Z3 Roadster (E36/7) I have a fuel pressure (or voulme) problem :-( - Bimmerfest - BMW Forums

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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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Old 08-02-2012, 02:33 PM
refacer refacer is offline
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Location: buffalo, ny
Join Date: Jun 2012
Posts: 6
Mein Auto: 2001 m roadster
I have a fuel pressure (or voulme) problem :-(

Hi, I'm Dave.
Sold my 04 Mazdaspeed MX5 (had it since new) and my 01 S2000 uber-turbo (completely unstreetabe..lol) and got me a 2001 z3 M roadster from a deceased surgeons wife locally. She has a 911 and a Benz crossover, and said she won't drive the M roadster because it would mess up her hair. Saw the add, and said "I'll sell the other cars later, but had to jump on this one. The price was right (less than I sold the 28k mile miata for) It certainly has been a love love love love -hate relationship. I love it more than any previous roadster I ever owned, but with 80k miles on it, it keeps giving me little problems I can fix, and a few I am not so sure of. I replaced the Rear shocks and RSMs, the brakes, rotors, oil and filter (I hope it goes 15k miles on that stuff! not a cheap oil change!! lol. Fuel pump, fuel filter, put in a remote door locks on the cheap (cost less than 30.00 with 2 remotes) I will post it later once I find out If it ever had a remote to begin with, because it does unlock ALL doors and trunk when you turn the key on any door). My goal is to put it back in great up to date level of maintenance. It looks great, and drives even better after I got rid of the squealing fuel pump and replaced the RSMs.

I don't know where to post my problem, so I'll put it here as well as in the Z3 section.

I'm a weekend mechanic with a bunch of tools, but not much BMW experience.
My 2001 bmw z3 M roadster will not start (right away) after sitting for even only 15minutes or so. I changed the fuel filter, and fuel pump assy. (500-1000 miles ago. it was making some sick groans on startup, and whirred verrry loudly always) when turning the key, the 5 second 'pre-pressurize' doesn't seem to be enough to pressurize the system. If I try 6 or 7 time it will sputter for a bit , then run. But if I hold the key in the starting position, but
do NOT press the clutch in, it will run the fuel pump for as long as I want, so I do that for 20 seconds, and it will start right up. I suspect a leak down of some sort (or does it always go pressureless when shut down?) , or a really weak fuel pump (it is no-name aftermarket, on the cheap side (78 bucks with adapters). I already failed with a denso, because it was nowhere near a "match" to the bmw, and came with no fitting kit. ($129.00). I replaced fuel pump gasket with new, put it in correctly (gasket first), and tightened unit down with the special wrench. Worked perfect for 1000 miles, now just won't start instantly like it used to. also went back and installed copper ring gasket on the filter at the regulator (OEM) I had forgotten the first time, and make sure there are no leaks I can see whatsoever.. again, does it always depressurize when shut down?

Is it time top pull the pump again? my car's tank is always full when this happens!

Thanks for putting up with me and I love reading all the stuff I find Here. AND I LOVE MY BMW. Finicky, but no worse than my wife of 30-odd years!
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Old 08-04-2012, 02:25 PM
tonywintn tonywintn is offline
Drivin' the dream
Location: Tennessee
Join Date: Jun 2009
Posts: 187
Mein Auto: 2005 BMW X5 & 2007 Z4 si
Three things in the fuel system that can cause rapid leakdown of pressure: 1) leaking pump check valve, 2) leaking fuel pressure regulator and 3) leaking fuel injector. Item one is the most common issue, but since you changed the fuel pump, perhaps the regulator is not sealing properly when you shut off the engine. Item 3 you will know about because the engine would idle rough at first and blow black smoke. Worse case, a leaking fuel injector can hydraulically lock the engine. If the system leaks down due to a leaking checkvalve or regulator valve, it can take up to 8 seconds to reprime and pressurize the fuel system. In a tight fuel system it takes no more than half a second to reach system pressure. If pressure is down when you start cranking, you will miss the enrichment cycle of the fuel injectors (like choking the engine) and the engine will not start until you key off and make a restart attempt to catch that enrichment cycle. If you bought a pump that has too little flow, the car will start ok. The problem of a low flow pump will be pressure loss at high engine speed/torque. That will cause a lean condition and can lead to catastrophic engine failure.

2007 3.0si w/Sport Pkg, Navi, Leather, Strut brace, garage door opener and delete airbag warnings on sun visors
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Old 08-05-2012, 11:01 AM
refacer refacer is offline
Registered User
Location: buffalo, ny
Join Date: Jun 2012
Posts: 6
Mein Auto: 2001 m roadster
Smile thanks for the answer

Thanks, Tony for the great answer. I thought about the regulator, because I did have it off the car when I was screwing on the new filter, and thought it might have something to do with it. The old filter was soooo plugged that it took over 5 lbs pressure just to push gas through it (measured it with my air compressor and a rubber tipped blow tip set tp 0 then upped the pressure 1 lb at a time till the gas in the old one squirted out) .
I ordered the OEM pump complete assembly, and will get it by tuesday, 8/11. I'll throw that in and check again, but wouldn't be surprised if it's the regulator.
I just needed someone knowledgeable to guide me to the next "improvement", as I explain it to my wife!
I likely did not NEED the OE fuel pump, gas gauge complete unit, but @ 230.00 less 5% shipped, I really couldn't go wrong.
Found it here, and talked to the guy, Michael, for 1/2 hour. very knowledgeable guy.

I'll plan on the regulator being bad also, since it happened quickly, and within a short time after changing the filter.

I really appreciate the help.
I assume the injectors ar ok, because when it does catch, the engine runs fine, but seems a bit lean for the first 10 seconds, and will restall if I don't keep a bit of gas on for 15 seconds or so till the engine warms a bit. So it is still lean enough to struggle for 5-10 seconds after start, not an overfill situation.

I can hardly wait to get everything back together again. Drove it 100 miles yesterday, but always had my fingers crossed that something wasn't failing and was ready to strand us..

Thanks again. I wouldn't have figured the regulator on my own, without someone suggesting agreeing.

Last edited by refacer; 08-05-2012 at 11:09 AM. Reason: adding signiture photo
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