I just bought a '97 540i S/C and it has a random fuel problem. Every once in a while (especially after WOT) it acts as if it isn't getting any fuel. I could swear that I've seen a post on these forums about a pump/regulator upgrade kit for this car, but after hours of searching, I've come up empty handed. So if anyone knows where I could get a bigger fuel pump and pressure regulator that is a drop in for the 540, please let me know.
Thanks,
Chris

BTW what is this? it was in a box of stuff the previous owner gave me. He said it was a "fuel sender", an aftermarket unit he removed because the car was getting too much fuel. It looks like a big regulator with an adjustment screw on the side and on top.
Thanks,
Chris

BTW what is this? it was in a box of stuff the previous owner gave me. He said it was a "fuel sender", an aftermarket unit he removed because the car was getting too much fuel. It looks like a big regulator with an adjustment screw on the side and on top.
Thanks,
Chris


LOL, thats a rising rate fuel pressure regulator, you need that installed... goes in line after stock fuel pressure regulator.

Unless your car has software written for it, which is probably does, then in that case you won't need that regulator, in which case I'd be interested in buying it from you.

It sounds like he does have some type of fuel problem.And I wonder why the previous owner had the RRFPR and took it off.

Why not tap a gage into the system and see what the fuel pressure is when this happens. I've seen M6 mechanics do this while working on a mixture problem.

The problem (until a few days ago) only occured when the car was driven hard and until then I thought it was a MAF problem. Now I know what it is, but don't have a fuel pressure guage, so I'll have to go buy one. I'm pretty sure that it's either the fuel pump or the relay. I'm gonna jumper wire the pump tomorrow to figure out which it is.
Thanks,
Chris

It sounds like he does have some type of fuel problem.And I wonder why the previous owner had the RRFPR and took it off.

apparently the FPR was causing a CEL because the car was running too rich at idle and the ECU couldn't lean it out enough.
Chris

Umm, Have we seen this S/C'd 540i?

Any pics? So we can be envious and jealous?

Umm, Have we seen this S/C'd 540i?

Any pics? So we can be envious and jealous?

Here's one :D :stickoutt :

http://www.eurowerkz.com/gallery/album/Jim/engine2_copy.sized.jpg

apparently the FPR was causing a CEL because the car was running too rich at idle and the ECU couldn't lean it out enough.
Chris
That tends to sound like the RFPR wasn't working properly. The whole point of one of those is to keep the fuel pressure normal a low rpm and bump it up at high boost. Since the flow rate through a given open injector is a function of supply pressure your problem could be that the injectors simply can't deliver enough fuel at high rpm (and thus high boost) when run at normal pressure. If the RFPR is working correctly it compensates for that by supplying normal pressure at low rpm and higher than normal pressure at high rpm.

I think what I'd do is to re-install the RFPR and add a gage to the output side. As a guess, the input side should probably be about 15% greater than normal. At idle you should see normal fuel pressure to the injectors and that pressure should rise to input pressure at full boost. If you don't see the change in pressure, or you see too high a pressure at idle a new RFPR would be indicated.

Using an RFPR seems to me to be to be a bit of a kludge for a system that only produces 6-8psi boost. A better approach is to swap out the injectors to ones having a greater flow rate. While more expensive this is what folks like ESS, Dinan, etc., do. As long as the increase in injector flow rate isn't too great the ECU can compensate by using shorter pulses at idle and low rpm.

Assuming that the RFPR was there because the injectors weren't swapped, it might be a good idea to talk to one of the S/C kit makers. They might be able to supply you with a set of larger injectors and the matching ECU code.

That tends to sound like the RFPR wasn't working properly. The whole point of one of those is to keep the fuel pressure normal a low rpm and bump it up at high boost. Since the flow rate through a given open injector is a function of supply pressure your problem could be that the injectors simply can't deliver enough fuel at high rpm (and thus high boost) when run at normal pressure. If the RFPR is working correctly it compensates for that by supplying normal pressure at low rpm and higher than normal pressure at high rpm.

