Denso 660cc injectors, but -5% low throttle correction?

[alIan]

I recently finished upgrading my fuel system (walbro 255 HP, AFPR, SAFC-II, Denso 660's). I had Roy (who used to work for RRE) tune my car (using tunerstein or something equivalent) right after these mods, then began to have idle problems.

I had idle surge with occasional dying. I checked for vacuum leaks, IAC, TPS. I decided to check Roy's Low Throttle settings on my AFC, and found them to be -10% at idle, and -20% from then on. I busted out the logger, and found my fuel trim to be at a positive 6 or so at idle. Ok, i said, and adjusted the 1000rpm SAFC setting to -5%, leveling the fuel trims off at an even 0 (both LT and ST). I repeated at 1600RPM, 22000, 2800. I then took the car out for a drive with an even -5% correction.

I kept my eye on the fuel trims while driving, and found that while my throttle was at around 20% (moderate load on the engine, 2-3k rpm), the STFT was at around -14 to -15%, but when i backed off the gas, it was dead on zero. I drove for ~10mins and went back home, and checked the fuel trims again at idle, 1.6k, 2.2k, and 2.8k. They were all still within 2-3% of zero.

Here is the guide i used to tune the low throttle settings

I have not tuned the high throttle settings at all, they remain at what Roy set them to.

The idle issues seem to be gone!!! ???

How in the world are 660 injectors only a -5% correction? Is there something drastically wrong? My high settings are at -38% above 4k RPM!!!! what the hell??

Some data:

FP: 43 psi (idle no vac), 34 psi (idle vac)
Idle vac: 18 in. Hg.
Do i have EGT? yes.
am i a Newbie to tuning? yes.

 

[CanadianTSi]

With 650's my Low's are at +3 from 800 to 2000...figure that one out.

Every car is different, as long as your Fuel trims are good then don't worry about it... or else you'll go crazy

 

[alIan]

so basically just worry about the fuel trims when i'm testing in neutral? because they change a bit when there's a little load on the engine.

basically, they are always within 15%, and when i'm in neutral, or slowing down in gear they are locked at a solid zero.

So i suppose i should just stop splitting hairs? I would still like to find a better tuning guide for low throttle on an SAFC II for a 2g DSM... any suggestions?

 

[Maglin]

their is a big chance that your lower injector seals are shot. They can be leaking under vacuum and thus pulling in a lot of unmetered air. That would accound for your very low amount of fuel correction at idle and under vacuum conditions. I had the same problem with my 1000cc injectors. Then when I fixed all my vacuum leaks post TB I can't get the motor to idle at all. The injectors are just to large and just turn on/off at idle. So their was a hugh difference from getting new seals and getting rid of that hugh vacuum leak. If it was tuned on a WB your high setting are probably way different probably more around -25%. They are cheap and can be gotten from the dealer for $12 for the set.

 

[spyderturbo007]

With 650cc injectors, my correction factors are between -8 and -12%.....Nothing to worry about, as your Hi throttle settings seem to be right where the should be.

 

[alIan]

So my idle surge came back temporarily today. It happened after i gunned it (for the first time in a week or two) on the freeway.

I have come to the conclusion that i have a boost leak, and here is why i think so:

1- idle surge happened after high boost conditions, i.e. after the boost leak was aggrivated and the fuel trims tried to make up for it.
2- excess fuel at idle (-5% for 660's) due to the ECU making up for excess bypass air.

I replaced the injector seals about 600 miles ago. Both the lower seals and the orings. I replaced both throttle body gaskets, sealed all IC couplings, sealed the cold side of my turbonetic 50trim...

What do you guys think about the vacuum leak assessment? as soon as i get back home to my garage i'll try a boost leak test again, even though i have always failed at it in the past (maybe because of a huge leak i couldnt find ??!! ).

On a lighter note, i just got 415 miles on one tank. My gas milage is still AWESOME!

 

[talonTSIDriver]

415 miles on a tank, HOLY CRAP, I get maybe 250on a tank. Anyways, my fuel correction at idle is -10% on my 650's. But as soon as I go over 1.5k it goes to about -25% or something like that, I can't remember what it is exactly. But do a boost leak test because any boost/vacuum leaks can make tuning a really big pain and cause your car not to run at its full potential. I've figured that out a couple times now.

 

[alIan]

so did you tune your low throttle like i did then?

I just put the ebrake on and throttled to the tune points in the AFC while in neutral, adjusting the fuel trims to zero. Then i took it for a drive, and repeated the process.

and yes, 415 on one tank was sooo awesome... that's better than before i modded!!! calculating it out it's about 29MPG... yay!