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Old 04-02-2023, 06:12 PM   #26
transmutation
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Update: switched out the smoke machine heating element and got it to work - smoked both the intake track from the intake filter location and also smoked the exhaust since the machine was set up and didn't find any leaks at all. I'm not completely ruling out a leak as I was having some issues getting a good seal at the intake but there doesn't appear to be anything significant and enough pressure was built up to inflate a latex glove i was using to block off the intake.


Quote:
Originally Posted by 19std View Post
Man im going with you got dirty injectors at this point, dump some fuel system cleaner in there and then next tank dump sume techron in there. Maybe a dirty fuel filter.

Are you using 93? Like only shell, marathon, bp top tier gas? Not convenient mart rusted underground special 89+ right?

Really don't think it's a vacuum leak, and if you find a tiiiny one with your smoker almost positive issue will persist.
Yeah I was skeptical of O2, it throws codes.

Are there any codes? Edit* any codes that happened any time, maybe you cleared one somewhere??

Throw up some logs if you have any.

Car has only used Shell or Chevron 92 (best we can get in this area) from a newer station which used to be a Shell and then switched to Chevron a few years ago so Chevron is what the car has been using. Car has never thrown a code since I bought it but will see if there is anything pending - i know I've seen that with other cars that the system will note something isn't quite right but not off enough to actually trigger a code. Don't know if Subarus work that way though. Edit: checked for codes with the AP and none found. Also checked for pending codes using my Ultra Gauge which also returned nothing.

Injectors are starting to look like the next possibility but wouldn't that likely cause other problems? Just seems weird that the car runs fine other than the idle drop off from a rev when no load is on the engine.
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Last edited by transmutation; 04-02-2023 at 10:23 PM.
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Old 04-02-2023, 11:41 PM   #27
19std
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I will say this: hope you are not chasing a ghost, you may never find it, I'm currently chasing a driveline gremlin lol.

But if it's definitely real then you just gotta go down the list. You have done the sinple stuff... Throw up a log if you have any, if not go get some logs!

Edit: your getting in deep, may also help to throw up what you haveneliminated so far, like air filter etc.

Also wouldn't hurt to call your tuner, sure he has heard this one before, just to get some ideas of where to go next...
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Old 04-03-2023, 11:28 AM   #28
transmutation
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Quote:
Originally Posted by 19std View Post
I will say this: hope you are not chasing a ghost, you may never find it, I'm currently chasing a driveline gremlin lol.

But if it's definitely real then you just gotta go down the list. You have done the sinple stuff... Throw up a log if you have any, if not go get some logs!

Edit: your getting in deep, may also help to throw up what you haveneliminated so far, like air filter etc.

Also wouldn't hurt to call your tuner, sure he has heard this one before, just to get some ideas of where to go next...

Good suggestion for logs - will try to get some this week which capture RPM, ST and LT trims.

In summary I've tried the following:
- Replaced Cobb filter with a new one
- Cleaned MAF
- Cleaned Throttle Body
- Disconnected battery for 30 minutes and did idle relearn procedure
- Smoked intake tract and exhaust and found no leaks
- Replaced front and rear AFR and O2 sensors
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Old 04-07-2023, 07:47 AM   #29
Eegoor
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Cool No boost leak

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Originally Posted by 19std View Post
Im not sure at what point that pressure measurment is, you know before or after the regulator...

But yes, just work backwards to the last time you had a working car lol, and slowly troubleshoot from that point to isolate most likely cause.
**Update**

