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Discussion Starter #1
Hi

I've had this problem for quite a while now, ever since I replaced the head gaskets, but I've been busy with work and just not had the time to spend on it.

I've finally 'given in' and let the local garage take a look and see what he can find out. He's come back to me and said he's put an oscilloscope on the coils and sometimes they're showing ~40kV and sometimes only ~20kV and has no idea why.

From RAVE I can see an 18 pin connector and a 9 pin connector from the ECM with switched earths and a common fuse/relay supplying a voltage. The coils themselves don't seem to require the bodies to be grounded.

Does anyone have any ideas what could cause intermittent low voltage on the secondary (HT) circuit? Could it simply be a dodgy connector or wire? Or something else? I'm assuming if the relay was poorly then the engine wouldn't run at all?

Both coil packs are new and recent new plug leads and plugs. Its a 2000MY 4.0 Bosch

Thanks
 

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did you have the intermittent misfire before the HG replacement ?

I've had a pattern part coil pack fail very quickly and reverted to the original bosch ones (i replaced the coil pack after my HG rebuild but kept the OEM coil packs as they were fine so thought keep them as a spare.) the pattern part coil packs went back for refund due to failure.

did you replace the coil packs with OEM bosch or pattern part.. do you still have the OEM coil packs ?
 

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Discussion Starter #3
Hi, it ran fine before the HG change. I think i put everything back together right!

I've still got the old coils but the same symptoms were displayed. The reason new ones (not oem) were tried is the scope wasn't showing output as high as it should have been and one of the HR terminals was corroded.
 

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I'm a bit dubious about 'putting an oscillosope on the coils' It's very easy to affect the coil voltage when trying to measure it. If you have an electrical misfire then the ECU should be able to detect this itself so my first choice would be to check for fault codes (any cheap OBII reader will show misfire codes). The ECU can distinguish between 'general misfire' and a particular cylinder misfire. The former could be a coil or maybe even a fuelling problem. The latter could still be the coil but more likely plug/ht lead and you would at least know which coil / plug is the problem.

One thing you could try is closing the plug gaps up a little (to about 3/4 of the recomended setting). I this improves things then it points to a weak spark.

Just a thought - you did put all the engine earth straps back when you did the HG didn't you?
 

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Discussion Starter #5
I'm only getting a general misfire code, not one for a specific cylinder, although it doesn't seem to be affecting all cylinders! Which is why I've started to wonder if it could be the switched earth wires causing the problem

I don't recall seeing any earth straps when i took the heads off! That could be an issue!! Where should the heads be earthed to? The block? Shouldn't the head bolts give a good earth?

I've already closed the plug gap a bit for LPG, but I'm not even trying to run on LPG yet until i get petrol sorted out.
 

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There is an earth ground on the rear of the right head and maybe the left as well but not sure of that side. Memory is a little fuzzy. Check that and then I would do a compression test on all cylinders Just to verify that it’s not a mechanical issue being that it started after HG change. Just my 2 cents.

Kevin
 

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Discussion Starter #7
Thanks for the info, not got round to it yet but I'll be checking the earths!

I've already checked compression and all good.

I'm wondering if I've damaged the connectors/loom that supplies the coils? But i suspect it wouldn't run at all if that was the case?
 

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earth leads for the head at the back of the block. 13mm bolt IIRC

you got the injector leads in the right injectors and the right HT lead from the coil pack to the right plug ?

i don't see how you can damage the loom or connectors the supply the coils there's not a huge amount of play on them and you know when they don't plug in.

personally, i would put the original coil packs back on and see if that makes a difference.

when you say the misfire is 'intermittent' when does it occur ... ? ( not when cold only when warmed up ? did you have a water leak into the cyl which led to the HG replacement? if the answers to these are yes, its possible one of the O2 sensors has gone faulty due to the water contamination through the exhaust.. the O2 sensor feed only comes into play when engine reaches operating temp)

the coil packs run on a redundant spark, so if you have a faulty coil pack go it will cause a misfire across two cyls from the corresponding coil. being a redundant spark could be your guy got 40/20 reading ?

honestly.. replace the coil packs with the original ones, check to make sure you have the right lead on the right coil and make sure the leads are fully home into both ends. try that. my replacement coil packs were faulty from the box, as i decides to replace everything during my HG rebuild.. so the OEM bosch ones went back on. no problem since
 

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Discussion Starter #9
Thanks for your thoughts!

