Why is injector balance not as important

moonhead911

moonhead911

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Why is injector balance not as important as TBB? Should injectors be removed cleaned and tested for flow rate?

Also, how easy would it be to replace them with injectors that delivered a few percent more fuel? Can they be bought in matched pairs?
 
Injector balance is at least equally important to TB balance. Each contribute equally to the cylinder AFR (air fuel ratio). For injectors: volume, voltage sensitivity, turn on time, turn off time and spray pattern can all affect AFR.

When AFR is unequal you can get rough running, vibration and surging. A good injector cleaning lab will measure, before and after, volume and spray pattern and send you a report. On an older twin, with one O2 sensor, it's a worthwhile maintenance procedure.

The issue is important enough to good running in a twin that BMW installed an O2 sensor per side so that the bmsk ECU could, through mixture adaptation, balance out injector problems. Too bad we don't have dual O2s on our 1150s.
 
The second question was about replacing injectors with matched, higher flow rate injectors. Precisely matched injectors would be good but in bikes with working stock O2 sensors, increasing injector flow rate makes no difference because closed loop mixture adaptation corrects the addition flow by reducing the Long Term Trim correction factors.

On the other hand if you shift the lambda value of your O2 sensor, there is a minor benefit to higher fuel pressure or higher flow injectors: shorter time to build long term trims.
 
Roger 04 RT said:
The second question was about replacing injectors with matched, higher flow rate injectors. Precisely matched injectors would be good but in bikes with working stock O2 sensors, increasing injector flow rate makes no difference because closed loop mixture adaptation corrects the addition flow by reducing the Long Term Trim correction factors.

On the other hand if you shift the lambda value of your O2 sensor, there is a minor benefit to higher fuel pressure or higher flow injectors: shorter time to build long term trims.
Click to expand...

Fair comment, but if the flow rate is increased, then max power (when it's open loop) can possibly be increased, assuming there is an initial deficiency. Increased fuel pressure is a good way of improving the spray pattern on these injectors in any case.
 
Roger 04 RT said:
Injector balance is at least equally important to TB balance. Each contribute equally to the cylinder AFR (air fuel ratio). For injectors: volume, voltage sensitivity, turn on time, turn off time and spray pattern can all affect AFR.

When AFR is unequal you can get rough running, vibration and surging. A good injector cleaning lab will measure, before and after, volume and spray pattern and send you a report. On an older twin, with one O2 sensor, it's a worthwhile maintenance procedure.

The issue is important enough to good running in a twin that BMW installed an O2 sensor per side so that the bmsk ECU could, through mixture adaptation, balance out injector problems. Too bad we don't have dual O2s on our 1150s.
Click to expand...

thats the problem i have vibration like a bitch even after full service can any one recommend a company to clean my injectors
 
uncle dick said:
Fair comment, but if the flow rate is increased, then max power (when it's open loop) can possibly be increased, assuming there is an initial deficiency. Increased fuel pressure is a good way of improving the spray pattern on these injectors in any case.
Click to expand...

Yes, you may improve spray pattern and will increase total fuel flow by increasing pressure. I ran mine at about 52 psi for a couple years with an add-on regulator in the fuel return line.

What you can't do is get more power by putting in bigger injectors OR increasing fuel pressure, even at wide throttle angles in the Open Loop area of the fuel map. I have extensively measured AFRs at higher and lower fuel pressure (and with and without a BoosterPlug). The reason that you get no benefit in a bike with a connected, stock O2 sensor is that the Motronic (and also the BMSK on the R1200) calculates Long Term Fuel Trims which it applies to the entire fuel map, including the Open Loop area.

These long term trims were thought not to exist on the Motronic or BMSK but I've measured their effect on both the Motronic and BMSK and confirmed them. Just recently Hexcode has updated the GS-911 software for the BMSK and it now reports the BMSK's long term trims, which are quite extensive. As an example, if the long term time was 1.00 at full throttle and you changed out the fuel injectors for units that delivered 10% more fuel, the long term trims would settle out at about 0.90 after several tanks of fuel. That lower long term trim would negate the effect of the larger injector.
 
Fitting a K1200 fuel pressure regulator will give you more fuel per bang.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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