Stumbling Acceleration

[catmanluge]

I am experiencing a problem with my 2000 Boxster 3.4 liter. The car under acceleration pulls strong though 1 gear stumbles slightly through 2 gear but starts to really have a noticeable stumble in 3rd gear approaching 5000 RPM and actually sounds like it starving for fuel but then catches and accelerates up to 7000 Rpm.

It a similar feeling to fuel detonation in older cars with bad gas.

I try to attach a photo of my Dynolicious chart where the yellow line can be seen showing where it stumbles…

[wvicary]

3.4l?? Have you done an engine swap? No check engine light or codes?

[Bladecutter]

Have you tried the simple stuff first?

Check to see if the air filter is clean.

Check to see if all the spark plugs are on tight, properly gapped, and working fine.

Replace the fuel filter (partially clogged one can cause the issues you are experiencing).

After that, I would suspect MAF sensor issue, O2 sensor issue, or ignition coil stick issue.

BC.

[PA3.4l]

Please post what ever results or test you end up doing to find out what is wrong. My experince has misfiring sounds at 2400rpm and I am looking for answers to.

[Glyn]

Sounds like a MAF to me.

Disconnect electrical connection and take it for a run - If all is well this will prove it is the MAF.

(Car goes in to limited opperation strategy with MAF disconnected and approximates the fuel air ratio which is better than a faulty MAF signal)

[catmanluge]

Sounds like a MAF to me.

Disconnect electrical connection and take it for a run - If all is well this will prove it is the MAF.

(Car goes in to limited opperation strategy with MAF disconnected and approximates the fuel air ratio which is better than a faulty MAF signal)

I tried your suggestion and the performance was slightly worse..

Here are the CEL codes and Fault codes produce without the MAF connected.

P0455 Fault 94 Tank vent System Error Major Leak

P0102 MAF Fault code 115 Below limits (Not Connected)

P0112 Fault code 124 Intake air temp below limit value

[catmanluge]

Additional Information From Durametric not sure what values to run for analysis?

Time Rpm Actual Cam Angles O2 Ahead Ristance O2 ahead

Bank 1 Bank 2 Cat Ahead CAT FRA Bank 2 Throttle Value

12:05:33.1875000 808 0.59 -0.19 0.07 192 0.99 0.71 2.2

12:05:34.4531250 821 0.61 -0.23 0.78 192 0.99 0.1 2.2

12:05:35.5781250 830 0.48 -0.05 0.59 192 0.99 0.75 2.9

12:05:36.6875000 1007 0.36 -0.03 0.84 192 0.99 0.8 17.4

12:05:37.7656250 1145 0.23 0 0 192 0.99 0.02 13.9

12:05:38.8437500 1538 0.42 -0.17 0.85 192 0.99 0.84 6.6

12:05:39.9218750 2122 -0.31 -0.41 0.07 192 0.99 0.03 9.6

12:05:41.0156250 3094 -0.14 -0.34 0.03 192 0.99 0.11 22.9

12:05:42.1093750 4609 0.97 0.67 0.74 192 0.99 0.22 28.8

12:05:43.2343750 4949 2.05 1.19 0.84 192 0.99 0.87 6.8

12:05:44.3125000 3971 1.44 0.53 0.87 192 0.99 0.85 99.7

12:05:45.4218750 5204 1.88 1.42 0.88 192 0.99 0.89 94.7

12:05:46.5000000 3934 1.28 0.73 0.88 192 0.99 0 6.2

12:05:47.5937500 3783 0.41 0.36 0.82 192 0.99 0.85 101.1

12:05:48.7187500 4365 0.67 0.17 0.91 192 0.99 0.91 99.9

12:05:49.8125000 4643 1 0.64 0.9 192 0.99 0.85 6.2

12:05:51.0625000 3282 -0.17 -0.38 0.01 192 0.99 0.07 5.9

12:05:52.2968750 3109 -0.31 -0.53 0 192 0.99 0 5.6

12:05:53.5468750 3058 -0.05 -0.38 0.03 192 0.99 0.11 12.2

12:05:54.8593750 3081 -0.11 -0.34 0.82 192 0.99 0.67 13.1

12:05:56.0625000 3123 -0.3 -0.84 0.03 192 0.99 0.03 23.3

12:05:57.2968750 3229 -0.36 -0.56 0.57 192 0.99 0.17 33.6

12:05:58.5468750 3397 -0.34 -0.53 0.82 192 0.99 0.74 101

12:05:59.8750000 3553 -0.67 -0.38 0.92 192 0.99 0.91 99.9

12:06:01.1250000 3586 -0.44 -0.33 0.88 192 0.99 0.89 6.1

12:06:02.3750000 4560 0.94 0.3 0.88 192 0.99 0.85 7.2

12:06:05 5163 3.2 1.42 0.87 192 0.99 0.9 99.9

12:06:06.1250000 5673 1.27 0.7 0.91 192 0.99 0.92 18.4

12:06:07.2031250 5048 1.67 1.09 0 192 0.99 0 7.1

12:06:08.2968750 4452 0.86 0.33 0 192 0.99 0 6.8

12:06:09.3906250 4100 0.84 0.14 0 192 0.99 0 6.3

12:06:10.4687500 3821 0.28 0.19 0 192 0.99 0 6.4

12:06:11.5781250 3608 -0.58 -0.14 0 192 0.99 0 6

12:06:12.6718750 3412 -0.36 -0.25 0 192 0.99 0 6.2

12:06:13.9531250 3132 -0.47 -0.56 0 192 0.99 0 5.7

12:06:15.2500000 2894 -0.13 -0.48 0 192 0.99 0 5.6

12:06:16.5781250 2682 -0.3 -0.5 0 192 0.99 0 5.2

12:06:17.7968750 2491 -0.09 -0.31 0 192 0.99 0 4.9

[JeTexas]

Sounds like a MAF to me.

