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Bad fuel-pump symptoms?

87K views 34 replies 14 participants last post by  Archbid  
#1 ·
Hi. I have an E46 325i that is "idle-hunting" The idle goes up and down. I've replaced and checked alot of different things to fix this such as Vanos seals, DISA-valve, intake boots, ICV and some more parts, but I haven't been able to solve it.
Now I'm suspecting a bad fuel-pump. But what would the symptoms of this be and could it be my problem? I've been reading a bit online and what tells me this is NOT the problem is that it should be hard to start. Which my car is not, in fact it always starts really easy even in cold weather. Could it still be the bad fuel pump?
The engine seems to start idle-hunting when it is allowed to drop from high RPM and high load to a low RPM and low load(Clutch engaged at redlight for example). But also when idling fine and a little load is added such as when the headlights or AC is turned on and the generator puts a little load on the engine.

Any help would be greatly appreciated! Thanks
//Benjamin
 
#5 ·
As someone who had a fuel pump failure recently, I don't think that's your issue. Actually, I sometimes get idle hunting on a cold start (goes away when warm), but after my fuel pump failed and I replaced it with a new one, that hasn't changed.

My symptoms were that the car would occasionally not start on the first attempt at cranking. The odd thing was that it would not start no matter how long I cranked, but if I stopped and tried again, it would fire up instantly, even if the first attempt only turned over once. Eventually it left me stranded and wouldn't run again with any amount of cranking.

Have you tested for vacuum leaks?
 
#6 ·
no it does not sound like the fuel pump. and if that one fool comes in immediately saying it is with usual fearmongering you tell him to tell boogeyman stories somewhere else. :slap:

sounds like a vacuum leak. it’s the most common for this issue.
have you done the smoke test to check for leaks?

what’s the status of your MAF sensor?
 
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#9 ·
Yes I've done smoke test which showed no vaccum leaks. My MAF is good, I think. I think this because I have no faultcode on it and also the problem remains when I remove the cable from the MAF. Although when I first scanned the faultcodes I had one on it, but after clearing and driving for many miles it never came back. And is still not back. However if you think it can be the MAF anyways please tell me how
 
#8 ·
1) Low fuel volume
2) A lack of power under load
3) An engine that dies after driving a while
4) An engine that is hard to start
5) An engine that will not start
6) A check engine light, with a lean code
7) A whine noise from the rear of the vehicle
 
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#11 ·
Fuel pumps are not lifetime parts and one the post 2002 E46 they seem to be failing earlier than expect.

While you do not have enough information to fully understand what is really going on, depending on the year, mileage and expected operating hours it might be wise to consider a fuel pump replacement. This also assumes you have done basic maintenance and replaced the fuel filter/pressure regulator at this point.

Fuel pumps both hard and soft fail, a hard fail is a no brainer to determine, but a soft failing fuel pump does typically have reduced pressure and volume, can cause driveability issues, starting issues, running out of fuel with 1/4 tank of fuel displayed. Not alwalyys a specific set of problems shows up, many people replace the fuel pump preventative and did not realize there were problems until they drive the car with the new fuel pump.

As for checking fuel pressure, this is just one part of checking for proper fuel delivery. You can often use a standard tire pressure gauge, but you need to be careful for fuel spray and often with a tire pressure gauge you cannot accurately check for pressure bleed down when the vehicle is shut down.

Suggest you check these threads:

http://forum.e46fanatics.com/showpost.php?p=16810793&postcount=11

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501
 
#15 ·
Okay. I haven't changed either fuel filter or pressure regulator yet. Maybe that would be suggested firt. Could a clogged fuel filter or bad pressure regulator have the symptoms I experience? For some extra info my car is an early 2001 with a little over 85k miles on the guage. Although it's imported from Italy to Sweden so that reading may not be correct. Will look into those links, thank you! Also, if I had a bad MAF, should'nt the symptoms go away if I disconnect the MAF? Because they don't
 
#13 ·
i notice now you’re in Sweden, not sure what your fuel quality is there. but before even considering the fuel pump you need to change your fuel filter if you haven’t done so already.

a “hunting idle” is not symptomatic of a bad fuel pump.
 
