well, i was messing around last night and zero'd all my ignition curves on my programmable dis2. i drove around like this and noticed something interesting. I have a built engine, eagle rods, je 8.8 pistons, rc 440 injectors, SFMU, SAFC, msd programmable dis2, hrc stage 2, blah blah blah.
well, I have the smallest disk in the sfmu that came with the kit, i think it is a 2.5~2.6 rise rate, idle FP at 25, static at around 28~30, i am boosting ~14 psi and my AFC is set all in the mid -30's to a -38 max at 3000 rpm.
The funny thing is with these settings and no ignition retard i get detonation at -.5 to +.5 psi boost, then no detonation and then more detonation at 7~8, and then again at 11~12 psi boost. all this appears to happen around the 3000 rpm range. one peculiar thing is that at 3000 rpm and -38 on the afc i get approximately -24~-25 LTFT. everywhere else i get about -20 LTFT when the AFC is at -35. so for some reason 3000 rpm seems to run really rich and only 3000 rpm. well, i reprogrammed the dis2 to pull out timing, a total of about 9 degrees at high rpm and full boost and the detonation goes away. do you think i am safe to assume that the detonation is occurring due to timing advance rather than a lean mixture since the theoretical fuel supply values exceed that which is required?
thanks
James

Rest In Peace Heidi Doggy

Well I'm still new to the timing and detnation game... But from what info I have gatherd I would agree with you. Did you notice what your timing was at these detination points? That would be my first suspect because by altering the map sensor voltage with the Safc it also alters your timing. Anybody else want to weigh in on this?

I edited to the wiki!

I'm really curious to see what your timing was during detonation. I'd bet it was close to almost 30 degrees advance under light boost. If i remember, DaveFL posted his datalog sheet from after he melted his pistons, and saw that he was getting mad timing advance at around 3000 rpms...Its the SAFC man... I would try lowering your fuel presure under all conditions, and richening out the SAFC so it doesnt have to lean the fuel mixture so much. With using less of the SAFC to lean the injectors, the lower fuel pressure should do a bit, and at the same time, it should give you less timing advance, cause its not playing around with the Map voltage so much. Dont let that detonation continue dude.. I would also run the next largest disk in the SFMU. With your static pressures where they are, it should be relitivly close to the proper fuel flow, WITHOUT using the SAFC. Since you have it leaned out quite a bit, you are getting too much timing advance at low vac, low boost, and its running too lean.

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
fuel injection)
My webpage: http://eclipsed4evr.home.comcast.net
-1998 Mitsubishi Eclipse RS-T- "Toy"
-1992 Plymouth Laser Turbo AWD(SOLD)
-2000 Honda CR-V(daily)

i cannot get my fuel pressure any lower than it already is. i tried, but it won't go. i think i am going to increase the diameter of my fuel return line to -6AN from -4 AN and see if i can get a lower FP.
I have been getting timing in the 30's at mid boost. but i have retarded it about 9-10 degrees with the Programmable dis2. i have no audible detonation now. the only thing is that the datalogger only shows what the ecu is advancing and i have to factor in the MSD's retard. that is a little tricky. Oh one thing, if i go to a larger fmu disk then the car will become more rich, causing me to have to lean out the afc more! i think you have it backward. I do have the 1.5~2.1 disk and adapter so i may put those in and see what happens. i just hope that disk gives enough fuel at 15 psi.
anyone know what the fuel requirement at 15 psi is for our engines in cc/min
thanks
james

Rest In Peace Heidi Doggy

>i cannot get my fuel pressure any lower than it already is.
>i tried, but it won't go. i think i am going to increase the
>diameter of my fuel return line to -6AN from -4 AN and see
>if i can get a lower FP.
>I have been getting timing in the 30's at mid boost. but i
>have retarded it about 9-10 degrees with the Programmable
>dis2. i have no audible detonation now. the only thing is
>that the datalogger only shows what the ecu is advancing and
>i have to factor in the MSD's retard. that is a little
>tricky. Oh one thing, if i go to a larger fmu disk then the
>car will become more rich, causing me to have to lean out
>the afc more! i think you have it backward. I do have the
>1.5~2.1 disk and adapter so i may put those in and see what
>happens. i just hope that disk gives enough fuel at 15 psi.
>anyone know what the fuel requirement at 15 psi is for our
>engines in cc/min
>

What spring you got inside the SFMU? I believe if you have the long, silver spring, that it will let you drop the fuel pressure a bit. I suggested to use a richer disk because you will be running lower fuel pressures, and less SAFC,if you do indeed drop the fuel pressure. IMO, you can run the 440's without a SAFC, just by running much lower fuel pressures. I believe Armond has said that Murix was running 550's with no SAfC and about 10 psi of idle fuel pressure. How the motor actually runs with only that fuel pressure, i dont know. If you want to play around with it, totaly take out the SAFC, and try and lower your idle fuel pressure to around 16-19 psi. Data log it. See what your STFT is, and LTFT. If you can lower the fuel pressure engough to get your trims at -10% or lower, closer to 0, then that would be awsome. Hell, if i can get stock like fuel trims using only the 315's and SFMU, i would think you can do the same with the 440's. I idle at 25 psi now, and get anywhere from 0 to -10% fuel trims. I may try this in the upcomming months after the rebuid, but if you feel adventerous, try it out..You never know, it just may work The reason you were getting 30 degrees of advance under light boost is because the SAFC is leaning the fuel out too much. So lower the SAFC settings, and run lower fuel pressure to account for the extra fuel. I havent had my SFMU adjusted any lower than about 20 psi, so i'm just not sure how low it can actually go. Upping the size of the fuel line is a damn good idea also. With my 25 psi idle, i thought i had much more room for adjustment to lower the pressure even more. I use the 2.72" disk, and dark, short spring. I believe the longer, silver spring will let you run less fuel pressure at idle, as I know for a fact that using the short, dark spring lets you run higher fuel pressure at idle.

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
fuel injection)
My webpage: http://eclipsed4evr.home.comcast.net
-1998 Mitsubishi Eclipse RS-T- "Toy"
-1992 Plymouth Laser Turbo AWD(SOLD)
-2000 Honda CR-V(daily)

Are you using the dark spring in the SFMU? I can get my idle pressure to 0psi w/ that one.

How do you know you are detonating?

Dave
05 Ford F150 SuperCrew FX4