Radiator busted, now misfires on cylinders 5 & 4

[Factory6speed]

I lost all the coolant on my m52 last year, I shut it off as soon as the red light came on and waited. But it was still cooked. It ran fine after, no smoke compression was good. The deck surface of the head didn't warp. But the cam ledges, the surface inside that the cam tray sits on warped. And the cams were all .. uh .. we can say not spinning true inside the engine. So it started putting metal everywhere and after a few days it developed a tapping. And after a few weeks the tapping got very loud and the oil filter is chock full of metal. So I destroyed the head, but because I kept running the car I ended scratching the cylinder walls too.

I would do a compression check, and get the exhaust gas in coolant tank test kit at the parts store. You can get a proper smoke machine for around $80, I'm not sure about the whole cigar thing. Sounds good though. I don't think an air leak would cause your misfire on two cylinders consistently.

[X5chemist]

Wow, I would replace all the spark plugs and test again. I've fixed so many misfires caused by bad plugs.

[jac]

I was able to run the cylinder compression test while the engine was at operating temperature:

Cylinders 1, 2, 4, 5: 160
Cylinders 3 and 6: 170

Those are decent readings, right?

Also, thank you @TryX5 and @Henn28 for the advice on cleaning/drying out the harnesses near the driver side of the radiator. I cleaned/dried that big plug going into the ABS unit and that seems to have cleared a few errors!

The mysfire is still on cylinder #5. But what is interesting is that the mysfire only shows up after I try to drive a bit aggressive. If I drive it without any hard acceleration it doesn't seem to occur.

What should I look at next to figure this out?

[Masospaghetti]

Originally Posted by jac

I was able to run the cylinder compression test while the engine was at operating temperature:

Cylinders 1, 2, 4, 5: 160
Cylinders 3 and 6: 170

Those are decent readings, right?

Also, thank you @TryX5 and @Henn28 for the advice on cleaning/drying out the harnesses near the driver side of the radiator. I cleaned/dried that big plug going into the ABS unit and that seems to have cleared a few errors!

The mysfire is still on cylinder #5. But what is interesting is that the mysfire only shows up after I try to drive a bit aggressive. If I drive it without any hard acceleration it doesn't seem to occur.

What should I look at next to figure this out?

Those numbers look fine for compression. if it's only one cylinder and compression is good, the only other thing specific to that cylinder is the fuel injector, although I don't know why it would have crapped out from a busted radiator. You could try swapping injectors between two cylinders to rule it out. It's fairly easy to do - the most annoying part is getting the electrical connectors off of the injectors, and you'll want to have replacement o-rings on hand. You could also try BMW Logger and record a drive session to get a bit more data.

[jac]

I swapped coils and spark plugs but the misfire remains on cylinders 5 & 4. :-(

Also did the "cigar" smoke test at night and saw nothing escaping. But, it is difficult to tell, so yeah, I am going to do a proper one with a smoke machine.

I have never done a compression test, but I have been looking into that and I am going to get the gauge to do it.

I figure all these tools I can still use in my other cars, so I don't mind spending a bit of cash on them.

I am also charging the battery, to rule out low voltage as a culprit.

If all those don't reveal issues, then I will try new spark plugs.

[paramax55]

Things like a compression gauge are good to get at Harbor Freight. They are super valuable tools, they are cheap at HF, and you will never use them enough to wear them out.

I like the idea of test plugs. You could get some cheap ones from the auto parts store. It shouldn't be more than about $10.00 for 6 of them.

[TriX5]

My first guess would be you got coolant in an electrical connector where it has caused some corrosion. The ABS unit and re-circulation pump sit close to the radiator behind the D/S headlight. I would start the hunt there. Issues with wiring in one place can affect a lot of seemingly unrelated systems.

[Henn28]

Originally Posted by TriX5

My first guess would be you got coolant in an electrical connector where it has caused some corrosion. The ABS unit and re-circulation pump sit close to the radiator behind the D/S headlight. I would start the hunt there. Issues with wiring in one place can affect a lot of seemingly unrelated systems.

My thoughts too. Was working on a valley leak a couple years ago in my driveway when a rain storm hit. An initial shop vac job, then blew all the water out of everywhere, let it dry for a long time, and ended up with cylinder 5 missing. I finally figured out it was due water intrusion in the harness. A few days more of dry weather and it ran like a top again.

[jac]

Thank you. Will try that when I get back.

I am going to be away for a few weeks so there won't be any updates on this for a while.

[X5chemist]

What are the ohm readings on injectors? 10% difference on compression on adjacent cylinders is acceptable.