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#18 ·
Fuel Trim values would be helpful, disconnecting the MAF helps mask Lean conditions (but not always) and will convert the engine Fuel Management to an Alpha N/Speed Density program. It can help rule things out by disconnecting the MAF.

Other things you need to think about are things like charging system, a leaking
power brake booster and looking at things like IAT and Ignition timing. A video of what is going on may be helpful so we can really understand what problem you are experiencing.
 
#24 ·
My 3.0L X5, same engine as the 330, recently had a fuel pump fail. I was in line waiting for the light to turn green, and the engine died as if the gas tank was empty. I had been to Costco for gas in the previous 30 miles, so an empty tank was not the issue. The light changed to green, I pressed the gas, the engine bogged badly then stalled. It had to be the weekend before Christmas in the parking lot driveway coming out of Sam's Club, but the car didn't know about any of that. It just died in the middle of the street. I have never had a fuel pump fail in any other way. One day it works, the next it doesn't. There was no warning of the doom that was soon to befall me. I had a Bronco with a dead fuel pump once, it failed in my driveway. But, I parked it and the next time I wanted to drive it, the pump had failed. Worked one day, but not the next. No warning.
 
#25 · (Edited)
My 3.0L X5, same engine as the 330, recently had a fuel pump fail. I was in line waiting for the light to turn green, and the engine died as if the gas tank was empty. The light changed to green, I pressed the gas, the engine bogged badly then stalled. It just died in the middle of the street.
sorry JD you had that problem. but just so everyone is aware, although the X5 may use the same engine, it uses a completely different fuel pump and fuel delivery system. so you can see now how your experience is incomparable to an E46.

Also the X5 has a known issue with it's fuel pumps from the Wiring. major issue with the wiring connection which causes it to immediately stop. Quote from BMW on the fix, "in-tank fuel pumps that may have insufficiently crimped wire contacts. The loose wires may cause the connector to melt. Additionally, the fuel pump may stop working, possibly causing an engine stall.."

either way this thread does not sound at all like a fuel pump issue. :hi:
 
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#26 ·
Are you still around friend?

I've been fighting a similar issue in my 325ci.

I've replaced everything rubber from the intake to the throttle body, as well as some misc. potential vacuum leaky areas like the oil separator return line, VCG, DISA, etc.

My issue gets very bad when I load the electrical system. If I'm at idle and turn on the headlights and fog lights at the same time, the revs will surge between 400-1000 until i give it some throttle. My alternator and battery are brand new also so I'm very puzzled.

Enough of my rant though, I was curious if you were able to get this resolved?

Thanks!
 
#27 ·
Hi! Nope I still haven't been able to fix the issue. I took out my DISA valve and found it was actually broken but after repairing it the problem with the idle is still there and I can't actually notice any difference at all. Very annoying issue indeed and seems like it almost can't be solved at this point. Good luck though!
 
#28 ·
Sporadic fuel delivery doesn't necessarily mean bad pump. Could be leaky injectors. How your long term fuel trims? If they are all negative you could be leaking fuel through the injectors. Get a hold of a fuel pressure gauge and do bleed down test on your fuel rail.
 
#30 · (Edited)
I had somewhat of a idle-hunting issue when I first bought the car but I don't remember exactly how it was fixed, just at this point everything is smooth. Things I did that could be related: fixed disa seal, cleaned pcv valve, checked air leaks/boot, cleaned MAF sensor, new spark plugs, vanos seal restore, replaced faulty ignition coil, changed oil from 0w-40 to 5w30, clutch fan delete, new battery (make sure connection is really tight).
 
#32 ·
I have 2 325s doing the same thing, and have been attempting to iron out the one on and off for a year. Does this ever happen to you when using electronics? For example, mine will fall into the loop sometimes when turning on my headlights, and often does at least a considerable drop when the steering wheel is turned from a stop. I'm relatively certain its a vacuum leak, but after replacing nearly every intake related component, I'm wondering if its more electrical.

I've also heard people just say its a quirk of the 2.5l. I don't believe that though.
 
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