I think what I'd do is to re-install the RFPR and add a gage to the output side. As a guess, the input side should probably be about 15% greater than normal. At idle you should see normal fuel pressure to the injectors and that pressure should rise to input pressure at full boost. If you don't see the change in pressure, or you see too high a pressure at idle a new RFPR would be indicated.

Using an RFPR seems to me to be to be a bit of a kludge for a system that only produces 6-8psi boost. A better approach is to swap out the injectors to ones having a greater flow rate. While more expensive this is what folks like ESS, Dinan, etc., do. As long as the increase in injector flow rate isn't too great the ECU can compensate by using shorter pulses at idle and low rpm.

Assuming that the RFPR was there because the injectors weren't swapped, it might be a good idea to talk to one of the S/C kit makers. They might be able to supply you with a set of larger injectors and the matching ECU code.


I am doing a s/c install on my car and it's 6.5 psi, i was going to find a RFPR but I have 30# injectors to install in place of the 17# injectors stock. Do you think that I could get away with using the injectors without a RFPR?

Originally the car had just the RRFPR, then they added ford racing 30# injectors and that's when the CEL started showing up and Oscar Valez told the previous owner that he needed to lower the fuel pressure to 45-55 lbs. I am absolutely certain that the problem is either the pump or the relay, so I'm gonna replace both, but I really need someone to guide me in the right direction as to what pump I should use and where I should get it from: PLEASE!!!!
Thanks,
Chris

Let's see if i have the sequence right. Originally the system used stock injectors and a RFPR. Then 30lb injectors were installed w/RFPR and the mixture was too rich at idle. So the RFPR was removed and the pressure dropped to the point that the idle mixture was okay. And now you have the symptoms of fuel starvation at full boost.

That tends to suggest to me that:

1) There is a problem with the pump, regulator, or filter that allows the system pressure to fall off at high flow rates. If that's the case it will be very obvious once you have a gage on the system.

2) The pressure necessary to allow correct idle mixture is too low to supply enough fuel at full boost. That would suggest that the 30lb injectors might be too big for this level of boost. The ECU has a minimum pulse width for the injectors and if they are oversized the low speed mixture will be too rich at the pressure necessary for full boost operation. Again, seeing what the system pressure is doing will tell if this is a possibilty.

I seem to remember 24lb injectors being used for BMW systems that used about 6psi of boost, which is what I'd assume you have. You can probably verify that by talking to ESS or one of the other kit makers. I'd also guess that that the ECU tuning needs to match the S/C & injector set up.

Let's see if i have the sequence right. Originally the system used stock injectors and a RFPR. Then 30lb injectors were installed w/RFPR and the mixture was too rich at idle. So the RFPR was removed and the pressure dropped to the point that the idle mixture was okay. And now you have the symptoms of fuel starvation at full boost.

That tends to suggest to me that:

1) There is a problem with the pump, regulator, or filter that allows the system pressure to fall off at high flow rates. If that's the case it will be very obvious once you have a gage on the system.

2) The pressure necessary to allow correct idle mixture is too low to supply enough fuel at full boost. That would suggest that the 30lb injectors might be too big for this level of boost. The ECU has a minimum pulse width for the injectors and if they are oversized the low speed mixture will be too rich at the pressure necessary for full boost operation. Again, seeing what the system pressure is doing will tell if this is a possibilty.

I seem to remember 24lb injectors being used for BMW systems that used about 6psi of boost, which is what I'd assume you have. You can probably verify that by talking to ESS or one of the other kit makers. I'd also guess that that the ECU tuning needs to match the S/C & injector set up.


Actually, the issue is that there is no rising rate fuel pressure in the system. His system is metered on the vacuum side of the blower so it thinks the air is normal... so it's adding fuel according to the MAF on the front side of the blower and its thinking it's normal. However, there is boosted air in there so the system is seeing the MAF airflow at WOT as a normal range of air, but unfortunately the volume going into the motor is higher, you're probably running your car lean without the RRFPR, UNLESS it's got a chip written for it. If you write the software correctly you can tell the ECU to raise pressure and change the pulse for the fuel injectors as RPM goes up to account for forced induction, but yeah it sounds like you are running a stock ECU with no FPR (manual fuel management) and the engine is leaning out at WOT and overly rich at idle.

