318Ti (M44) automatic: Intermittent hesitation while driving

[gjm123]

Our daughter's car has decided to demand attention. On a Sunday, of course.

While driving at a constant speed and throttle position, the engine will hesitate. It is as though it is running out of fuel - there's no warning lights (and 3/4 tank of fuel). The hesitation will last from a fraction of a second up to 2-3 seconds, during which no throttle activity makes any difference. Then the engine will pick up again and run as if nothing is wrong.

It might do this several times in a minute, or it might not happen at all for several minutes. It happens under acceleration as well as under constant throttle.

When ticking over, the 'hesitation' can be enough to stall the car. Tickover - idle - is typically very (very) slightly rough but I had put this down to it being a few rpm below ideal idle speed rather than any significant issue.

When stationery the engine will typically rev freely and without problem. We have sat in the car with the engine idling for 10 minutes without an issue.

I've not been able to read any codes - I was recently made redundant, and the laptop went at the same time the job did. I do have an older Compaq which I'm waiting for a PSU for, but (of course) that's not arrived yet. I'll obviously check codes ASAP.

Any ideas? Given circumstances cheap fixes rather than random replacement of expensive parts is much preferred! I was thinking of starting with a fuel filter given I've not replaced that.

TIA.

[Eric93se]

Pull all the spark plugs to see if any are fouling. Re-gap them and you can clean them with a torch (propane) cook them till all the soot turns white. Run a bottle of cleaner with the next tank of gas. When you can afford it, change the pre-cat oxygen sensor. Make your own smoke machine to test for vacuum leaks (youtube for ideas).

- - - Updated - - -

before you pull the spark plugs, shine a light down the tubes to check for oil in the spark plugs tubes (indication of failed valve cover gasket).

[gjm123]

Pull all the spark plugs to see if any are fouling. Re-gap them and you can clean them with a torch (propane) cook them till all the soot turns white. Run a bottle of cleaner with the next tank of gas. When you can afford it, change the pre-cat oxygen sensor. Make your own smoke machine to test for vacuum leaks (youtube for ideas).

- - - Updated - - -

before you pull the spark plugs, shine a light down the tubes to check for oil in the spark plugs tubes (indication of failed valve cover gasket).

Will do!
Thanks. I'll let you know how I get on.

[Eric93se]

Also might want to check fuel pressure, pump could be weak or relay could be going. Relay can be tested, energize it and measure resistance across switch.

[gjm123]

Also might want to check fuel pressure, pump could be weak or relay could be going. Relay can be tested, energize it and measure resistance across switch.

Checking fuel pressure is going to be more difficult - I've nothing to measure with other than a No.1 eyeball and assessing flow that way.
Resistance across the switch - any value represent good/better/terrible, or is it a simple 0 ohms or some resistance?

[gjm123]

Almost definitely the cam position sensor - finally received the OBD2->OBD adapter, plugged it in to the BMW Scanner 1.4.0 and the results say 'yes'.