Technical 2011 Twinair missfire cyl 1 only on idle and when warm

[dan1979]

Bought a 2011 TA that has missfire on cyl 1 only , and this only happens when i have driven the car for a while(you can drive the car without any problems for as long as youlike but when stopping and let it idle for 10 sec it loses cyl 1 , Mil is on and only get 2 DTC P0301 and P0300 (missfire cyl 1 and random missfire) , changed following coils,sparkplugs, upper+ lower oxygen sensor,camshaft sensor,map sensor, fuel pressure regulator,crankshaft sensor, injectors , ground under battery is checked and good but nothing helps,as soon as a part has been changed i have done replacement in autocom for that part.
Got new oil+ filter + the mini filter is checked and ok

I can see that it gets to much fule on idle when warm thats why cyl 1 dies , but if i rev it it starts up again and works until it idles again
idel is 850 rpm
It got spark (took of the coil and placed a sparkplug in it and it works but as to much fule goes in it cant ignite it.

I have autocom and what i can see the map sensor is reading 900mbar on idle and atmosfere pressure is 1000mbar so its only have 0.1 vacuum to pull the fuel regulator and i think that is to low?

Any ideas?

Tested leak with smog mashine but there is no trace at all ?

Have no more ides what i can do???

only has 120000km

 

[Tropicalmike]

I think we need Dan1979 to say and clarify and interpet what his readings were. I read it as the boost pressure (map sensor) was 100-150 mBar below atmosphere at idle. Not the intake reading vacuum.

 

[Tropicalmike]

Hi,



Does the intake manifold have any vacuum ? I thought twin air doesn't have a throttle plate because the air flow is controlled by the unfair module.

BTW There is throttle body with motorised flap (plate?) before the inlet manifold on a twin air .See attached. Top right with a blue dot.

 

[jackwhoo]

That's interesting I wonder under what engine conditions the throttle plate closes?

I was under impression main point of the uni air system was to control air flow into cylinders by controlling inlet valve opening therefore reduce pumping losses instead of using a throttle body.

Bmw used an inlet valve control system that had a throttle body as a standby system in case the variable valve open system failed. Good thing too because the variable inlet system wasn't reliable.
When it failed unplugging a wiring plug set the system to fully opening position and actuated the throttle body=performance restored.

 

[Tropicalmike]

The uniair can, not open the inlet valves at all if required so I would think the throttle flap could be closed then too. So if you are driving along at say 2500 rpm and just take your foot off the gas but stay in gear then that would seem to be a time to shut off the air to inlet until the engine slows down .

 

[jrkitching]

I don't think looking at gross inlet vacuum is going to help on an engine with no throttle plate. It appears that graphing the pulses from the map sensor can show an issue between cylinders.

I'd agree with this. Unfortunately the kind of kit that has a sub-millisecond transducer response and oscilloscope functionality isn't readily available to most of us, or most garages for that matter.

It's buried deep inside Mark Stammer's document, but he did say that when running on one cylinder only, there was a discernible difference between cylinders. Now this is something that can be tried without specialist equipment, though I don't believe running a TA on a single cylinder is ever going to be easy or comfortable, even on a good one.

If we could find a non destructive way of determining the condition of the uniair module that doesn't require thousands of pounds worth of specialist equipment, this would not only help folks trying to diagnose a problem, it would also be useful to anyone contemplating a prospective purchase.

Meanwhile, I'd avoid buying one that had any sort of running issue (and it helps if you know what a good one should run like!), and as always, be wary if the seller has prewarmed the car immediately prior to you seeing it.

 

[Tropicalmike]

In my case the uniair misfired on one cyl when cold. This thread seems to point to a problem once warm and at idle rpm only. It would be nice if dan1979 would tell us if he sorted his engine or not! I think that he may be a busy professional independant mechanic who just wanted some advice on these unusual little engines.