Got my e34 back from the tuner yesterday. For some reason I have having issues with fuel delivery past 5700 RPMs (as you can see by the AFRs on the graph). My fuel pump is a TRE 255
http://treperformance.com/i-656-bmw-...nd-models.html
Which is supposed to be able to handle 600hp. Any other ideas as to why I am going so lean up there?

 

No tune, no datalog, no fuel pressure gauge on the rail during pull, no help.

 

Unfortunately this was all I got from the shop when I picked the car up. Sam Miller was the tuner (got his name from this board). Before I had the car tuned I had driven it around with a pressure gauge that maxed out at 60 PSI and could barely get the needle to lift off the max peg. Now that the engine is semi-tuned I plan to do the same. I was hoping someone on the board would have some insight if the TRE 255 would be adequate at these power levels.

 

I can tell you I see more fuel pressure problems on transplants than just about any other problem. Only a fuel pressure gauge at those rpms will tell.

 

http://youtu.be/aoaRds8Apmk

Sorry for the crap video. Looks to dip to about 51 PSI under load. Nothing drastic seems to change up top though...

 

When I switched from a 525 HP LS2 to a stroker LS3 (presumably around 600 HP) I also installed a new TANKS gas tank with a 340 lph pump as I didn't think my previous Walbro 255 would be enough.

Keep in mind that a pump's "255" rating is at an optimal pressure (typically lower than 58 psi) and at a high voltage of 14+ V. It is counter intuitive, but as you raise the pressure of most pumps, the volume goes down. Also if you are running anything smaller than 10 gauge wire to the pump, it might not even see 12 Volts. And 12V might only give you 70% of the capacity of 14V. The manufacturer's tech sheet will show you all this.

Look at your pump's specs, notice that while it delivers 235 lph at 40psi, it only delivers 204 lph at 60 psi.

Put a volt meter on the pump and if it is more than 1/2 volt below the output of the alternator, you might want to upgrade the wiring.
If the injectors are big enough, you might be able to run them at only 40 psi and thereby get more volume out of the pump.

 

Is there a GM spec for LPH requirements for these engines? I could see needing a bigger pump at high power levels. I guess I am just surprised that my relatively stock LS is running out of fuel. I am using stock LS1 injectors also.

I will check pump voltage vs alt voltage tonight and see what my delta is.

 

Yeah me too. Its either fuel pressure or they didnt use a good 12V IGN source for the standalone harness, two biggest problems I see.


OP the fueling doesnt look right on any part of that pull, not just past 5700 rpm.

 

Are you talking about the AFRs on the dyno or the pressure in my video or both?

 

The AFR on the dyno sheet.

 

^ this

Why does it go pig rich at 4k then lean out?

What FPR are you running and how is your fuel system configured?

255lph pump should not be an issue for your hp.

 

I have no idea why it is tuned like that... kind of why I spent money and took it to a highly recommended tuner.

I am using a stock corvette filter/regulator mounted where the stock BMW fuel filter is mounted. (close to the fuel tank)

I would call my tuner and ask more questions, but I am trying to educate myself further so I know the right questions to ask...

 

Sorry, I may have caused some confusion because I thought you were aiming for 600HP and I completely overlooked the dyno sheet showing 350 whp which is about 425 flywheel.
For that a 255 lph pump is plenty. I would still check it voltage with the engine running - even running at idle is fine.

 

I can't see much in that video but 51 PST under load is not proper or good.

 

I am going to try moving my filter/regulator closer to the fuel rail. I think I may be losing pressure at the rail due to head loss from the length of travel the fuel has after the regulator.

 

Moved the filter/regulator from one end of the car to the other right up next to the fuel rail. Indicated idle pressure is about 63 psi and under load it drops down to about 57. Is this closer to normal?

 

58 psi is normal.

 

So I also removed some fittings that reduced fuel line diameter and replaced the feed line with 3/8ths fuel line. Here is a video of fuel pressure now. Is this still too low?

http://youtu.be/OZrXpnX9yWk

 

Thats better than before but it shouldn't even drop that much. I tune swaps all the time with the filter/regulator in the rear and they hold psi rock solid. Is your pump internal or external?

 

Perhaps your BMW fuel tank has too small a feed line. While a 3/8" feed line should be plenty for your power level, you have to ensure there are no too-small restrictions.