Well, no boost leak, I ran out of things to check and I ran out of time before my tune. I called my tuner and explained to them what was going on. They said with all the bolts ons I have and going from the STI OEM injectors to 1050x that my car is NOT going to run right at all. I had to get it towed to the shop. It passed inspection and they tuned it on the dyno. It runs GREAT now! Sorry for hijacking your post. I just wanted to give an update.
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Old 04-07-2023, 01:15 PM   #30
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Glad you got your problem figured out!
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Old 04-07-2023, 01:42 PM   #31
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Forget all that vacuum/boost leak crap - negative fuel trims mean you have a rich condition - to much fuel. The ECM is reducing the fuel. Vacuum leaks would give positive trim - adding fuel due to too much air.
Since you have swapped the A/F sensor next thing I would look at is what the ECM sees for coolant temperature. an open wire, open sensor, or incorrect reading (too cold) would cause a rich condition. One big clue would be extreme fuel smell in exhaust and possible black smoke.
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Old 04-07-2023, 01:55 PM   #32
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Quote:
Originally Posted by Elbert Bass View Post
Forget all that vacuum/boost leak crap - negative fuel trims mean you have a rich condition - to much fuel. The ECM is reducing the fuel. Vacuum leaks would give positive trim - adding fuel due to too much air.
Since you have swapped the A/F sensor next thing I would look at is what the ECM sees for coolant temperature. an open wire, open sensor, or incorrect reading (too cold) would cause a rich condition. One big clue would be extreme fuel smell in exhaust and possible black smoke.

Thanks for your input. The car does smell rich but no smoke (of any color) is visible. Dumb question - how can i see what the ECU is seeing for temps? Is that the same as what would be reported by the AP? I haven't noticed anything odd as far as temps and the car does get warm enough to kick on the fans but sounds like possibly there is more to consider here?

Last edited by transmutation; 04-07-2023 at 02:03 PM.
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Old 04-10-2023, 05:40 PM   #33
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Quote:
Originally Posted by transmutation View Post
Thanks for your input. The car does smell rich but no smoke (of any color) is visible. Dumb question - how can i see what the ECU is seeing for temps? Is that the same as what would be reported by the AP? I haven't noticed anything odd as far as temps and the car does get warm enough to kick on the fans but sounds like possibly there is more to consider here?
Yeah you have intake, ambient, coolant and maybe oil. If any of those are whacked out it could lead you to a cause is what EB is saying to check. Those are all on AP.
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Old 04-15-2023, 05:33 PM   #34
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Quote:
Originally Posted by 19std View Post
Yeah you have intake, ambient, coolant and maybe oil. If any of those are whacked out it could lead you to a cause is what EB is saying to check. Those are all on AP.

Thanks! Took the car out today and verified that coolant temp and intake temps seem to be reading correctly (coolant was between 180-185 for most part and intake between 59-73 with ambient of mid 50s). I have an STI so no oil temp gauge unfortunately.

I have an appointment with my shop this next week so hopefully they can figure out what is going on.
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Old 04-15-2023, 05:36 PM   #35
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Originally Posted by transmutation View Post
Thanks! Took the car out today and verified that coolant temp and intake temps seem to be reading correctly (coolant was between 180-185 for most part and intake between 59-73 with ambient of mid 50s). I have an STI so no oil temp gauge unfortunately.

I have an appointment with my shop this next week so hopefully they can figure out what is going on.
Yeah coolant and intake completely normal.
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Old 04-28-2023, 05:55 PM   #36
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Update but not really update:

Car went back to the tuner shop that installed some of the mods and did the dyno tune. They redid all the same intake tests that i did and eventually found a small leak on the driver side intake manifold. Replaced the gaskets and said all was well. Picked the car back up today and no real change - might be slightly better but definitely still not solved. Car almost dies when revs drop with no load on the engine.

Thinking next steps now are pulling the spark plugs (as i will be there) and injectors and see if i can find a place to clean and test the injectors. Open to any recommendations for that if someone has had a good experience with cleaning and flow testing. Also, is there a way to test the fuel pressure regulator just to rule that out?

Last edited by transmutation; 04-28-2023 at 06:31 PM.
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Old 04-28-2023, 05:55 PM   #37
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Double post, double no real update.
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Old 04-28-2023, 08:21 PM   #38
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Dont got much man, but sounds like a crappy tuner shop if they cant rule out spark and fueling. I mean its a 2018, so shouldnt even be an issue.

