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Old 01-28-2015, 07:59 PM
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Default Reduced Power Above 2500 RPM

While driving on an Interstate at 60-65 MPH, I needed to get up to the 70 MPH speed limit as I merged left. The accelerator pedal was pretty far down, but not to the floor, and I stopped accelerating.

During my drive, I also climb 3 fairly long hills and the engine behaved the same way.

The transmission shifted to 3rd as it should have but I did not get normal acceleration as the RPMs climbed.

There was a noticeable hiss coming from the engine that I did not recognize. I've had this car for about 3.5 years and put on over 35K miles so things are way off. The RPMs climb but I do not get the expected increase in power.

Also, I do not get the same noise with shift lever set to N or P and rev the engine.

I tried the following one at a time but have not isolated or fixed issue:
- PCV valve: Replaced because a pretty good general auto site suggested hiss could come from here.
- Fuel Filter: Just wanted to be sure fuel could properly flow.
- Took to a shop for diagnosis: They did a smoke test and found leaks:
-- Overlap of accordion tube and throttle body
-- EGR Valve Gasket
-- Evap System (but they explained this will not cause loss of power)
- Took diagnosis results, went to parts store and:
-- Added a band clamp around the overlap of throttle body and intake accordion tube
-- Installed a new EGR Valve Gasket

- My next step is to get a fuel pressure gauge. Hopefully this can help isolate the problem.

I do not think it is an ignition issue because of how well it accelerates and cruises up to 2500 RPM, but I could be mistaken.

Suggestions are appreciated but I mainly want to post up as I resolve this issue.
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Old 01-28-2015, 08:59 PM
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hmmm, What if the Cat has stopped flowing as well as it should. I've clogged 2 stock cats and ive had the hissing. it sounded like a Turbo diesel. it only hissed under a load. it let the car idle fine. yours might be getting clogged to the point that the exhaust isn't able to get out thus reducing the performance past a certain throttle.
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Old 01-29-2015, 12:05 AM
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Originally Posted by xpbr2000 View Post
hmmm, What if the Cat has stopped flowing as well as it should. I've clogged 2 stock cats and ive had the hissing. it sounded like a Turbo diesel. it only hissed under a load. it let the car idle fine. yours might be getting clogged to the point that the exhaust isn't able to get out thus reducing the performance past a certain throttle.
That is definitely worth checking too. Thanks for the suggestion. It is definitely easier to replace than the fuel pump.
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Old 01-29-2015, 12:10 AM
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I found these helpful videos for troubleshooting the fuel system. They are made by an actual automotive instructor.

His example vehicle is a 3800 Series II Buick. The first video is 1 hour and second about 20 minutes. He explains all the tools, observations and conclusions very well.

http://www.youtube.com/watch?v=RyEPOeQB0Zg

http://www.youtube.com/watch?v=EAvoz4kqw9g
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Old 01-29-2015, 03:11 AM
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i might need to spend some time watching that. My fuel system has a leak somewhere and I'm certain its in the tank.
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Old 01-29-2015, 11:10 AM
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i might need to spend some time watching that. My fuel system has a leak somewhere and I'm certain its in the tank.
If that video doesn't help, maybe he's got another.
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Old 01-29-2015, 02:09 PM
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Thanks for pointing me to the exhaust.

This video shows how to test backpressure. I will try that next instead of fuel system.
https://www.youtube.com/watch?v=9TlygJMxTps
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Old 01-30-2015, 12:54 AM
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I went ahead and got a fuel pressure gauge. The pump and pressure regulator seem to be operating normally.

I will take it to an exhaust shop for a backpressure check tomorrow morning. Hopefully that will lead to an answer instead of more questions.
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Old 01-30-2015, 01:01 AM
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cool i'm glad its not fuel related. you dont have a hatch cut already
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Old 01-30-2015, 10:10 AM
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Got code P0420 on way to exhaust shop. I think we are on the right track. Waiting on them to check it.


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