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Mini Cooper 1.6 120HP On the third cylinder misfire on a warm engine

mxas123 14679 15
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  • #1 16853216
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    As in the subject. After warming up, the mini stops working on the 3rd cylinder.
    As of today they have been mentioned:
    * candles
    * coil
    *distribution
    * gasoline injectors
    * sensors from rollers
    * Vanos regulator
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  • #2 16853233
    sanfran
    Network and Internet specialist  
    Posts: 9792
    Help: 953
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    I would suggest checking the compression pressure on a hot engine.
  • #3 16853249
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    Compression pressure checked the same as on cold and above all equal
  • #4 16853488
    Ireneo
    Level 42  
    Posts: 7818
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    Completely stops working?
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  • #5 16853734
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    So totally zero reaction
  • #6 16853790
    moto-kord
    Level 28  
    Posts: 800
    Help: 137
    Rate: 501
    Check what is missing when the 3rd cylinder stops (spark or fuel).
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  • #7 16854015
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    It cuts off the fuel.
  • #8 16854162
    ladamaniac
    Level 40  
    Posts: 5317
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    He probably cuts the fuel because he sees the ignition falling out. Error p0303? Or something else?
  • #9 16854185
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    exactly that

    Added after 2 [minutes]:

    and the best part is that when you stop working on the third cylinder pushes off for a moment, the sensor will fight indifferently, which from the machine starts working on all cylinders
  • #10 16854332
    mario 77
    Level 23  
    Posts: 510
    Help: 66
    Rate: 335
    mxas123 wrote:

    and the best part is that when you stop working on the third cylinder pushes off for a moment, the sensor will fight indifferently, which from the machine starts working on all cylinders

    You write that then it goes to all cylinders but is it even or still something going on on this cylinder? And you watched in the parameters whether the ignition falls out and with what frequency on this cylinder immediately after starting a cold engine and what changes with the increase in temperature? With this engine I would not be surprised when it will be necessary to make the head.
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  • #11 16854360
    carrot
    Moderator of Cars  
    Posts: 8375
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    Quote:
    push back for a moment the sensor will fight indifferently which from the machine begins to work on all cylinders

    The controller switches from sequential injection mode to group injection and that's why it happens
  • #12 16854361
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    I know that much too

    Added after 1 [minutes]:

    but what is the reason, because there are no ideas
  • #13 16855410
    moto-kord
    Level 28  
    Posts: 800
    Help: 137
    Rate: 501
    mxas123 wrote:
    It cuts off the fuel.

    Have you changed the injections?
    Have you measured the injector resistance?
    Did you check the current record when the fuel was cut off?
  • #14 16856154
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    everything is checked but there is one idea
  • #15 16856155
    carrot
    Moderator of Cars  
    Posts: 8375
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    This is not a problem with injections, the controller registers the ignition loss on one cylinder and turns off the injector on it to prevent unburned fuel from entering the catalyst
  • #16 16856241
    mxas123
    Level 7  
    Posts: 8
    Rate: 18
    gentlemen, I made one more pressure test on a hot engine, but on a detached phase adjuster motor and it turned out that there is only 3 bars so the problem has been solved thank you all for suggestions and best regards
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Topic summary

✨ The discussion revolves around a Mini Cooper 1.6 with a 120HP engine experiencing a misfire on the third cylinder after the engine warms up. Initial suggestions included checking compression pressure, which was found to be equal to that of a cold engine. It was noted that the engine completely stops responding on the third cylinder, leading to further investigation into whether the issue was related to spark or fuel delivery. It was determined that the fuel was being cut off due to detected ignition loss, possibly indicated by error code P0303. The conversation also touched on the controller switching from sequential to group injection mode, which could contribute to the issue. Ultimately, a pressure test revealed low pressure (3 bars) when the phase adjuster was detached, leading to the conclusion that this was the root cause of the problem.
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FAQ

TL;DR: Warm misfire on Mini 1.6 (120 HP) traced to low hot compression: "there is only 3 bars" after unplugging the phase adjuster motor. [Elektroda, mxas123, post #16856241] Why it matters: This FAQ helps DIYers quickly isolate heat-related cylinder 3 misfires without shotgun parts swaps.

