horrible misfire

[eg2]

So I've bought a zafira gsi to use as a donor in something a little older

Previous owner said it was using a fair bit of oil so decided to get it running right before pulling the engine for the swap - at least then I'll know any issues after are swap related...

It was smoking on lift off so removed the head, had it skimmed, replaced stem seals and refitted with new head gasket and cambelt kit...

At firs turn of the key it sounds fine for a second or two, then idle starts to fluctuates for a few seconds then it starts misfiring /knocking / banging and generally running lumpy.

I turn it off at this point as I don't want to be damaging the engine

Any ideas as to what I've done wrong?

[nomad]

Just a guess - a loose connector or one of the wire has cracked inside when you were doing the work on the head?
Try remove-clean-refit the connectors you took off?

[eg2]

Cleaned all the connectors but no luck. Bought a compression tester, its 60-65 psi across all cylinders which would indicate valve timing is out, but re-checked timing belt and marks are spot on :/ and as it's an interference engine, of the timing was out wouldn't it have gone bang by now?

[ChasR]

How noisy is the engine when it runs?

How is the timing set up when disturbing the timing gear? On some Pugs the bottom crank pulley is used as a reference. If this slips, that reference is as good as useless.

[taurus]

Jun 23, 2015 16:18:05 GMT eg2 said:

Cleaned all the connectors but no luck. Bought a compression tester, its 60-65 psi across all cylinders which would indicate valve timing is out, but re-checked timing belt and marks are spot on :/ and as it's an interference engine, of the timing was out wouldn't it have gone bang by now?

Depends how far out it is, iirc they can take up to 30 degrees out, not a lot but it makes a difference.

When you did the work did you take the cam sprockets off the camshafts, ie are the timing marks actually correct for the camshaft positions?

[theheap]

Did you actualy torque the head down?

[eg2]

Sorry for late reply, had to put the project down for a few days and do actual work

Yes I torqued the head down lol

and no, I left the cam sprockets on.

Turns out the valves on the compression guage was duff - actual compression was 165, 150, 155, 140 would that sort of variance cause it to misfire to the point of pretty much stalling? :/

possibly due to the valves leaking on 2/3/4 (z20let forums seem to suggest 160-170 is healthy...)

[taurus]

Shouldn't do - it ought to run. But if the valve timing is out that would do it.

[eg2]

Cam timing deffo ok. Lines up where it was before it came out, and it's deffo at tdc when it should be.... I'm gonna regrinding the valve seats and do the piston rings today to try and get better compression out of it c4 came up to 155 with a teaspoon of oil - does that count as enough increase to make it worth doing rings? (I'm a bit of a n00b with engine building)


but I can't think what would be causing the misfire... :/

Intake air leak maybe? :/

[taurus]

Check the state of the bore on it of course.

Misfire - usual suspects are plugs, coilpack then injectors before you start looking elsewhere.

[hornchurchmale]

thats very low compression. have we put cam back correctly? crank may show correct timing but if cam is out? we ought to b e looking at around 145-75 psi cold cranking. with a 10% difference between cylinders max.
even so with low compression it ought once started run even if poorly. sounds a though we have a fuel supply issue or spark problem. bit more investigation needed in both areas. go back along each section see if can pinpoint any faults e.g. do we have a bright spark ? is it near our timing point? do we have a fuel supply? have we displaced a sensor ?

[avengertec]

Did you squeeze the oil out of the hydraulic tapets as they can cause all sorts of problems iff you didn't

[gavs1]

What's the spark plugs telling you? Which cylinder is misfiring, does sound like an air leak