Engine stumble/hesitation around 2500 RPM?
Registered User
Joined: Feb 2010
Posts: 360
From: ATL
Rep Power: 62
Day 4 report to address my original four problem areas:
1) My idle still seems a bit rougher than when I first got the car and the RPMs hunt around a bit, but it's not *that* bad. When I first got the car sometimes it was difficult to feel if the car was even running it was so smooth. Now I definitely feel it. Not that that's a bad thing I guess :-). It's just different.
2) MOST IMPORTANTLY: My terrible, rough acceleration through 2000-3000 is smooth! It feels like a sportscar, dammit. I'm no longer dreading putting the throttle down. It really drives totally differently than before. This morning my commute to work was actually enjoyable.
3) The hesitation under light throttle at 2300 RPM hasn't really been noticed *much*. I say that because I think I felt something yesterday, but it's nowhere near the level it was before.
4) Larger stumble right at 3000 (Variocam). They must have remapped something because the transition can still be felt, but it's much smoother and more intentional. Before it felt like a clunk that was totally out of place. Now when I reach 3000 - 3400 where the VarioCam decides to adjust it's still slightly noticeable, but doesn't feel broken or wrong, if that makes any sense.
Overall, I'm very happy after 4 days. Will keep everyone updated. I've noticed some of my issues in the past would vary with temperature/humidity, so I'll keep an eye on that.
1) My idle still seems a bit rougher than when I first got the car and the RPMs hunt around a bit, but it's not *that* bad. When I first got the car sometimes it was difficult to feel if the car was even running it was so smooth. Now I definitely feel it. Not that that's a bad thing I guess :-). It's just different.
2) MOST IMPORTANTLY: My terrible, rough acceleration through 2000-3000 is smooth! It feels like a sportscar, dammit. I'm no longer dreading putting the throttle down. It really drives totally differently than before. This morning my commute to work was actually enjoyable.
3) The hesitation under light throttle at 2300 RPM hasn't really been noticed *much*. I say that because I think I felt something yesterday, but it's nowhere near the level it was before.
4) Larger stumble right at 3000 (Variocam). They must have remapped something because the transition can still be felt, but it's much smoother and more intentional. Before it felt like a clunk that was totally out of place. Now when I reach 3000 - 3400 where the VarioCam decides to adjust it's still slightly noticeable, but doesn't feel broken or wrong, if that makes any sense.
Overall, I'm very happy after 4 days. Will keep everyone updated. I've noticed some of my issues in the past would vary with temperature/humidity, so I'll keep an eye on that.
How has the car continued to drive? Has it gone back to its old ways?
Registered User
Joined: Apr 2014
Posts: 325
From: Northern VA
Rep Power: 38
It's not perfect, but it continues to drive better than before. Specifically, the stumbles on medium acceleration through 2000-3000 are pretty much gone. There is still the larger stumble sometimes at 3000-3200 (VarioCam repositioning?) but even that seems more smooth.
I would like to start to poll 991 owners about their idle. If anyone cares to chime in - does your idle in non-Sport mode stick right at 600? Does it vary at all? Mine still varies from 600 to 700.
Registered User
Joined: May 2012
Posts: 302
From: Cape Town - Somerset West
Rep Power: 37
It's not perfect, but it continues to drive better than before. Specifically, the stumbles on medium acceleration through 2000-3000 are pretty much gone. There is still the larger stumble sometimes at 3000-3200 (VarioCam repositioning?) but even that seems more smooth.
I would like to start to poll 991 owners about their idle. If anyone cares to chime in - does your idle in non-Sport mode stick right at 600? Does it vary at all? Mine still varies from 600 to 700.
I would like to start to poll 991 owners about their idle. If anyone cares to chime in - does your idle in non-Sport mode stick right at 600? Does it vary at all? Mine still varies from 600 to 700.
I cannot notice any form of hesitation. The "Go" paddle does just that...
There is a marked surge in power on my C2S at around 3000-4000 RPM, kinda like a turbo boost coming in late. I like it. I would not call it hesitation. The only reason I am not getting a GTS - it's missing there. Call me a philistine if you will...
