M54 Loss of power

[clarko74]

Morning all,

My M54 swap is now up and running and was MOTed last week. I have driven over 100 miles in it now and while it is fine most of the time I have noticed that it does occasionally seem to lose power, especially if I am driving up a hill. Changing down a gear seems to make no difference when this happens it struggles to maintain speed to the top of the hill. When I get to the top it sorts itself out and power returns.

I am thinking this is a fuelling issue and given I have never replaced the fuel pump in the 15 years or so I have had the car thought I would as a precaution. My E30 is a prefacelift with the fuel pump is located on the left hand side in front of the rear wheel.

Upon removing the existing pump I have realised that the original fuel pressure regulator is also located here. As my E30 originally had an M20B20 I am assuming that this is a 2.5 bar FPR. I did not realise this was there and as part of the M54 install have fitted another FPR, a 3.5 bar one, in the engine bay below the fuel filter. So my question is could having two FPRs be the problem with the fueling and the cause of this loss of power? I assume as I now have the 3.5 bar one that I can get rid of the original 2.5 bar one in the back? The ETK calls it a damper but the FPR in the front will be all the dampening if pressure required won't it?

I can't work out in my head if having a lower pressure FPR and then a higher one will make any difference but I can't imagine it's good to have two of them and it fitted and they may be restricting the flow of fuel? Am I doing the right thing by getting rid of the old one?

[flybynite]

I can't work out in my head if having a lower pressure FPR and then a higher one will make any difference but I can't imagine it's good to have two of them and it fitted and they may be restricting the flow of fuel? Am I doing the right thing by getting rid of the old one?

Well done getting it on the road I would hope Dan would be along with a definitive answer but my take is to simplify it as much and replicate the M54 fuel supply.

Has yours got the dual pumps like my 323i? My first thought would be to bypass the external pump and FPR, see how it runs then put somthing like the Walbro pump in the tank if it needs it. Should be easy enough to try with a straight piece of pipe.

If the tank is only supplying 2.5 bar to an engine needing 3.5 it may be the pressure is dropping below what it needs to run especially if it is fighting gravity. Worth a try.

My plan was to put a walbro in the tank of my FL and hopefully be done with it but that obviously only has 1 pump.

[DanThe]

Definitely get rid of the old FPR as it will be restricting pressure to the front

[clarko74]

I thought that was the case but just wanted to make sure. Cheers Dan.

[clarko74]

I can't work out in my head if having a lower pressure FPR and then a higher one will make any difference but I can't imagine it's good to have two of them and it fitted and they may be restricting the flow of fuel? Am I doing the right thing by getting rid of the old one?

Well done getting it on the road I would hope Dan would be along with a definitive answer but my take is to simplify it as much and replicate the M54 fuel supply.

Has yours got the dual pumps like my 323i? My first thought would be to bypass the external pump and FPR, see how it runs then put somthing like the Walbro pump in the tank if it needs it. Should be easy enough to try with a straight piece of pipe.

If the tank is only supplying 2.5 bar to an engine needing 3.5 it may be the pressure is dropping below what it needs to run especially if it is fighting gravity. Worth a try.

My plan was to put a walbro in the tank of my FL and hopefully be done with it but that obviously only has 1 pump.

Cheers, my thoughts were to simplify it as much as possible too. To be honest I don't know if I have two pumps, I know that I have a 55l tank and definitely have the external pump next to the tank. I'm going to change the pump, filter and get rid of the original FPR and see if that sorts it out.

[clarko74]

I can't work out in my head if having a lower pressure FPR and then a higher one will make any difference but I can't imagine it's good to have two of them and it fitted and they may be restricting the flow of fuel? Am I doing the right thing by getting rid of the old one?

Well done getting it on the road I would hope Dan would be along with a definitive answer but my take is to simplify it as much and replicate the M54 fuel supply.

Has yours got the dual pumps like my 323i? My first thought would be to bypass the external pump and FPR, see how it runs then put somthing like the Walbro pump in the tank if it needs it. Should be easy enough to try with a straight piece of pipe.

If the tank is only supplying 2.5 bar to an engine needing 3.5 it may be the pressure is dropping below what it needs to run especially if it is fighting gravity. Worth a try.

My plan was to put a walbro in the tank of my FL and hopefully be done with it but that obviously only has 1 pump.

Cheers, my thoughts were to simplify it as much as possible too. To be honest I don't know if I have two pumps, I know that I have a 55l tank and definitely have the external pump next to the tank. I'm going to change the pump, filter and get rid of the original FPR and see if that sorts it out.

[clarko74]

I sorted this out a couple of weeks ago so thought I should let eveyone know to close this thread off.

I removed the second FPR and installed a new fuel pump, it was slightly better but was still running very rough. I swapped the coil packs over from my E46 and checked the spark plugs (which are new) and all seemd to be well. then I checked the lambda sensor wiring and discovered I had them plugged in the wrong way around, swapped these over and all is well.

It's running beautifully now, and is considerably faster than my E46, I suppose lighter weight, no cat and a lightened single mass flywheel all help. It also has loads of torque which is a bonus.

[flybynite]

I sorted this out a couple of weeks ago so thought I should let eveyone know to close this thread off.
I removed the second FPR and installed a new fuel pump, it was slightly better but was still running very rough. I swapped the coil packs over from my E46 and checked the spark plugs (which are new) and all seemd to be well. then I checked the lambda sensor wiring and discovered I had them plugged in the wrong way around, swapped these over and all is well.
It's running beautifully now, and is considerably faster than my E46, I suppose lighter weight, no cat and a lightened single mass flywheel all help. It also has loads of torque which is a bonus.

Result! Well done, glad you found the issue, new fuel pump is never a bad thing to do and you know you have a good spare.

Nice to have it on the road for the summer