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Gas mileage pretty bad


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  • 2 weeks later...

Update. Been out of town. So I replaced the exhaust manifold gaskets and on one of them had black staining all the way through it. The other one failed the soap and water test I think. Hard to tell if it was boiling or building bubbles. Haven’t had time to get a normalized mpg but it is up to 20mpg without changing driving habits or routes. Matches super close to what the digital mpg states. So I’m not concerned about that anymore. I think the car is running much better now.

 

I’m still getting wierd fluctuations in rpm only when I hold the accelerator between 1000 to 1700 rpm and on warm up. Never at warm idle though. Also, it’s been warming up and at the hottest part of the day I parked the car for about 20mins after being fully warmed up. When I went to start it again, it acted like it didn’t want to run for about 5 seconds before smoothing out. From my research I found that the evap purge solenoid May be suspect but I just replaced it with an oem one because it was the cause of a major vac leak. Im thinking maybe I crossed the vac lines. It should be arrow pointing in the direction of vacuum right? Other people said it’s super common and to get used to it. Not gonna happen. Another suggestion was the tune may be a little wonky. Other people said injectors as big as mine can cause low rpm stuff and gave an analogy of using a sledgehammer to nail a tac.

 

I’m kind of leaning in the direction that I need a retune because everything I just fixed could have been present at the initial tune. Any input on this? Could a bad tune cause those rpm fluctuations and rough hot start? Pretty sure I have found everything it could be maybe not though. On my next couple days off I’m thinking about just rebuilding the entire vacuum system to be 100%.

 

Recap of things done:

Cleaned MAF

Replaced front and rear O2 sensors

Pressurized system to 10psi and found all vac leaks

Replaced exhaust manifold gaskets

Replaced evap purge solenoid

Reflased tune

Datalogs in first couple of posts for reference

 

Thanks for all the help so far everyone!

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where are you located? if Denver, someone like Dave at Cryotune usually does a thorough pretune inspection as part of the tuning process. probably a good next step. that rpm fluctuation you describe was exactly what i experienced with an uppipe leak at the collector. i could see values from the O2 bounce in real time logging while holding the car at that rpm. but also log throttle angle to rule out something wrong with the TB or pedal sensor.
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where are you located? if Denver, someone like Dave at Cryotune usually does a thorough pretune inspection as part of the tuning process. probably a good next step. that rpm fluctuation you describe was exactly what i experienced with an uppipe leak at the collector. i could see values from the O2 bounce in real time logging while holding the car at that rpm. but also log throttle angle to rule out something wrong with the TB or pedal sensor.

 

Good point there I’ll log that. I didn’t want to stray too far away from an AP tuner but may if it’s worth it. What’s their price by chance? Stupid question but what is the collector? Basically where it connects to the turbo? It’s a single piece of piping from the manifold to the turbo.

Edited by boostaru
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Dave uses AP, not sure what he charges for in-person work, only ever had a remote tune from him: https://www.cryotuneperformance.com/

 

By collector I meant where the exhaust manifold meets the uppipe that connects to the turbo, the part by the O2 sensor that you can see close to the bottom of the engine.

 

Do you have aftermarket header? otherwise there should be a 2-bolt junction by the O2 where the exhaust turns up towards the turbo

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It’s one solid piece which actually really sucks but whatever. At this point I think I’m going to pay someone to smoke test the vac, boost and exhaust. I’ll let you all know the outcome. Edited by boostaru
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  • 3 weeks later...
Alright final update just to close a thread. Took it to Dave at Cryotune and we sorted things out. It actually turned out to be in the tune. And he really opened this thing up a bit as well. Turns out the previous tuner was on speed density which I guess was a bit weird. Some other odd things Dave mentioned but didn’t make sense to me. Thanks for the recommendation I didn’t realize he was so popular on this site. Now I know why.
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