Disconnect electrical connection and take it for a run - If all is well this will prove it is the MAF.

(Car goes in to limited opperation strategy with MAF disconnected and approximates the fuel air ratio which is better than a faulty MAF signal)

I tried your suggestion and the performance was slightly worse..

Here are the CEL codes and Fault codes produce without the MAF connected.

P0455 Fault 94 Tank vent System Error Major Leak

P0102 MAF Fault code 115 Below limits (Not Connected)

P0112 Fault code 124 Intake air temp below limit value

The P0102 and P0112 are due to the MAF being disconnected. However, the P0455 is most likely your problem. Check your vacuum hoses for leaks and do a search of P0455 on here for more troubleshooting info.

[catmanluge]

Sounds like a MAF to me.

Disconnect electrical connection and take it for a run - If all is well this will prove it is the MAF.

(Car goes in to limited opperation strategy with MAF disconnected and approximates the fuel air ratio which is better than a faulty MAF signal)

I tried your suggestion and the performance was slightly worse..

Here are the CEL codes and Fault codes produce without the MAF connected.

P0455 Fault 94 Tank vent System Error Major Leak

P0102 MAF Fault code 115 Below limits (Not Connected)

P0112 Fault code 124 Intake air temp below limit value

The P0102 and P0112 are due to the MAF being disconnected. However, the P0455 is most likely your problem. Check your vacuum hoses for leaks and do a search of P0455 on here for more troubleshooting info.

I have checked vacuum lines, air Filter, intake, spark plugs, and many other possibilities. There is one thing that I did that may be contributing to this problem as I use the Boxster Fuel Rails with the 996 Injectors but had to make a bracket to hold the injectors in place due to utilizing the 3.4 intake manifold.

Is it possible that the injector rails are senitive to how they are mounted?

[catmanluge]

Not sure what tests to run with the durametric that may lead to solving this problem....

[tholyoak]

There is no issue with using the boxster rails as long as you mounted them so they seal properly. They use the same injectors and same FPR.

Get rid of your error codes first and then see if you still have a problem. Sounds to me like you don't have the tank vent system hooked up correctly.

Lots of people leave it attached to the old 986 intake manifold and then wonder what to hook to the side port on the throttle body.

-Todd

Sounds like a MAF to me.

Disconnect electrical connection and take it for a run - If all is well this will prove it is the MAF.

(Car goes in to limited opperation strategy with MAF disconnected and approximates the fuel air ratio which is better than a faulty MAF signal)

I tried your suggestion and the performance was slightly worse..

Here are the CEL codes and Fault codes produce without the MAF connected.

P0455 Fault 94 Tank vent System Error Major Leak

P0102 MAF Fault code 115 Below limits (Not Connected)

P0112 Fault code 124 Intake air temp below limit value

The P0102 and P0112 are due to the MAF being disconnected. However, the P0455 is most likely your problem. Check your vacuum hoses for leaks and do a search of P0455 on here for more troubleshooting info.

I have checked vacuum lines, air Filter, intake, spark plugs, and many other possibilities. There is one thing that I did that may be contributing to this problem as I use the Boxster Fuel Rails with the 996 Injectors but had to make a bracket to hold the injectors in place due to utilizing the 3.4 intake manifold.

Is it possible that the injector rails are senitive to how they are mounted?

[catmanluge]

Todd

Not sure if I understand. There is only one line connected to the TB from the AOS then it is connected to a value of some type under the drivers front side of the engine. I wil have to look at it again as its been a while since I studied the actual path of that line. Its about 5/8 inch in size...

Bill

There is no issue with using the boxster rails as long as you mounted them so they seal properly. They use the same injectors and same FPR.

Get rid of your error codes first and then see if you still have a problem. Sounds to me like you don't have the tank vent system hooked up correctly.

Lots of people leave it attached to the old 986 intake manifold and then wonder what to hook to the side port on the throttle body.

-Todd

Sounds like a MAF to me.

Disconnect electrical connection and take it for a run - If all is well this will prove it is the MAF.

(Car goes in to limited opperation strategy with MAF disconnected and approximates the fuel air ratio which is better than a faulty MAF signal)

I tried your suggestion and the performance was slightly worse..

Here are the CEL codes and Fault codes produce without the MAF connected.

P0455 Fault 94 Tank vent System Error Major Leak

P0102 MAF Fault code 115 Below limits (Not Connected)

P0112 Fault code 124 Intake air temp below limit value

The P0102 and P0112 are due to the MAF being disconnected. However, the P0455 is most likely your problem. Check your vacuum hoses for leaks and do a search of P0455 on here for more troubleshooting info.

I have checked vacuum lines, air Filter, intake, spark plugs, and many other possibilities. There is one thing that I did that may be contributing to this problem as I use the Boxster Fuel Rails with the 996 Injectors but had to make a bracket to hold the injectors in place due to utilizing the 3.4 intake manifold.

Is it possible that the injector rails are senitive to how they are mounted?