Zetec dropped a cylinder?
Discussion
2L Zetec in a Caterham.
Car has been faultless then slowed at a junction and a misfire started.
I drove home 2 miles incase it refused to start after stopping to look .
No2 exhaust is cold, swapped the plugs and still cold, the plug is getting wet.
My compression tester won't fit as there's a collar before the thread starts and the the testers thread doesn't reach.
There is a spark.
I've new plugs on order but won't get a chance to investigate till Saturday so any help on what else to check would be good.
It runs on fuel injection.
Car has been faultless then slowed at a junction and a misfire started.
I drove home 2 miles incase it refused to start after stopping to look .
No2 exhaust is cold, swapped the plugs and still cold, the plug is getting wet.
My compression tester won't fit as there's a collar before the thread starts and the the testers thread doesn't reach.
There is a spark.
I've new plugs on order but won't get a chance to investigate till Saturday so any help on what else to check would be good.
It runs on fuel injection.
If it's got fuel but not running, I'd start by looking for an ignition fault. Given the other cylinders are still firing you can rule out the common parts.
I have a cheap passive strobe timing light which connects in series with an HT plug lead which I can use to check the spark visually while cranking/running. I've also got some HT lead adapters that connect between the plug and the HT lead, but these are harder to see.
I have a cheap passive strobe timing light which connects in series with an HT plug lead which I can use to check the spark visually while cranking/running. I've also got some HT lead adapters that connect between the plug and the HT lead, but these are harder to see.
Swap the fouled plug with one of the unfouled ones,preferably with a hot engine. If the misfiring cylinder then starts firing and vice versa you will know its not the plug at fault,it is possible that the previously fouled plug will then fire correctly, I would still fit a set of new plugs when they arrive.
The other old trick is to heat a fouled plug in a gas flame until it is too hot to hold , then refit, again best performed with a hot engine, and the gas flame well away from the engine bay!
The other old trick is to heat a fouled plug in a gas flame until it is too hot to hold , then refit, again best performed with a hot engine, and the gas flame well away from the engine bay!
Do you mean the compression is literally zero? That suggests either a broken/bent valve, or a holed piston. You could put a boroscope down the plug hole and/or do a leakdown test to see where the air is going, if you want to verify. Does sound like the head will need to come off to fix it either way, but personally I'd look for conclusive proof rather than rely on a compression test, before taking on a job that big.
Sudden loss of literally all compression, I would expect to be valve related, as from my understanding you would have noticed a failed rod!
I presume the plug was intact? My 1900 CVH dropped the inlet valve and holed the piston, other than a bit of oil out of the inlet it was as you describe. The end plug looked like it had been hit a few times by a valve however I guess its possible for it to get through the piston before hitting the end of the plug.
Edit. No missfire either, just a sudden 25% drop in power while pulling away from a junction.
Daniel
I presume the plug was intact? My 1900 CVH dropped the inlet valve and holed the piston, other than a bit of oil out of the inlet it was as you describe. The end plug looked like it had been hit a few times by a valve however I guess its possible for it to get through the piston before hitting the end of the plug.
Edit. No missfire either, just a sudden 25% drop in power while pulling away from a junction.
Daniel
Edited by dhutch on Friday 11th May 15:14
Thanks, It's odd as it sounded like a misfire whilst slowing for a junction, I was sure a plug had failed, then maybe a blocked or stuck injector.
I did put a rubber bung over the plug hole and there was pressue, and it felt quite a bit but when I eventually got a extension for my pressue tester
it fails to register on that bore at all.
I've taken the exhaust off and the valve bits I can see look fine.
The spark plug that came out showed no damage.
Ordered a borescope this morning that should arrive tomorrow
I did put a rubber bung over the plug hole and there was pressue, and it felt quite a bit but when I eventually got a extension for my pressue tester
it fails to register on that bore at all.
I've taken the exhaust off and the valve bits I can see look fine.
The spark plug that came out showed no damage.
Ordered a borescope this morning that should arrive tomorrow
Camera from Amazon has only just arrived, first impression is the piston is fine with no damage.
Exhaust valves look ok but I don't think one of the inlet valves is closing properly, i should have a bit more time tomorrow to check.
This pick the valve should be fully closed.
The clean part of the valve stem at the top i would expect to be hidden?
Exhaust valves look ok but I don't think one of the inlet valves is closing properly, i should have a bit more time tomorrow to check.
This pick the valve should be fully closed.
The clean part of the valve stem at the top i would expect to be hidden?
Edited by tight fart on Monday 14th May 07:59
Peanut Gallery said:
An idea to try a very old school bodge - but with your camera to confirm you have done it properly - obtain new valve spring, wedge something through the spark plug hole to hold the valve fully closed, change valve spring, job jobbed? - no removal of head, etc.
I have done this on a Honda GX-160 generator engine in a Kart. Feed soft rope into the cylinder via the spark plug hole, move piston round towards top dead centre to support the valve, change spring. I have no idea how well this could be applied to a Zetec.Obviously if the alternative if head off, you have lost nothing bar the time even if it doesn't play out?
Daniel
I would not change just one weak valve spring (if indeed thats the issue) I would be pulling that head and renewing the set the consequences of another failing could be catastrophic, I would be inclined to find out what brand were fitted and avoid using again 
thats a very unusual failure IMO even on a performance build
thats a very unusual failure IMO even on a performance build Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff