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Firing on three cylinders

iMacThere4iAm

Tom Long
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750
Location
Morecambe
Hello folks, long time no see - that's because Felicia's been running pretty much flawlessly for months!
However the other day I was trying to overtake a lorry on the motorway and one cylinder just stopped firing.

I've ruled out electrics as the cause but I can't figure out what else it could be. Valve trouble? What can I check next?
 
Valve trouble would tend to start off making it run on 3 cylinders at idle while running fine in normal driving.

It's more than likely a bad HT ignition lead. They can be a pain to trace as sparks find it much easier to jump a gap when you are testing them by holding the lead near an engine block, but find it more difficult under compression inside the cylinder.

Could be a bad spark plug too, but I'd replace the ignition leads first. Could replace both for a small investment.
 
Hi Malcolm,
Did some more investigation today. There's no compression on the cylinder so I can rule out electrics. Now suspects include a blown head gasket, burned valve, and burned piston rings - in rough order of annoyance. There's a smell of petrol in the oil so head gasket feels probable.

So it looks like the next step is to take off the head - a first time job for me. Are any special tools or precautions needed? I know about tapping off the head sideways and then clamping down the liners.
 
What were the results of your compression test? It can't surely be zero in that cylinder?
I think that a broken head gasket would result in water in your oil. Perhaps the petrol is trickling down past the rings
 
A comprehensive compression testing kit is about £11.00 delivered from eBay, may be worth checking properly before committing to even more costly works.
 
The only thing I would try is setting the valve clearances. You can do that with the head in place.

Unlikely to be that if the failure was sudden. Let us kniw what you find.
 
Thanks Malcolm but I did check the valve clearances before christmas and they were fine. Fingers crossed for tomorrow, I've never gone this far into engines before.
 
I'd double check the valve clearances again, I've had them muck up on me after my early years attempts at engine maintenance!
 
This sounds like what's happened to mine, if I pull leads 1 & 2 off together it runs and sound the same, pull 3 or 4 off and it stalls. Leads are ok, new plugs. it judders badly in 4th below 70kmph but ticks over and runs fast ok. Pipes on carb checked too.
 
Intriguing... What happens if you take off either lead 3 OR 4 in turn? If disconnecting leads 1 & 2 doesn't alter the engine's running then something IS wrong somewhere as it ought to stop or at least run very badly! Try removing just 3 and then just 4 and see which one makes things worse. A compression test might help sort things out.
 
Pulling 3 or 4 both have the same significant affect of revs dropping or stalling. I'm starting to think that the valves in 1 & 2 are gone. I will take all 4 out and see if I can feel a difference between the compressions but only have my finger over the hole as a check for now. I'll try tomorrow after work.
 
It seems as if cylinders 1 & 2 are doing very little work & that all the graft is being left to 3 & 4! If the valves are only slightly damaged the car would probably run reasonably well at speed and only suffer when under load (cf poor running at about 40 MPH in top.) The emissions will be all over the place, too!

A compression test's a must here!
 
Andrew4, my thoughts too, it does run well at speed and tick over but just not able to drive through a village in 4th without juddering. I put lead additive in the petrol do the rest of you?
 
These engines were built for leaded fuel (l'essence avec plumb) and if they've been used for a considerable time on unleaded (l'essence sans plumb) fuel then this may cause the valves and the valve seats to wear out. It depends on the length and how hard the engine is used. I'm a believer in having the head off & the valve seats hardened, allowing unleaded fuel to be used without needing an additive for evermore!
 
These engines were built for leaded fuel (l'essence avec plumb) and if they've been used for a considerable time on unleaded (l'essence sans plumb) fuel then this may cause the valves and the valve seats to wear out. It depends on the length and how hard the engine is used. I'm a believer in having the head off & the valve seats hardened, allowing unleaded fuel to be used without needing an additive for evermore!
Had the rocker cover off at the weekend to check the valve clearances, should be IN 0.15 OUT 0.2, they were 0.9-0.7,0.5-0.25,0.13-0.22 & No 4 was 0.11-0.15. Just received my Haynes book, been years since serious work on cars, is the head off much of a job and any particular special tools recommended? I know it will say in the book but just asking for experienced view.
 
I put lead additive in the petrol do the rest of you?

I do (in a 1990 GTL), but I don't think it's necessary for pottering around at low revs. More likely it's good to have added protection for long periods of high revs (e.g. motorway driving). I use Castrol Valvemaster (not the 'plus' version). See these threads:
http://renault4.co.uk/forum/threads/lead-replacement-petrol.5/
http://renault4.co.uk/forum/threads/which-fuel-additive-to-use.6546/
http://renault4.co.uk/forum/threads/petrol-additive-or-not.4284/
http://renault4.co.uk/forum/threads/fuel-additive-castrol-valvemaster-plus.2794/
http://renault4.co.uk/forum/threads/leaded-petrol.2327/

Hope that helps!
 
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