Fuel pump location e28, early model, rhd

[Kodachrome 151]

Before it's suggested, this Model does not have it located beside the fuse box in engine bay!! 

 

Im actually running an M54b30 in it and I just put an AEM fuel pump (online type) in it. This worked but struggled to start so I added the supplied AEM check valve. And that's when problems arose! Car cut out about 5min from home. Got it towed back and found :

 

- no power to pump

- Fuse 4 was blown. This fuse is not associated with the fueling anywhere I've read.

I had replaced it with one of those cheap plastic bodied bullet fuses..actually fuse had not blown but plastic got soft and scorched. 

- replaced fuse 4 and engine fires right up! 

 

But why did it blow? Overcurrent, overheated fuse. Temp on fuse is 91c if left idling. The ceramic fuses don't melt.. but the fuse box was getting hit and sticky! 

 

Voltage at pump is 8.4v, which means Amp current is way higher than the 11amps this pump is rated for and high current is high heat. 

 

Tried running a second ground wire to pump.. No change. The only other thing I can think of is to run new wires straight from battery via my own relay. Or check the exiting isn't but to do that properly it would be good to know where the pump relay is on this 1983 M30 525i

 

 

Before it's suggested, this Model does not have it located beside the fuse box in engine bay!!

 

Im actually running an M54b30 in it and I just put an AEM fuel pump (online type) in it. This worked but struggled to start so I added the supplied AEM check valve. And that's when problems arose! Car cut out about 5min from home. Got it towed back and found :

 

• no power to pump
• Fuse 4 was blown. This fuse is not associated with the fueling anywhere I've read.

I had replaced it with one of those cheap plastic bodied bullet fuses..actually fuse had not blown but plastic got soft and scorched.

- replaced fuse 4 and engine fires right up!

But why did it blow? Overcurrent, overheated fuse. Temp on fuse is 91c if left idling. The ceramic fuses don't melt.. but the fuse box was getting hit and sticky!

Voltage at pump is 8.4v, which means lots of resistance in that circuit and presumably high amps and therefore heat. 

Tried running a second ground wire to pump.. No change. The only other thing I can think of is to run new wires straight from battery via my own relay. Or check the exiting relay isn't broken. To to do that properly it would be good to know where the pump relay is on this 1983 M30 525i!?

Before it's suggested, this model does not have it located beside the fuse box in engine bay!!

Im actually running an M54b30 in it and I just put an AEM fuel pump (inline type) in it. This worked but struggled to start so I added the supplied AEM check valve. And that's when problems arose! Car cut out about 5min from home. Got it towed back and found :

no power to pump
Fuse 4 was blown. This fuse is not associated with the fueling anywhere I've read.
I had replaced it with one of those cheap plastic bodied bullet fuses..actually fuse had not blown but plastic got soft and scorched.

- replaced fuse 4 and engine fires right up!

But why did it blow? Overcurrent, overheated fuse. Temp on fuse is 91c if left idling. The ceramic fuses don't melt.. but the fuse box was getting hit and sticky!

Voltage at pump is 8.4v, which means lots of resistance in that circuit and presumably high amps and therefore heat. 

Tried running a second ground wire to pump.. No change. The only other thing I can think of is to run new wires straight from battery via my own relay. Or check the exiting relay isn't broken. To to do that properly it would be good to know where the pump relay is on this 1983 M30 525i!?

Edited November 28, 2022 by Kodachrome

[jon dee 500]

That pump is rated to over 1000hp so if you are making 250hp (or something similar) the pump is WAY TOO BIG !!! Neither the factory fuel lines, fuel pressure regulator or pump wiring will be adequate to handle what that pump can deliver. I can't guess how many amps it will be drawing, but if the supply is down to 8.4 volts the current draw will be about 50% higher than it would be if you had 12.5V at the pump. 

Sounds like the fuse was right on the verge of blowing before you put the check valve in line, and the extra bit of added resistance to flow was enough to finish it off. I think that you can count yourself lucky that your car didn't burn to the ground  

You need to find a pump with a flow rating more appropriate to the flow your engine needs. If you think you have 250hp then get a pump rated at 300-350hp, that will be all you need and the factory lines, wiring etc MAY be able handle the load. 

Cheers... 

[Kodachrome 151]

Quote

 

Hah... maybe but I didnt think it was all that big power wise or that you could really go too big. Its rated from 35PSI to 70PSI and yeah, upto 1200hp... but crap maybe you are right.

Its this one specifically: 

https://www.aemelectronics.com/products/fuel-delivery/high-flow-fuel-pumps/400lph-metric-inline-high-flow-fuel-pump

Current Draw (40 psi): 9.73 amps no check valve, 10.68 amps with check valve (13.5v)

I also was of the view that the current would climb as the voltage dropped, but elsewhere people are saying no, current would drop if voltage drops because the (electrical) resistance is the same. But clearly, from experience if you restrict a pump/motor it gets hot and trips switches.  Their own diagram suggests amps should be way lower at 40psi.. but perhaps thats irrelevant as its being so restricted. To further complicate matters, the M54 engine is returnless, as in no fuel returns from engine but instead is recirculated right at the fuel filter (beside pump) back to tank, regulated by the integrated FPR. Which, to my mechanics shame wasnt connected properly which was of course my core problem with the other (also aftermarket) pump. Which Im thinking due to your post will be going back in tomorrow morning.

