No fire on #3 cylinder?

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.

Cheers, I will have another look tomorrow. I'm just wondering if a Gunsons Colourtune will show me if the cylinder is firing as I think I may have one somewhere?

That'd only tell you what you've already worked out from pulling off the HT leads - No.3 isn't firing.

To check if it's the plug, pull off the HT lead, and plug it into a spare plug. Hold the thread of the plug against the block and it should spark. If not, then, given you've already swapped out that coil and lead, the coil isn't being driven for some reason.

Testing the injector will be a bit more tricky. You could try swapping injector connectors with another cylinder. If it starts firing, then you've found the problem. If not, then it's a bit in-conclusive.

Cheers,

Colin.

Not sure about these, but I'm sure it would be standard wasted spark system. So if 3 wasn't being driven, then neither would 2. I could be wrong, in which case...bleh

I removed and checked all the plugs and swapped them around so the plug from the bad #3 was swapped with the known good plug from #1 cylinder. Before placing it into #3 I tested it on the block and it was sparking ok. Before trying a different coil I also temporarily swapped over leads 2&3 as they both fire at the same time. Pull #3 and nothing happens. Pull #2 and the engine revs drop. Connect #3 lead into #2 sparkplug and the revs rise again, but connecting #2 lead to #3 makes no difference.

Yes I tried that. If I disconnect #4 injector plug the revs will drop. Disconnect #3 and nothing happens but if I put #3 onto #4 the revs rise again, but putting #4 onto #3 makes no difference.

Any chance of getting hold of a compression tester and testing No.3?

Reason I ask, looked at a car a while back with similar symptoms. After much head scratching we found the inlet valve was not seating properly. We had spark but bugger all else.

PDH

From the OP

"I did a compression test with the engine at normal temp with plugs removed and throttle fully open and the results are;

1 180psi 2 180psi 3 140psi 4 160psi"

Yes, posted the compression test results in my first post. They are;

1 180psi 2 180psi 3 140psi 4 160psi

Although #3 is the lowest I beleive it's still within acceptable limits.

Ok, that counts out the ignition and the injector drive. Looks like we're left with that slightly dodgy looking compression, and a blocked or jammed injector. I'd bet on the injector, but I never was much good at gambling...

Cheers,

Colin.

140psi is ample compression to fire, hell 70-80psi and it'll fire pretty well and idle ok-ish.

Either you have no fuel or no spark. simple as that. (I'd bet no fuel- as you dont mention the plug being wet)

Tim..

"Tim (remove obvious)"

No the plug didn't look wet and no smell of neat fuel. In fact it's appearance didn't look too bad actually with a brownish rusty colour and not a great deal of difference between the other plugs. Should the plug be completely black & sooty if no fuel was getting in?

What do you think?

If no there's no fuel coming in then the plug will be dry.

Tim..

No. It's not as simple as that. If we're sure it's not the compression, then it's far simpler than that.

Given the tests that've already been done, it's not just "no fuel", it's almost certainly No.3 injector that's duff - like I said :o)

Cheers,

Colin.

Inlet manifold gasket/leak.

Graham

I'd agree.

I *was* going to say that the OP had swapped injectors 3 & 4, but he hadn't - he'd only swapped the drive signal, so we've got signals down all the wires, sparks at all the plugs, and what appears to be fuel at all the injectors.

It's just not no 3 that's squirting, so there's your problem.

Pete.

Apart from getting a test meter set to read resistance and compare the reading on the injector with adjacent units there is little else but to swap in a replacement and see if it cures the problem. Injectors do get gummed up though, and a swapout is te only option for this if a internal coil fault on the injector is not apparent.

PDH

I did swap over #3 fuel injector and it worked ok in #4 pot. Today with the injectors connected to the fuel rail I lifted them clear of the pots and turned the engine over and there looked even pulses of fuel spray from all 4 injectors.

I cleaned all the breathers, throttle body, idle valve and shot a can of injection cleaner down the intake and although it feels smoother there's still nothing happening in #3. I also squirt some around the inlet manifold to find any leaks but made no difference to the pitch of the engine.

Just read this article

aboutdoing a running compression test so I'll see what that throws up tomorrow.

But he did say in the original post

So that should rule out the injectors.

Graham

If there is no inlet manifold leak, and the vehicle is a Daewoo Lanos

8v sohc which I assume is a Vauxhall SOHC derivative I'd check the camshaft for wear on no3 cylinder lobes.

Graham