M42 (swap into 2002) Tries, but just won't start

[Gerta]

Did you hit up JakeB? I know he had done a number of these swaps and is headed home from the Vintage. You should give him a shout.

[bmwman91]

The M42 operates in wasted spark during start-up, until it has a cam sensor signal lock. It will also operate in WS mode if the cam sensor is broken or missing. Otherwise, in normal operation, the M42 runs in coil-per-cylinder mode with each coil firing one at a time. A sort of similar thing goes on with the fuel injectors. When cranking, or if the cam sensor signal is bad, it will fire all 4 injectors simultaneously in a batched fashion. When the cam signal is locked, it fires injectors 1+4 and 3+2 together in a banked arrangement (it is not wired for full sequential since the grounds for pairs of injectors are tied together.).

[TobyB]

Is the m42 actually wasted spark? It has 4 coils...

t

[pklym]

Thanks for the replies. I was traveling for awhile which is why I haven't checked back in.

We went COP because the wires were bad that we had and its just as cheap to switch.

Still need to find a timing light to run that test.

Good to know about the wasted spark, I figured it had to be intentional.

Have since replaced the new cam position sensor with another one, and replaced the old coil/spark plug boots with new ones. Still no go.

Did discover that that we have two slightly different diagram/pinouts for the Motronic 1.7 that show the fuel injector bank pins switched. Tried jumping them to reverse them and still no go.

My buddy has removed the harness and is going to check every pin at this point. Its getting really frustrating. My next plans are new coils and maybe new injectors (these are the 4-pintle ford ones people use, but perhaps they are flowing too much??).

Any other ideas would be helpful. The C123 plug shouldn't affect whether it runs should it? (The one to indicate whether a catalytic converter is present).

[bmwman91]

During cranking, coils 1+4 will fire simultaneously, as will 2+3. This is a typical wasted spark setup, and once the engine is started and the ECU has a good cam position signal, it will go to single spark / COP mode.

Are you certain that none of the coils connectors got swapped? If it barely starts and then stumbles/dies as soon as it is about to run, then chances are that connectors are swapped. When in wasted spark mode, you will get proper ignition, but once COP mode kicks in the spark will be 180 degrees off (end of exhaust stroke/start of intake stroke). You may even get a little backfiring since there might be a little bit of fresh air+fuel entering already for the intake stroke.

[TobyB]

We've got COP set up wired 1-2-3-4 from front (radiator) to firewall.

Get a timing light, and make marks on the front pulley at 0 and 180. Like, a + and a - so that you can tell them apart.
Plugs 1 and 4 should light up the 0 degree mark, 2&3 should light the 180 mark.
It doesn't tell you if they're on the right stroke (compression or exhaust) but it'll tell
you if they're wrong.

Because I agree, it sounds like they're not in the right order.

<edited out opinions on value of coil- on- plug>

t

[pklym]

Varg,

Thanks for that info, helps narrow down what we should focus on.

For that coil order, are you talking about at the coil pack? We've got COP set up wired 1-2-3-4 from front (radiator) to firewall.

Check out this video of the coils. It appears to fire 1+4 then 2+3 several times before going into the proper firing order? What the heck could cause this?

https://youtu.be/BZBhMZtRdDM

Additionally, after replacing plugs and trying a few times it seems that cylinders 1 + 4 may be the culprits, they are noticeably fouled and 2 + 3 look fine.

Is it normal for the check engine light to turn off while cranking? Wondering if there is possibly some ignition switch issue.

[varg]

Trying to start and backfiring usually indicates a timing problem. I'd double check that the coils are wired correctly (1342 not 1324). If they are, I'd double check cam timing and cam sprocket position (assuming they were removed at some point). As long as the fuel pump isn't the low pressure (pickup) pump from a dual pump 325 it won't be an issue. The only sensors needed to get it to run are the cam and crank position sensors. It will run without the TPS and MAF, just not well, and very rich.

[pklym]

Added more engine to chassis grounds, no change unfortunately

[pklym]

Did you ground the engine? I had trouble with a friends car until we added another ground from the engine to the chassis.

Thanks. It is grounded but that is something we will look into improving. Where is the best place for grounding the engine from?

[ccsdo5]

Did you ground the engine? I had trouble with a friends car until we added another ground from the engine to the chassis.

[pklym]

We feel like we've tried everything here.

It gets spark, it gets fuel, timing has been checked repeatedly. All the sensors ohm out correctly, replaced the CPS anyway, swapped ECUs, cleaned injectors, compression is 185 across the board, stomp test shows no codes, fuel pressure is right around 40 psi. coils fire.

It tries to start, stumbles, bucks, backfires, just won't go. It feels like an ignition problem but the coils (on plug) are in the right order as traced back to the ECU. watching them fire it looked like they all sparked at once quickly before going into the proper firing order. Not sure if that is normal.

Had ran some old/bad fuel through that seemed to stick the injectors open, but fuels been drained and swapped and injectors cleaned, they appear to function properly.

What are we missing?

I think the fuel pump is from an m20 car which may be slightly lower pressure than the m42 pump? But I doubt that could cause this type of problem.

What are the bare minimum sensors that need to be functioning to get it to run at all?