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Originally Posted by XfireZ51
Paul,
Injector Bias is part of the overall Pulse Width. Its there so you can fine tune the actual amount of time the injector is open. Sort of like Spark Advance. The larger the Injector Bias the more advance time allowed for injector to open. In the case of TBI, the fact that there were onyl 2 injectors made it critical to get every bit of effciency from the injectors.
Increasing the Injector Bias gave you more "effective" pulse width because less of the overall pulse width was devoted to opening the injector. PW is measured in msec in the LT5 also, just like TBI.
Regarding the bad O2 sensor scenario, I'm not sure that if the O2 is dead whether that bank would be running open loop, in which case the INT would be at 128. If the O2 is reading 0, that would indicate a dead lean condition requiring gobs of fuel. BLM should be high and INT dropping like a rock.
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Me bein' edumuhkated in E-lectronix enjuneerin, I totally understand bias and the reduction of hysteresis biasing affords; makes perfect sense to bias the injectors (biased voltage selected at a point just below cutoff, i.e. class "C"). However, biasing raises a question: It may be splitting hairs, but
I wonder if the cutoff for the various injectors is a standard value, or should a different bias be applied according to injector type? (I'm guessing the ECM can accomodate various injector characterisitcs, provided they are "in the window". But, it could make another case for not mixing primary and secondary injector types, huh?)
Well, (the AutoXray 1000) scanner s/w for the LT1 did divulge the injector pulsewidth, and I gather from what you said, there is pulse width data available (no big surprise) for the LT5....Dayahm! I really wish the "upgrade" I downloaded to my scanner would have included pulse width!!
Maybe someday I'll make the plunge and get into the ECM code - just "for fun". In the mean time, I'll have to muddle through by using indirect (BLM and INT) to evaluate sensor or other possible issues, when/if they arrise.
Check me out:
- If an O2 shows lean, and the fuel delivery indicates lean, that would cast a shadow on the ECM, methinks. Swapping the location of the O2s to see if the problem follows might be worth doing, and if the O2/delivery does not change sides, the O2 proves OK, and there and the focus would be on the ECM, no?
- If an O2 shows lean and the fuel delivery indicates rich, then the O2 itself is in my crosshairs first, especially if the instant fuel mileage is dips into the mid teens and the exhaust smells bad (assuming cats are installed). However, it could be a fuel pressure issue, and even tho it isn't likely to affect just one side of the engine, it is a lot easier to check and eliminate pressure issues as a possible cause than it is to jack the car and swap those pesky O2s!
Well, I'm rambling. Can you tell I'm intrigued? Apparently I have a hunger to get into the meat of these LT5s, and am feeling frustrated by the limits (pointed out by you) of my current scanner.. I want more!
Thanks for the response. I'm enjoying the journey upt the LT5's learning curve. It is a sweet piece of engineering, to be sure, and the expertise present on this board is top drawer, "fer sher"!!
P.