My Fix for Hesitation/Stumble/Buck/Surge LOW RPM

[rednekbmw]

Hmm failing fuel pump come and go? Freaking car has been starting fine since the other day.

[slvrXI]

Hmm failing fuel pump come and go? Freaking car has been starting fine since the other day.

Its an electric motor, just like a starter, or a blower motor, or air pump... Depending on many things including temperature, humidity, and vibrations the motor may choose to run properly or sit there and do nothing.

[xaxis360]

I am having this EXACT issue on my 97 328 with an M52. Stumble under 2000 RPM in high heat with light throttle, no codes... I was about to blow $300 on 6 new coils. Trying a fuel filter first, but after reading this, it's most likely the pump!

**UPDATE**

Replaced the fuel pump today.. problem GONE! Dealership gave it to me for $200 which was a really good deal. I'm going to do the fuel filter tomorrow for the heck of it, but the problem was for sure the pump.

Thank you!

[dlandon]

An old thread but was this the sound you guys heard when turning the key to the ON position?
I've had random jerks and dips in RPM at idle but it would subside after letting off the brake and giving it a bit of gas. Vanos seals done, CCV replaced, ICV and TB cleaned with brand new intake boots.

http://youtu.be/YDY6f7gRwgk

[dlandon]

An old thread but was this the sound you guys heard when turning the key to the ON position?
I've had random jerks and dips in RPM at idle but it would subside after letting off the brake and giving it a bit of gas. Vanos seals done, CCV replaced, ICV and TB cleaned with brand new intake boots. Fuel filter swapped last year.

[Benny Beemer]

This is a great thread. I'm having the same symptoms. I'm at 230,000km and I expect that my fuel filter has never been replaced. Having researched both fuel filter and fuel pump replacement, I'm actually going to replace the fuel filter first and see what improvement I get. My fuel filter is likely clogged, and this can cause the same symptoms as a fuel pump soft fail. Furthermore, the fuel filter costs around 1/4 the price of the fuel pump, so it is the most economical starting point. I've been putting it off because I have to invest in jack stands and a trolley jack to get the job done, but I'm going to go ahead and I expect to update the forum with my progress in a few weeks.

[Benny Beemer]

Update: I replaced the fuel filter. I actually did it about a month ago. No improvement really. Although I now know that I have both a bad VANOS and DISA so I've got to get those done before I think about doing the fuel pump. If I still get the symptoms after repairing those two things, I will check the fuel pressure at the rail. If it is low, I'll replace the fuel pump too.

BTW, during the install I reused the "one time" hose clamps and it just niggles at me LOL. That's the only thing I would have done differently - I would have bought new clamps.

[mry82]

Hey guys... I haven't had my 01 325xi long, and recently I have had some serious episodes of missing/hesitation (stumble/buck), under light to moderate load, immediately after fueling... It has only happened once each tank, but not on every tank. You might say it has a little "stutter" on occasion too. I also have the occasional howl/groan on startup; I thought it might be the oil separator (but that seems to take a noise when shutting down, so fuel pump might make more sense).

After reading through the forums I figured the fuel pump is probably the culprit, and the fuel filter seems to be one of the few things the previous owner lapsed on (filter's at 80,000 mi, I have a Mahle on the way!). There's about 173,000 mi on the car, it's had cooling system refreshes, window regulators, spark plugs, and the typical driveshaft PM, etc...(I recently put in a Valeo non self-adjusting clutch and single mass flywheel, and did a CDV delete as well... so the car is finally starting to show it's potential!).

So, I plan on ordering a pump, relay, and new gasket from BMA... here are my questions:

Has anyone else had this specific just after fueling missing problem?

Is it possible the symptom could be from the other transfer pump? I noticed the description at ECS said it can cause "misfire"? It also mentions the 1/4 tank no start thing... which I have NOT experienced. I usually do not run much under a 1/4 tank, but I have run it well under a 1/4 at least once in the last few months.

The cheap part of me wanted to take a chance on this "Vemo" pump from ECS...
80 bucks, and it is a German company, outsourced to China I suppose, but that's how you get those savings, lol... I'm afraid I'll have a "uro" by another name if I do that... BMA makes it worth the upgrade to VDO I do believe... ~40 bucks extra can be seen as insurance! Sorry Vemo, not enough noise on the forums yet! I'll try your resistor if I need one...

[rad40052]

I'm hearing that sound too every once in a while. I'm also getting hesitation. I've done the fuel filter/regulator, intake boot with a smoke test, and new ngk spark plugs. Still having the same issues tho. My mechanic said could be fuel pump. We tested the pressure and everything came back good. He was saying pressure could be there but not have the volume it needs...I've also had a second opinion who also said the same bout the volume issue with the fuel pump...so fuel pump looks to be next on my list.

[mry82]

^interesting... I think it becomes obvious that we just need to do this, after reading on the forums!

[SilverSaloon69]

^interesting... I think it becomes obvious that we just need to do this, after reading on the forums!

I agree. If your fuel pump is over 10 years old, replace it like a tune up item. At $130 - $160, and the ease of replacement, it's a cheap upgrade. I replaced mine, and my car feels like new again.

