M62tu Not Starting All of a Sudden

[dannyzabolotny]

Hey guys,

I've been working on an X5 4.6is for a person recently, which has the same M62tu engine as our 540i's. I did the whole chain guide job, put everything back together, and the engine started right up and ran pretty well. I then turned off the engine, topped up the fluids, checked for leaks (there were none), and started the engine up again. This time I got a CEL with a P0348 code (cam sensor bank 2) and one for injector open circuit cylinder #4 (don't remember the code number). I double-checked that all the wiring was connected correctly, and then tried to start the engine again... nothing.

The engine cranks but doesn't fire. Here are the facts and the diagnostic steps I've already taken:

- The battery is fully charged and on a trickle charger.
- There's plenty of gas and the fuel pump is working correctly, based on the fact that I'm getting around 40psi at the fuel rail.
- I've swapped camshaft sensors around and swapped in ones from my 540i/6 to see if that was the issue. No change.
- I've unplugged the camshaft sensors completely just to try it. No change.
- I used INPA to look at the RPMs while the engine is cranking to rule out the crank sensor— I got RPM when starting so that isn't the issue.

INPA reports the same things as the code reader, with an injector error and a camshaft sensor bank 2 error. When I clear the errors and try to start the engine again, the errors come back immediately. Here are the screenshots of the errors:

Photo Jan 03, 10 40 53 PM.jpg

Photo Jan 03, 10 40 43 PM.jpg

What's perplexing about this is that the engine started just fine one minute and then like 2 minutes later it didn't start at all. I didn't really change anything in that time, so I'm kinda scratching my head trying to figure this out.

I definitely have air and compression, based on the fact that the engine ran smoothly, so fuel/ignition is the likely culprit. While there is fuel in the fuel rail, if the DME isn't happy about something, it won't open the injectors, correct? I haven't checked for spark yet, I'll probably do that tonight when I have a friend helping me with this.

If anyone's got any ideas, please let me know. Thanks!

[JimLev]

Supply voltage looks low.
Maybe a pinched wire that blew one of the fuses in the DME box?
Injector connector not pushed on good?
Possible bent tab on the trigger wheel for that cam code?
that's all I can think of at the moment.

[dannyzabolotny]

Supply voltage looks low.
Maybe a pinched wire that blew one of the fuses in the DME box?
Injector connector not pushed on good?
Possible bent tab on the trigger wheel for that cam code?
that's all I can think of at the moment.

Thanks for the ideas! I'll check the DME fuses tonight with my friend, he's got a test light and knows a lot more about electronics than I do.

I'll re-connect the injector connector tonight just to check. That being said, I've started cars with injectors not plugged in (accidentally) and they still ran, albeit rather poorly.

The trigger wheels were both straight when I was reassembling the engine. I did have the bent trigger wheel issue on a previous car I fixed, so I replaced the trigger wheels on that.

[edjack]

A bad crank sensor will inhibit spark and fuel injectors. However, you have seemingly absolved the sensor.

Jim may have a point: DME is fussy about supply voltage. Have you ruled out a failing battery?

[dannyzabolotny]

A bad crank sensor will inhibit spark and fuel injectors. However, you have seemingly absolved the sensor.

Jim may have a point: DME is fussy about supply voltage. Have you ruled out a failing battery?

Yeah, my Porsche 944S has a bad crank sensor so it doesn't start. However I see in INPA that the crank sensor is reading the RPMs when the engine is cranking (because on these cars the tach doesn't move until the engine fully starts). If the crank sensor was bad I wouldn't be getting any readings at all.

I've mostly ruled out the battery in that it's been plugged in to a trickle charger constantly for the past few days and the charger shows the battery at 100%. I've tried starting it with the charger connected and that's made no difference. My charger is strong enough to start a car with a completely dead battery after a few minutes so I don't think it's a voltage issue at this point. Also, the starter cranks strongly, not at all like it's lacking in voltage.

[TheAngryBear]

I think Jim may have it with the fuse and/or wiring. Those readings are saying signal missing (discontinuity) or implausible (too big) if I am reading the log correctly. Checking the wiring, connections, and fuses.

Edit: and shouldn’t fuel pressure be 50? Don’t think 40 is to low to start but something to watch.

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[dannyzabolotny]

I think Jim may have it with the fuse and/or wiring. Those readings are saying signal missing (discontinuity) or implausible (too big) if I am reading the log correctly. Checking the wiring, connections, and fuses.

Edit: and shouldn’t fuel pressure be 50? Don’t think 40 is to low to start but something to watch.

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I checked all the fuses, perfect continuity everywhere. Also, an injector error and a cam sensor error would not prevent the car from actually starting... I've run these engines with 7 cylinders or less before.

Anyways, here's what I did tonight with a friend:

- Pulled all of the spark plugs, they smelled quite a bit like fuel. Engine wasn't full of gas though, because when I cranked it with the plugs out there wasn't anything coming out. The fact that there's gas on the plugs means the injectors are opening at least somewhat.
- Checked for spark by grounding out various ignition coils. Great spark all around, no issues with that.
- Checked all of the fuses for continuity — all of the ones in the trunk, in the glovebox, and in the DME box. No problems at all.
- Swapped out the crank sensor for a known good one. No change at all.
- Checked the injector connectors, all fine.
- Sprayed starting fluid into the throttle body while my friend cranked the engine... not even a single blip or attempt to fire.

