Running Lean... Fuel pump question

[JedzE36/5]

OK guys. I dynoed the car yesterday and i am running really lean at low RPMs. the ratio is suitable above 4500 but it is still a little on the lean side. when i got the swap put in my mechanic told me that i should change the fuel pump. he then proceeded to open the pump from a 328 and a ti and the part number was the same. the only difference was the length of the feeder and return lines. anyhow did all of you change your fuel pumps in the process? how about the fuel filters? help would be appreciated. here is the dyno sheet.

[JedzE36/5]

forgot to mention that i just recently put in a 540 HFM and some software from Active Autowerkes.

[J!m]

That second post was the important one...

I'd contact AA and ask them why it runs lean at low RPM. I imagine you also have a 'cold air intake' installed on the engine.

I have the stock ti fuel pump, and even with the Dinan stage 1 software, it has plenty of fuel to the redline. No hesitation at all right to the (raised) rev limiter.

[JedzE36/5]

i contacted AA and they said it was because of the HFM and that i should get the chip tuned for the HFM. the chip was supposed to be tuned for the HFM but apparently it is not. i am sending them my dyno runs and some spreadsheet data.

[snwbrdrbum10]

Originally Posted by J!m

That second post was the important one...

I'd contact AA and ask them why it runs lean at low RPM. I imagine you also have a 'cold air intake' installed on the engine.

I have the stock ti fuel pump, and even with the Dinan stage 1 software, it has plenty of fuel to the redline. No hesitation at all right to the (raised) rev limiter.

how do u remove the rev limiter?

[J!m]

That seems logical to me.

I know if the flow meter is changed, the ECU HAS to know the correct formula for air mass based on the area (read: diameter) of the flow meter. Also be sure your air temperature sensor is not bad (but you would probably throw a code for that).

[andy]

Interesting - I just got my 328ified ti dynoed too. With a stock 325 MAF and software it was running pretty lean too. We tried several off the shelf M3 chips and the best one made things a little rich, but a very smooth afr line. It looks like I need to get a larger MAF to fix things up, or perhaps go to smaller injectors. IAC, I don't mind it running a little rich (12-13.1 range) while breaking it in.

[J!m]

Rich is OK for break-in, but you want to correct that AFR to get maximum potential from the air-fuel charge. If it is not optimum, you are not at peak efficiency. If not at peak efficiency, you're not at peak power... But you probably already knew that.

[andy]

Originally Posted by J!m

Rich is OK for break-in, but you want to correct that AFR to get maximum potential from the air-fuel charge. If it is not optimum, you are not at peak efficiency. If not at peak efficiency, you're not at peak power... But you probably already knew that.

Yup, just looking at the chart the tuner (Dynospot in San Jose) thought we'd get 5-7hp across the board just by getting less fuel in there. I still have a little research to be sure going to a larger MAF is legal for USTCC, though. Otherwise I'll probably try smaller injectors.

[JedzE36/5]

ok so i cant figure it out. turns out my chip was tuned correctly. but i am still running. lean. this leads me to believe it may have been how the fuel system was hooked up. the guy who put the motor in for me just did an S50 swap into his ti and he has about the same air/fuel as i do. so i asked a few questions and the filter is ok, pump from ti is ok, my injectors are not leaking... i did develop a leak right in the old fuel hose near the fuel filter however about 1 week before the dyno run. i am replacing the hose and filter tomorrow. could a small leak cause a significant loss of fuel pressure causing the motor to run lean? this is starting to boggle me... i dont want my investment to blow up.

[J!m]

All the hoses should have been changed as a matter of course...

Anyway, a leak that looks small may be bigger than you think. Change the hoses and try again.

A pressure check at the fuel rail may be a good idea as well. I'm sure the TIS has the recommended pressure...

[andy]

Originally Posted by JedzE36/5

could a small leak cause a significant loss of fuel pressure causing the motor to run lean?

Short answer - YES!

[JedzE36/5]

thanks guys!