Quick Facts

What caused the warm-engine cylinder 3 misfire in this Mini?

Low hot compression on cylinder 3 was the root cause. With the cam phase adjuster motor unplugged, compression measured only ~3 bar. That mechanical loss created the misfire, and the ECU then halted fuel on that cylinder. "There is only 3 bars" confirmed the diagnosis. [Elektroda, mxas123, post #16856241]

How can I tell if the issue is fuel cut or lost spark?

Observe live data or use a noid light and spark tester during the fault. In this thread, the owner confirmed the ECU cut fuel to the third cylinder when the misfire occurred on a warm engine. That distinguishes a commanded fuel shutoff from ignition failure. [Elektroda, mxas123, post #16854015]

What does code P0303 mean on this car?

P0303 flags a misfire detected on cylinder 3. The ECU uses crank acceleration to spot combustion loss. When it counts enough misses, it sets P0303 and may protect the catalyst by cutting fuel on that cylinder. "Error P0303?" was the clue in the thread. [Elektroda, ladamaniac, post #16854162]

Why does unplugging a sensor make all cylinders run briefly?

Unplugging forced the ECU from sequential to group injection. Group injection can temporarily mask a misfire pattern caused by timing or per-cylinder control. Once the ECU returns to normal strategy, the misfire shows again. "The controller switches... to group injection," explained one contributor. [Elektroda, carrot, post #16854360]

Should I perform compression testing hot or cold for this symptom?

Test on a fully hot engine. Some mechanical issues appear only with heat, so cold compression can look normal while hot compression reveals the fault. This thread’s guidance started with, "check the compression pressure on a hot engine." [Elektroda, sanfran, post #16853233]

Cold and hot compression both looked equal—am I done?

No. Re-test with the cam phase adjuster actuator disconnected if symptoms persist. In this case, repeating the test hot with the phase adjuster motor unplugged exposed only ~3 bar on cylinder 3. That pinpointed a cam-timing or head-related issue hidden in earlier checks. [Elektroda, mxas123, post #16856241]

What ultimately resolved the misfire for the poster?

Identifying the mechanical cause: hot compression dropped to ~3 bar on cylinder 3 when the phase adjuster motor was unplugged. The poster reported the problem solved after acting on that finding. This directs repairs toward cam phasing or head work instead of fuel or ignition parts. [Elektroda, mxas123, post #16856241]

How do I reproduce the winning diagnostic steps from this thread?

  1. Warm the engine until the misfire on cylinder 3 appears.
  2. Perform a hot compression test.
  3. Repeat the test with the cam phase adjuster motor unplugged; compare readings. The owner found only ~3 bar on cylinder 3 under step 3, confirming a mechanical/timing fault. [Elektroda, mxas123, post #16856241]

Is swapping injectors or coils enough to fix this warm misfire?

No. The ECU can cut fuel after it detects misfire, so injector swaps won’t help if the root cause is mechanical. In this case, ignition and injection components had been replaced already, but the ECU’s catalyst-protection strategy kept fuel off the failing cylinder. [Elektroda, carrot, post #16856155]

Can a cylinder really go completely dead only when warm?

Yes. The poster confirmed the third cylinder had "totally zero reaction" once warm. Heat can worsen sealing or timing issues, dropping effective compression. That turns a marginal cylinder into a dead one at idle and low load. [Elektroda, mxas123, post #16853734]

What is sequential vs. group injection in this context?

Sequential injection times each injector to its intake stroke. Group injection fires multiple injectors together. When a sensor is unplugged, the ECU can fall back to group injection, briefly smoothing symptoms but not fixing the cause. "Switches... to group injection" captured this behavior. [Elektroda, carrot, post #16854360]

When should I consider cylinder head work on a warm misfire?

Consider head work if hot testing shows compression loss or timing-related issues. A contributor noted, with this engine, a head job might be required when misfire data trends with temperature rise. That aligns with the final low-compression finding on cylinder 3. [Elektroda, mario 77, post #16854332]
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