

Thanks all - if it ever stops raining I'll start investigating?

So, there's nothing that might cause the rear left/right cylinders to fail together?

[California Dreamin]

The metal shrouds can be removed using tin snips or similar, they only serve as radio suppression (reducing possible interference to TV's & nearby radios) there is no actual detriment to the engines running when the shrouds are removed.
As I've mentioned before, Volkswagen used to recommend their removal where vehicles presented with misfires at the dealership.
Alternately you can remove the metal shrouded plug caps completely and fit some of these:

http://www.gsparkplug.com/1x-ngk-resist ... -8511.html" onclick="window.open(this.href);return false;

Martin

[MidLifeCrisis]

The metal shrouds can be removed using tin snips or similar, they only serve as radio suppression (reducing possible interference to TV's & nearby radios) there is no actual detriment to the engines running when the shrouds are removed.
As I've mentioned before, Volkswagen used to recommend their removal where vehicles presented with misfires at the dealership.
Alternately you can remove the metal shrouded plug caps completely and fit some of these:

http://www.gsparkplug.com/1x-ngk-resist ... -8511.html" onclick="window.open(this.href);return false;

Martin

That would be great advice but unfortunately I took your advice on this a while ago and replaced with those spark plug caps already !!!

[tobydog]

Plugs can sometimes create a `weak' spark in air, but fail under compression. Check the gaps?

[MidLifeCrisis]

Plugs can sometimes create a `weak' spark in air, but fail under compression. Check the gaps?

Interesting thought - thanks.
Sunday is going to be tinkering day!!

[California Dreamin]

The metal shrouds can be removed using tin snips or similar, they only serve as radio suppression (reducing possible interference to TV's & nearby radios) there is no actual detriment to the engines running when the shrouds are removed.
As I've mentioned before, Volkswagen used to recommend their removal where vehicles presented with misfires at the dealership.
Alternately you can remove the metal shrouded plug caps completely and fit some of these:

http://www.gsparkplug.com/1x-ngk-resist ... -8511.html" onclick="window.open(this.href);return false;

Martin

That would be great advice but unfortunately I took your advice on this a while ago and replaced with those spark plug caps already !!!

Lol......

Other suggestions: Compression issues (fingers crossed that it isn't this)
Air leak...I can't for the life of me remember the details but I'm sure I read someone on this forum (might have been Kev?) talking about a vacuum leak somewhere on the manifold.
Manifold gaskets leaking (loose bolts)
The brake vacuum take off? again drawing in air etc, however yours are two opposite cylinders sooooo...dunno.
Plugs breaking down.
Distributor cap (hairline cracks) carbon bush missing....large rotor to distributor air gaps (some users mistakenly using emery cloth to rub down the rotor)
Hydraulic tappets propping open the valves (not a known fault on wasserboxers, well not one I've heard of, however other engines with similar hydraulic elements do have this issue, where occasionally, from cold, the tappets will overfill and not allow the valves to fully close) this cures itself after a short engine run.

[California Dreamin]

The metal shrouds can be removed using tin snips or similar, they only serve as radio suppression (reducing possible interference to TV's & nearby radios) there is no actual detriment to the engines running when the shrouds are removed.
As I've mentioned before, Volkswagen used to recommend their removal where vehicles presented with misfires at the dealership.
Alternately you can remove the metal shrouded plug caps completely and fit some of these:

http://www.gsparkplug.com/1x-ngk-resist ... -8511.html" onclick="window.open(this.href);return false;

Martin

That would be great advice but unfortunately I took your advice on this a while ago and replaced with those spark plug caps already !!!

Lol......

Other suggestions: Compression issues, burnt out valves (fingers crossed that it isn't this)
Air leak...I can't for the life of me remember the details but I'm sure I read someone on this forum (might have been Kev?) talking about a vacuum leak somewhere on the manifold.
Manifold gaskets leaking (loose bolts)
The brake vacuum take off? again drawing in air etc, however yours are two opposite cylinders sooooo...dunno.
Plugs breaking down.
Distributor cap (hairline cracks) carbon bush missing....large rotor to distributor air gaps (some users mistakenly using emery cloth to rub down the rotor)
Hydraulic tappets propping open the valves (not a known fault on wasserboxers, well not one I've heard of, however other engines with similar hydraulic elements do have this issue, where occasionally, from cold, the tappets will overfill and not allow the valves to fully close) this cures itself after a short engine run.

[MidLifeCrisis]

Lol......

Other suggestions: Compression issues, burnt out valves (fingers crossed that it isn't this)
Air leak...I can't for the life of me remember the details but I'm sure I read someone on this forum (might have been Kev?) talking about a vacuum leak somewhere on the manifold.
Manifold gaskets leaking (loose bolts)
The brake vacuum take off? again drawing in air etc, however yours are two opposite cylinders sooooo...dunno.
Plugs breaking down.
Distributor cap (hairline cracks) carbon bush missing....large rotor to distributor air gaps (some users mistakenly using emery cloth to rub down the rotor)
Hydraulic tappets propping open the valves (not a known fault on wasserboxers, well not one I've heard of, however other engines with similar hydraulic elements do have this issue, where occasionally, from cold, the tappets will overfill and not allow the valves to fully close) this cures itself after a short engine run.

Excellent advice thanks - will have a go at compression test and I'm collecting some new plugs tomorrow so that'll rule a few things out ....
Vacuum leaks are def a possibility but can't see how that'd effect only two cylinders (especially as it's left and right so it's not 'sided'?!?)
Tappets is an interesting thought ? I'd did struggle through a bit of a run out with it (maybe only 5 minutes) - would that have been enough to 'cure' a tappet problem?? (And I had it idling for a good 10 mins while I was messing with the HT leads)

[ajsimmo]

Tappets can take 20 mins to sort themselves out (or a lot longer if you don't drive it, just running stationary). Have tappet preloads been checked?

Only thing common to two opposing cylinders is they share the same two cam lobes...just a thought.

[MidLifeCrisis]

Tappets can take 20 mins to sort themselves out (or a lot longer if you don't drive it, just running stationary). Have tappet preloads been checked?

Only thing common to two opposing cylinders is they share the same two cam lobes...just a thought.

That's a bad thought !!!!