[mry82]

^these stories make me happy.

Anyone think that the missing issue occurring just after fueling is more likely to be soft failure of pump or a sign that I have junk in the tank getting stirred up?

I have a pump, filter, and relay here ready to go when I have time, so I guess I will see if my problems continue after the install....

[SilverSaloon69]

^these stories make me happy.

Anyone think that the missing issue occurring just after fueling is more likely to be soft failure of pump or a sign that I have junk in the tank getting stirred up?

I have a pump, filter, and relay here ready to go when I have time, so I guess I will see if my problems continue after the install....

Easiest fuel pump to replace. You could do it on the side of the road if you had to.

[mry82]

Let's hope it doesn't come to that, but I'll throw the Bentley in there with some tools, haha.

[Benny Beemer]

I never actually got around to replacing the fuel pump, but I did do the DISA and the VANOS and it didn't help. It would be good to hear from someone who replaced the fuel pump and it fixed the problem!

[mry82]

I'm on it... will try to remember to report back to you when I get the parts installed, as I am able, this week!

[mry82]

I never actually got around to replacing the fuel pump, but I did do the DISA and the VANOS and it didn't help. It would be good to hear from someone who replaced the fuel pump and it fixed the problem!

Benny... Got the new pump and filter in (have not done the relay yet)... Here's what I have noticed so far...

Improvements:
No more "stutter" when accelerating... power feels "smoother" overall...
I had run the car down to an 1/8th a tank, and when I refueled I did not experience the immediate hesitation issue...(granted this was intermittent, so we will see if this remains the case)
Possibly more power at high rpms (but was the loss the fault of the pump of the filter/pressure regulator?)...
No more intermittent groan/honk from fuel pump (so far... I used to think it might be the CCV)...
I feel better driving it without an 80k+ mi filter on it!!!

Possible remaining issue:
I did have a couple episodes of hesitation when "jabbing" the throttle abruptly rather than "rolling into it" smoothly... I was able to reproduce this a couple, but not every time I tried to... (I do NOT have any issues with idle or power otherwise...)...

Here are my next steps if I continue to experience trouble (plugs, intake boots, and 02 sensors have been replaced recently):
Evap purge/breather valve?
TPS?
CCV?
Vacuum leak(s)?
MAF?
ICV/TB?

I will be due for an air filter in 10-20k miles or so, and plan to clean MAF, ICV, TB, and inspect for any issues.

[DiscoSux]

I am having the same issue as Mike described in the original 2012 post - hesitation/miss/bucking when accelerating from 1000 - 2000 rpm. It seems like a new fuel pump would take care of the issue. What I can't understand is that my issue only came after I replaced the Vanos seals.

I tested all the coils as I had to remove them to pull the valve cover so I thought I may have disturbed them and that caused a failure. They all checked good. I am reluctant to blame the fuel pump as it should not have been affected at all by the Vanos seal change.

I am not getting any codes with the Peake reader. It looks I am going to start throwing parts at it and I'm not sure where to start! Coils? Fuel Pump? CPS? All likely original parts (2000 328i - 180k)

[twotrinis]

My car had similar symptoms (99 328i, 275K miles). Fuel pressure was near or above borderline at ignition turn on and went up to about 57psi at idle. I took it to some dealer techs who have an outside shop, and they pointed out that it needed a decel valve (or control valve ~$375 at dealer before CCA discount), and the and the oil seperator (they also changed some vacuum lines). These guys are sharp they listened to the car and looked in the engine bay listened to the car and made that determination, and later the read the codes and told me that there was an intermittent miss on cylinder 4 (I had already done the plugs and they did the coil). They fixed those things and now everything is fine. Car feels more powerful too, and the gas mileage has jumped back up to 27+mpg from 25. The kind of honking noise I got when the car is shut off or when the accelerator is blipped at idle, is also gone.

I will be taking my car back to them in future when it needs work I cannot do myself, or have trouble diagnosing.

[Dandydog]

I stumbled upon this continuing thread when my treasured ‘88 325ic developed the low-rpm stumble that slvrXI originally described. I fixed mine, too, but I’ve got an alternative hypothesis about causality.

IÂ’d be willing to bet good money that all of the guys who addressed this problem by replacing their fuel pumps also replaced the (included) rubber gasket. (Possibly some of the dealerships, also.)

Since this is a pressurized system, is it possible that the gasket and not the fuel pump was at fault (with the press-down,-twist-and-pray closure being an unindicted co-conspirator)?

‘Cause when I went to replace my pump, I discovered that $40 had bought a crappy knock-off (surprise!) which wouldn’t accept the fuel-level tube, So I re-installed the original WITH A NEW GASKET, and the problem went away.

(For me, too, fixing the problem brought a host of Heisenberg-type improvements: better fuel economy, better 0-60 times, and I think my complexion cleared up.)

So: Has anyone replaced his pump and re-used the old gasket (and is willing to cop to it)? Is there anyone out there who is experiencing the problem and wants to try installing a 50c hardware-store O-ring before taking more expensive steps? (And post the results of the experiment to this thread? Please?)