Intermittent loss of power
 

On a couple of occasions over the last two weeks my car (M44 with DASC) had lost power for about 10 seconds. There doesn't seem to be any consistency as far as it happening at certain engine temperature or whether under load.

Fault code was showing some camshaft position sensor errors, so I bought a second hand genuine part but had the same issue and same error.

The problem did start after I washed the engine bay, although I'm not sure whether this is related or coincidence.

It also started after I started smelling fuel in the engine bay. I replaced some old cracked fuel hoses and found a loose hose clamp which improved this but there is still a small fuel smell. I thought when the car lost power last time that I could smell fuel strong while driving.

Is this a limp home mode? Any other possible causes for CPS error codes? Any help greatly appreciated.

Are you running the rising rate fuel pressure regulator setup from Downing? Could the regulator be acting up causing a fuel pressure fluctuation and also possibly the source of the gasoline smell?


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Yes,I have the RRFPR.

I don't have anything to check fuel pressure, but maybe I need to get that checked.

How long has it been since you fixed the sketchy fuel hoses? If it's been a while and you can still smell fuel, then there's another leak somewhere. If you can't find a leak in the engine bay or underneath, then maybe pull up the back seat and check the lines to the fuel pump.

A while back, I was having some mysterious engine problems - turned out it was the fuel pressure regulator. And at one point, the increased pressure caused one of the fuel hoses to pop off. A faulty FPR is definitely a possibility.

So I would find the leak, and check the fuel pressure.

I replaced two of the rubber fuel hoses in the engine bay a week ago. There is a third one that I didn't change as it looked okay, but maybe I should change.

I have a spare fuel rail so I could try another FPR, although not the RRFPR.

I ran the car today with the camshaft sensor disconnected to see how it would drive. Aside from a slightly worse idle, it drove fine, and did not seem down on power.

Can anyone tell me what the procedure is for checking fuel pressure for a DASC equipped M44, and what the pressure should be?

The problem happened again last night.

This time the car lost power and there was some banging noise from the engine bay, not sure what (can they back fire in the intake system?).

I pulled over but the car started running normally then.

The problem is intermittent, and has only happened within ten minutes of driving home from work. It has strangely never happened on my way to work.

I took the vacuum hoses off both fuel regulators and can smell fuel in the hoses. I ran the engine with the hoses disconnected but can't see any fuel coming out. Probably not the right way to test them though?

I had a spare fuel regulator so I've put that on to see if it makes a difference.

I was thinking of blocking the vacuum hoses to the RRFPR and the super charger bypass to disable the super charger. Is that worthwhile?

This morning the car would not start at all. Maybe the FPR I put in is faulty. There was some banging or popping going on in the engine bay when trying to start it.

Possible misfire issue and you said it showed up after you washed the engine. Check very closely for a fault in the ignition system. Wires, coils, plugs etc.

Also with the RRFPR the hoses need to be watched closely as the pressures get up there to compensate for the extra fuel required by the boost and the last thing you want is a fuel fire.


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You said you washed the engine bay, did you take out your spark plug boots and make sure their is no water down in the head grounding the spark plug

The intermittent stalling did happen the day after I washed the engine bay, but I did have a fuel leak which seemed to start quite a few days before I washed the engine bay.

I had covered many electrical parts in plastic bags before washing so it may just be a coincidence. I also checked the spark plugs out and there was no water.

I suspect that I have a fuel pressure issue which may have caused the leak.

The car is now not starting at all when cold in the morning. Yesterday it started fine in the afternoon when it is a bit warmer. Not sure if the temperature is the cause or just coincidence.

I put my spare fuel pump in last night and it ran fine but wouldn't start this morning. It just cranks and cranks and starts popping and banging inside the engine bay.

Check those spark plug holes and replace the plugs if their corroded.

Where do you live? Is the car stored inside or out at night when this is happening? What's the weather been like? Still think you are having an electrical/ignition issue.

Australia - in a colder part of Sydney (can be about 5C/40F in the morning).

Could be electrical/ignition.

I was presuming fuel as I can smell fuel and had a fuel leak.

One thing I do have is an intermittent cam sensor fault code. I switched to a used cam sensor I bought now but it shows the same fault code. Not sure if it is faulty too or if there is something causing it to appear as this fault code.

So far I have tried fuel pressure regulator, fuel pump, swapped fuel pump relay, changed rubber fuel lines, fuel filter was replaced a few months ago.

Of course I can't say for sure but my guess is that there is moisture getting into the ignition system some place. One place that I recently heard when all the other normal places turned out okay was the coil pack. Looked good but when swapped was the problem. If I remember correctly that problem appeared after an engine cleaning as well.

Go through the ignition system is my best advice. The absolute last thing you want with a blower is a through the intake backfire.

Thanks for all the advice. I will see if I can try another coil.

Tonight I got it started, took a lot of cranking, and eventually started with some throttle. Ran very bad and would stall if left to idle, but after it warned it seemed to run okay.

I pulled off a few things to check, and one thing I did find was that at first I couldn't blow through the PCV. After a bit it did seem to free up and I could blow through it.

I have a catch can fitted before the PCV and I emptied it and out came a reasonable amount of oily liquid, the consistency was closer to water than oil. Photo attached.

I put in a spare PCV and bypassed the catch can but will need to try it in the morning to see of it made any difference.

http://autos.johnavis.com/blog/uploa...n-contents.jpg

I gave up and took it to a mechanic.

He says that the fuel pressure is too low, about 20psi at idle, and that both fuel pressure regulators should be replaced.

He also says that the fuel pressure drops to zero when the engine is turned off, which means the fuel pump could also be faulty.

Well it seems you were on the right track, sorry for doubting you.


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I hope I'm right, but waiting on a new FPR to confirm. However I am worried my mechanic did not test the fuel pressure correctly as he didn't have the right attachment for the valve on the fuel rail. I haven't asked yet but I worry he may have checked the pressure on the return line. That would result in exactly the readings he came up with, low pressure at idle, zero as soon as engine is turned off... Right?

Unfortunately you are very right. The return line would behave exactly as you describe and if that is what he did your fuel pump/pressure regulator and RRFPR may all be in proper working order.


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Uh oh... I picked up the car and asked the mechanic where you check the fuel pressure. He showed me the return line from my RRFPR. Fail.

Too early to tell if the new FPR solves my problem or not, but I suspect not :(

Unfortunately I was probably wrong about it being a fuel pressure problem.

But I was right about the mechanic getting it wrong (unfortunately).

On my way to work this morning, after about 28km the car lost power again. This time worse than usual as it jerked as it lost power. There was backfiring through the exhaust and some through the intake. It sort of kept going and I struggled up a small hill as there was no place to stop then let it idle down the hill and by this time it seemed back to normal. I switched off and restarted to be safe and it drove fine the rest of the way.

I haven't much idea what to do next... I guess the clues are the backfiring, possibly the cam sensor fault code being reported (but mechanic says this often appears due to misfiring), possibly some relation to the fuel leak I had, or possibly due to the washing of the engine bay.

I noticed when looking in INPA that at idle the "lambda sensor voltage 1" alternates between a high reading on the scale and a very low reading. Is this normal?

I also have some variation in "smoothness", but I think it has been like this since I got it. Cylinder 1 and 4 are zero. Cylinder 3 and 4 are around 400 and 300.

And "needed air i.s. controller" is always above maximum rating on the scale (about 10.25)?

Not sure what the high and low end of the scale is for the lambda sensor is but I suspect probably 1 volt and 0 volt as that is typical. If so than what you are seeing is normal. A good sensor on a good motor should swing rapidly between 0 and 1 volt as a normal reading.

The needed air being high makes me wonder what the MAF is doing? Might want to just give it a good look and maybe clean with MAF cleaner or aircraft grade electronics cleaner.


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Thanks maverick for your continued help.

I have a spare MAF so I will give it a try. I assumed "i.s." was idle speed so didn't think of the MAF, and I also though that a bad MAF would give a fault code. But I have read that the MAF can be a cause of backfires so you might be onto something.

If the MAF is acting up it can make the DME assume that more idle air is needed when it's not. This is just one possible issue but it's not an uncommon fault. Since you have a spare it's a very worthwhile idea to try and swap it.

Dave


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I did have a cam sensor make my car fall on its face and it never would set a check engine light. Finally changed it one day on a hunch and hasn't done it again.

I've also have seen some bad tape up jobs on the wiring harness under the intake on the dasc cars. May also want to check that you dont have wires rubbed through and grounding on the block or back of starter.

Well I put in a spare MAF and drove 45km home without any problems. But it doesn't do it every day so not sure if it has made a difference yet or not.

I checked on INPA when I got home and that "needed air i.s. controller" value is still over maximum value. There are no fault codes relating to the MAF so looks like the MAF I put in was okay.

I might try a spare idle speed motor to see if that changes this value too.

The cam sensor fault is still there, with more frequencies than usual, but the misfire I experienced earlier in the day was worse than usual so may have caused that fault.

andakn, your suggestions are worth investigating. I did try a second hand cam sensor already, but I guess I can't be sure that it was okay (although would be a coincidence to have the exact same intermittent fault?). I will try and have a good look over the wiring.

Finally had some time to work on the car. Pulled much of the intake system apart to check for vacuum leaks, etc. Cleaned the throttle body. Found my dipstick tube was not pushed all the way in so have tidied that up. Also changed spark plug leads. Have ordered a coil but hasn't arrived yet. Have taken it for a short drive only, idle is fantastic after cleaning isv. Will drive it to work tomorrow and see if any improvement in the loss of power problem.

Problem happened again this morning :(

I am hoping that the coil might solve the problem when it arrives.

