XSeries-forum

On a cold start the X will start and die, will continue to do this unless caught on the throttle and will then run but is rough. When warm will generally start and run but is still rough. Once you have moved of everything is smooth and normal. Have used carb cleaner with no noticeable improvement. Can’t at the moment get codes as I’ve loaned out the diagnostics and can’t get it back till the weekend. Any initial thoughts? Same rough idle on lpg.

Morning Henry
If you shut the LPG down, does it start and idle OK? Could be the LPG is feeding in to early while air temp in the inlet is low. My 4.4 had a similar issue a massive flat spot if I tried to accelerate when it was cold 1/4 temp on the gauge and no problems.
Dave

Hi there, I have lpg on my 4.4 , luckily have not experienced this fault, but now filed away for reference.

Regards,
Lez

Greydog I tried that this morning made no difference. Payed a little more attention this morning and roughness improves as the aux air pump switches off and improves some more if the MAF is disconnected?

First pic is using petrol and second is on LPG
Fault codes difficult to find answers
28 fuel trim adaption low/high OR Lambda sensor
2D can’t find anything
12 can’t find anything
So if fuel trim then it could be an air leak. Need smoke test.
Problem is by the time you get lambda readings the idle is not bad.
I’m leaning toward air leak or MAF
Opinions appreciated
BTY much pestering got my foxwell back

Morning Henry
Thats the simple thing off the table then
Just had a quick look at https://bmwfault.codes/ but it doesn't give any more information than your Foxwell other than two codes to link back to the O2 sensors
I think an air leak is the possible cause a perished hose somewhere The MAF is testable so that should be easier to rule out

Nice you got the Foxwell back, that won't be leaving the garage again I bet
Good luck with the hunt

Dave

I’ve got a few load carrying jobs to do so by Thursday I should be able to concentrate on the faults. I’ll dig out my home made smoke tester and give that a go but carb cleaner didn’t show any air leaks. Problem is your in that area where their are a lot of bits that must be near end of life at 164k. The short term fuel trim on bank 2 is way off and it throws a code when it gets to the end of adaptions. If there is no air leak and I don’t think there is I suppose it could be an injector leaking. So a pressure test might be needed. After that I’m struggling. There are no external cam cover leaks but I’ll pull the coils out and check the plug wells aren’t full of oil and the plugs are tight.

Question, are the o2 sensors the same pre and post cat the only difference being that the part number differentiates the length of the wire?

Morning Henry
As far as I know they are the same with different length cables or the universal ones that many garages use wouldn't work at all.
O2 sensors have a life, and it is normally the heater circuits that fail (2 white wires you should be able to measure between 8 and 9 ohms)
I changed all 4 when I rebuilt the engine at 90k now on the same miles as you, and last scan showed an issue with bank 2 sensor after cat.

As I have mothballed the 4.6 to save pilling the miles on it, it is not a priority job.

Dave

That’s a very helpful answer. Was really difficult to start this morning and had to be held on the throttle for the whole warm up period. Then it was fine runs well no stalling

What about fuel pressure? Thinking out loud, if fuel pressure is down fuel wouldn't atomise correctly making starting difficult more so on a cool morning. Once temp rises and the LPG is there no issue or is it OK on Petrol when up to temp

Dave

This morning I had turned the gas off. All the symptoms above were on petrol After it was running good on petrol I switched the gas back on and once it reached temperature switched to the gas.
I’ve started stripping stuff and have checked the plug holes and tightness of plugs. All good. Removed the throttle body, fairly dirty.

May be the crankcase ventilation needs a clean out that will put crud back into the inlet and throttle body. The fact it smooths out on petrol with temperature in my mind rules out injectors as normally if they aren't atomising it won't improve with a little heat. Still thinking a fuel pressure sensor
Good Hunting
Dave

Temperature sensor (not sure which one on the V8s) but don’t these cars have a ‘cold’ and ‘hot’ mode so a sensor could be sending the wrong data that lets the engine think it’s warm when it isn’t? We all used to have chokes but they vanished decades ago with the advent of fuel injection. Run a cold engine off-choke too early and they didn’t idle well. Might be a red herring, but just wondered.

I checked for fault codes before stripping down and bearing in mind how awful it was yesterday there wasn’t one single code for engine. The Foxwell normally picks up faults pretty accurately. Anyway I checked the fuel pressure this morning and with ignition on read 3 bar and after 10 minutes was at 2.8 bar which seems pretty normal and suggests the injectors are not leaking. Next up is smoke test but rain has chased me indoors. When it’s back together I will look on the Foxwell at the intake temperature readings to ensure they do vary from cold to running temperatures.
PS Greydog, when I removed the throttle body the inside of the inlet manifold was impressively clean and oil free. No oil puddles like I had years ago when I changed the whole system. Checked the pipes to/from the oil separator and absolutely no mayo/gunge or softness which would allow collapse. Thanks to everyone for suggestions.