Bucking when underload

M

Ms3.Owen

Greenie N00B Member
2010 mazdaspeed 3
I’m trying to figure out why my car is bucking saw some thread with people having similar problems but never saw an answer. Sometimes while starting the car normally when it’s warm the idle is at 500rpm until I tap the gas after that it seems to be normal. Also when accelerating only seems to be when I’m more then 50% throttle the car bucks and what seems to me like misfires. I’ve done the test where you shut the car off while warm and check fuel pressure with your Cobb ap and it’s supposed to go up and then drop down but mine just drops down. I’ve had the problem a few months ago but replaced my spark plugs and it fixed it until a couple weeks ago but this time it seems worse. If anyone had this similar issue let me know what you did to solve it. Thanks in advance!
 
I gapped them when I replaced them a couple months ago they shouldn’t be bad this quick I’m guessing there’s a fuel issue cause if them to foul out
 
So did you conduct the PRV test with a HOT motor. The test relies on the heat from the engine to cause the fuel pressure to rise.

Template public:_media_site_embed_youtube not found. Try rebuilding or reinstalling the s9e/MediaSites add-on.

Also take a data log of this behavior while driving and see what your fuel pressure is doing. This potentially sounds like a bad PRV but it could be other things. Post that data log here if you want as well.

Also can you look at the Troubleshooting sheet at the top of this section and include all that info here, it will help in trying to figure out what's going on.
 
Mtnbker3531 said:
So did you conduct the PRV test with a HOT motor. The test relies on the heat from the engine to cause the fuel pressure to rise.

Template public:_media_site_embed_youtube not found. Try rebuilding or reinstalling the s9e/MediaSites add-on.

Also take a data log of this behavior while driving and see what your fuel pressure is doing. This potentially sounds like a bad PRV but it could be other things. Post that data log here if you want as well.

Also can you look at the Troubleshooting sheet at the top of this section and include all that info here, it will help in trying to figure out what's going on.
Click to expand...
Yes I did it when motor was hot multiple times and watched this video over and over to make sure I was doing it correctly
 
Agreed your plugs "should" be fine. How many miles do you have on these plugs? Have you pulled them and checked the gap since youve started having this issue?

Do us a favor and include all the info included in the Troubleshooting Sheet.

What coil packs are on the car?
 
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Dumped a bottle of fuel injector cleaner in the tank and two days later she’s running perfectly no more bucking at wot !!!
 
Well I hope that works out for you long term. I wouldn't call this "fixed".

Fuel injector cleaner doesn't actually do anything to clean the injectors in these cars. They need to be professionally cleaned and flow tested.

Not exactly sure why this solution "worked" but I honestly won't be surprised if you are revising this issue.
 
I’m honestly not sure what happened to fix it I tried a few things a couple days ago I’ll see if it does it again today or tomorrow and update in here. It’s been rainy here for about the past month except for yesterday so it’s quite possible that has something to do with it
 
Forgot to mention these are what my plugs looked like when I pulled them
 

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Mtnbker3531 said:
Not sure what you are after at this point but it would help out A LOT if you could give us all the requested information for troubleshooting.

https://mazdaspeeds.org/index.php?threads/troubleshooting-sheet.13117/
Click to expand...
Sorry didn’t know where to find this I’ll fill it out now

Year/Make/Model: 2010 mazdaspeed3
Mileage: 250k km
Location: Canada
Concern: bucking under load (normally at wot or close to it)
DTC's: P0455 (P0302-showed up after bucking but doesn’t stay) abs and traction control light (abs pump according to a scanner)
Modifications
Cork sport short ram intake
Corksport Catless Downpipe
Corksport Catless Race pipe
Cobb boost controller
GFB Bov
Corksport intercooler piping (top mount)
ECU/Tuning Software: Cobb ap V3
Tuner: freeke tune
Is the concern intermittent? Kinda
Can you duplicate the concern? Yes
Recent Repairs: nothing engine wise
Correction:
 
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