I also have some wiring and connectors to check still.

If not, maybe another cam sensor.

Do you have a boost or vacuum/boost gage installed?

Yes I do have a cheap digital gauge that does both. I haven't watched it though when the problem is happening, usually too busy finding a place to pull over...

On my way home from work today the problem was much worse than usual. Happened about ten times. Stalled a few times, once when stopped waiting at some lights. I guess its good its getting worse as it should make it easier to diagnose, but I'm not going to drive it to work as it is now as it's to stressful wondering when and where is going to happen next.

(My drive to work is country type highway roads but with quite a bit of traffic, and also a narrow mountain pass. There's lots of places where there is no room to stop, and there are lots of large trucks that use the highway. So far I've mostly been lucky where I have had to stop, and sometimes I have been able to keep moving at a slow pace, but I also want to avoid damage from backfiring.)

I think I'll try a crank sensor if I can find a cheap used one, as from research that seems like a likely cause too. I did measure mine and it showed around 650 ohms but maybe it could have an intermittent fault. I would like to check the wiring more as suggested here, but it's hard to get to. Would be great to remove some of the DASC parts to get access but probably a big job and new gaskets required?

I noticed when I last was checking codes, with the ignition on but engine not running, INPA was showing a voltage reading of 11.75 volts. With the engine running it's 13V+.

I understand a good battery should be reading 12.5V when fully charged.

Could I have a battery or charging issue that might be causing ignition problems too?

It is possible I guess as it's all computer controlled and susceptible to voltage issues.

I would try testing at the battery posts and again at the actual attached terminals with a reliable voltage meter. Testing the posts and then the terminals lets you know if corrosion maybe blocking some of the current.


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Ok, had some more time to look at the car.

Battery is ~12.5V at rest so that is okay.

I received my new coil (looks like it has been dropped in transit though) and the car would not start at first. It did start after a few attempts but stalled. Then it ran for a little while and I was able to check with INPA while it was running. No change to any of the readings and smoothness is way out on cylinder 2 and less so on cylinder 3.

Then it died again and wouldn't start.

INPA was reporting cam sensor fault code again (112) so I unplugged the sensor and it started next attempt. I turned it off and re-connected the cam sensor and it started fine again.

Cam sensor fault code is appearing almost immediately now. As mentioned I had replaced it with a second hand one so maybe that one is faulty?

Is there anything else that can cause this error code (unplausible value it says)? Timing chain slackness or mis-firing perhaps?

I may have to try another cam sensor but I am getting sick of spending money on things that may not be needed.

Thinking outside of the box.

Okay this all started after an engine cleaning. You are still getting unusual readings on the cam sensor that you swapped and the problem persists.

What's the chance of water getting into the harness someplace? One thing that wouldn't cost you maybe ordering another unneeded part would be to make sure no water got the DME itself. Unlikely but stranger things have happened.




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I agree that there is a good chance it is related to the engine bay cleaning, except that the car started and ran fine after the cleaning and then drove at least 50km the next day before failing in this way for the first time.

I have had a look inside the dme compartment and it was dry. I haven't pulled apart the dme itself though.

I wish the wiring under the intake was easier to get to so I could check out better than I have. I also wish I had a known good cam sensor to try without having to buy another one.

When I measure the wiring socket for the camshaft sensor both the +12V and GND pins measure short circuit to ground, but with ignition on I see 12V. I'm not sure if this is normal or there is a short circuit. Any ideas?

With the ECU/DME disconnected that possible short circuit disappears. Not sure if this is how it should be or not.

Pin 54 of the ECU is where this connects to. It measure short to GND when the ECU is connected. When I disconnect the ECU there is no short from 54 to GND. If I check for short to GND for all the other sensors and devices that share the 12V from pin 54, none of them measure short to GND. I am confused.

Probably not related, but I also had a closer look at the piggyback computer that is mounted above my ECU (photo below). I never looked at it properly before but I see that it is not actually connected. The connector has been unplugged and some wires very poorly jammed in the connector to short some pins together (presumably re-connecting some of the ECU wires that were being modified by this unit).

I have found someone with a wrecked E36 who is sending me a cam sensor, crank sensor and O2 sensor, so will have these to try next week.

http://bmw3series.johnavis.com/blog/...ntrol-unit.jpg

Just tried another cam sensor and a crank sensor. The crank sensor bolt was loose which I hoped might be the cause. But no good, I still have a constant cam sensor fault code being reported. I didn't bother driving it.

So I need some help from a fellow M44 owner.

My 12V line that is shared with most sensors measures short circuit to ground. This may be normal, but I don't think so. Can someone with a multimeter check if there's is the same. This is simple to do - just pop off the plug to the idle speed motor and measure the middle pin (pin 2) to ground and see if it measures short circuit (use continuity test or ohms/resistance check).

I found if I disconnect the O2 sensor the short circuit goes away. Another O2 sensor does the same thing, though, so this must be normal.