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tatasta
November 27th, 2009, 05:54 PM
Hello,

Recently, my stock fuel pump was going out and I ordered and installed a direct fit Racetronix fuel pump in my 99 A4 Trans Am. Prior to my old pump going out, the fuel presser ran at ~ 58# with a WOT AFR of 12.8:1. Also, my MAF calibration is spot on and my VE was working well.

Since installing the new pump, which went very well, my pressure at the rails is ~ 70 psi at idle and drops a few psi under a load. I am not using a Hotwire kit, still off the stock harness.

Anyway, the car still starts and runs decent except that my AFR has become too rich by 0.5 -0.6:1. I am assuming that the increased fuel pressure is causing this. So, the question is, what is the best way to fix this? I am not too excited about tweaking my VE or MAF calibrations since they are correct and help to make other tuning aspects accurate.

I am using FIC 33# @ 43.5# LS1 injectors that I had before changing out my fuel pump. I calibrated the IFR for them and had no problems at all except for rich off throttle coasting.

Is it possible to adjust/alter injector settings to compensate for the higher fuel pressure? And, if so, how would I go about doing that?

I have attached the tune that ran well at 58# of fuel pressure but is too rich at 70# and a log file of this tune running at 70 psi.

Thank you and any assistance would be appreciated,

Robert

mr.prick
November 27th, 2009, 06:11 PM
Increase {B4001}.

tatasta
November 28th, 2009, 08:59 AM
Increase {B4001}.

Thanks for the comment Mr. P.

I attached a partial copy of a popular IFR spreadsheet that basically shows the difference in IFR settings for my injectors at rail pressures of 58# and 70#

It will certainly be easy enough to put the new values into my tune. Is there any other areas of my tune to modify other than IFR or just try it and log some data?

Last question. In your opinion, what problems, if any, could high fuel pressure cause?

Thanks

mr.prick
November 28th, 2009, 09:26 AM
Do you have a sensor to log FP with or are you using a gauge on the rail?
I ask because I had a gauge on the fuel rail and it kept creeping up for some reason.
I installed the Autometer sender because I could not believe the unexplained increase
and sure enuff the gauge was wrong.

As for higher FP causing problems :nixweiss: unless of course
the increase is from a blockage or a faulty gauge/sender,
causing you to make unnecessary changes to the tune. :hihi:

tatasta
November 28th, 2009, 12:09 PM
Do you have a sensor to log FP with or are you using a gauge on the rail?
I ask because I had a gauge on the fuel rail and it kept creeping up for some reason.
I installed the Autometer sender because I could not believe the unexplained increase
and sure enuff the gauge was wrong.

As for higher FP causing problems :nixweiss: unless of course
the increase is from a blockage or a faulty gauge/sender,
causing you to make unnecessary changes to the tune. :hihi:

I have a mechanical fp gauge on the rail but also confirmed it with a digital meter that was attached at the schrader and put it inside so I could see it while driving. I think it is true and I know that the return line, feed line, etc are not damaged. The change in AFR also confirms the variance in fp.

When I called Racetronix about it they said "Well, I guess you got a good one".

That was really helpful, huh? lol

Did the charts I attached make sense?

Thanks

mr.prick
November 28th, 2009, 12:19 PM
Do you have this one?
Injector setup(IFR) (http://www.marcintology.com/tuning/injectors.xls)

tatasta
November 29th, 2009, 10:37 AM
Yeah, I have that one. It's the one I used for the attachment on my earlier post. Guess you didn't see it.

Thanks

joecar
November 29th, 2009, 03:57 PM
The spreadsheet you attached looks to be calculated correctly.

tatasta
November 30th, 2009, 02:03 PM
Thanks joecar.

I am going to try and log it this weekend, if possible.

It's getting kinda wintery around here. :santa2::tree::santa2:

Naf
January 12th, 2010, 06:04 PM
I have the same problem, i increased the fuel table to the point i am scared to add more. But i am still runnin excessively rich 10.5-11.3AFR at idle. When the voltage drops to 13.5 my fuel pressure drops to 55psi. This is annoyin and now my cats were found to be glowin, and i am puffin black/white smoke out the rear...

NOT COOL

Naf
January 12th, 2010, 06:04 PM
LABELS Injector Flow Rate (Grams/Second)
Manifold Vacuum kPa {link: GM.MANVAC} Value
0 6.531250
5 6.609375
10 6.687500
15 6.773438
20 6.851563
25 6.929688
30 7.007813
35 7.093750
40 7.171875
45 7.250000
50 7.335938
55 7.414063
60 7.492188
65 7.578125
70 7.656250
75 7.734375
80 7.820313

mr.prick
January 13th, 2010, 02:10 AM
What injectors do you have?
InjectorsFromFP.xls (http://marcintology.com/tuning/InjectorsFromFP.xls)
I have the Walbro 255 and logged FP averages 62.37psi (4.3bar)

Naf
January 15th, 2010, 05:08 AM
Bosch 42# injectors with a LS2 fuel rail...I have a Fuel pressure gauge on the end of the rail so i pretty much know how its runnin around idle...