ATTN: Adjustable FPR owners; turn up your fuel pressure! :D

[Stu]

70 pounds of fuel pressure seemed a bit extreme (for a relatively stock, stroked M50) and I wasn't even sure if standard Motronic could handle it...but apparently it can. E46 PTG cars run 70psi on Motec management with much more compression, a LOT more cam duration and race ignition maps.

Ambient temperature was around 30 degrees tonight (cold for NC!). I typically run my rising-rate FPR at 48psi (58 at WOT). On a dyno 2 years ago, this seemed to make the best AFR's across the board, and we never bothered to go past ~60 psi. AFAIK, stock regulators run at 52psi. I decided to make some adjustments and do 10mph-90mph highway runs at different pressure levels. At WOT, I started with my original 58, then to 65, then 70. The difference was HUGE--3rd gear from 2500 rpm at 70psi makes the 3.0 feel like it has the stroke of a 3.2. There is that much difference--midrange punch was INSANE! On the other hand, I went through about 2 gallons of gas in not much time--it drinks fuel at that pressure level + WOT.

Point being, I need to get back on the Dynojet and play with the FPR a bit more. I think the 3.0/3.2 M50's like high fuel pressure, atleast in combination with cold ambient temps.

BTW--motor is M50 with 3.0 M3 rotating assembly, head, no cats, 17# injectors

[matt]

Have you thought about doing some real tuning instead of playing with fuel pressure?

Do you have a wideband?

Are you running 70lbs base pressure and then ramping up from there? Are you running an O2 sensor?

Unless you're pushing the limits of your injectors (shouldn't be) there is nothing you can do with an RRFPR that we can't do with software.

[Stu]

Have you thought about doing some real tuning instead of playing with fuel pressure?

Do you have a wideband?

Are you running 70lbs base pressure and then ramping up from there? Are you running an O2 sensor?

Unless you're pushing the limits of your injectors (shouldn't be) there is nothing you can do with an RRFPR that we can't do with software.

Matt,

I started with a 3.0L RD chip, then switched to a chip made by Jim Blair of BMW NA, only because the latter chip made a good bit more power on my local dyno. Other than that, no, I havn't done any real tuning. I'm sure there is power to be realized with a custom mapped chip. The chip that's in the car was built by Blair in '95 when the M3 came out and is setup for a 3.0L with just the Euro MAF. I was satisfied with the baseline data and never really sought more power.

Yes, car has an 02 sensor. I don't have a wideband but might have access to one. If it will make more power on this Dynojet with a bit more fuel pressure, I'd be surprised (based on baseline data)...but the motor felt completely different at 70psi vs. 58!

I'm not keen on swapping chips right now due to cost. Like I said, the motor makes a lot of power, but I think I'll be upping the fuel pressure occasionally for trackdays or general shenanigans. :)

[matt]

How high is the compression? We can probably come up with something. Or you're not far, you could come down here for one of our dyno days and we'll come up with something really great.

I'll tell you right now, if you have your fuel pressure set between (best guess) 45 and 60 psi base, you might as well run the stock FPR, the ECU is putting the fuel back in or taking it back out, whichever way you have it set. What you've done with this adjustment is raise the fuel pressure high enough that it maxes out the adaptation (on the lean side) so now you actually are running richer than before. Only the wideband can tell how much.

If you really want to benefit from an adjustable FPR (which I highly un-recommend), you need to unplug the O2 sensor (or turn off adapation in the software) so that the ECU isn't constantly fighting you in sometimes unpredictable ways. And you need to be constantly adapting the tuning yourself with a wideband, because the computer can't for you.

[Stu]

How high is the compression? We can probably come up with something. Or you're not far, you could come down here for one of our dyno days and we'll come up with something really great.

I'll tell you right now, if you have your fuel pressure set between (best guess) 45 and 60 psi base, you might as well run the stock FPR, the ECU is putting the fuel back in or taking it back out, whichever way you have it set. What you've done with this adjustment is raise the fuel pressure high enough that it maxes out the adaptation (on the lean side) so now you actually are running richer than before. Only the wideband can tell how much.

If you really want to benefit from an adjustable FPR (which I highly un-recommend), you need to unplug the O2 sensor (or turn off adapation in the software) so that the ECU isn't constantly fighting you in sometimes unpredictable ways. And you need to be constantly adapting the tuning yourself with a wideband, because the computer can't for you.

Matt--

Thanks for the info. I understand that it should be effectively be running richer with more fuel pressure. I assume unplugging the o2 sensor relay will have the same effect as unplugging the o2 sensor [a bit simpler]? If so, I'll give that a shot this weekend.

Stu

[matt]

No, unplugging the relay will just disable the heater. The signal to the ECU doesn't run through the relay.

I would suggest leaving the O2 sensor until you get a wideband to see where your AFRs actually are.

Seriously, you should come down and run on the dyno. I'm sure we can work out a reasonable price.