Rainier
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Joined: Jul 2015
Posts: 7
From: Hawaii
Rep Power: 0
I had the same hesitation around 2500 rpm. I installed a sprint booster as recommended by other forum members and it went away. I used the auto model on a manual transmission, which turned out perfect.
Registered User
Joined: Feb 2010
Posts: 360
From: ATL
Rep Power: 62
Can you please elaborate? What model do you have? Base or S? Can you describe the hesitation you had? Totally corrected? Thanks!
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Joined: Jun 2009
Posts: 188
From: Calif.
Rep Power: 30
http://outbackjoe.com/macho-divertis...s-it-worth-it/
http://www.crosslake.net/~dbipes/spr...intBooster.pdf
Registered User
Joined: Apr 2014
Posts: 325
From: Northern VA
Rep Power: 38
Brought my car in for a lifter issue (drained after a week of sitting, made terrible clacking for five minutes after start). While dropping it off I of course had to once again mention my hesitation issue. If you remember I had my engine management system software updated on my previous visit, and it seemed to be better for a while, but the stumbling has returned, albeit feeling slightly different. Once again they said it was normal.
However, when picking up my car, the service advisor mentioned another customer with a similar issue. 2-3K RPM, stumbling, no codes. They are going to be swapping out his high pressure fuel pump next week. They think it's a fuel pump issue, and it's interesting that the high pressure fuel pump is driven mechanically by the engine. I thought it would be a separate pump motor or something. They said they also intend to investigate spark plugs and ignition coil, but they are leaning towards a fuel starvation issue where pressure in the cylinder is actually pushing back on the fuel delivery and not allowing a smooth firing). When driving around with the tech laptop hooked up he said the only thing they noticed was a drop in the high pressure fuel pump from normal 120 bar down to 114 bar.
Anyway, just another data point. I intend to follow up with the service advisor in a week or two to ask how the experiment went with this other car.
While I was there I also drove another 2013 911 (7MT) with the service manager. It also had some hesitation in the 2-3K range but not as severe as my car. He admitted that the VarioCam Plus system is *not* seamless like Porsche says it is.
However, when picking up my car, the service advisor mentioned another customer with a similar issue. 2-3K RPM, stumbling, no codes. They are going to be swapping out his high pressure fuel pump next week. They think it's a fuel pump issue, and it's interesting that the high pressure fuel pump is driven mechanically by the engine. I thought it would be a separate pump motor or something. They said they also intend to investigate spark plugs and ignition coil, but they are leaning towards a fuel starvation issue where pressure in the cylinder is actually pushing back on the fuel delivery and not allowing a smooth firing). When driving around with the tech laptop hooked up he said the only thing they noticed was a drop in the high pressure fuel pump from normal 120 bar down to 114 bar.
Anyway, just another data point. I intend to follow up with the service advisor in a week or two to ask how the experiment went with this other car.
While I was there I also drove another 2013 911 (7MT) with the service manager. It also had some hesitation in the 2-3K range but not as severe as my car. He admitted that the VarioCam Plus system is *not* seamless like Porsche says it is.
Registered User
Joined: Feb 2010
Posts: 360
From: ATL
Rep Power: 62
Brought my car in for a lifter issue (drained after a week of sitting, made terrible clacking for five minutes after start). While dropping it off I of course had to once again mention my hesitation issue. If you remember I had my engine management system software updated on my previous visit, and it seemed to be better for a while, but the stumbling has returned, albeit feeling slightly different. Once again they said it was normal.
However, when picking up my car, the service advisor mentioned another customer with a similar issue. 2-3K RPM, stumbling, no codes. They are going to be swapping out his high pressure fuel pump next week. They think it's a fuel pump issue, and it's interesting that the high pressure fuel pump is driven mechanically by the engine. I thought it would be a separate pump motor or something. They said they also intend to investigate spark plugs and ignition coil, but they are leaning towards a fuel starvation issue where pressure in the cylinder is actually pushing back on the fuel delivery and not allowing a smooth firing). When driving around with the tech laptop hooked up he said the only thing they noticed was a drop in the high pressure fuel pump from normal 120 bar down to 114 bar.
