Ignition coil cracks

[owas]

So I'm having abit of a mare getting my e34 m50 engine running right.
I've got a huge missfire/backfire when you try to accelerate from stop,basically boggs down to the point it barely moves,which goes away once you get above around 3k revs and then it behaves normally, doesn't always do and mainly when it's warm.

4 out the 6 coil plugs are new now.
1 of the 6 originals were definitely bad, putting that back in brings the missfire back immediately.

What I noticed was they all seem to have exactly the same crack on all of the originals.

I have orderd the last 2 coils but I'm trying to work out if I should be looking elsewhere ..

Does it mean they're internally wrecked?

 

[slim_boy_fat]

I'm assuming you've read the codes? [just in case there's another fault 'lurking' but being overlooked for the obvious]

 

[RichardM]

Dyna coils used to crack like that on my old Z1000 and they were fine. Check primary and secondary windings for value, resistance and to earth, both when cold and hot.

 

[nickk]

I had one on a motorbike where something chafed through it,I just araldited the slit.

 

[Ubique]

I'm assuming you've read the codes? [just in case there's another fault 'lurking' but being overlooked for the obvious]

It should also give you misfire detection, indicating which cylinder(s) has the problem. While you have the coils out, I'd be checking the spark plugs for gap, contamination and tracking marks on the ceramic, also check the extension tubes for tracking or burn marks on the outside. A compression test on all cylinders would also give you an indication as to whether it's solely an electrical issue or whether there are other factors contributing.
If there is a misfire indicated by the DTC read, move the coil to another cylinder (number them beforehand with a Sharpie) then drive until it misfires and re-check the DTC, if the misfire has moved with the coil, then it's a fair bet the coil or tube has a defect. If it hasn't, then best case is the spark plug...

ETA - OP, do you actually mean backfiring as in popping / banging due to combustion in the exhaust pipe? if so, there may be a problem with variable valve timing (if your engine has it - I've managed to avoid the pleasures of BMW's) or timing belt tension/chain stretch

 

[premmington]

It should also give you misfire detection, indicating which cylinder(s) has the problem. While you have the coils out, I'd be checking the spark plugs for gap, contamination and tracking marks on the ceramic, also check the extension tubes for tracking or burn marks on the outside. A compression test on all cylinders would also give you an indication as to whether it's solely an electrical issue or whether there are other factors contributing.
If there is a misfire indicated by the DTC read, move the coil to another cylinder (number them beforehand with a Sharpie) then drive until it misfires and re-check the DTC, if the misfire has moved with the coil, then it's a fair bet the coil or tube has a defect. If it hasn't, then best case is the spark plug...

ETA - OP, do you actually mean backfiring as in popping / banging due to combustion in the exhaust pipe? if so, there may be a problem with variable valve timing (if your engine has it - I've managed to avoid the pleasures of BMW's) or timing belt tension/chain stretch

Not all these M50's had variable valve timing - the ones that did were single Vanos units.

Vanos units on early BMW's are a weak point and do give you multiple misfire codes.

They will also "bog down" if the exhaust path from exhaust valves are not opening fully. Not all will give you chain noise (chain can still be good even if Vanos failing/failed).

 

[Tom O]

Years ago on my Norton I had a backfire that couldn’t be fixed no matter how many times I took it to the shop. I found the answer myself later on, the cam for auto advance was worn varying the spark/timing.

 

[jsf55]

Have you checked for vacuum leaks ?

 

[owas]

I don't have anything to read the codes with, it's the old round plug.
I know you can buy an adapter to obd2 but not sure what reader would actually work.

It is a single vanos,
The most I've tested on that so far is to pull off the actuator and test it with 12v, the pin extended and retracted fine.
Would've thought it would do it all the time if the vanos was bad though? It can go a week without any symptoms.

So far I've changed the fuel pump, filter and FPR and tested pressure which was bang on.
Spark plugs and most the coil packs. (Last 2 are comming tomorrow)

Valve cover gasket, oil cap and numerous dodgy vacuum connections, I've rigged up a smoke tester I'm going to try tommorow because if I pull off one of the vacuum lines and push down on the throttle a few times I can make it backfire .. so it could still be a vacuum leak I havnt found.

Got an o2 sensor comming too as the mpg is quite bad and the exhaust does smell abit.

 

[jsf55]

The other thing it might be is the ecu engine temperature sensor, without it giving a proper reading it will always run rich

 

[Keithmac]

That's prime o2 / lambda feedback region, worth logging O2 sensor output while it's faulting (voltage in mv and any O2 trims, Instant and Long Term).

 

[Keithmac]

Normally bogging down is Lean and and a stutter is Rich.

Unplug MAF just to test, if the car runs better you have a fault MAF or an air leak / evap leak.

 

[owas]

Found a leak on the intake boot where the hose clamp is ..
This was a new part
Possibly opens up alot more when the engine is warm

Got quite a lot of smoke out my little makeshift tester and nothing leaked anywhere else.

 

[dobbslc]

Can you tell us more about the smoke tester?

 

[owas]

Can you tell us more about the smoke tester?

Just a glass jar with two 2 tubes glued into the top,
One side to a latex glove with a finger chopped off clamped on the intake, the other to a tyre air compressor.

Bits of cardboard burning inside

It did leak at the jar but pushed enough smoke through

 

[slim_boy_fat]

This was a new part

New old stock? Those rubber elbows are known to perish and crack, usually on the underside where it's not easily seen. Had the same on my 535i back in the day.

Glad you got it sorted though.

 

[owas]

The vacuum leak certainly improved things, I havnt been able to make it backfire yet, but it does start doing it randomly so I'm a little uneasy about taking it more than around the block yet.

It's still very hesitant before 3/4k revs which does seem to be prime vanos territory so I've orderd the seals and timing tools.

I've got what seems to be quite a lot of ticking from the fuel rail but I don't know if this is normal? Its quiet until it warms up

 

[owas]

It's the fuel injectors,
One of them was sticking on at times and leaking when it did close, I've replaced that one with a spare I had and it's a lot better,
I don't think the others are too healthy, when testing them with carb cleaner and one of those plastic adapters to the bottle, they spray out nicely and hold pressure till I apply 12v but occasionally I get a slight drip from all of them as its spraying.
I'm not sure if this is just because it's carb cleaner and not petrol?

 

[jsf55]

What you've done too find the fault is great, but I'd spend the money and get them all cleaned professionally now

 

[owas]

Look like they're the originals and with 180k on them it's probably best I source some new ones.