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Discussion Starter · #1 · (Edited)
For some time now, I've had a throttle that was less than smooth. Unless I would apply the throttle very gingerly, the engine response was jerky, almost as if the butterflies were opening slowly, then suddenly opened a large amount. It made driving difficult, especially around town or in traffic when transitioning from small throttle opening to moderate. The power at WOT seemed OK, though. I chalked it up to similar reports on this board following the ECU reflash campaign (to correct a problem with the ability of the ECU to communicate with certain smog checking equipment), and/or the US throttle map, which people suspected had less than optimal mixture spots in it as compared to its EU counterpart. Basically, then, I was resigned to live with it. It was not "bucking bronco" bad, mind you, just not fun to drive. Perhaps on a lighter car the effect would be worse, but the M5 is fairly heavy and has a refined drivetrain, which probably ameliorated the issue to some extent.

Fast forward to last month. As my odometer turned past 114k miles, I started to worry about my fuel pump giving out and stranding me unexpectedly. I use my car as a daily driver and I wanted to minimize the chances of this happening to me. I have seen reported failures of fuel pump on this board happening around the 100k mark, so I figured I was on borrowed time.

I thus had the fuel pump changed recently. This is no small expense. The part itself is quite expensive and there is obviously some labor involved. I did not want to do this myself due to the inevitable fuel spillage and fire risk.

To my surprise, there was an immediate improvement in driveability. Throttle inputs now are smooth, no matter how quickly or slowly I open the throttle. There is more seat-of-the-pants feeling mid-range torque. The engine responds smoothly, more strongly, and has returned to being a pleasure to drive. I theorize that my old fuel pump, while it had not gone bad as in non-functional, had been marginally performing and possibly erratically delivering pressure or providing low or less than optimal pressure.

I had a similar experience with my M3, a far newer car which exhibited similar, though greatly worse symptoms that my tech could not track down at first. Like that car, there were no codes thrown, but the driveability definitely suffered. Having eliminated all the other possible causes, I insisted my tech/dealer change the fuel pump. Even though the car at the time was still under warranty, I offered to pay for the job if the swap did not solve the problem. Turns out I was right; a pump swap solved the problem. To their credit, though I suggested the fix, the dealer insisted they would pay for the work even if it turned out I was wrong.

Like the other car, my M5 did not exhibit any symptoms other than the less than smooth throttle response. It threw no codes. It started fine and ran fine, and accelerated strongly at WOT. If you are experiencing driveability issues and have high mileage, consider a fuel pump change. BTW, I changed the fuel filter not all that long ago (15-20k miles ago, maybe), but swapped in a new one anyway with the fuel pump change. I doubt the improved throttle response was due to the filter change alone. I hope reporting this experience helps others. If you experience similar problems and results, please post them. :M5launch:
 

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Glad to hear the problem is solved, but a couple of hours to install a fuel pump? That seems excessive. I can have the fuel pump out of my car in about 5 minutes.
 

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I have seen a number of reports on the board about fuel pumps causing strange things to happen.
Coupled with reports of fuel pumps failing at 100k-120k miles, people should start considering pro-active replacement of the fuel pump.
I changed mine last year at 90k miles as preventative maintenance. Where the car ran fine before, it seemed to run better after. The fuel flow readout on the dash also went up 5 L/H.

I think the fuel pump is an easy DIY, there are a couple write-ups here on the board. No special tools are needed, don't have to get under the car, if you are careful, you won't spill any fuel, and unless you have a Marlboro dangling from your lips as you pull the pump out of the tank, there really is no fire danger.
 

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Interesting... I too noticed that the throttle can be a bit jerky especially at low speeds. I figured this had mostly to do with the ECU mapping as the other M5's I test drove seemed to feel similar. How much was the fuel pump? Are there any upgrade options?

Thanks
-- Ed
 

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Need4spd - did the car seem to be getting worse over time with regard to the throttle jerkiness? I just can't believe these cars were like this from the factory (I would be one PO'd dude if I had dropped $70K on a car that had this issue!)