Anyway, just another data point. I intend to follow up with the service advisor in a week or two to ask how the experiment went with this other car.
While I was there I also drove another 2013 911 (7MT) with the service manager. It also had some hesitation in the 2-3K range but not as severe as my car. He admitted that the VarioCam Plus system is *not* seamless like Porsche says it is.
However, when picking up my car, the service advisor mentioned another customer with a similar issue. 2-3K RPM, stumbling, no codes. They are going to be swapping out his high pressure fuel pump next week. They think it's a fuel pump issue, and it's interesting that the high pressure fuel pump is driven mechanically by the engine. I thought it would be a separate pump motor or something. They said they also intend to investigate spark plugs and ignition coil, but they are leaning towards a fuel starvation issue where pressure in the cylinder is actually pushing back on the fuel delivery and not allowing a smooth firing). When driving around with the tech laptop hooked up he said the only thing they noticed was a drop in the high pressure fuel pump from normal 120 bar down to 114 bar.
Anyway, just another data point. I intend to follow up with the service advisor in a week or two to ask how the experiment went with this other car.
While I was there I also drove another 2013 911 (7MT) with the service manager. It also had some hesitation in the 2-3K range but not as severe as my car. He admitted that the VarioCam Plus system is *not* seamless like Porsche says it is.
Hopefully they're on to something. Please stay in contact with your dealer and thanks for keeping us posted.
Registered User
Joined: Jun 2009
Posts: 188
From: Calif.
Rep Power: 30
HP fuel pump is in fact mechanically driven:
"The electric fuel pump in the fuel tank delivers the low-pressure fuel via the quantity control valve (see Fig. 2_419_11, 1.1) at approx. 72.5 psi (5 bar), directly into the 3-piston high-pressure pump (see Fig. 2_418_11, 1). The high-pressure pump driven by the camshaft delivers the fuel high pressure (approx. 580 to 1740 psi/40 to 120 bar) to the fuel rails (4) on the left and right cylinder banks and to the injectors (6) via the connecting lines (3) when the engine is running. The fuel high-pressure sensor (5) is located in the right fuel rail".
"The electric fuel pump in the fuel tank delivers the low-pressure fuel via the quantity control valve (see Fig. 2_419_11, 1.1) at approx. 72.5 psi (5 bar), directly into the 3-piston high-pressure pump (see Fig. 2_418_11, 1). The high-pressure pump driven by the camshaft delivers the fuel high pressure (approx. 580 to 1740 psi/40 to 120 bar) to the fuel rails (4) on the left and right cylinder banks and to the injectors (6) via the connecting lines (3) when the engine is running. The fuel high-pressure sensor (5) is located in the right fuel rail".
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Joined: Jun 2013
Posts: 448
From: Raleigh, NC
Rep Power: 32
Fascinating. Who woulda thunk?
I was hesitant (no pun intended) to publicly share my experiences because I tried to sell my car myself (I ended up trading it because no one would buy it) and I didn't want potential buyers to be turned-off by this issue. But my car did experience the hesitation/surging similar to but not as seriously as the OP's car. I can share though that it did seem to get better once I got a few thousand miles on the car. Or maybe I just got used to it?
It is interesting to read that although the dealer says that the operation is normal, they are working on another customer's car with similar symptoms. Even though it's normal.
I was hesitant (no pun intended) to publicly share my experiences because I tried to sell my car myself (I ended up trading it because no one would buy it) and I didn't want potential buyers to be turned-off by this issue. But my car did experience the hesitation/surging similar to but not as seriously as the OP's car. I can share though that it did seem to get better once I got a few thousand miles on the car. Or maybe I just got used to it?
It is interesting to read that although the dealer says that the operation is normal, they are working on another customer's car with similar symptoms. Even though it's normal.