5 Liter Eater

Well, Thursday I installed my VAFC without any issues. I was able to get some noticable butt dyno gains by lowering the VTEC to 4000 with a +5% mismatch correction. It's also nice to find out that my tach is off pretty bad.

I ran like this for a day just to verify the install of the VAFC. Since all went well I went ahead and put in the DSM 450's and 10 Ohm resistors, took out the Cartech, moved the MAP to the other side of the supercharger and plugged up the old orifice. Then I leaned out the VAFC by 40% across the board. Everything seemed to work well; the car started right up, no CEL's, idled fine. When I took it out off boost driving was snappy without any holes like when I had the RC 310's in. Boost transition was seemless, it was really hard to tell when the change was made from vac to boost. My Autometer boost gauge is more off than my tach is. It shows just over 11 PSI and peak hold on the VAFC shows 67 Kg/CM2 which converts to 9.6 PSI which makes me feel better. Overall I am pretty happy to have done away with the 100+ PSI fuel pressures and the latency inherent in building all that pressure. But here are the couple issues I have:

1. I seem to be pretty rich in open loop. I have 4-5 greens on the A/F pretty much throughout the powerband. Right now my pressures are 42/52 vac/static. What pressures do you other VAFC hackers run? I am thinking of lowering to ~35/45 and see where that gets me. I could try going to -45% or even -50% but then I'd have no room for adjustment and I'd like to be running good at -40% so I'm right about in the middle of the adjustment range.

2. In closed loop, there is a weird feeling when I let off the gas, like the brakes are on. When cruising it feels like the A/C compressor is turning off and on. If I put it in neutral and rev to 3k it will stay there for like 2-3 seconds and then dip down to 2500 for like 2-3 seconds and then go back rythmically. The A/F goes way lean when at 2500 and pretty rich at 3000. It's almost like the changes in pulsewidth the ECU is making to maintain stoich are too great for the 450's. Like I said, it idles fine but this 500 RPM up and down thing goes on anywhere from 2000 on up. Does the ECU just need to do some learning? I have done several ECU resets.

I'd really like to keep this setup but I need to get these two things sorted out. Any help is greatly appreciated!


[Modified by 5 Liter Eater, 11:14 AM 4/8/2002]

chri5

I was running it at 32/42 and had -40%going up to i think it was -30% at redline. Its been awhile so i dont really remember.

5 Liter Eater

Thanks, I couldn't remember if running stock pressure was the way to go or to lower it. It's been so long since I was stock I can't even remember what stock pressure is! That should help with running rich and maybe even help with the revving up and down 500 RPMs.

Anyone else expreienced the RPM fluctuation? Rio, Liam, DBMAN?

5 Liter Eater

TTT

dbman96

I noticed that when I was right on the edge of "off-throttle" and "light throttle" cruising, it ran kinda rough - I attribute it to switching in and out of fuel cutoff when you're coasting (engine shuts off injector completely when your foot is completely off the gas, but if you're just TOUCHING the throttle it delivers the shortest pulse it can, which is a LOT more fuel than it would get with stock injectors, so it runs kinda rough under those circumstances). You get used to it and your driving style kinda "adapts" around it after a couple weeks. It is a bit bothersome though.

5 Liter Eater

Doh!

That's the whole reason I went this route, so I didn't have to adapt my driving style. With 310's I had to adapt to keeping it out of that "just before boost" range to avoid flat spots. Still, there are no flat spots now, transition into boost is totally seemless and for the majority of the time, off boost driving is very snappy, just like stock injectors. Like you said, the transition from 0 throttle to very little throttle has a bit of a buck to it.

So far I'm really happy with how it's going, I just have to tinker with it some more and get it on a dyno to get the fuel curve perfect. It will be nice to be able to go to the dyno and tune the entire curve. I'm pretty rich now and have less power than w/ stock injectors and Cartech. I got my *** handed to me by a modded 4.6 Mustang while in this overly rich untuned state.

rioninja

mine has been running great, but the same jerky problem you've been having is there on mine as well. I figured what dbman said, that it had something to do with the fuel cutoff.

dbman96

If you know you're running rich, dropping your idle fuel pressure should significantly help the "bucking" problem. Did somebody say "TOO Relief hole?"

I've not tried doing this yet as I reverted to naturally aspirated when the smog gods frowned upon me and I'm waiting for my new groupbuy turbo before I reassemble.

5 Liter Eater

Well, I'm halfway there then. I have already done the TOO FPR drilling and have a clamp on to the stock FPR. I'll let you guys know how much it helps the no/little throttle issues.

chri5

Cool. All it takes is a little playing around

rioninja

Using the sensor check feature on the vafc, i adjusted the throttle position sensor from .45v up to .50v. It actually removed about half of the jerkyness, and makes it a lot easier to drive. It only jerks when the computer knows the throttle is just about to close, so i think if i ajust it up a couple more .volts, i should be able to remove the jerkyness all together. This shouldnt affect the a/f ratio at all since the computer makes fuel adjustments almost entirely by map signal. I imagine it would make the switch from closed/open loop sooner because the computer would think the throttle is farther open than it really is. The only drawback i see is idle problems. I'm worried that idle quality will suffer since it will think the throttle has not yet closed. So far moving from .45v to .50v has not affected the idle and reduced the 'jerk', so i'm gonna try going up another .05v to see what it does.

Its late, so anyone have anything to add to this? Anything i'm missing?

5 Liter Eater

Hmmm... I was thinking about doing something similar only I didn't think it would be this easy. What does the sensor check say the TPS voltage is at 0% throttle? It makes sense that this would eliminate a lot of the jerkyness if the injectors never stopped firing since it seems to be the transition from no fuel to very little fuel that makes the jerk. I would also be interested to see what effect this has on idle but I would think you could just take more fuel out at 1000 RPM to compensate for any raised idle. Keep us posted. If you still like it in a week I'll change mine.

PS: Did you do an ECU reset afterwards? I'm wondering if the ECU will re-learn the throttle zero point to be 0.5 volts and would just start cutting out the injectors at that voltage rather than 0V.


[Modified by 5 Liter Eater, 8:14 AM 4/12/2002]

rioninja

I havnt checked a helms, but most people have said that the closed voltage should be .45v, while other said that it should be .50v. If someone has a manual handy and could make sure of the correct voltage while closed, i'd appreciate it.

Tonight after i change my oil i'm gonna try to set the tps at either .55v or even .60v and see what happens. I'll keep everyone posted.

-Ben

rioninja

And no, i didnt reset the ecu for the exact reason you said. I'll keep everyone posted.

deacs

did u ever try the tps at .55 or.6?? I would be interested to know if this got rid of the jerkiness and /or if it caused any other issues?

thanks

deacs

so what kinda reading are u getting for 02 sensor voltage at WOT and part throttle cruising etc?

Deacs

deacs

anyone used this TPS adjutment to good success