From memory, i think its 1 and 4 which are having the problems, which didn't line up to a wasted pair. I've triple checked I've got the plug leads in the right order!

I was having the problem with the original coils which is why i swapped out. That made no difference.

I've had the offending plug out and earthed it so i can watch the spark and can see it's not regular, there are definite gaps where a spark is missing. Done the same with a different cylinder and not seen misses. Happens both warm engine and cold.

I really hope it's just an earthing problem!!
 

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Discussion Starter #11
I'll try to check when i get a minute to myself! I was pretty sure I'd worked out it wasn't a pair, memory isn't the best on a good day!! Maybe it was 1+6

I'll update as soon as i get chance to check, hopefully in the next couple of days
 

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You checked the heads being straight when you did the HG?
Didn't stuff up while putting the heads back on?

Connected all the ground wires?

Put all the plugs back together propperly?

All vacuum hoses connected and not damaged?

Go back through all your steps when you did the HG, you probably forgot something small ;)
 

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Discussion Starter #13
Hi, think I've found the issue! Finally got to spend some more time and found the new coil to be worse than the old one! By worse, I mean the resistance of the secondary windings is much lower than 13.3k ohms I was expecting!!

The only replacement I can find is Britpart, which is usually decent, do I need to be going to the main stealer?
 

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the thing I like of LR Direkt, you can choose the brand you like, there is most of the times a reasonably quality for a reasonable price.

Quite often theoriginal Land Rover part is (way) more expensive as most likely the same part with a different brand on it.
 

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LR Direct often give 3 options, Britpart at a price that is so cheap you just know you are going to get what you pay for, OEM (usually supplied through Bearmach or Allmakes) or genuine at an eye watering price. Go for OEM, same quality as LR but a lot cheaper.
 

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Hi, think I've found the issue! Finally got to spend some more time and found the new coil to be worse than the old one! By worse, I mean the resistance of the secondary windings is much lower than 13.3k ohms I was expecting!!

The only replacement I can find is Britpart, which is usually decent, do I need to be going to the main stealer?
Did say the new coil pack was likely faulty :wink:

Britpart.. aka S**tpart !

Go to a main stealer ?? There's loads of alternative suppliers out there rather than be fleeced by a main stealer who will not carry it in stock and need to order it anyway Try. Britcar, John Craddock, Paddock Spares, P38 Spares, Island 4x4 LR Direct, etc

IMO you'd be better off getting a used OEM Bosch one off the bay of e there's a pair up at the moment for £20 !

If you for non OEM go for Bearmach.
 

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Discussion Starter #18
Cheers. I'll definitely go for Bosch oem. And i might as well go for new ones and hopefully forget about the whole subject. At least I'll have some kind of warranty as well.

Aside from checking the plug leads are ok, anything else that could kill a coil? New plugs so they should be ok, I've checked the leads they seem to be ok too. I'd hate to put an expressive new cool on then find an underlying issue kills that one too
 

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Discussion Starter #19
Before i went out and bought a new pair of coils, i thought I'd revisit the old original ones. Checked out the resistances and they are all within tolerance. The lowest was on 7 and 4 which i measured at 12.8k ohms. The rest came in at 13.2-13.3k. Is that my problem right there? I'm happy to buy new ones, but not if these are good.

I'm still only getting code p1319 with my generic reader, i still think the fuel pressure is ok sure to running the same on lpg. Thoughts?
Thanks
 

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Discussion Starter #20
Just a thought, if the rf suppression capacitor is damaged or has a dodgy connection, could that cause a misfire? Our just lots of radio interference
 
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