Question about a Miss, OR A missing Question?

[JoeGuzzi]

My 2004 Ballabio will miss every once in a while. This happens at most all engine speeds, while moving down the road or sitting at idle. This usually happens at light throttle positions. I have never noticed this under accelleration just at steady engine speeds. At idle it will miss just a beat and will usually not die but pick right back up to a smooth idle. Sometimes it will miss just as you come to a stop and the engine will die. When this happens it will start right back up and idle fine.

I'm not sure why this happens, the idle speed is correct 1100 to 1300 rpm's. Valves set correctly and using premium fuel. Could this be due to the ethenol content in the fuel, plugs, plug wires, bad karma, position of the moon, bad dreams the night before, etc,etc,etc.

Any suggestions would be welcomed. I have never set the TPS and not really sure if that would be the problem because it happens at many throttle settings. It's just one miss fire then runs normal again. Not really a show stopper but I would like to figure it out.

Thanks in Advance

 

Joe in Atlanta

1972 Eldorado

2004 Ballabio

2003 Buell Blast hers

[Guest ratchethack]

Joe, I was semi-irritated by this one for years. As you noted, when the engine is under load or accelerating, the intermittent "miss" never occurs. It's only when the engine is at idle or not under load that it shows up, and it appears to miss completely erratically.

 

We had some threads on timing chain tensioners about a year back where we got into the idea of the ridiculously weak stock spring on the tensioner allowing "chain whip" at idle and "off load". On the V11, the timing sensor picks up it's signal from the phase sensor wheel next to the camshaft sprocket, which is separated from the drive sprocket on the crank by 5 links of chain. It was my theory that the stock tensioner allows enough chain whip to throw an "out of phase" advanced signal due to the 5 links of chain between the crank sprocket and cam sprocket erratically bunching up to varying degrees when off-throttle engine pulses overcome that wimpy little tensioner spring, and the ECU "throws out" the resulting signal anomaly when it's far enough out of phase like it didn't exist, and you get a dead miss.

 

I figured that if I upgraded to a Valtek type tensioner (which I did) that the signal scatter that I measured with a timing light with the stock tensioner (up to 6-7 mm variance on the flywheel -- in the direction of an advanced signal only, not in both directions) from a fixed point -- exactly where you'd expect to see it under this theory -- would all but disappear if the chain tensioner worked properly. Keep in mind that the number of degrees "out" of full tension measured on the cam sprocket gets translated back to a read on the flywheel by a 2:1 multiplier. This fits both my theory and the signal scatter I observed.

 

Haven't actually got around to measuring the signal scatter again with the Valtek type tensioner in place, but since I haven't experienced any of the former symptoms (exactly wot you describe) ever since I installed it, I haven't been much interested. Will have to get a Round Tuit some time soon!

 

Valtek tensioner installed. . . . . Stock tensioner installed