Selecting correct coil pack

JustAnotherSaver

Prices seem to vary wildly.

Our 2007 Astra Z16XEP is having starting issues. It struggles to start at times (getting more frequent). It'll turn over but just doesn't fire up.

Bought the car 2016-2017 and not sure when the spark plugs were last changed (have receipt for 2012 but can't find anything after that). Picked up some GM ones for £20 so will try that. It was put to me that it's likely not the cause/solution and instead i should be looking at the coil pack.

I did this but it seems to go anything from about £70 up to double your money and a bit for various brand names. I saw a Delphi one, a name of which i've heard before. Seen a Bosch one which i suspect may be OE as from previous experience many things seem to be Bosch as an original part but i wouldn't want to bet £150 on it.

I guess if i got the part direct from Vauxhall then it'd be 100% genuine but then it'd be 200% genuine price as well.

Seems simple enough to change. Unscrew, remove, refit, screw, done. Just need to make sure i get the right one if the spark plugs don't solve the issue.

molerat

A fair chance the original is either Bosch or Delphi which is one of the largest parts manufacturers in the world and in fact used to be owned by GM.

red_eye

personally not knowing if the plugs have been done I would start with the plugs.
plugs and coil pack would cause a misfire so if it’s not misfiring when it does finally start it’s not coil or plugs. 

Possibly a lazy starter or weak battery 

oldagetraveller1

If the cheaper option of a sparkplug change dosn't solve the problem don't just fire parts at it, e.g. coils. As you mention, they might not have been changed since 2012 anyway so that would not be wasted.

Get a proper diagnosis first. e.g. is there a beefy spark, is there enough fuel and air, is everything happening at the correct time etc..I can't envisage all the coils failing at one time.

EdGasketTheSecond

Throwing parts at a car is not a cost-effective way of fixing a specific issue. I would remove the crank sensor  and measure it's resistance to see if it is within specification. If you don't know the spec, ask on a vauxhall forum or look up the part and see what the specifications are. A cheap multimeter to measure the resistance can be had for under £10

JustAnotherSaver

And then you've got to know what you're doing with said multimeter

Thanks though. I figured for £20 no harm done. I don't notice any misfiring (am i right in thinking you should experience some kind of juddering? Or not?).

Once the car starts it actually runs perfectly fine. The battery isn't that old - it was bought either last year or the year before, i can't remember which. One of those Halfords '4 year' batteries. May even be a '5', i'd have to check.

Starter motor though .... who knows.

red_eye

JustAnotherSaver said:

And then you've got to know what you're doing with said multimeter

Thanks though. I figured for £20 no harm done. I don't notice any misfiring (am i right in thinking you should experience some kind of juddering? Or not?).

Once the car starts it actually runs perfectly fine. The battery isn't that old - it was bought either last year or the year before, i can't remember which. One of those Halfords '4 year' batteries. May even be a '5', i'd have to check.

Starter motor though .... who knows.

Misfire you can feel it though your bum Or by putting you hand on the engine it’s sort of an imbalance you’ll know it when you feel it.

EdGasketTheSecond

A failing crank sensor can cause starting problems but be fine otherwise. That is because when starting the metal fins that 'fly' past it are only rotating slowly so you don't get much of a signal. Hence check it with the meter; if in range it isn't that; if outside then it is almost certainly the crank sensor. Had exactly same thing on a Hyundai; it ran fine but wouldn't start without a lot of difficulty.

JustAnotherSaver

Regards fitting of spark plugs...

do you oil the threads slightly or not?

ive been told yes but I’ve read online no. Yes because you don’t want issues getting them out, no because it messes with the torque settings. NGK apparently advise against it but I’m using GM own spark plugs, not NGK. 

Also depends on your version of ‘slightly oil’. I ‘slightly lubed’ my wheel bolts with copper grease and the tyre fitter when removing them said chuff me there’s some copper grease on them bolts isn’t there!!!

its like the ‘nip up’ for sump plugs. I prefer to do it to the specification. I ‘nipped up’ my radiator at home. Story short I ended up needing to call an emergency plumber because my living room floor was then flooding. 

red_eye

No need, no point, don’t bother.
drop some oil on your exhaust manifold run your engine you’ll see the oil smoke away. Spark plugs will be sealed at top of the threads so any burning oil can go into the cylinder and out the exhaust 

EdGasketTheSecond

You should put a little anti-sieze, or copper grease on the threads; not oil. That will stop them seizing into the cylinder head. Then do them up by feel; not torque wrench as the torque specifications are always for clean dry and new threads. If the plugs have a washer, they are easy as you can feel the washer compress and then no more; at that point they are tight enough. Plugs without a washer need very little torque so be careful.