XFI tune issue..Inj. dc spike in first gear...tune and log file enclosed
- Thread starter STP
- Start date
turbobitt
Well-Known Member
- Joined
- Feb 14, 2002
I'm not that surprised. Look at this link and see what you think. Says 60# injectors are good for 450 HP @ .65 BSFC and 80% DC.
http://injector.com/injector_selection_guide.php
Allan G.
Wow, that's scary...nice link. I'm curious about the 80% dc limit they suggest though. Does an injector start to go crazy over 80% duty cycle? Personally, I've never ran over 80% dc, but have been around cars through the years that ran well over 80% dc and performed ok. Every car is different, I guess.
Meaning, I've never ran over 80% dc on my personal cars and other cars I've tuned on over the years. This is the first car in recent memory that I have tuned that has shown inj dc's that high. So, I really don't know what to expect...Hence, my question concerning how the inj acts over 80% dc. I wouldn't expect a set of injectors at 80% dc to be done. But maybe I'm wrong.
OK, Iv;e had some bad experiences with that particular 60l injector on a FAST 2.0 and classic fast, we took them out and put in low impedance injectors, and never had any issues with lean spots. No matter what we did it would go lean, those injectors can run up to 87 PSI, so I would raise the base fuel pressure to 60 psi and put in 72 lb injector size into the fast, and see where that takes you. This should get your DC down where it will be more stable.
Never thought of that, what pump is he running?
What exact model of aeromotive pump? if it the intank 340 here is the chart.
Looks like the injectors at 60 psi static will out flow that pump @13.5 volts at 100% DC
61lb inj@60 psi static= 72 psi flow rating x 6 =432 lbs/hr
1 gal weighs 6.152 lb@60F
432lbs/6.152=70.22/ gal/hr
1 us Gal= 3.7854 L
70.22 x 3.7854=265.81 l/hr@ 60 psi is required
Remember injectors only flow based on the differential psi, so if you add 20 psi boost the pump still has to support 265l/lb at 80 psi, but the injector is actually not flowing any more into the motor than before.
Note: the injector pintel opens way faster than the regulator can might cause your lean spike as the demands are too high for for s few ms.
61lb inj@60 psi static= 72 psi flow rating x 6 =432 lbs/hr
1 gal weighs 6.152 lb@60F
432lbs/6.152=70.22/ gal/hr
1 us Gal= 3.7854 L
70.22 x 3.7854=265.81 l/hr@ 60 psi is required
Remember injectors only flow based on the differential psi, so if you add 20 psi boost the pump still has to support 265l/lb at 80 psi, but the injector is actually not flowing any more into the motor than before.
Note: the injector pintel opens way faster than the regulator can might cause your lean spike as the demands are too high for for s few ms.
turbobitt
Well-Known Member
- Joined
- Feb 14, 2002
It looks to me that even with a base pressure of 45+20 psi boost the pump is near its limit.
Looks like it's upgrade time....
Allan G.
Wow, alot of info here. I figured once leaned on the car will run out of pump and injector pretty quickly. Tonight, I put a set of 83's in it. Did a quick tune on the VE and made a couple pulls with the XFI boost controller on14-15lbs. Noticed the same spike in inj dc and 5* of knock again. So, back to the shop for some more head scratching. Went back to the datalogs over the past few days. Decided that we needed a rock solid boost setting to get a better idea of what the car was doing/needing. Took the Ingersoll Rand boost control solenoid out of the loop along with XFI PA boost table. Installed a manual boost control valve and made a couple pulls...Well guess what???? No boost spike whatsoever at the hit and inj dc looked normal with it slowing rising throughout the pull. So, I think I have narrowed the issue down to boost control. The Ingersoll Rand solenoid isn't able to act fast enough to control the boost accurately, hence the spike in boost of 2-3lbs and correllating spike in injector duty cycle....Now what?????
turbobitt
Well-Known Member
- Joined
- Feb 14, 2002
I think what you did is masking the problem. I think the spike is a combination of AE fuel(Map and TPS) + demand in the transition cells really pushing the limits of the current system. The pump and injectors should be able to keep up with that spike. The boost spike is only 2.5 psi. Based on what Norbs has posted on the pump, I would look into that. It is not impossible that it could maintain pressure but not enough volume although with the 83's I would think a fuel supply problem at 100% DC should be easier to detect.
It would be interesting to see a pressure trace using a transducer during the spike. A FP gage may be unreliable and is probalby dampened making pressure fluctuations imposible to see.
Allan G.
The fast boost control is not the best design, not sure what they were thinking, but in closed loop control it keeps the boost DC to "near" 100% and ramps down, even with PID settings maxed to the moon, good chance you will get a psi spike. I have been pushing to get this changed so that the max boost duty cycle can be set by the user during closed loop, but no changes yet.
Allan all my calcs were based on 100% Duty cycle so if its lower it may be able to support more than what we are calculating. You may want to dual feed the rails this cuts the fuel velocity in 1/2 and the reg would probably respond better. What type of regulator are you using? gn stlye rail mount?
Allan all my calcs were based on 100% Duty cycle so if its lower it may be able to support more than what we are calculating. You may want to dual feed the rails this cuts the fuel velocity in 1/2 and the reg would probably respond better. What type of regulator are you using? gn stlye rail mount?
- Joined
- May 28, 2001
Am I reading the AE/MAP rate of change screen wrong?? I reviewed other FI tunes I have, and none come close to the huge jump you have programed in. [2.7ms to 7ms in the next step up.]
Yes it does seem really excessive...
- Joined
- May 28, 2001
From 13 cts/50ms to 18cts/50ms, the inj pulse is being increased 259%...Big jump.
