318ti.org forum - Intermittent loss of power

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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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Quote:

Originally Posted by maverick (Post 384823)

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

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?

Quote:

Originally Posted by john318isau (Post 384847)

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)?

Quote:

Originally Posted by john318isau (Post 384910)

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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Quote:

Originally Posted by maverick (Post 384912)

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.

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.

Quote:

Originally Posted by john318isau (Post 384913)

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, but I read that the MAF can be a cause of backfires so worth trying for sure.

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?