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Power Hesitation


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I believe the flex up pipe is needed if you do a EL header. With stock header any solid up pipe is fine. Or a used STi up pipe.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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hard to say what all is going on without some more detailed diagnostics. Pulled timing feels like a hesitation, or drop in power, but the power loss you describe sounds more pronounced.
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You do know that the O2 sensors also act different for the first 60 miles.

 

Emissions testing can tell if the car hasn't been driven the 60 miles after a reset.

 

 

I see your was replaced....? Can you trust them ?

 

What's FB price for a MAF, $140 ? Fredbeans is a Vendor on here.

 

If you clean the MAF and get the car to a Tuner so he can data log he may be able to fix the stumble while he's plugged in.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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@Max Capacity: thanks for the Fredbeans lead. I cleaned the MAF, but am thinking its the MAP sensor (or fouled up EGR?). I'm thinking MAP because when I disconnected it from the ECU while the car was running it ran the same. Or am I wrong?

 

I figured bad O2 sensors would definitely throw a CEL since the car passed emissions running like this. Go figure.

 

As for trusting if the dealer did anything they said they did... I have zero confidence.

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I unknowingly installed a MAP for a 2010-2014 LGT. It ran great for 2 days then went back to the same ole hesitation. The MAP came out of a 2005 parts car and apparently the previous owner put this newer MAP on. He had done a bunch of mods (turbo, intake, up-pipe, etc) so I don't know if that makes a difference or not.

 

My question is: is there a major difference from a 2005 MAP sensor from 2010? The 2005 part# 22012AA160 vs 2010 part# 22012AA230

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It's just a MAP sensor, I don't think it should really be that different. But may be the Tuner can make the small adjustment to the math that it sends to the ECU.

 

You should contact a Tuner and ask.

 

I know a good one if you want his name, I may have posted it earlier here.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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I figured bad O2 sensors would definitely throw a CEL since the car passed emissions running like this. Go figure.

 

NOPE.

 

I had a bad front O2 Sensor (OEM) in my car and was having similar (albeit less severe) hesitation problems and it threw NO codes ever. I didnt throw a code until I swapped in an after-market sensor (which didnt work). It might be worth checking out. If you replace, replace O2 with an OEM O2 sensor. Here's what I found:

http://legacygt.com/forums/showthread.php/stumble-stutter-thread-182559.html?p=4801849#post4801849

 

That full thread has a lot of useful info too!

 

Good luck!

Go Cardinals!

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@Meltdown: Awesome, thanks! I'll look it over tonight. I was also thinking the O2 today. Even though there is no code would real-time data detect an issue with the O2?

I did not log any real time data myself, but I believe I read in that thread where someone had do that to determine their O2 sensor was bad (also without throwing any codes). As for me, I was fairly certain it was an O2 sensor, so I just bought a new one. Again, if you replace, replace OEM. There is something about the Denso aftermarket that isnt up to the OEM specs, not sure what...

 

I wish you luck, sir!

Go Cardinals!

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  • 1 month later...

Bank 1 is the front O2 in the right wheel well, Bank 2 is the rear O2 in the end of the downpipe.

 

As far as I know GT's don't have a sensor 2.

 

The front O2 is the one that helps meter fuel flow, yes use a OEM sensor.

 

When you talk the the guy's at fredbeans ask them about sensor 2 ?

 

Or ask the guy's at EFI, they'd know too.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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  • 2 weeks later...

Okay, replaced bank1 O2 (pre-cat passenger side wheel well), and it fixed a lot of problems with power hesitation. During this whole diagnosis process I noticed a power surge while driving. I figured it was all related to MAP & O2, since putting the old MAP back in (after I replaced the O2) the car just fell apart hesitating bad. Popped the replacement MAP back in and reset the CPU and it rain marginally better (still surging power).

 

But I'm now thinking it could also be the fuel pump since power surging is an indicator that it is on the way out. From what I've read the fuel filter is unserviceable, so has anyone replaced their fuel pump? I believe it is in the gas tank for an 2005 LGT. Or am I wrong?

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I think it comes with the filter or you use the OEM one on the pump frame.

 

Don't forget to replace the o-ring too.

 

There's a DIY here somewhere.

 

Google it. how to replace fuel pump on a 2005 Legacy GT

 

https://www.google.com/search?hl=en&source=hp&q=how+to+replace+fuel+pump+2005+subaru+legacy+GT&gbv=2&oq=how+to+replace+fuel+pump+2005+subaru+legacy+GT&gs_l=heirloom-hp.3...1482.25802.0.26535.50.19.2.20.22.0.2620.5989.0j3j12j9-1.16.0....0...1ac.1.34.heirloom-hp..25.25.6051.1qvsqSbgbjc

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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filter comes with the pump (at least it did with the 65c). it's basically just the screen at the intake that presses onto the pump. I added an inline filter in the engine bay to help dampen injector pulses and add another level of filtration.
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  • 2 weeks later...

Replaced Crankshaft Sensor today - no change. Replaced Boost Control Solenoid today - no change. Cleaned the MAF Sensor today - no change. Thursday I'm replacing the Cam Shaft Sensor on the passenger side because being near the turbo probably isn't good for any sensor.

 

I find that when I reset the CPU the car will run marginally better for the first 60 mile drive cycle. After the CPU learns it is then relying solely on sensor data - and apparently a sensor is malfunctioning and not giving a CEL (please correct me if that sounds completely bonkers!). Also, in the evening when its cool out, or on a cool day, it will also run marginally better.

 

For anyone else who may have stumbled across this thread because they are going through the same hell, look to this thread as well:

http://legacygt.com/forums/showthread.php/lag-2000-3000-rpm-bad-coil-pack-boost-control-solenoidi-213409.html

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So, I replaced both Cam sensors, and the problem one was not the passenger side next to the turbo, as originally thought, but was the driver-side. Go figure. BUT, the hesitation is GONE! I'm going to clean the OCV's next week and inspect for anything fishy with them to be safe - and if need be replace them.

 

I really appreciate everyone's feedback. This is a great community!

 

These are for Furious George since he asked for the location. Unfortunately the driver-side sensor was buried under a lot of engine chaos and was installed blindly - so no pics.

 

Cam Sensor Passenger Side:

http://machinenoise.com/subaru/cam-sensor.jpg

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