MyE28.com

Hey guys, I have a 1985 535i w/ 745i setup. I have a tcd 30lb injectors, a highflow external fuel pump, a stock in tank pump, and a rrfpr. I am always running real rich initially on a full throttle pull. After running through a couple of gears, if I try to floor it again it runs super lean, way less than stoich. If I come to a stop or push in the clutch and let it idle for appox a minute, and floor it again, it is back to pig rich. This issue is extremely annoying and will prevent me from going to a track day at Lime Rock on friday if I do not get it fixed. Any input is greatly appreciated! Thanks.

Sounds like your fuel pump cannot keep up. Check fuel pressure under boost. It's besst to have a passenger stare at a gauge while you drive.
Todd

Yeah, I think the fuel pressure drops under load. Would that be a function of the intank pump or the rrfpr. I just upgraded my external pump to one much better than oem.

TheGraye28 wrote: I just upgraded my external pump to one much better than oem.

How. What is its flow rate? What psi you running at idle and under full throttle? Installing a inline pressure gauge is very easy. Spice it in the return fuel line at the back of the fuel rail.

I do have an inline pressure gauge. Right now at idle im running about 43 psi fuel pressure. If I rev it up a little while watching the gauge the fuel pressure drops slightly, then if I rev it again, it drops some more. I would suppose that the rrfpr would raise the fp under acceleration, no? This is why I'm kinda baffled.

TheGraye28 wrote:I do have an inline pressure gauge. Right now at idle im running about 43 psi fuel pressure. If I rev it up a little while watching the gauge the fuel pressure drops slightly, then if I rev it again, it drops some more. I would suppose that the rrfpr would raise the fp under acceleration, no? This is why I'm kinda baffled.

Idle psi s/b ~38psi. The fmu only raises fuel pressure under load not rpm. You could rev the engine to redline in neutral and the fuel pressure s/b be ~42psi. Above atmospheric the fmu will increase fuel pressure.

Todd

Alright, so if i lower the idle psi to 38, will this help the problem?

What Todd is trying to say is you need to check the fuel pressure under load. Attach a longer piece of fuel line to the gauge, run it out the back of the hood and stick it under the wiper so your passenger can see it. Then go drive and have your passenger note what is happening with fuel pressure under various conditions.

does your fmu have 2 adjustments?
i had a cartech one and had the same problem because i didnt have the static knob set right. ( the one on the top with a locking nut ).

when your rrfpr siganl is at atmospheric pressure , it should read slightly higher than your stock fpr. ( say 45- 46 psi ).
then the knob on the side is your rising rate regulation.
i had mine with the same set up about 1/2 a turn from totally turned in.

Hmmm, interesting. I dont have the cartech one, but ill have to check if I have that adjustment.