A Daewoo Lanos 8v sohc which is not firing on #3 cylinder and idling very lumpy. I checked this by pulling the HT leads from each sparkplug in turn as the engine was idling. The engine revs drop to almost stall when I pull the leads to cylinder 1, 2, & 4 but make no difference when I pull # 3.I swapped #3 plug & HT but made no difference. Also tried another coil pack from a known good lanos but still no joy. The same thing happens when I disconnect the injector plugs. 1,2 & 4 drop the revs but removing #3 makes no difference. Thinking it may be a blocked injector I swapped #3 & 4 around but still no fire on #3. Also did the same with the electrical connectors.I did a compression test with the engine at normal temp with plugs removed and throttle fully open and the results are;1 180psi2 180psi3 140psi4 160psiDo you think #3 compression would cause it not to fire? I read that the lowest compression reading should be within 25% of the highest, so in this case about 22%. Any pointers welcome.

You need to see if the plug is actually sparking and the injector squirting fuel before eliminating those things from the possibilities. However clearly there's an internal problem, possibly a head gasket starting to blow between 3 and 4, but I don't think the readings are low enough to stop the cylinder firing.

No fire on #3 cylinder?

Apr 03, 2006 28 Replies

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Colin Stamp 20 years ago

Do you mean you swapped over the injector itself, or just the connectors? I'd read your previous post as if the injectors had been in their original positions all along. If you really did swap the injectors themselves over, that puts a whole new complexion on it.

Injector cleaner down the inlet won't clean the injectors. The only way to get it to go *through* the injectors is to mix it with the fuel. Even then, if one is not opening at-all, it won't help.

Yep. I've no experience of poor compression (slightly or otherwise) so I'm still in two minds as to whether it might be an issue.

Cheers,

Colin.

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redwood 20 years ago

Yes I had already swapped the actual injector around. The #3 injector worked ok in #4 but 4 still didn't fire #3 cylinder. Also swapped the electrical plugs over with the same result and cranked the engine over with the fuel rail lifted out to see the injectors all squirt so I think that pretty much rules out the fuel / injector side.

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redwood 20 years ago

I believe these are the same lumps as Vauxhall. Would a camshaft problem have shown up on a cranking compression test? I'm just off to do the running comp test now.

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Graham 20 years ago

A worn cam lobe could give good compressions but give bad running.

Also check any vac pipes that come off the no3 cylinder, inlet manifold runner. Often on Vauxhalls there was a pipe going to a small vac valve that gave problems. It used to split apart creating a vac leak. Also does the brake servo pipe come off no 3 runner?

Graham

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redwood 20 years ago

I am getting around 50psi at idle on #3 which I think is ok but the gauge on my Gunsons compression tester has broke so I can't complete all the tests. Will need to get a new gauge but the puffs of air from the compression tester valve appear similar across the cylinders.

Everything appears connected can't see anything coming off #3 inlet. Had a look at the EGR valve but that has it's own chamber going back to the main intake block.

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Pete Smith 20 years ago

Bugger, I missed the "same with the electrical connectors". I assumed it was all with the connectors.

I'd now check the inlet lobe of the cam.

If the inlet is working, but the exhaust isn't, you'd get monster backfires.

If the inlet is not working, you'll get no fuel/air inside the cylinder, but there will still be the opportunity to suck exhaust gas back inside via the partially open exhaust valve.

Maybe :-)

Pete.

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Colin Stamp 20 years ago

Ah. I mis-understood then - sorry. So we've got fuel, spark and apparently good compression but still no bangs - hmmmm....

One thing that might cause all these symptoms would be a stuck-shut valve, maybe a knackered hydraulic tappet or a broken rocker or something.

I think I'd be taking off the cam cover next.

Cheers,

Colin.

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redwood 20 years ago

The engine doesn't sound too bad considering #3 isn't working but I suppose the ecu & gizmos will be working overtime. From the exhaust it does make a pup pup pup sound.

Thanks for the replies, my local friendly mechanic is going to take a look Friday but I'm leaning towards it been a problem in the valves or that area.

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redwood 20 years ago

Had confirmation from the mechanic that it is a worn camshaft lobe. Now deciding if it's worth spending on!

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