PROM calculations
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PROM calculations
Hi everyone,
I've been searching around but can't seem to find a reliable answer to some questions.
1) How do the TBI ecm's calculate injector pulse width (the 8063 specifically ...but I assume they're all the same)?
2) What's the minimum PW that the GM injectors can tolerate. I know they can go down to ~0.8 ms before they enter asynch mode.
3) How does the injector bias factor into the pulse width calculation? Is it added afterwards and so isn't actually considered in the pulse width calculations?
If I'm right about question 3, then question 2 takes care of itself as I'm assuming the injector bias is there to take care of the opening and closing times of the injectors.
One more question, not really related to the above ...how much timing is typically added when going from swirl port heads to non-swirls? I've seen some info on 6 cylinder motors but not for the 8s.
Any help anyone can give me will really be appreciated.
I've been searching around but can't seem to find a reliable answer to some questions.
1) How do the TBI ecm's calculate injector pulse width (the 8063 specifically ...but I assume they're all the same)?
2) What's the minimum PW that the GM injectors can tolerate. I know they can go down to ~0.8 ms before they enter asynch mode.
3) How does the injector bias factor into the pulse width calculation? Is it added afterwards and so isn't actually considered in the pulse width calculations?
If I'm right about question 3, then question 2 takes care of itself as I'm assuming the injector bias is there to take care of the opening and closing times of the injectors.
One more question, not really related to the above ...how much timing is typically added when going from swirl port heads to non-swirls? I've seen some info on 6 cylinder motors but not for the 8s.
Any help anyone can give me will really be appreciated.
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From: Moorestown, NJ
Car: 88 Camaro SC
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I put out a complete, or nearly so, hack for the 8063 a year or two ago. There are a few things like the transient throttle and startup SA that arnt commented, but IIRC the fueling is all commented. Its available as '$4D.ZIP' on www.moates.net on the file section. It lives in the source code and hacks section of the file server. Theres tons of info on how everything works. That may answer alot of your questions, and any you didnt know you had.
Im a bit foggy on how the bias was factored in but teh min Pw is something like 1.2 ms and the pulsewidth is based on the fueling needs of one cylinder. The ecm estimates the mass of air by using the VE, MAP, inj. volume, air temp, etc. and then factors in the flowrate of one injector to arrive at a time based calc. Its a bit convoluted as its not a true speed density system but basically the ideal gas law is what its based off of.
Im a bit foggy on how the bias was factored in but teh min Pw is something like 1.2 ms and the pulsewidth is based on the fueling needs of one cylinder. The ecm estimates the mass of air by using the VE, MAP, inj. volume, air temp, etc. and then factors in the flowrate of one injector to arrive at a time based calc. Its a bit convoluted as its not a true speed density system but basically the ideal gas law is what its based off of.
Last edited by dimented24x7; Jun 13, 2005 at 12:38 PM.
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From: Marietta, GA
Car: '91 Firebird Convertible
Engine: 305 TBI (LO3)
Transmission: 700r4, Vette Servo
Axle/Gears: 3.27 9 Bolt, PBR disks
Originally posted by Casey_Butt
Oh my ***, I've hit the jackpot! Thanks a million
Oh my ***, I've hit the jackpot! Thanks a million
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Hey Adam, I owe you deeply for that hack. I'm relatively new to assembly code but have some background in programming. I'm trying to make sense of the BPW equation but I've run into a few stumbling blocks.
The equation is:
BPW = BPWC x AFR x VE x MAP x Cool corr. x BLM corr. x DFCO x decel. x FPV corr. +/- INT prop. term
What I don't get is the AFR is higher for leaner conditions, but that would make the BPW in the above equation greater (richer). So shouldn't the inverse of the AFR be used? Also, I assume the inj. bias is added in afterwards ...is the BPW converted to msecs and then added to the bias (in msecs) or is the bias converted to something and then added to the calculated BPW?
Sorry if the answers are in the hack ...I can't print it at at the moment and it seems pretty hidden reading as an assembly virgin
The equation is:
BPW = BPWC x AFR x VE x MAP x Cool corr. x BLM corr. x DFCO x decel. x FPV corr. +/- INT prop. term
What I don't get is the AFR is higher for leaner conditions, but that would make the BPW in the above equation greater (richer). So shouldn't the inverse of the AFR be used? Also, I assume the inj. bias is added in afterwards ...is the BPW converted to msecs and then added to the bias (in msecs) or is the bias converted to something and then added to the calculated BPW?
Sorry if the answers are in the hack ...I can't print it at at the moment and it seems pretty hidden reading as an assembly virgin
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