 

[jon dee 500]

Some useful information here.... https://help.summitracing.com/app/answers/detail/a_id/5245/~/what-size-fuel-pump-do-i-need%3F 

The 400lph pump wants to push 400lph down the pipe and if there is no more than 40psi backpressure it will draw 10.68amps. However, if you are utilising the factory fuel lines and bypass regulator sized for less than (say) 115lph, then having to pass more than three times as much fuel is very likely to be creating quite a bit more than 40psi backpressure. Your pump is now a fuel heater recirculating all that excess fuel back into the tank and drawing more amps than expected. 

The pump motor will be a series wound DC motor and and is rated to deliver a certain amount of power (Watts) at 12.5V. So long as the power demand (load) stays constant, there is an inverse relationship between amps and volts. As the volts go down the amps will go up, and vice versa. 

Cheers...

[Kodachrome 151]

Thats true and I agree generally, though in this implementation the excess fuel recirculates back to tank right at the filter. There is no long round trip to the fuel injectors and back. Also its unlikely my car is delivering the correct voltage anyhow, ignoring the scenario where resistance/load was causing voltage sag, Im pretty sure measured voltage when running is barely 12v which will be way down on the best case 400LPH figure.

Ive found other people complaining about AEMs Check Valves and I pulled it out this morning. There is no way I installed this correctly (it must be designed to be mounted into something, has banjo bolt holes etc) as I just plumbed it in as per normal check valve and fueling. As per complaints, its crazy restrictive too, 1.5mm opening and a stiff spring valve to open afterwards. 

 

The fact that even with the pump basically choked (/pressure must have been through the roof), nothing ruptured or popped off (noting these is just fuel hose o-ring tied to the ends of fuel rails and pump), Im less concerned now about this pump in this application.

 

 

 

Edited November 28, 2022 by Kodachrome

[jon dee 500]

Give it another go without the check valve. Keep an eye on the electrical wiring, fuses and relays associated with the fuel pump. If any of them get hot to touch then they are either faulty or overloaded. If you can lay your hands on a clamp meter try and get a reading on just what current the pump is drawing. 

The pump motor uses fuel as a cooling medium, so every time the fuel circulates thru the pump and back to the tank it picks up heat. In itself that is not a big deal unless you are racing and want to keep your fuel temperature down.

That check valve is most likely intended to be used in the fuel line to the rail, possibly screwed into the outlet of a fuel filter installed next to the engine. Even so, a 1.5mm orifice is tiny, and whatever pressure drop is caused by the spring would be dropping the rail pressure by an equivalent amount while the engine is running.  

Personally, I would not use anything branded by AEM. 

Cheers...

[Kodachrome 151]

Thanks again, I'm of two minds still despite what I said. Noted on AEM, this is the second pump as the first (more appropriately size, in tank version) was dead on arrival. I had only loosely knew the brand from years ago when they had a better rep. I got this model as "an upgrade" from the faulty one. 

 

On the plus side, the m54 is on 3.5bar, so over 50psi, so the delta isn't as big as feared. 

[Kodachrome 151]

Ok, so tested without check valve installed:

 

- 10.05v at pump (vs 8.3v with valve.. so a significant reduction in load on pump). 11.8v in the car on the USB adapter thing with the volt display (same fuse circuit), so the volt sag due to load is 1.75v.. which isn't terrible sounding.

- 55c when idle on fuse (which ironically is worst case scenario for this circuit due to high load on pump via resistance) vs 91c+

- Drove it around in a mix of fast and slow and steep hill climbs etc. Runs so nice now. Temp on fuse is 42c after driving (and therefore has more airflow and less resistance in circuit.

 

So.. maybe all is well? If I just remember to let the pump prime before cranking, maybe the lack of check valve wont be that annoying?

 

PS: I definitely need an amp clamp!  My multimeter has an amp mode but Im always afraid to use it as last time someone demo'ed it to me there were sparks..

Edited November 29, 2022 by Kodachrome

[jon dee 500]

At that kind of boost I would expect you to have a pretty sophisticated fuel management system and a programmable ECU to keep your AFR's safe !!! Your FPR should be manifold pressure compensated to maintain constant pressure at the injectors, which means adding 2.5bar to the standard 3bar injector rail pressure i.e. 82.5psi at the pump at full noise plus whatever losses occur in the lines. Bear in mind I don't know anything about your engine and am just quoting figures for old school boosted Jap engines   

I believe return-less systems may operate at a higher rail pressure, something like 65psi, so probably easier to compensate. 

In tank pumps usually have a check valve built-in to prevent drain back. In the case of return-less systems the check valve helps to prevent hard hot starting by maintaining pressure in the rail to reduce the chances of vapor-lock after the engine is turned off. 

Cheers...

[Kodachrome 151]

Sorry to clarify, it's on 3.5 bar fuel rail pressure, not boost.. Which would indeed be spectacular! 

[jon dee 500]

37 minutes ago, Kodachrome said:

Which would indeed be spectacular! 

I was thinking that also... hahahahah   Compound turbos on diesel pickups trucks are all the rage in the US . Go well on the dragstrip but I don't know that they would make much of a daily driver though. 

Cheers...