M42/44 ignition coils--only slightly off topic

[Mike Self]

Not completely off topic because I know more than a few M42 and M44 motors have wandered into 2002 engine compartments--and I know several of us have E30 318is's ...

 

I think I may have a coil going bad...Driving to Vintage my check engine light came on--intermittently and randomly... anywhere from a split second to 10-15 seconds.  It also seems to be heat-related.  Driving down to Vintage with the air temps in the 80s this happened, but coming home with the temperature in the 70s and high s 60s, the light never flickered.  

 

In all but one instance there was no engine hesitation, and that one time it acted like a very soft misfire--barely noticeable as a little flutter.  

 

Three questions: 

• does that sound like one of the ignition coils on its way out (seemingly temp related tends to rule out spark plugs)
• if so, do the E36 and E46 cars with that engine use the same coils, and
• how the heck do you get the plastic cover off the coil pack?

 

TIA

mike

[cda951]

Hi Mike,

 

Did you scan the thing for fault codes? These early OBD-I engine management systems aren't super sophisticated, but they do have a primitive means of detecting ignition misfires by using a ground shunt circuit. 

 

The M42 and M44 have a unique coil near plug setup which uses individual ignition coils, but still has a plug wire going to each spark plug.

 

The earlier M42 setup uses individual coils and primary plugs from the engine wire harness, and the individual ignition coils (BMW part # 12 13 7 599 218) are the same as early six-cylinder E36, E34, etc that use the coils directly on the plug with a boot as a secondary lead. If you have some spares of these coils, you can swap individual coils around to see if the fault follows.

 

The later M44 used a different coil pack with all 4 coils inline, and only a single round plug as a primary lead, so disassembly is not practical. 

 

If you know of a shop with a good oscilloscope and the leads and knowledge to scope this type of ignition system, that would be your best bet.

[TobyB]

Personally, owning a coupla M42's, I'd suspect the plug wires first.

 

They're about 4' long and contorted in all sorts of special ways.

And check the ends first- both to see if they're not corroded

and to see if they're still firmly attached to the wires.

 

In the both that I own, they came to me with original wires on 'em.

Which, at 30 years now, is pretty good for a consumable.

 

t

 

[AustrianVespaGuy]

Hmm, I really wouldn't think the M42 DME would be able to detect a misfire unless something was shorting out.  This leads me to think along the same lines as Toby and would suspect wires before coils.  Easy enough to just measure primary and secondary winding resistances on the coils though; see if one of them is much 'different' than the others!

[JsnPpp]

Wish I could help here. Best I can say is starting with plug wires makes sense to me too. Easy to check, even though the wire loom on top of the head is a bit complex.

 

Could it also be gas grade? On the way down it was one tank, the way up another?

 

On my 318is, the coil pack block is held on by 9mm nuts (or is it 10mm), if that is what you are thinking of.

 

Good luck Mike!

 

Jason

[bergie33]

When I was looking into an M42 swap for my E21, I was planning on doing a coil-on-plug conversion. It uses the newer, less expensive coils and no expensive spark plug wires.  If either the wires or could are your issue, you might consider the COP conversion.

[cda951]

14 hours ago, AustrianVespaGuy said:

Hmm, I really wouldn't think the M42 DME would be able to detect a misfire unless something was shorting out.  This leads me to think along the same lines as Toby and would suspect wires before coils.  Easy enough to just measure primary and secondary winding resistances on the coils though; see if one of them is much 'different' than the others!

 

I could be mistaken about the specific DME of the M42, but other BMWs of the era (early-mid 1990s OBD-I) which use the MS 3.x and later DME have a 235 ohm shunt resistor wired in series with the ignition coil ground point. The DME has dedicated circuit to monitor the voltage drop across the resistor as the secondary ignition coil firing induces a voltage spike in the circuit. If no voltage drop is present, the DME can detect which cylinder isn't firing via the camshaft position sensor. Crude, but it kind of works.

 

All that said, crispy old ignition wires could certainly be a cause, but a good first step would be to find someone with the old 20-pin BMW code reader and see which faults are set.

[jimk]

On 5/23/2022 at 8:38 PM, bergie33 said:

When I was looking into an M42 swap for my E21, I was planning on doing a coil-on-plug conversion. It uses the newer, less expensive coils and no expensive spark plug wires.  If either the wires or could are your issue, you might consider the COP conversion.

I got tired of plug wires too.

[Mike Self]

Thanks for all the input, folks.  I  have (I think) one of those early 20 pin diagnostic tools so will try it next time that light illuminates.  

 

It's been relatively cool here since returning from Vintage, and the check engine light has stayed off--and there's not a hint of hesitation.   So I'm pretty convinced that the problem is either heat related, or my wiggling the wires did something (wishful thinking--it's never that easy!). The plug wires I'm sure are not original as they're nice and soft--no cracks at all.  

 

But I still can't find any method of attachment for the plastic cover that is atop those four coils.  I hesitate to try prying it for fear of breaking it, but I sure can't see any screws or bolts holding it in place. 

 

mike

[m42002]

Does rhe cover look like this?

 

 

been awhile sibce I did this, but remove the two round, slotted covers on either side of the “BMW”.  There are nuts under there. Might be a little stuck if it’s been on there awhile. Heat and plastic and all that.
Do the COP. So much tidier. Of course, then you  will not be able to use that cover. 
 

[jgerock]

2 minutes ago, m42002 said:

Does rhe cover look like this?

 

 

been awhile sibce I did this, but remove the two round, slotted covers on either side of the “BMW”.  There are nuts under there. Might be a little stuck if it’s been on there awhile. Heat and plastic and all that.
Do the COP. So much tidier. Of course, then you  will not be able to use that cover. 
 

That’s the valve cover insert. Mike’s asking about the funky black cover for the (4) coils. I’ve not removed that cover yet on my e30.

[jimk]

3 hours ago, Mike Self said:

But I still can't find any method of attachment for the plastic cover that is atop those four coils. 

If it is clamped like a relay cover on a 325ix then from the picture in RealOEM, on the fender side just inboard of the cable connectors and centered on each connector, there are two tabs on the cover that clamp around the laminated coil core of each outboard coil.  Try removing the connectors and the tabs might be visible.

[m42002]

5 hours ago, jgerock said:

That’s the valve cover insert. 

Doh. I did tear that apart on mine. But, if ya think my reading apprehension is bad, my memory is worster. 
Went and looked for it but apparently did not keep it. Sorry Mike.