[maxor]

So i've been having this issue for a few weeks now. I think i've narrowed it down to something fuel related as it only happens with half a tank of gas.
When it has a full tank, there are no issues, runs like a dream.


Anyways, When i have half a tank, i step on the gas and the car studders, loss of power is felt and then a few seconds later the power kicks in.
Kinda feels like a kick in the nuts, it's so bad i can hear things in my trunk flopping around. Issue is remedied by putting gas passed the half tank mark.

Now, this issue only happens at half a tank only. I am either thinking its fuel pump related or something. I am just looking into what it may be. I don't think its "bad gas" as i've put enough gas from several different shell locations to fill the tank two times over.

No codes or check engine light or anything. Any ideas are welcome, crazy or not.


Video

[mrnuke]

Originally Posted by maxor

So i've been having this issue for a few weeks now. I think i've narrowed it down to something fuel related as it only happens with half a tank of gas.
When it has a full tank, there are no issues, runs like a dream.


Anyways, When i have half a tank, i step on the gas and the car studders, loss of power is felt and then a few seconds later the power kicks in.
Kinda feels like a kick in the nuts, it's so bad i can hear things in my trunk flopping around. Issue is remedied by putting gas passed the half tank mark.

Now, this issue only happens at half a tank only. I am either thinking its fuel pump related or something. I am just looking into what it may be. I don't think its "bad gas" as i've put enough gas from several different shell locations to fill the tank two times over.

No codes or check engine light or anything. Any ideas are welcome, crazy or not.

Do you think you may have gotten any floating debris in the tank? I had a friend who got pranked with the ping pong ball prank (cut it and shove it in the tank) and the symptoms were similar especially as the tank was draining. Needless to say, the individual who got caught had a hefty bill to pull out the pump and drop the tank!

[GreaseJunkie]

This probably isn't much help, but I had the same issue when my DMTL pump quit on me. The only difference is that it only happened for the first 20-30 miles AFTER filling the tank to full. Eventually it threw an MIL which lead me to replacing it. Never had an issue since.

Are you able to replicate the shudder with the vehicle in P or neutral with ebrake up?
How about while under load while parked? ie. car in drive or 1st gear, give it gas while applying the brake (ebrake, lightly let off clutch if its 6mt) If so, try to put a fuel gauge on the car and have someone watch the gauge while you replicate the studder.
Any codes stored in the DME?

[maxor]

Originally Posted by GreaseJunkie

This probably isn't much help, but I had the same issue when my DMTL pump quit on me. The only difference is that it only happened for the first 20-30 miles AFTER filling the tank to full. Eventually it threw an MIL which lead me to replacing it. Never had an issue since.

Are you able to replicate the shudder with the vehicle in P or neutral with ebrake up?
How about while under load while parked? ie. car in drive or 1st gear, give it gas while applying the brake (ebrake, lightly let off clutch if its 6mt) If so, try to put a fuel gauge on the car and have someone watch the gauge while you replicate the studder.
Any codes stored in the DME?

While in park, no issues at all its only when i give it some gas that it has issues.

Don't get me wrong, it will drive 80 mph + without a problem on half a tank of gas but i have to keep it stable, if give it gas at any time, for example trying to pass a car on the fwy, i feel the knock / loss of power.

Can be felt in first gear as well, No codes stored.

Originally Posted by mrnuke

Do you think you may have gotten any floating debris in the tank? I had a friend who got pranked with the ping pong ball prank (cut it and shove it in the tank) and the symptoms were similar especially as the tank was draining. Needless to say, the individual who got caught had a hefty bill to pull out the pump and drop the tank!

Could be debris, However i don't want to think about that right now

I know the bill on that would be astronomical

[GreaseJunkie]

So its an automatic? Try this: Put in in D with your left foot on the brake and the parking brake on. Give it some gas. 1500-2500 rpms, do you feel the shudder like you would when you're on the highway? If so, do the same thing with a fuel pressure gauge on it and have a buddy watch for any pressure drops.

