Question about Fuel cut and Injector compensation

onegee · 03-10-2005, 01:45 PM

Well i've been trying to get my car to run decently fast with the MAFT but I etiher get knock when I lean it out or hit fuel cut when I add in fuel. I decided to take out the MAFT for now and run stock maf to see if I could simplify the problem. Fuel cut occurs at 15psi for me, once at 9psi in a 2nd gear onramp pull.

I still hit fuel cut around the same area (4800rpm-5000rpm) and my timing is usually pretty good (15-19). One thing that concerns me is my injector P/W is 19.xx and my Duty Cycle is close to 90% if not more at times. Airflow peaks out on the logger at about 3500-4000rpm depending on gear. Im running 450cc still and have my mods listed in my profile.

Now Ive read quite a bit about fuel cut, and I wanted to eliminate the possiblity that it isnt an ECU thing at this point but some fuel/mechanical problem Im running into due to injectors being old and maxed out or more boost leaks I havent found. I checked for boost leaks and found two, however I'm going to try again and see if there is any I overlooked. I changed plugs also (NGK 7s) and fuel filter was changed about a year ago.

Now comes my questions, when doing injector compensation via a chip, it makes the ECU think the bigger injector is stock, but how does the chip make the ECU drop the duty cycle down? Is it due to the fact the injector is working less hard to spray the same amount of fuel than a smaller injector would?

If I put in 660 Densos and compensated using a chip, will that bring my injector D/C down and at the same time allow me to lean out my 5knob AFC thus bringing down what my ECU thinks is too much airflow. Im richening it up so much (at times almost 20%), and I'm hoping that the reason Im hitting FC is my ECU is seeing wwaaayyyy too much airflow.

With that being said, it just make sense to eliminate fuel cut at the same time doing the injector comp on the chip, but I really wanted to figure out why my car was hitting FC in the first place and see if larger injectors would cure FC BEFORE taking FC out all together.

Thanks for reading this long post, but Im at my wits end with tuning this car. I'll be doing a compression check to see if everythings still fine, redoing base timing, and check for more boost leaks to see if that helps any.

Appreciate any help and feel free to add suggestions. If my understanding of FC is wrong, feel free to re-educate me. :o

-R

steve · 03-10-2005, 03:04 PM

Nothing short of changing the ECU code eliminates fuel cut and you wouldn't want to compensate for larger injectors in the chip without either raising the FC trigger or removing it. Since the ECU will see the same airflow numbers as it does now, unlike lieing to the ECU with a SAFC by reducing the airflow to make up for larger injectors, you would still hit FC.

If you compensated for putting in the 660s via the chip you would zero out the SAFC corrections and just use it for minor adjustments.

Steve

onegee · 03-10-2005, 03:09 PM

Thanks alot for the reply Steve. Appreciate it big time.

-R