[mike1967]

Hi all
I recently bought a 2008 Mini Cooper S with a rough idle problem. I was aware of this when I bought it and got it for a good price so decided to take on the challenge of fixing it. I have tried a few things but with no luck and am looking for some guidance on what to check next.

The Car:
2008 Cooper S, N14 engine, 90k miles
The car was serviced just before I bought it with new spark plugs

The problem: When started from cold the engine idles fine for about 2 minutes. After this the idle becomes lumpy and rough, when pulling away in low revs there is very slight hesitation but at high revs there is no problem and the car accelerates very well.

Steps I have taken:
Sent it to the dealer for a walnut blast of the intake valves. Unfortunately this has not cleared up the problem. The mechanic observed that it cranked for a while before starting and suggested it could be the HPFP.

I have a BMW Scan tool C110+ which I have been using to try and diagnose the problem.
This has shown:
HPFP pressure 4.67 MPa at idle to around 20MPa under full throttle

Some misfire codes which I have since cleared and have not returned.
It shows a high misfire rate on cylinders 2 and 3, swapping the spark plugs and coils does not move the misfire.

Engine temperature shows to be 75-82 Degrees Celcius. I took the car for a good blast and it hovered around 78 Celsius. When stopped this climbs to 82 Celcius. The engine itself does seem quite hot when you pop the bonnet. I am right in thinking this reported temperature is quite low?
The engine has a burning oil smell which is due to an oil leak, I have topped up the oil just below the max mark.

My current thinking is perhaps a stuck thermostat or cracked housing? Or a faulty Coolant temp sensor? I have looked around a couple sensors on the side of the engine and noticed one that may have a broken wire (Photo attached). What steps can I take next to identify the issue? Many Thanks

thats not a broken wire its a single wire from ecu to oil pressure switch in the heat, it gets its earth return from the casing, thermostat housing is prone to failure , there is a update version now with a updated piece of wiring to it, run liva data on the temps sensor and see how car from cold increases temp with diagnostics ie should start at 20c ihs then slowly increase on idle over a 20 minute timing span see if at any point it stops increasing or takes its time then jumps up say or down, also worth doing this and more the wiring harness around see if that effects etc,, below is pic of temp sensor and what voltages you should have off the feed wire for temp sensor , and also the 02 sensors at temps etc, i would lean more towards 02 sensor, and also think about if it's the 02 sensor or a mechanical issue causing it like timing chain stretched, another clue is misfires on 2 cylinders next to each other might find head gasket blown between the two bores compression test needed

 

[mike1967]

Hi Mike, thanks for your reply, that's some useful information. I think I'll start out with a compression test to rule out head gasket, in terms of normal running temperatures what shall I be looking for? How would I go about testing the sensors, do I need to test on the sensor terminals with the connector off? Any way that I can check the thermostat?
Many thanks

to check thermostat, start off car cold start car let run at idle with diagnostics tool attached monitoring coolant sensor this will take a good 40 minutes from start to stop watch the temp it should rise from around 15-20c to 71-76c at this point the thermostat should start to open by keeping your hand on the top radiator hose you will be able to watch the temperature and make note of when the top pipe gets hot to what temp ie the above temps, if pipe dont get hot until 100c then i would say its out of spec compared to others, if gets warm from the off once again it is faulty or just lazy from age, very common.
the electrically controlled thermostat runs off the bosh mev17.4 ecu ie engine management its earthed through the ecu and runs 0 to 12volts depending on when open or closed, ie fully open 11volts cold closed 0volts. where they fail it will cause a high resistance or open short circuit to positive ver common this can take out the ecu at worst very rarely, there is a recall on some prince engines for thermostat housing worth checking if your car is under that recall might get it done for free, the after market housing dont do well seen many fail from new or not long after,
the temp sensor runs on a 5v rail has two wires one is a switched earth to ecu and the other is a 5v reference wire for ecu to use as method to read the temps, ie -48=0.1v 167c=5v 20c=3.2volts ish the hotter the temp sensor gets the higher volts to 5volts , trouble is all these figures give is the circuit works etc, and a guide to what should read what and when but many are intermittent hence why most mechanics will say really we need to change the whole housing and see what we have based on a age and mileage ie 70k 7 years old its not long from failing anyway,, and to be honest the thermostat and temp sensor have so much impact on the running of these low emissions engines they must be correct otherwise get loads of running and cooling issues , that make a good mechanic look silly as all the aove looks right some of the time until driven and forced as such.
below link is the genuine updated housing latest version with the 4 pin plug and the wiring loop needed to convert
https://www.ebay.co.uk/itm/Genuine-...6-Petrol/282811653986?fits=Car+Make:Mini&hash=item41d8e35f62:g:Q3UAAOSwgLlaXjxs
i honestly would not use any other than a genuine one of these as so many of the cheaper ones bought from random seelers dont do well. the above link they specialise in mini bmw and saab parts uk based, their timing chain kits are good as well