(EQTuning - GetBMWParts has the pump for $346 - not cheap, but not as painful as some parts for these cars)
 

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Discussion Starter · #6 ·
The throttle response thing kinda snuck up on me. The throttle wasn't always jerky. I'm sure it got that way over time. The pump itself was just under $400 with a BMWCCA discount.
 

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Thanks for the report. My car seems to have recently become more touchy with the throttle too (58k miles on it), and I know it wasn't like that in the past (into year 8 with it now). No codes. Does over 140L/h corrected, runs like a beast should at WOT. This thread has me wondering now if I should swap in a new pump...

Thanks,
Chuck
 
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I've had this on the list for a while. I've posted previously that on my previous car, a Fiat Coupe 20v Turbo, I had some odd running issues. Research (using the Search feature :applause:) showed it to be likely down to a fuel supply issue, somewhere. I therefore resolved to revamp the fuel system, and did : fuel pump (uprated Walbro 255, it did benefit that car over standard when going up in power), fuel pump power supply fix (taking the power feed for the pump from an alternative direct 12V feed, that meant the pump actually got a full 12V feed), reconditioned injectors, showing an even, proper flow over all 5, fuel filter, fuel pump relay, just in case, and a couple of wiring mods where things could go Pete Tong, especially the 'yellow' connector... I had all the hosing checked and connections remade but there was nothing to note.

The result was a car that felt very different, in all manner of driving, throttle response, city driving, WOT, the lot. Was very happy with it.

When I had my new battery, I was sure the car felt better from a jerky response PoV. I put this down again to the pump getting correct voltage and supplying the correct flow, but then this car has so many bits and bobs that depend on correct power supply, I might have been well off on that.

Looking at doing the same sort of thing for the M5, once it's done, it will last for the time I have the car, I would have thought.

Many thanks for the feedback on the pump, good to know it can make a discernable difference, and that it should be a reasonable DIY :goldcup:
 
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$346.98 at Tischer (getBMWparts.com)

Item Number MSRP Core Price Price
16146752369 $433.72 $0.00 $346.98

Fuel system - Fuel supply - Fuel pump
Fuel pump, m5 2000 - 2003
 

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I have a Walbro in mine, but my car isn't exactly stock ;)
 

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Discussion Starter · #14 · (Edited)
I did not do the MAFS test before or after, as I wasn't really expecting any improvement. My main reason for the swap was to reduce the risk of being stranded somewhere with an inop pump. I did not notice any idle irregularities before the swap. The improvement in driveability and mid-range torque was a bonus, and somewhat unexpected until I thought back about my experience with the M3. Strong, adequate flow volume is key, I think. Bottom line is that if your car is at around 100k miles and you have no plans to sell the car any time soon, it would not be a bad investment to replace the fuel pump and filter (the latter of which does result is some fuel spillage, so if you DIY, be sure you don't have any open flames or sparks in your garage (like in your water heater)). You access the fuel pump from the back seat, but the filter is under the car.
 
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Tech day at Brian's?! I'm sure this would be a good piece to replace on my car with 104k...
Yep, sounds like a plan, and after we bugger up your car and make all the mistakes we can, we can then do the pump on mine. :)
 

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Which walbro? Does it drop in? I have a bunch of them on the shelf here ;).

-- Ed
IIRC, GS340.

Not quite drop in, but no real fabrication required either. I removed the housing that the stock pump fits into and used a hose clamp to secure the Walbro to the rest of the frame. It is hard to describe, but you will understand when you get in there. It isn't as pretty as the OEM part, but it flows a lot more and the price is right. I am considering dual pumps, since I am maxing out one with a Boost A Pump, but that is OT for this thread ;)

There was a pinhole leak in the hose that goes from the pump to the "cap" that attaches to the top of the tank (it was causing fuel pressure to bleed off when the car was parked) so I had to take it all apart to repair that after the fact.

I would imagine that you have plenty of those in stock :) I just bought another one for a friend's STi.
 

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Sounds simple enough. You should see what we have to do on the 08+ STI's to get those suckers to fit!

Anyone know the flow rating of the stock pumps?

Thanks
-- Ed
 

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