Hey all,
i got a peculiar situation, I have an HRC kit with fmic 8.8:1 je pistons, eagle rods, RC 440 injectors, SFMU with static set at 36 psi, SAFC with settings all around -40. Boost mod for the AFC, CM stage 4, ported gasket matched and polished manifold and head. standard size SS swirl polished valves, CAI, all -6 AN steel braided fuel lines, walbro intank and HRC inline pumps, Programmable DIS-2, 91 octane gas poop.
my situation is this.
When i drive around I do not get any detonation except at or around 0 boost. it starts a little under 0 and keeps going to a little over 0. it is a very short little stint of it, but it bugs the heck outta me. I got rid of it by retarding the ignition at 0 boost like almost 10 degrees, but i don't think this is the real cause. My hypothesis is that i am not getting enough fuel at that point. because in vacuum i actually add PSI to the pressure on my fuel pressure gauge. the engine at that point is sucking gas in through the injectors. so say at -7 psi vacuum at a fuel pressure of 30 psi, i am actually getting 37 psi of fuel pressure. then at static where i have 36 psi of FP and 0 vac or boost i'm only really getting 36 psi of fuel pressure, whatever the fmu is set at. so in vacuum my FP is actually higher than it is at 0 boost/vacuum. i tried to increase my FP a little but id did not help. i think i will turn it up to maybe 40 psi static and see what happens. Has this happened to anyone else, or do you have anny suggestions on ho i can remedy this? i really do not want to band aid it by pulling out timing.
thanks
james

If your S-AFC is set to like -40%, then the ECU will be advancing timing considerably. I bet your fuel supply is just fine. The timing is probably too advanced at part throttle. I bet you would be better off lowering your fuel pressures way down (20's) and backing off on the S-AFC (-30% or so).

My story:
I once used RC 440's, S-FMU at 32 psi at static, S-AFC with boost mod set to -39%. Sound familiar? Those are the settings that I calculated to give me proper fueling. That was before I knew that the ECU advanced timing when you lean with the S-AFC. I would get this crazy rattling noise at part thottle. The only way to eliminate it was to set the S-AFC to like -20% which was WAY too much fuel at that point (as shown by A/F). So, I drove around with my S-AFC set way too rich for months because I didn't know it was timing related. I eventually figured it out and swapped everything out for stockers for a few months and then went to 8 injectors.


Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

so corbin,
are you recommending that i lower my static down to 20?
or my idle?
20 static would yield really really low idle FP
won't the injectors have problems with spray patterns and delivery?
thanks
for the info
James

Well, its the differential pressure accross the injectors that really determines how they spray. So if they spray OK at 20 psi static, they will spray OK at 15 psi fuel pressure and -5 psi manifold pressure. I'd try the low thirties and mid twenties while backing off on the S-AFC. You may have spray problems at 20 psi (never tried it). The lowest I went was 26, I think. I moved the S-AFC to like -20 to -18%, I believe. That was the only way I could stop the low throttle knocking. Low throttle knocking isn't nearly as detrimental as the detonation under boost that most have heard about...but it will damage the engine over time. I really think S-AFC's have been responsible for alot of engine damage on turbo conversion cars here.


Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

I
>really think S-AFC's have been responsible for alot of
>engine damage on turbo conversion cars here.


me too ;-)

>When i drive around I do not get any detonation except at or
>around 0 boost. >>

When you say "getting detonation", how do you know? Can you hear or feel detonation? I was under the impression that detonation happened once, and after that it goes boom... I'm sure I don't even have any stress put on the engine at 5psi, but how do you know your getting detonation? Just so I know if I ever do...right now everything runs great.

you can hear it
it sounds like a rattling
like rolling ball bearings down a corrugated sheet
it happens
your engine sould take a little bit of it, but if you get alot, your engine is gone
lates
james

okay i tried to lower my fuel pressure last night and it won't go any lower than like 25 idle. so i would say that is like 30 static. i'll check again today. and see what i can do. i gotta log again and start to retune now to get things right.
thanks
james

I know fiorst hand what detonation sounds like. Its like taking a soda can and putting some BB's in it and then shaking it up. Its a rattle sound. I was getting it and I didnt want to believe it so I kept pushing it. I thiought my engine was "BUILT" so it could take it. Boy was I wrong. I always seem to learn the hard way.

Hey Jamesman, how did you know to tune your afc to -40 for most rpm ranges?? Right now I have my fuel pressure set to 40psi at idle with the Cartech and I only have -20 at 1000rpms and it goes up by 2 every thousand rpms til I get to -10 at 5000. I have it zeroed out after that cuz i doubt I'll be over 5000rpms without going WOT. So, are you tuned too lean, or am I tuned too rich??

I know I can lower my fuel pressure with the Cartech some, so maybe I'll try that so I can bring my fuel curve closer to zero with the AFC. From what I understand, the closer to zero the better because leaning it out causes advanced timing.

i have 440 cc/min injectors,
and a pocketlogger, the injectors make me need to lean things out more, and the pocketlogger tells me how much i gotta lean it out
lates
james