 

[mike1967]

the best cheapest scanner for diagnostics link below i dont rate much else below £500 ie entry level snap on etc, autocom cdp plus is good live data runs are very good ie if says a misfire there is one,
https://www.ebay.co.uk/itm/Bluetoot...oZBsi/e2x0X3VsoYC0kBzlng=&checksum=202691983104543d1046cb3446d8bc13bd8bad025591
also best fuel system cleaner will cause white whispy smoke tails from exhaust but really does clean it out well, seafoam
the twin pack with inlet spray helps prevent carbon build up on inlets melts carbon and dirt
https://www.ebay.co.uk/itm/2-CAN-KI...EAFOAM-SRAY/253102669524?epid=2185630474&hash=item3aee183ed4:g:OEUAAOSwCdJZlwY9

 

[mike1967]

I've ordered that seafoam pack so will use it this week and see if it makes any difference.

The car seemed lacking in power the other day so I plugged in the code reader and it came up with a code 2786 Additional Mixture adaptation. What does this mean? After turning the car off and on again the power seems to have returned.

I carried out a compression test and it all seems fine, got 170,160,160,165 PSI.

could be air leak somewhere best way to find it is by a cheap smoke machine tell you what its a must have bit of kit for finding these breather and boost pipe work faults or to rule it out etc, piece of pipe from machine to the inlet of pipe system use some duct tape to seal it some how all i do works a treat, also can add ultra violet dye in the stuff you add to the tank shows up every leak in dark with a light
https://www.ebay.co.uk/itm/Fog-Mach...e-Control-DJ-Disco-Party-UK/143271471566?hash=item215ba529ce:g:VM4AAOSwP3Jc8e15
you do need to know the timing chain is right as this will flag up all kinds of inlet and exhaust faults from over lap of valves bleeding of the pressures and adding to them either side of the engine as such

 

[mike1967]

the fact you have had rattle on start up would be enough for me to replace the timing chain with a kit, when they get worn out tensioner spring gets weak and some times the engine will back fire a bit and release the tension on the chain as such,

 

[mike1967]

another added thing when chain gets stretched the over lap on valves will change depending on loads ie throttle on or off this will will bleed boost off and so many people get lost in the problem, hence why i say if done over 60k change the chain save all that hurt as chances are it doe tend to be this

 

[mike1967]

factory fitment is produced by febi bilsteen after market ones are around FAI do a complete kit around £230 ish but comes with earlier adjuster ie short throw one, its worth putting a genuine chain adjuster in from mini if after market chain kit used,febi branded chain kits are tad cheaper than factory parts, on a 100k engine i woud do the vanos sprockets as well but if on a 50-70k one just do chain and guides and genuine tensioner ie updated longer one, ie n18 engine tensioner will fit all the early cars as well and is better, as for special tools ho yes this is the main in arse for diy the cheap lock kit are hit and miss ie can time engine wrongly must buy the kit with the tensioner preload tool and know how to use it, cams and crank bolts MUST BE RENEWED as stretch bolts genuine they are cheap must do bottom oil seal as well on 100k engines do the oil pump chain as well,

and or below

all prince engines have same chain process to replace turbo car early have 1 or no vanos sprockets the n18 has two but locking etc is all same game as such,

Pardon our interruption...

or

Pardon our interruption...

 

[mike1967]

you will need a crankshaft bolt as well genuine ones are cheap, yep the tensioners from main agents are updated ie longer pic below shows this

 

[mike1967]

use the locking tool locking pin to hold crank i always do never had a issue, do not use the cam locks to hold camshafts when undo or do up bolts a narrow 27mm spanner must be used, try buying the later type tensioner from a Peugeot Citroen, in uk at plymouth vospers very helpful, MUST REPLACE ALL STRETCH BOLTS,
sump needs to come off, engine mount off as well on top driver side i use a axle stand on side on car subframe then the other one on the driveshaft support at rear of engine, its handy to use jack to mover engine up and down etc to get at bolts for jockey wheel,, i would also when in there replace the water pump and its friction wheel if around 70k and above for piece of mind and job done once as such,

 

[mike1967]

you must remove the oil pump and clean around it as i have before had bits of plastic guide get caught up on the top of it and then when car gets driven drops down and blocks the oil strainer and causes oil pressure faults and vanos fault codes as well, hopefully it has not bent anything

 

[mike1967]

I have the identical problem after an engine rebuild!

could be many things was it DIY rebuild or garage