Random Misfire sounds almost like air leak

[jamman]

Hi I have '99 885i Tiger and I get a misfire that occurs maybe once a minute, sounds like a air leak when it happens .. like when you pop a air tool out of an air compressor fitting

Get a bit of backfire also on decel ... especially when warmed up ...

Run pretty good when winding her up ...

Any suggestions ?

[Bixxer Bob]

Some popping on decel is normal.  The backfiring obviously isn't.  You don't say how many miles the bike's done or how long you've had it, but I'd take a look at the valve clearances first.  If you have an inlet valve not closing properly it needs urgent attention otherwise you risk burning it out.

Just in case you don't know,  shimmed valves are the opposite of old fashioned tappets; the more they wear, the smaller the gap gets (the valve recedes into the head) whereas in the old days with tappets the gap got bigger, so if they're quiet, that's not a good sign.

[jamman]

Some popping on decel is normal.  The backfiring obviously isn't.  You don't say how many miles the bike's done or how long you've had it, but I'd take a look at the valve clearances first.  If you have an inlet valve not closing properly it needs urgent attention otherwise you risk burning it out.

Just in case you don't know,  shimmed valves are the opposite of old fashioned tappets; the more they wear, the smaller the gap gets (the valve recedes into the head) whereas in the old days with tappets the gap got bigger, so if they're quiet, that's not a good sign.

32K on it ... not sure of service history

[Bixxer Bob]

The clearances should be ok at those miles unless it's been thrashed. 

You could also be looking for a faulty plug, faulty wiring to the coil stick, an air leak.  It's hard to know where to start.  Do you have any way of reading the ECU to see if there are any fault codes?  We generally use free software called TuneECU but any OBD fault code reader will do.  It might help show where to look.

[jamman]

The clearances should be ok at those miles unless it's been thrashed. 

You could also be looking for a faulty plug, faulty wiring to the coil stick, an air leak.  It's hard to know where to start.  Do you have any way of reading the ECU to see if there are any fault codes?  We generally use free software called TuneECU but any OBD fault code reader will do.  It might help show where to look.

Just changed the plugs and air filter is good ... will check for air leaks and get a code reader or cable and install Tune ECU and go from there ..

Will post back with results

Thanks much !!

[Bixxer Bob]

Once you have TuneECU up and running, look at the dwell tiime for the coils, they should all be roughly the same.  If one is lagging behind the others you could be looking at a coil stick issue.

[JayDub]

Referring to your tune ECU thread. Did it miss and pop on deceleration BEFORE you  drilled holes in the cans?

[jamman]

From what I remember it did do that some ... seems more after the baffle holes were added .. 

[jamman]

What is bothersome is the random sputter issue or misfire ... happens randomly at idle and when at a stoplight she will occasionally die but it will starts right up ... kinda embarassing ...

It's is very loud wish I could post the sound .. almost like a steam engine or when you plug in an air tool to a compressor hose

[JayDub]

I think the popping is due to the extra holes you drilled, but the spitting does sound more like valve gear or coil stick(s) like Bixxer said.

[jamman]

Once you have TuneECU up and running, look at the dwell tiime for the coils, they should all be roughly the same.  If one is lagging behind the others you could be looking at a coil stick issue.

Here is a snapshot when running .. anything stand out ?

[jamman]

I cleared the fuel pump codes as I removed the tank etc when changing the plugs

[Bixxer Bob]

Dwell time for the middle coil is a bit behind the other two, and it's always the middle one that goes first.  And they are now down to £45 each as opposed to over £100.

But before you do that, use TuneECU to cycle the IACV and make sure it's working properly (it will cycle through the full range of movement a couple of times) and check the corrugated tubes for leaks.  These are common faults and easy to check and fix.

Also, you might find that simply reloading your map sorts it.  The reload resets the trims, which can have wandered off if the battery voltage has been low for any reason.  If you have an O2 sensor in the exhaust down pipe, ride it after the reload and it'll trim itself after 20-30miles.  No O2 sensor, do the 12 minute tune.

[jamman]

Thanks so much for the valuable input !!

Any place to get them at that price in the US ?

Thanks

[jamman]

Found a set on ebay from a very low mileage bike (7K) and grabbed them ...