My PCM is a 98 PCM in the car and I am running into a little bit of a problem. I have the Racetronix double fuel pump in my tank. I was expecting the injectors to stay fairly close to the stock fuel pressure but with both pumps I"m seeing 72 psi of fuel pressure. This is causing my l-trims to be about +25. So per the slowcar.net I tried to scale it by 129% to achieve a -4 l-trim. The Maf table in LS1-edit says byte out of range. I guess the numbers are going to high. Is there a solution to this are am I going to have to spend 400 bucks on a second set of new injectors. Any help is greatly appreciated.

Thanks

 

I am by far no expert but I have seen plenty of people with aftermarket injectors modify their injector flow rate table. By how much I am not sure but I believe its done the opposite way of changing the maf table. Instead of increasing the IFR table by 129% you will multiply it by 71%. I would email ChrisB before doing that though, there may be other things to consider before doing that. Good Luck !

 

See that is what I would have figured but the tuning guide says the opposite. It says if you have positive 5 and you are shooting for -4 then you would scaled the table by 109%. So if I had positive 25 then mine should be 129% and I'm sure he knows much more about this than I do. I have an injector table for my car but it is based on a 58 psi stock fuel pressure and with my fuel pump setup I am seeing 72 with no way of regulating it.

 

I wouldn't try to scale the injectors, I would be trying to get the fuel pressure under control! Is the stock FP regulator still in the tank with your new setup? Did you eliminate it, or are you overpowering it?? If you are dead-heading your pump(s) you just heading for trouble later. You need to incorporate a regulator in some fashion!

 

Are you sure they are +25? I would think they would be at a negative level if anything?

+25 means they are adding fuel to account for a lean condition. Was the pump/lines the only change?

I bet you have a vac leak somewhere around your PCV, EGR or MAF. 72psi FP shouldn't cause your LTRIMS to jump to +25

you can add an AFPR to your return line under the car (if you dont have a dedicated line off the rail) and dial down your FP with that.

Good luck,
Chris

 

you could have very easily pinched your return line on the tank re install, i would look into that, otherwise you need to install a better regulator.

i pinched my return line on my first install and it pegged my meter at over 100psi. needless to say the car ran like crap.

if the fp is up that high, tuning it is just not the right approach.

 

I've been told this is normal when running the dual Walbro pumps in the tank. It is just overpowering the regulator. When I called to see what the fuel pressure was running at on some other cars they said 70+ psi was normal.

Its definitely +25 on the l-trims. Looks like I have a faulty O2 sensor but not sure that would cause that kind or problem. I'm swapping it this weekend regardless.

Any suggestions on how to use an external regulator. Would I have to change all my lines? I already have a line running from a 3rd Holley fuel pump that is dedicated strictly to nitrous use and arms with the nitrous switch. These two pumps are feeding motor only.

 

With the help of John from Pace we just redone the injector flowrate table to compensate with the new fuel pressure. We had already done this to compensate for using the injectors at 58 psi rather than 43 so now we just adjusted from 43 to 72. It will be Friday before I can load the program in the car because I work 3 hrs away but this will probably help a lot more than scaling the MAF table. I will update this thread when I have more information in case someone else ever uses the double pump and has wild and crazy fuel pressure like me <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />