Loss of power at WOT
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Loss of power at WOT
Hello all, been having an issue with my '01 ex. Under WOT there is a significant loss of power, if I back off the throttle to maybe 80% the power is regained and everything feels normal. This happens basically everywhere in the rpm range. It did throw a code once and it was the dreaded P0171 System too lean. Searching the forum for this code brings up multiple threads but none really seem to go anywhere. I initially cleared the code (while removing another I had fixed) and it has not come back after 3-4 test drives going WOT each time but the power issue persists.
I've done a little bit of data logging trying to track down the issue but I don't know enough about the short term fuel trim and primary o2 sensor readings to understand what's going on.
-Cruising down the road at about 55 mph with the cruise set the STFT% is around 35-40%.
-Cruising down the road at about 55 mph with the cruise set the primary o2 sensor constantly fluctuates between 0V and 0.8V.
-Under WOT through first and second the STFT% seems to be between 30-40%, my scan tool only pulls data every few seconds so this is difficult to get.
-Under WOT through first and second the primary o2 sensor is fluctuating between 0V and 0.8V, again, scan tool only pulls every few seconds so it is difficult to read.
Does anyone have any insight on these? Any recommendations for next step?
I've done a little bit of data logging trying to track down the issue but I don't know enough about the short term fuel trim and primary o2 sensor readings to understand what's going on.
-Cruising down the road at about 55 mph with the cruise set the STFT% is around 35-40%.
-Cruising down the road at about 55 mph with the cruise set the primary o2 sensor constantly fluctuates between 0V and 0.8V.
-Under WOT through first and second the STFT% seems to be between 30-40%, my scan tool only pulls data every few seconds so this is difficult to get.
-Under WOT through first and second the primary o2 sensor is fluctuating between 0V and 0.8V, again, scan tool only pulls every few seconds so it is difficult to read.
Does anyone have any insight on these? Any recommendations for next step?
Re: Loss of power at WOT
Sounds like low fuel pressure. The in tank filter on mine clogged and caused the same thing. Check the fuel pressure at idle AND on a snap throttle test. T in a gauge by the fuel rail, and see what the pressure is with the motor running. O’reilly Auto will rent you a gauge kit for free. The fuel pressure should be about 45 PSI with the engine running, and it shouldn’t drop much when you snap the throttle. I hope this helps.
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Thanks for the reply.
My first thought was there wasn't enough fuel, and reading some of the other threads seemed that was possible. I was trying to avoid having to buy a fuel pressure test kit but I was not aware O'reilly had them available to rent. I will have to try that soon.
My first thought was there wasn't enough fuel, and reading some of the other threads seemed that was possible. I was trying to avoid having to buy a fuel pressure test kit but I was not aware O'reilly had them available to rent. I will have to try that soon.
Re: Loss of power at WOT
Thanks for the reply.
My first thought was there wasn't enough fuel, and reading some of the other threads seemed that was possible. I was trying to avoid having to buy a fuel pressure test kit but I was not aware O'reilly had them available to rent. I will have to try that soon.
My first thought was there wasn't enough fuel, and reading some of the other threads seemed that was possible. I was trying to avoid having to buy a fuel pressure test kit but I was not aware O'reilly had them available to rent. I will have to try that soon.
"Marge, anyone could miss Canada! All tucked away down there."
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From: Barrie, ON Canada
Rep Power: 221 Re: Loss of power at WOT
Thanks for the reply.
My first thought was there wasn't enough fuel, and reading some of the other threads seemed that was possible. I was trying to avoid having to buy a fuel pressure test kit but I was not aware O'reilly had them available to rent. I will have to try that soon.
My first thought was there wasn't enough fuel, and reading some of the other threads seemed that was possible. I was trying to avoid having to buy a fuel pressure test kit but I was not aware O'reilly had them available to rent. I will have to try that soon.
Re: Loss of power at WOT
Correct. But once you return it undamaged, you get all your money back like you said, so it’s free in the end. Another tip: Make sure that the gauge comes with all the pieces and that nothing is damaged before you accept it. You don’t want to get blamed for something someone else broke, stole or lost. They tried blaming me for a small scratch on a compression tester that was there when I rented it. Fortunately, I had a picture of the gauge on the counter in the store before I took it home, so they refunded my money.
"Marge, anyone could miss Canada! All tucked away down there."
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From: Barrie, ON Canada
Rep Power: 221 Re: Loss of power at WOT
any other parts stores closer? all the big chains should do the tool rental
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I originally checked Autozone's website as they are the closest to me but I couldn't find anything (I really dislike their website). I just checked again though and was able to find one available at a store 10 minutes away. I'll have to stop by on my way home from work. I'll keep you updated with results.
If you think a good mechanic is expensive, try hiring a bad one
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From: Midwest. Aiming about mid-chest
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You can have good pressure in a test at idle but still have insufficient fuel delivery (low pressure) during high demand conditions.
Make sure to drive it hard enough to experience the problems so you can read fuel pressure during the problem
Make sure to drive it hard enough to experience the problems so you can read fuel pressure during the problem
Re: Loss of power at WOT
Correct. This is why I said to do a snap throttle test also.
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Well fellas, I was able to hook up the test kit well enough to get a good fuel pressure reading. At idle it was only at 30 psi, looks like I'm in need of replacing the fuel filter and strainer as others have done.
Re: Loss of power at WOT
If you think a good mechanic is expensive, try hiring a bad one
Joined: Dec 2011
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From: Midwest. Aiming about mid-chest
Rep Power: 517 Re: Loss of power at WOT
At idle it was only at 30 psi,
Honda only sells the filter assembly complete with pump as a single unit.
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To close this thread off I got the filter and strainer replaced yesterday. I also discovered a previous owner had been in the tank before me and broke a piece off the cage thing that the fuel pump goes in. They broke the fitting that the output of the pump connects to and tried to hold it together with zip ties 
This could have been why the pressure was so low because there wasn't a good seal between the two. Anyways, got it all back together and went for a drive, no more stumbling at WOT. Thanks for all the help 
This could have been why the pressure was so low because there wasn't a good seal between the two. Anyways, got it all back together and went for a drive, no more stumbling at WOT. Thanks for all the help Re: Loss of power at WOT
To close this thread off I got the filter and strainer replaced yesterday. I also discovered a previous owner had been in the tank before me and broke a piece off the cage thing that the fuel pump goes in. They broke the fitting that the output of the pump connects to and tried to hold it together with zip ties This could have been why the pressure was so low because there wasn't a good seal between the two. Anyways, got it all back together and went for a drive, no more stumbling at WOT. Thanks for all the help
This could have been why the pressure was so low because there wasn't a good seal between the two. Anyways, got it all back together and went for a drive, no more stumbling at WOT. Thanks for all the help 
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