[maxor]

Originally Posted by GreaseJunkie

So its an automatic? Try this: Put in in D with your left foot on the brake and the parking brake on. Give it some gas. 1500-2500 rpms, do you feel the shudder like you would when you're on the highway? If so, do the same thing with a fuel pressure gauge on it and have a buddy watch for any pressure drops.

Yes, its an auto.

Will test it soon, Currently have a little more than half a tank.

Will rent a pressure gauge as well.

[GreaseJunkie]

Okay, keep me posted. I may not log on over the weekend, but if you send me your results in a PM I'll see it in my email and try to get back to you.

[m_thompson]

Since you have an N51 and live in California, shouldn't this be covered under the 15 year 150,000 mile SULEV warranty?

[maxor]

Originally Posted by GreaseJunkie

Okay, keep me posted. I may not log on over the weekend, but if you send me your results in a PM I'll see it in my email and try to get back to you.

Will do,

Going to take it out in a bit, Gonna see if it acts up again at half tank then run some tests.

Originally Posted by m_thompson

Since you have an N51 and live in California, shouldn't this be covered under the 15 year 150,000 mile SULEV warranty?

Only certain emissions related parts are covered under warranty. If it turns out to be one of the warrantied parts that needs to be replaced. Will get the dealer to do it.

[maxor]

Originally Posted by GreaseJunkie

Okay, keep me posted. I may not log on over the weekend, but if you send me your results in a PM I'll see it in my email and try to get back to you.

Managed to take it out and get down to a quarter of a tank without any problems. Could it be possible that the fuel level sensor is going bad and intermittently displaying a bad fuel level (at times)?

Saying that the tanks are holding more gas than it currently has. Then when it gets really down low, issues with acceleration come back due to low fuel level?

Might take it out till empty with a 5 gallon gas can and test it out.

[maxor]

So i've managed to finally replicate the issue as well as take a video!

Finally found some time to be able to take it out and run it till empty-ish - about 30 miles left on the tank.

At around 30 miles left i started to feel studdering and rpm lag as you can see in the video. Speed also rising slowly at full throttle. At the beginning of the video you can see the rpms jumping between 2,000 RPM before jumping to 3k rpm and so on.

[ahlbe1cl]

Could be some sort of Vacuum Pressure lock in the fuel tank, possibly caused by the evap system or a vent hose that’s plugged.

[maxor]

Originally Posted by ahlbe1cl

Could be some sort of Vacuum Pressure lock in the fuel tank, possibly caused by the evap system or a vent hose that’s plugged.

Could be possible, however wouldn’t this affect a full tank as well? Issue only occurs when low on fuel.

[ahlbe1cl]

Originally Posted by maxor

Could be possible, however wouldn’t this affect a full tank as well? Issue only occurs when low on fuel.

Picture this, if a tank does not have proper ventilation, when you get towards the bottom of the tank, you start to bulge in the sides and effectively create a vacuum inside the tank.

When the tank is full, this is still present, but with less effect because a liquid does not compress.

So, my theory is that the tank is creating a vacuum due to a blocked vent line, and this is most present when there is more air in the tank than fuel.

[ahlbe1cl]

What ever came of this? Did you fix your issue?

[maxor]

Originally Posted by ahlbe1cl

Picture this, if a tank does not have proper ventilation, when you get towards the bottom of the tank, you start to bulge in the sides and effectively create a vacuum inside the tank.

When the tank is full, this is still present, but with less effect because a liquid does not compress.

So, my theory is that the tank is creating a vacuum due to a blocked vent line, and this is most present when there is more air in the tank than fuel.

Will try to take a look at this.

Originally Posted by ahlbe1cl

What ever came of this? Did you fix your issue?

Still haven't gotten around to opening up the tank yet, been very busy out of state and will continue to be for the next few weeks. Will update this whenever i get back home with info.

[B0ysiE90]

Any updates? I have the same issue.... but my car stalled and said fuel pump .. stutters at higher mph and loses power esp. uphill ... i ended up bringing it to my dealer since my local shop can't find anything wrong. Hopefully it'll be covered under warranty Sulev in nj .