Actually, the issue is that there is no rising rate fuel pressure in the system. His system is metered on the vacuum side of the blower so it thinks the air is normal... so it's adding fuel according to the MAF on the front side of the blower and its thinking it's normal. However, there is boosted air in there so the system is seeing the MAF airflow at WOT as a normal range of air, but unfortunately the volume going into the motor is higher, you're probably running your car lean without the RRFPR, UNLESS it's got a chip written for it. If you write the software correctly you can tell the ECU to raise pressure and change the pulse for the fuel injectors as RPM goes up to account for forced induction, but yeah it sounds like you are running a stock ECU with no FPR (manual fuel management) and the engine is leaning out at WOT and overly rich at idle.

The MAF being on the atmospheric pressure side isn't a problem. It will simply report a much larger flow rate at boost than the ECU would see without the supercharger. Now that flow rate would probably be "off the map" of a standard fuel map, but the re-tuning that would have to be done for the S/C would take the higher flow into account. And having the MAF on the atmospheric side of the system makes it much easier to get good flow numbers. Were the MAF to be on the pressure side its reading would have to be corrected for pressure and temperature.

A the risk of sounding redundant... There are two ways to compensate for the increased air mass flow (and thus the fuel requirement). One is to use stock injectors and increase the fuel pressure at boost to push more fuel through the injectors. The other is to leave the fuel pressure alone and use injectors with a higher flow rate. In both cases the presumption is that the fuel pump and regulator can supply the higher demand. That may, or may not, be happening here. But a bit of time with a gage will tell.

Using either method it is imperative that one stay within the dynamic range of the ECU. At idle the flow rate through the injectors must remain low enough for the system to set the correct mixture. And at boost you have to have enough fuel flow to keep from leaning out. You really don't want to be running lean at high boost. That's a great way to burn pistons and valves. Since the correct fuel flow translates into injector pulses from the ECU, and since there are minimum and maximum pulse widths, you can't push the pressure too high or use too large an injector just to satisfy the boost requirement without screwing up the idle mixture.

A good S/C kit will be a matched set of parts and ECU tuning and that requires lots of engineering time on a dyno with all of the instrumentation in place. Recovering that engineering time is what makes a good S/C kit expensive. Since this car has diverged considerably from the original design (and I don't know that we know that it was originally done correctly), it would make sense to me to talk to someone that has done the engineering correctly. Most of a good kit is already on the car and it may be possible to get the right injectors and matching ECU code from a good kit supplier. To me that makes more sense (unless you happen to have a dyno and fast response EGA handy) than trying to second guess the overall system by just fiddling with components.

Again, the problem is that the fuel pump is bad. Initially the car only had a problem after the pump had been put under load. Now it is constant, sometimes it won't even start and if it does, it will only idle/ no more revs than that. So my question is: What fuel pump should I replace it with????? and where do I get it from?
Thanks,
Chris

An OEM pump should work fine as a replacement. While I've never heard of one failing in such a manner that it would still run but not produce enough pressure/flow I suppose it could happen. The usual failure for a BMW fuel pump is a total failure where it won't run at all.

Again, the problem is that the fuel pump is bad. Initially the car only had a problem after the pump had been put under load. Now it is constant, sometimes it won't even start and if it does, it will only idle/ no more revs than that. So my question is: What fuel pump should I replace it with????? and where do I get it from?
Thanks,
Chris

Have you heard noise from your trunk area?That is an indication your Fuel pump is going bad.But then again on my 535i it has been noisy for 3 years.

I don't hear any sounds at all. I'm gonna remove the rear seat and hook a volt meter to the pump while driving and see if I can find a power drop.
Chris

Have you heard noise from your trunk area?That is an indication your Fuel pump is going bad.But then again on my 535i it has been noisy for 3 years.

What pressure do you see at the injector rails? You have checked that by now, right?

Here's one :D :stickoutt :

http://www.eurowerkz.com/gallery/album/Jim/engine2_copy.sized.jpg

Not yours!

Besides, is your upgraded S/C in yet?

