1078 fouling spark plug - MVAgusta.net
 
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post #1 of 7 (permalink) Old 07-04-2009, 10:37 AM Thread Starter
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1078 fouling spark plug

Dears,

For those who remember my 1078 fouled twice the spark plug in cylinder 1. Result was loss of power and cylinder 1 working with 30C less temperature than the other 3 in all temperature range. The plugs were fouled after 2000kms and with slight warning both time (on/ off working till dead). No deposits on plugs just nice gray color only last time the tip was evidendly burned. More current through the plug was our best estimate.

Finally after checking ignition coils, injectors, fuses, any oil leakage contaminating the plug etc etc all found normal except we found out that the Air temperature/ pressure sensor at the front left air intake was measuring 2.3 V and -24ΚΩ at room temperature during a feed test. As per service manual values should be 4.5V and 2.6KΩ respectively. This is a Magnetti Marelli part by the way and it seems damaged (purely from these values).

Has anyone experienced a faulty air pressure sensor and could that lead to more current through the spark plugs? I think that sensor converts pulses /readings to voltage through the ECU (which decides the volume /measure of ignition) but still it should foul all cylinders not just one and specifically the left one and also immediately not after 2,000 kms..

Appreciate thoughts please.
Thanks again
Phil

Last edited by PP1098; 07-04-2009 at 02:34 PM.
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post #2 of 7 (permalink) Old 07-04-2009, 08:52 PM
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Dears,

This is a Magnetti Marelli part by the way and it seems damaged (purely from these values).
Phil
That sounds very odd. That's not a part you expect to fail. No moving parts. Still, stranger things have happened eh?

That sensor delivers two feeds to the ECU yes?... A Voltage reading and a Resistance value. Sounds like you've done some good work narrowing it down but more and more it's starting to point to the ECU again. Sounds like the plug was a sympton not a cause.

Pity there wasn't another one close by to swap just to check. Doesn't explain the difference in compression figures does it.
Sorry to say no answers here (me not the forum) i'm afraid. Moral support is cheap.
Stiv

Last edited by Stiv; 07-05-2009 at 02:25 AM.
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post #3 of 7 (permalink) Old 07-05-2009, 05:34 AM Thread Starter
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That sounds very odd. That's not a part you expect to fail. No moving parts. Still, stranger things have happened eh?

That sensor delivers two feeds to the ECU yes?... A Voltage reading and a Resistance value. Sounds like you've done some good work narrowing it down but more and more it's starting to point to the ECU again. Sounds like the plug was a sympton not a cause.

Pity there wasn't another one close by to swap just to check. Doesn't explain the difference in compression figures does it.
Sorry to say no answers here (me not the forum) i'm afraid. Moral support is cheap.
Stiv
Hi Stiv, thanks.
Well compression of the engine has nothing to do with this (i.e. faulty sensor fouling sparks). I guess it must be my breaking-in of the engine, not done in the best way!?
ECU gets info from 3-4 sensors and then decides what to send/ do with volumes (especially air/ fuel ratio). So all this makes sense assuming that the sensor is indeed faulty.
I'll wait to see reactions if anyone had this before. I only hope this is the solution otherwise I am out of ideas.
Rgds
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post #4 of 7 (permalink) Old 07-05-2009, 10:01 AM
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The air pressure sensor is a potentiometer and gives a signal to the ECU from the center tap. Power and ground are the other 2 wires. The ECU uses this signal, along with others, to compute injector duration (fuel mixture) and ignition advance.

All 4 cylinders will be affected if it is sending an erroneous signal.

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post #5 of 7 (permalink) Old 07-05-2009, 01:39 PM
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Just a dumb question, have you move the coil and injector around to see if the problem follows?
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post #6 of 7 (permalink) Old 07-05-2009, 03:03 PM
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Just a dumb question, have you move the coil and injector around to see if the problem follows?

Not a dumb question...a very good diagnostic tool.

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post #7 of 7 (permalink) Old 07-05-2009, 05:49 PM Thread Starter
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yes we did. just the coil as injectors seemed to be pressed in and we did not want to cause any problems. So coil of cylinder 1 is now in cylinder 2 and waiting to see results. That sensor though.. strange.
Esq'z me you are right it should affect all 4 cylinders. Thing is maybe it does and we can't see it. Although all other spark plugs were OK still the firing /mixture could be wrong and not visible by just looking at the plugs. Maybe the effect on rest 3 cylinders is to a lesser extent..I do not know. Engine feels numb at times as if air filter is clogged..

Thanks for comments.
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