Absolutely nothing changed, it still doesn't start. I've ruled out fuel, air, and spark, so the only variable left is compression. Tomorrow I'm going to do a compression test to see if that's the issue.

[vinyldude]

Since DME measures low voltage, even when your battery seems fine, it could be an indication of short-like condition or something drawing too much current somewhere. Considering what you have already done, I would probably keep checking the wiring and electrical items. I would perhaps try to disconnect sensors and injectors and see if the DME errors change in a way that makes sense, to make sure DME is in full senses first.

I'm sure you'll figure out though with enough time.

[geargrinder]

Since DME measures low voltage, even when your battery seems fine, it could be an indication of short-like condition or something drawing too much current somewhere. Considering what you have already done, I would probably keep checking the wiring and electrical items. I would perhaps try to disconnect sensors and injectors and see if the DME errors change in a way that makes sense, to make sure DME is in full senses first.

I'm sure you'll figure out though with enough time.

I would agree w/ this. Test the actual voltage at the DME terminals, if it really is only getting 11V then it may not have enough juice to fire injectors and coils and may be forking up the sensor readings if the supply voltage droops to 10-11V while cranking. There's gotta be a reason its saying 11V. Test it 'standing' and also while cranking.

BTW if the battery has a shorted cell or two it might be enough to suck up even the juice your charger is trying to put in that is normally enough to override a dead-charge battery.

And I hate to say it but you've triple checked battery terminals? There's been a spate of "oh after days and days of input and questions and headscratching I just noticed my battery terminals were loose" over last few months.

[philly98540]

But he's got spark. If voltage was too low for DME, they would not fire.

[geargrinder]

Not so sure... could be he's just seeing a weak spark, could be there's enough juice to drive the coil drivers but not enough current to get injectors opening? The logging says 11V so there must be something going on there... Maybe its something else but until that's assplained I wouldn't look elsewhere frankly.

[dannyzabolotny]

I tested the spark by putting a screw driver (with a rubber handle) into the ignition coil while my friend cranked the engine. I was getting 1" sparks to the ground on the body, I'd say that's a pretty strong spark. Consistent spark no matter which coil I checked.

The fact that it doesn't even try to fire on starting fluid is a little odd though...

[philly98540]

That is odd. Spark and starter fluid and nothing? Head scratch....

[Mach540]

How does it sound turning over? If it is not getting enough compression, it should sound like it's turning over faster than usual. I'd assume your ear is tuned enough to notice something like that.

[dannyzabolotny]

How does it sound turning over? If it is not getting enough compression, it should sound like it's turning over faster than usual. I'd assume your ear is tuned enough to notice something like that.

It definitely feels like it has compression. When I had the spark plugs out it turned faster and much more freely, but with everything installed it feels correct when it's cranking.

- - - Updated - - -

That is odd. Spark and starter fluid and nothing? Head scratch....

Maybe the spark somehow isn't getting from the coil to the spark plug? It is kind of a head scratcher for sure... I ran through a lot of troubleshooting steps with my friend yesterday and he was stumped too. My friend has been wrenching on cars for over 30 years and he was a full-time mechanic for GM for a while and has owned BMWs for longer than I've been alive, so if he's stumped I'm a little worried.

[JimLev]

Might be time to pull the valve covers off to make sure the trigger wheel nuts and the vanos bolts didn't loosen up.

[dannyzabolotny]

Oh and one more thing I checked last night before going to bed— I got into the secret cluster tests and looked at how much gas was in the tank: 14.2L in the left side and 1.8L in the right side, for a total of 16L. A far-fetched idea I had is that maybe it's not getting enough gas due to a non-functioning suction pump in the gas tank? It *is* a saddle-type tank in the X5, much like in the E38 and E39...

[philly98540]

But starter fluid.... should make some puff of combustion even with zero fuel.

[JimLev]

Maybe you sprayed in too much starter fluid, it's easy to flood it using it.
Just 2 very short bursts should be enough.

[dannyzabolotny]

I did spray a bunch straight into the throttle body... like continuous spray for a few seconds. I guess I overdid it, haha.

[geargrinder]

Did you measure the actual DME voltage yet Danny? That should be like a 2 minute check.

[dannyzabolotny]

Did you measure the actual DME voltage yet Danny? That should be like a 2 minute check.

I have not, since I unfortunately have work on every weekday from 8:30am til like 6pm. How would I go about checking the DME voltage? Multimeter on some pins?

[JimLev]

The DME power relay could have crapped out.
The DME connector that is closest to the engine is the 12 volt source.

[StRaNgEdAyS]

The DME power relay could have crapped out.
The DME connector that is closest to the engine is the 12 volt source.

If that is the case then he wouldn't be able to pull DME codes, as the DME won't power up fully to be detected.
Been there done that lol

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[geargrinder]

Nope. What part of "DME says it only has 11V" don't you understand? Very simply and obviously that requires some checking.

There's easily a scenario where there's voltage enuff to boot up and crank and whatnot, but due to insufficient current availability, the voltage droops under cranking and stuff goes haywire without crashing the ECU. Electricity is not binary, "ECU boots so must be fine" is absolutely untrue, although I'll for sure grant that mostly these ECUs are fault tolerant and mostly you find if the starter cranks the sparks and sensors are be all fine.

Danny here's the power connector pinout... check voltage on those before (can even pull connector for that) and while cranking (need helper and to measure while connected) and compare to what INPA reports.

You could also measure ohm resistance to a known good ground on the ground pins.