I won't believe until you let me drive it...... :D

okay, well it isn't the fuel pump. Now I'm starting to think that it is something major like the ecu. I hadn't driven the car for 3 days and decided to remove the fuel pump relay and replace it with a jumper wire to run the pump. The car ran amazingly, I thought the problem was cured. I drove the car around for about and hour and a half. Parked it at work. Then on my return trip, after about 20 minutes, it started acting up again. First it felt like the car was going really lean, then the motor stopped running and the ASC light came on. It took about 2-3 minutes to restart and even then it would only idle, if you depressed the accelerator it would stall. Then the Service light came on. finally the car restarted and was fine for about 3 minutes and then it started going through it's fuel starvation routine. I have not yet checked the fuel pressure b/c I can't find anyone that sells an inline tester in my area. As soon as I do, I'll hook it up. But it seems like either the TPS is toast and telling the motor that the T/B plate is closed, or the injectors are not getting a signal any longer.

BTW: does anyone know of a really good bmw tuner on the east coast that can also write ecu software if that is the case? ERT made the supercharger and installed it, but I can't find anything about them anywhere.

Thanks,
Chris

Try NickG.He used to be a FI mod. and now runs TT.

Since you had a service light there'll be a stored fault code. Knowing what the code is might help in figuring out what's wrong.

Get yourself an A/F gauge to see how the car is running...

Since you had a service light there'll be a stored fault code. Knowing what the code is might help in figuring out what's wrong.

Can I jumper a wire and get the light to blink or do I need to buy a BMW code scanner?
thanks,
Chris

I hooked a fuel pressure tester up to the car today and found that it was running 67lbs at idle and would continue to push that even after the car died. I was using a jumper wire in place of the relay. I guess this eliminates the pump, but I think the next step is pop in a noid light to see if the injectors are still getting a signal. My money is on no, I think the ecu has taken a crap.
Thanks,
Chris

If that's what you measured at the injector rails it's probably too high. Certain Motronic systems used 55-61, but the other BMW systems are either 43 or 48. If I recall correctly you've got a BMW FPR in and none of them should run that high a pressure.

Maybe the current problem is that you are flooding the engine from excessive pressure. That's easy enough to find out. Try cranking the engine and if it doesn't start pull a plug or two from both banks and see if they are wet with gas.

I measured this on the fuel line going to the motor. it runs along the fender. This is the hose my manual said to tap into. It also said the pressure should be between 45 and 75psi. Besides, the car will start up and run fine at the 67psi, but every once in a while (maintaining the typical fuel pressure) it will die completely, feeling like it is leaning out on it's way.

If that's what you measured at the injector rails it's probably too high. Certain Motronic systems used 55-61, but the other BMW systems are either 43 or 48. If I recall correctly you've got a BMW FPR in and none of them should run that high a pressure.

Maybe the current problem is that you are flooding the engine from excessive pressure. That's easy enough to find out. Try cranking the engine and if it doesn't start pull a plug or two from both banks and see if they are wet with gas.

I believe what you measured is the raw output from the pump, and it could be that high, or higher. The more important measurement is at the injector rails after the pressure regulator.

I took the car to Tischer BMW about a month ago, they decided the intake manifold gaskets were bad ($1000). I had them replaced and the codes reset. When I picked the car up, it started w/ the same problem not 10 minutes after I left Tischer. I then drove the car back to the dealer, had the tech go for a ride with me (of course it acted fine the entire trip) and then went on my way. The car was totally fine for about a month, now the problem is back and every bit as severe.

Sorry to hear that.That is what I hate about dealers.It is not that they try and openly rip you off,they try and find the most expensive money making way to solve an issue.I would find someone in Ala.(used to live in Dothon :) )
or even Fla. who has experience in S/C BMWs.

I'm moving to Miami this fall (that's the only reason I haven't junked this car) and am well aware of how many tuners there are in that area. Unfortunately, I have to sell my supra in order to buy my house in Miami, and I can't sell the supra unless the beamie works or I'll have to buy a temporary beater car which I'd hate to do. I'm just curious as to why the car worked for a little while and then stopped.