BlazinOR

Seems I read differing opinions all the time - the question is -

Does higher fuel pressure help normal driving at less than WOT? If so, how? Purely better atomization?

Learning, learning, learning..............soaking it up like a sponge - thanks to YOU guys.

bjankuski

It has been claimed by TPIS that a higher fuel pressure setting will also help part throttle because you are getting better atomization of the fuel charge. The O2 sensor will adjust the air fuel ratio to maintain the correct ratio for the current driving condition.

Kevin G

In closed loop, you have a block learn number that tells how rich you are running. GM recommends a number near 128 block learn at idle. Now in non WOT conditions in closed loop, the number can be less(it is adding more fuel to be at 14.7.1) or more( means adding less fuel to be at 14.7.1), and still be running ok up until a certain point. There is a limit of how far off the block learn can be from 128 before setting a code which means there is a problem causing this. Now the reason why GM recommends "128" in my theory is that at this point, the best atomization is occuring.

You can use a AFPR to tweak the block learn numbers.

Grim Reaper

The one thing people don't realize about increasing fuel pressure is that it is not linear in it's increase in fuel flow.

When I first got into eprom burning, I initially had setup all of my VE tables for my AFPR being at 40* psi. I then wanted to increase my fuel pressure (for the better atomization) and thought I could get away by just increasing my Injector Flow Constant - the same as if I had installed larger injectors. WRONG!

I found the higher fuel pressure had its greatest effect at "high load" like WOT and that required the greatest change to my fuel tables. While there was virtually no effect at "low load" like idle and light part-throttle, requiring very minor tweaking of my fuel tables.

I do agree with the "higher pressure = better atomization" theory. But I do not agree with the "higer pressure = larger injector" - that is only true at low vacuum/high load. At high vacuum/low load fuel pressure has it's least effect.

With "eprom burning", you actually do things differently. You pick the fuel pressure you want to run and then optimize the fuel tables accordingly. I personally like 46-48 psi as this gives you good atomization without taxing the fuel pump.

smokin87iroc

please correct me if i'm wrong but the way i understood it is if you have a blm greater than 128 then the computer is trying to add fuel to the mixture (meaning the cylinders are running lean) and if it was less than 128 then the computer is taking away fuel from the mixture (meaning the cylinders are running rich)

please let me know if i'm wrong

Andrew

TC602

You are correct, higher than 128 you are lean, lower than 128 you are rich.

Grim Reaper

Ditto.

smokin87iroc

thanks guys

Guest

I agree with what was said, except this:

This doesnt make much sense. The fuel flow rate is supposed to be constant vs. duty cycle. If it wasnt, there is a problem somewhere. Maybe what the difference is that you saw is that when the vacuum is removed, the pressure increase and subsequent flow rate change isnt reflected the same.

Kevin G

Oops, sorry. I wrote it backwards.

Grim Reaper

What I noticed when I was playing with fuel pressure and the effects on the SD calibration, was that when I increased my fuel pressure (measured with the vacuum line on), it had minimal effect on the pressure I was running before the change at high vacuum (Deceleration, idle and light part throttle). But in WOT, my fuel pressure change was greatest and was virtually identical to what I measured with the fuel pressure with the vacuum line off.

I had measured my fuel pressure with the vacuum line both on and off and drove around with (with the vacuum line on) with my fuel pressure guage taped to my windshield/

Thus the fuel flow was virtually the same at high vacuum and much higher in WOT. Maybe because I am running SD and I have a direct relationship in metering my fuel based on MAP (inverse of vacuum) that this is more readily noticeable. I have discussed this with other SD owners and they too have noticed this.

Not owning a MAF car, I can only predict how you may notice this to confirm. On MAF, captured data with low MAF gm/sec flows with low TPS readings would represent low load on SD. And, high flow (but not over 200) with higher TPS (but not WOT to avoid going into PE and open loop) to simulate high load. Then cranking up the fuel pressure should show should show little change in the BLM/INT in the low flow/low TPS sample and you should see a decrease (richening) in the BLM/INT is the high flow/high TPS sample.