5 replies to this topic

[Portugal]

Can anybody help!
I've got a Mini Cooper S Works 1999 twin point injection and the engine is miss firing on tick over and upto 2000 rpms?
I have had a garage check the plugs, cables, distrabution, but still the same problem.
The mechanic thinks it could be the oxygen sensor or the cat back, but is not 100% sure? I don't what to buy both parts. Credit crunch!!!

Can anybody advise which part, or if it is another problem?

Thanks

Stuart
Algarve
Portugal

[Sprocket]

First thing I will say is, how will the cat cause the engine to misfire? sounds like a statement from a garage that doesnt know what they are doing.

Is the missfire regular or irregular?

What are the exhaust emissions results like? Any decent garage should have a four gas analyser even in portugal and they should be able to tell you HCs, CO%, O2% and CO2% and if you are real lucky you might find a garage with a five gas analyser which also gives NOX%

That will give you the biggest clue. Then there is the oxygen sensor itself, is this functioning correctly and the best way to test that is with a diagnostic unit connected to the ECU. This will also tell you what the sensors are reading so you can compare with actual measured temperature. I did a write up on testing the oxygen sensor using simple tools, its in the pinned topics at the top of this section of the forum. One other thing to consider is the oxygen sensor relay. I myself had been chasing a missfire at idle for a long time. I eventualy found that the relay was faulty. this caused the oxygen sensor to read a constand high voltage, other symptoms included a clean spark plug, almost looked new, no soot whatsoever.

Other things to consider is that it might not be the fault of the electronics, it could be mechanical. Has a compression test been carried out? whats the mileage on the car? Valve clearancies set correctly? Correct spark plugs for the engine?

[Portugal]

Cheers for the reply Sprocket.

I think you could be right about the garage. They don't install confidence. I'll go else where.

The missfire is irregular.
I'll go to another garage and get the exhaust emission test and also a compression test.
The milage is low 20700.
Valve clearance is set at .016 - .406mm this was the setting I was given by John Cooper garage.
The spark plugs are quite new and the same as the original specified.

I'll have a read of your write up regarding the oxygen sensor.

I guess it's just a process of elimination!

Thanks again.

[Portugal]

First thing I will say is, how will the cat cause the engine to misfire? sounds like a statement from a garage that doesnt know what they are doing.

Is the missfire regular or irregular?

What are the exhaust emissions results like? Any decent garage should have a four gas analyser even in portugal and they should be able to tell you HCs, CO%, O2% and CO2% and if you are real lucky you might find a garage with a five gas analyser which also gives NOX%

That will give you the biggest clue. Then there is the oxygen sensor itself, is this functioning correctly and the best way to test that is with a diagnostic unit connected to the ECU. This will also tell you what the sensors are reading so you can compare with actual measured temperature. I did a write up on testing the oxygen sensor using simple tools, its in the pinned topics at the top of this section of the forum. One other thing to consider is the oxygen sensor relay. I myself had been chasing a missfire at idle for a long time. I eventualy found that the relay was faulty. this caused the oxygen sensor to read a constand high voltage, other symptoms included a clean spark plug, almost looked new, no soot whatsoever.

Other things to consider is that it might not be the fault of the electronics, it could be mechanical. Has a compression test been carried out? whats the mileage on the car? Valve clearancies set correctly? Correct spark plugs for the engine?

Hi Spocket,

I've been away for a while and only just got the emissions CO% reading which varied from 6.25 to 6.75! and the oxygen sensor lambda came out at 0.745.
Does that give any indication of the problem?
Would appreciate you advise.

Cheers

Portugal

[minicooper1.3i]

How's the car whilst driving? Will it actually drive or is it so bad that won't move off properly? What you've described so far sounds like the problem I had with mine, where some muppet had changed the clutch and not refitted the flywheel properly so the reluctor ring was being read incorrectly by the crankshft sensor. It started as a slight flat spot during acceleration but progressed to the complete misfire and an undrivable car. If the flywheel has not been touched then it should still be ok, but you may have a problem with the crankshaft sensor itself. I've had one fail before and also had one with breaking wires where it had not been secured to the bracket on the clutch housing (where it joins the main loom) and the movement and caused the wires to break down.

[Portugal]

The car drives OK. It's only tick over and below 2000 rpm where it miss fires. I'm not a mechanic, but I more convinced it's something to do with the Oxygen sensor. It's running rich, alot of unburnt fuel coming out the exhaust. You can really smell it! If you've got any other ideas, let me know.
Thanks anyway.