I've got an 88 T2 with an aggressive street port (Turrentine said it was practically the most aggressive you can do without going bridge etc) and s5 turbo. On the stock ECU with a fuel cut defender the car runs lean once it hits about 12psi (i have been winding it out to about to about 14, I know this is a lot but I've got FMIC). AFR's have climbed into the 13's--I am currently running 100 octane unleaded as I've been trying to sort this problem out.

I have the SAFC richened up 20% and it doesn't help much once the boost climbs (it makes it run mad rich in 1st though b/c the boost doesn't climb very high).

The car has a rewired Warlbro 255 with stock FPR. It's only lean when the boost is high--so when it will richen up again by redline once the stock turbo can't hold the boost.

I've been looking at this fuel injector calculator thing http://rx7.com/cgi-local/2ndgencalc.cgi . It says that the stock ECU runs the injectors 58-63% duty cycle. I really don't believe that number though--I thought the rule of thumb was closer to 80%. Like it says that the stock 550/550 can only do 200 at the flywheel at 63% duty cycle, but I know plenty of people break 200 at the wheels on stock injectors just fine.

So do you guys think I just have injectors that are too small? The car dynoed 250rwhp a while back running no boost controller but a lot of boost creep (about 12psi maybe). I'm going to upgrade the injectors when I install my FPR anyway, and obviously the solution for now is to keep the boost down.

 

hence tuning fuel to boost is better than rpm, i wonder if your boosting at different parameters than the AFC will handle. Most likely tho if you hit around 250whp, its time to up your injectors

 

I think you should pull your turbo and port the WG more agressively to prevent the boost creep you're getting in the higher gears... If you're running a 3" TID and full 3" exhaust, you should be able to keep the boost at or below 10psi with a good port on your s4 WG... So yeah, do this and then you can hopefully tune your SAFC better for all the gears (instead of just 4th gear where you get the most boost-creep).

It's a good thing you've got 100 octane and a FMIC. 13 AFR's wouldn't last long for any other setup.

 

well I'm just waiting to get some more money and i'm going to rip this bitch apart to give it a standalone, injectors, and FPR.

 

Either way, you should probably redo the WG port to get more consistent boost IMO. It will make tuning that SAFC a LOT easier.

 

Jeez I wish that'd remove that BS claim for that page. Firstly, injectors are not run at a certain duty cycle as that statement implies, the duty cycle varies massively depending on load and rpm. DC at idle for example is only 3-4%. Secondly, the injectors peak at ~60% when the engine's stock, but this is not a limit. I have a dash-mounted digital injector duty cycle meter and I can assure you it can get higher than 63%.

 

Well, it is a marketing tool to convince you to buy their injectors etc.

 

Check your AFM flow % on the S-AFC.
At WOT the AFM could be 100% as low as 4K RPM.
Above that the ECU is speed/density mapping & the S-AFC can't adjust above 100%.

My work-around was to use a Cosmo AFM so I could use the S-AFC at higher flow rates.

Otherwise you're looking for a stand alone.

(edit)
I just realized you have an S4.
You could tighten the spring on the AFM & re-tune the S-AFC.

 

Even with 100 Octane, you are out side the efficiency range of that turbo. Keep up the 13.x AFRs too much longer and Turrentine will be revisiting the inside of your motor. Why would you have such an aggressive motor built just to run it on a stock ecu with an SAFC?

A good rule of thumb is, if you add more fuel, yet your AFRs continue to decline, you are out of injector or fuel pressure/volume.


Okay, that takes care of the fuel volume part of the equation. And it wont richen up. Just because the boost falls off at high Revs, doesnt mean your fuel requirements will fall accordingly.


Hailers disproved this years ago. He saw 99% on his cycles with just a stock ECU using a type of multimeter thats designed to measure this type of thing.

Get a hold of that boost.. PRONTO!

 

Its only "speed density" so much as it may correct up to about 8 ish psi or so. This also assumes that we have a MAP sensor, which in the truer sense, we dont.

 

My stock pressure sensor on the 91 had a 2 bar range.
It would give a linear reading from -14 to + 14 PSI.
I had the blue wire from the S-AFC hooked up to it so I could monitor and plot manifold pressure.

 

In order for the car to be SPEED DENSITY, it would have NO AFM. Speed density relies solely on MAP inputs to interpolate a point on the look up table..

Source: http://www.carcraft.com/techarticles...uel_injection/

 

From what I observed with the stock AFM on my mildly modified setup, the AFM would hit 100% before 5K at WOT & 11PSI.
The stock ECU was just "winging it" above that. (A scary feeling)

Whatever the default map was, it kept increasing fuel to 8K.
I didn't like flying blind, so I swapped to the Cosmo AFM.
It was crude, but effective.

 

But its still not speed density.

 

The turbo's coming out this weekend and then I am taking it to a shop to get the wastegate ported further.

and let it be known that I only discovered this problem recently when I got my wideband working (bought one and it was defective, and spent months hassling with customer service people). The boost creep really only got bad when it got cold outside. Last summer and fall it would hit like 10-11psi.

I probably won't get the standalone in until this summer.

 

For sure it was getting more fuel as the revs went up.
I have never seen or tested if the pressure was factored in that corner of the ECU tables.

In the end I was getting ~300HP from 720 secondaries with a rewired 255LPH pump & an S-AFC with a Cosmo AFM, stock turbo, ported WG, MBC set to ~11PSI.
O yea - - & that big header dump, street port, beveled rotors.

Bottom line - the 720s were enough.