91chevz71

So I hit 100% VE at 3k and 80 Kpa.
I'm running 90 lb inj's at 14 psi, feeding 330 HP and 380 TQ (so the dyno sheet says from GMPP).
I did the math and the numbers say I have enough injector, my BPC is 91.
Anyway, my last WB WOT run had it lean up top. Since the VE table looks normal up until about 70 Kpa I was thinking of keeping my current BPC up until 70 Kpa then at 75 increasing by 10 and 80 increasing by 10 again. VElearn after that. Maybe this could give it the fuel it needs with having to retune the ENTIRE VE. Here in Denver, I only have 85 Kpa of air to work with...5300 feet above msl.
I need to post a datalog, I know. workin on it
Whaddya guys think?

91chevz71

Ok here's a pic of the log
problems I see
1. peak rpm 4400
2. Target AFR for PE is 12.8 across the board. maybe BPC is off.
A. The AFR leans out towards the top, but DC% is only at 60!!!
3. SA is 31 deg. Maybe I could do 33.?

There is a bottleneck here somewhere...


What do you guys see

V8Astro Captain

iTrader: (1)

Before you fudge the BPC too much lemme tell you a story...

I've been going around and 'round with this issue. The more VE learns I did the worse the tune got.

I emailed RBob about a problem I was having. There were situations during throttle lift and idle where my AFR hit 25:1. At idle I'm running the 90# injectors at 20 psi, 32 psi at WOT. RBob noted that my injector PW was .9ms. The higher the fuel pressure the longer the injector takes to open. When my IPW was .9ms the injector wasn't actually opening, verified with clever use of a timing light and some courage to stand over a screaming blower at 2500 rpm...

RBob suggested I try raising the values in the "injector correction offset" table. This way the IPW won't get so short to the point where the injector fails to open.

I'm sure you have a copy of the EBL.bin. Compare it to the table I'm using now. I've lowered my fudged BPC values down from 1.7x to 1.12x.

The main point is...fudging the BPC table as far as I had caused a multitude of tuning issues. I would try raising the "injector correction offset" values first.

Looking at your datalog...I would add some fuel in the 75-80 kPa column of the VE tables to make the AFR match the target WOT AFR. 14 (AFR actual) / 12.8 (AFR target) = 1.09. Highlight the 85 kPa column and multiply that column by 1.09 and go for another drive. You should be close.

91chevz71

My INJ offset is still stock 7747 EBL. I'll raise the values about 2.25x and see what happens. THe values are measured in usec, so that's extra fuel?
Thanks V8

I can't add anymore fuel to those areas- already maxxed out, which makes me think the BPC is off.
So maybe the offset is too small, prohibiting the injectors to flow more fuel?
not tracking 100 percent on the offset thing

RBob

iTrader: (1)

I wouldn't increase the SA until the fueling is squared away. IF the VE table is normal up to 70 KPa, then jumps, it sounds like the fuel delivery system isn't up to par. It may be that the fuel pressure is falling off.

RBob.

91chevz71

That could be it- still the OEM TBI pump. With key on, engine off the PSI jumps to 14 then bleeds back down after about 3 seconds. When I start the engine, the PSI falls to about 11 then slowly climbs back to 14. That couldbe a sign...
Back when I started my build I bought a big fuel pump (FPG002 255LPH) from Apeusa.com, but decided to run big injectors so I didn't think I would need to change the pump. 17 years is a long run for a fuel pump!! Is the 255 pump too big for stock regulator? I still want to run 14 psi, but I don't want to blow the regulator housing throught he hood...lol

RBob

iTrader: (1)

The 255l/hr pumps move too much fuel for 14 psi. The TBI unit can't bypass the excess fuel and it drives up the fuel pressure.

The 190l/hr pumps are OK for the lower pressures.

RBob.

Sierra GT

91chevz71,

How do you find those 454 injectors at idle? Are they ok at low RPM? I was thinking about running them but got scared off by some of the things people were saying.

Thanks,

John

91chevz71

I messed with injector offset today for about 5 hours.
my engine - 212/222 cam, vortec heads, .435 .460 lift
I got a 98 percent smooth idle with a VE of 41, BPC of 90, FP of 14, and inj offset of 550 usec. This gave me an AFR of 12.8/9 at 650 RPM.
That gave me best quality- then I tried to get to 14.7 (thought I had it, but nope) at idle.
Tried lowering VE to lean the AFR- surging with only a 1 percent change. Tried retarding timing- only got rougher.
I sacrificed quality (probably about 80 percent smooth now) but I got an AFR of 14.5-14.8 at idle by changing the INJ offset to 315usec. I couldn't drop the VE-surging. I wanted to stay away from changing the BPC, also.
Tried closed loop idle- what a nightmare. Surging immediately, even with the AFR decently in line. What I don't get is that bigger injectors require more offset, so why is my offset lower than stock EBL? Maybe because this is not a stock engine. That's probably why.
Point is, you can get it to purr. The 350 HO (in my truck, anyway) likes a rich idle with healthy offset- makes sense. I'm trying all this 14.7 stuff because I want to give it a sniffer check.
I
----------
I think I'm trying to make this engine (350HO) do something it can't- a totally perfect idle with AFR 14.7

Fast355

iTrader: (2)

Exactly the case sir, so why try it. Too lean will just drive up the hydrocarbon emissions and the NOx readings.

My ZZ4 cam idles at 13.6:1 a/f ratio AND passes the dyno sniffer with ease. Functioning cats help.

91chevz71

Good stuff, Fast. I have two cats, both <6 months old. That's a confidence booster. Thanks man V8capt too

91chevz71

Have 255lph, need 190 lph. Anybody wanna trade? lol

Dominic Sorresso

Guys,

I ran for the last 3 years with an INJ Correction Offset of 732mv. That along with the VAFPR had my Xfire idling at 47kPa and 850rpm with a 218/218 duration and a 528 lift on a 108d LSA.

91chevz71

I left my offset at 550 Usec, it idles pretty darn good. I'm still a little hazy on how this actually functions- offset from what?

Dominic Sorresso

Think of it as spark advance. Increasing the Inj. Offset minimizes the amount of PW duration required to get the injector open. As you increase the IB, you'll drop the VE required to properly fuel the motor because more of that PW is tthe injector actually being open. I think RBob found that an 80 or 90# injector takes about 700+msec to open. Ergo the offset. Make sense?

91chevz71

Yep. Thanks Dom S.
I like that analogy- makes it easy for guys like me.

Thank you
Mike