Slim Shady
DEATH BEFORE DISHONOR
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I won't get into the optic bump fray, but I have been running a bump for quite some time. I like it, now that being said I have been tutored by the BEST (GMCTD) regarding the optic bump, he does not recommend it and I don't either.
As Buddy said it you are fooling the computer, the long and the short of it is that you are adding fuel the computer does not see, hence the rough idle if you go to far and the touchy accel pedal, both indicative of the optic bump.
A smooth idle on a ds4 pump is controlled by the pump/PCM controlling the amount of fuel *injection time* of each injector at idle as it relates to crankshaft rotation speed per cylinder pulse. The pcm monitors crank speed from the crank shaft positioning sensor and uses that to monitor cylinder pulse speed.Time between each pulse or tooth on the sensor. (hope that makes sense)
If you use a scanner (the only way) to set your optic bump you can achieve a smooth idle and a relatively livable accel pedal feel. You will get a trailer hitch effect when running cruise control going down an incline, it is inherent, That being said Kojo's tune did minimize that as well because we had discussed my truck before he made my chip.
The bump also adds some inherent wear to the pump because of the added pressure on the rollers, That is all I am going to say about that.
If you would like to experiment, you can do this set your pump to your desired TDC offset and then do a timing relearn, now that everything is ok. Manually move your IP to different positions. See what happens as you do. This will change your Timing and fuel events without changing anything the pcm sees. (note this will not last past 50 key cycles on the OBD1, I am not sure on the OBD 2 how long this will last. It is a fun experience. The GM manual will tell you that this will not effect timing (it does) after all we are mechanically moving the pump which changes injection timing as a mechanical event.
As Buddy said it you are fooling the computer, the long and the short of it is that you are adding fuel the computer does not see, hence the rough idle if you go to far and the touchy accel pedal, both indicative of the optic bump.
A smooth idle on a ds4 pump is controlled by the pump/PCM controlling the amount of fuel *injection time* of each injector at idle as it relates to crankshaft rotation speed per cylinder pulse. The pcm monitors crank speed from the crank shaft positioning sensor and uses that to monitor cylinder pulse speed.Time between each pulse or tooth on the sensor. (hope that makes sense)
If you use a scanner (the only way) to set your optic bump you can achieve a smooth idle and a relatively livable accel pedal feel. You will get a trailer hitch effect when running cruise control going down an incline, it is inherent, That being said Kojo's tune did minimize that as well because we had discussed my truck before he made my chip.
The bump also adds some inherent wear to the pump because of the added pressure on the rollers, That is all I am going to say about that.
If you would like to experiment, you can do this set your pump to your desired TDC offset and then do a timing relearn, now that everything is ok. Manually move your IP to different positions. See what happens as you do. This will change your Timing and fuel events without changing anything the pcm sees. (note this will not last past 50 key cycles on the OBD1, I am not sure on the OBD 2 how long this will last. It is a fun experience. The GM manual will tell you that this will not effect timing (it does) after all we are mechanically moving the pump which changes injection timing as a mechanical event.
