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Cylinder 1 and 2 misfire


Hhornsey98
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Hi ive got a 2003 siat arosa 1.0 with a misfire on cylinder 1 and 2 spark plugs leads and coil pack has been changed and still no different anyone got any ideas what it could be runs and drives but cuts out when left to idle 

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Does it stay on 2 cylinders or revert back to 3 or 4?

Error codes?

Confirm spark on 1 and 2, confirm fuel at 1 and 2, do a compression test (burnt valves, head gasket etc).

TB might need alignment procedure if you have cleaned it.

Edited by Sausage
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Fix the issues with the injector wiring if you have any that might be a problem. If the plugs are wet on the duff plugs after a run then fuel is getting thru though.

Compression test next, buy a kit (£20) if you dont have access to one, no point paying someone to do it for more than a kit costs.

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permanent missfire or only sometimes? only when cold and goes when warmed up? did it start missfiring suddenly or get worse and worse over the last few days/weeks? what do the plug tips look like (colour)?

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sounds like when at WOT, its ok. that'd be compression my guess. compression test needed. yeah, valves or more likely HG.

you could swap injectors round to eliminate them being the problem. so instead of 1&2, swap to 1&3... unlikely to be TB. not cam or crank sensor. O2 also fine.

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Redo with WOT and all plugs out 10 seconds cranking to confirm but that is knackered. 

Head off after confirmation.  Head gasket, valves, piston rings most likely suspects. Has it overheated?

Edited by Sausage
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agreed with what sausage says...

yeah, basically the pressure in 'bar', you can approximate to compression ratio. so if you get about 10 bar, that is about 150psi which is about right. so it does look like something is way out. and when testing do it with a hot engine. they're all low, which isn't good.

Edited by mk2
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just buy another engine, cheapest option with the 1.0 crap.

you may think this is hasty but I have done a few and once you begin then you will just be chasing yourself forever.

head gasket will be fine, doubtlessly it has just chosen to give up having compression.

what's the mileage on it? Motorways?

they rev too high for the cheap components. This applies to all lupos bar the diesels, change the running gear constantly and they rule engine wise.

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Rich is spot on as usual, it will be cheaper to find another engine than fix this one, but you can learn plenty by finding the problem on this one before making decisions. But seriously just find another engine.

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wow that was bad... looking much better now! i bet the engine will purr with freshly lapped valves. good job!

if it's still in pieces, you could balance up the combustion chambers and very slightly radius that cut edge next to the valves. will give you slightly better idling and slightly better efficiency (but not more power). to do that you'd need to skim the block or head by 3-5 mm or so (and alter the cam timing a fraction).

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44 minutes ago, Rich said:

fill the bores with a nice even amount of  diesel overnight & check again in the morning.

you mean combustion chambers? or do you think the rings are glazed...? I hadn't thought of that

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