Did you get any logs?
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Old 05-20-2023, 09:59 PM   #39
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What's fuel pressure when it acts up? Maybe an injector is hanging open? That's my bet... Was it doing this before or during the first tune? Or did it randomly start doing that recently?
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Old 06-02-2023, 10:46 AM   #40
transmutation
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Quote:
Originally Posted by 19std View Post
Dont got much man, but sounds like a crappy tuner shop if they cant rule out spark and fueling. I mean its a 2018, so shouldnt even be an issue.

Did you get any logs?

Yeah not gonna lie pretty disappointing. Haven't pulled logs yet as other life things have been busy but will do some research on the whole Green Speed thing (my AP hasn't been plugged into a computer in several years) and look into that. Just trying to be careful as I'm running the older flex fuel system which Cobb discontinued. What data points would be good to pull?

Last edited by transmutation; 06-02-2023 at 11:14 AM.
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Old 06-02-2023, 10:54 AM   #41
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Quote:
Originally Posted by spoolinsti05 View Post
What's fuel pressure when it acts up? Maybe an injector is hanging open? That's my bet... Was it doing this before or during the first tune? Or did it randomly start doing that recently?

Fuel pressure sits between 34-35 or so measuring final pressure on the AP while the car is bogging. Raw pressure seemed to be about the same. Seems to stay at the same pressure when the idle settles out also. Issue was not present when car was stock or for maybe 1.5 years after mods and tune and just started earlier this year.


At this point I'm also wondering if something is going on with an injector as i believe i have ruled out a vacuum/boost leak, replaced both O2 sensors, cleaned MAF and TB, and also put in a new air filter. Once the car corrects itself it does idle fine and otherwise runs and accelerates great.
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Old 06-19-2023, 06:46 PM   #42
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Hey All,


I've recently over the last few months noticed this issue and wanted to see if anyone had any suggestions I could try to correct the problem.

The car is a 2018 STI (i am original owner) at 19K miles with the following mods:

Cobb turbo-back exhaust (with GISI cat)
Cobb intake
Cobb fuel lines, rails, fuel pressure regulator and 3 port boost controller
ID1300 injectors
AEM 340 fuel pump
IAG AOS
Cobb Flex Fuel kit
Pro tune by Drive Auto Sports

Install of the fuel parts (except pump), intake, AOS and E85 kit were installed by the shop that also pro-tuned on a dyno in April 2021. They also replaced the spark plugs at that point before the tune. Car has been running fine up until roughly a few months ago.

What I've started to notice is after the car is warmed up if I come off throttle and come to a stop the idle will drop really low and the car will almost die but it hasn't actually died up to this point. Note it doesn't always do this when coming to a stoplight but has displayed the same but milder symptoms. I can recreate the issue 100% of the time after my drive home from work after i come to a stop at my driveway and prepare to back into my garage. I've also noted that the short term fuel trims will drop to -25 to -35 when the bogging happens. LT fuel trims are generally between -5 and -6 depending on RPM. After the idle drops and the car almost dies the idle will pick back up, then drop, then pick back up sometimes for a couple of cycles and then will idle fine. Car starts and runs fine otherwise, accelerates great no other issues or codes. I can hit target boost of 19 and idle is around -9.8. I've cycled through a few tanks of gas thinking that might be the issue but that hasn't helped.

I've tried replacing the Cobb air filter and also tried cleaning the MAF using CRC cleaner (did not touch anything just used the pressure from the cleaner). The MAF didn't look all that dirty but easy to do so figured i would try it. Does this sound like a vacuum leak? Ideas you all would suggest i try before throwing in the towel and taking to a shop?

Updated list of things I've tried: cleaning throttle body, disconnected battery for 30 minutes and doing idle relearn procedure. I've noticed that the car seems to be running rich so hoping a new O2 sensor fixes the issue.
I'm battling a similar issue on mine. Once it warms up my idle becomes erratic. A/F starts bouncing rich to lean. Before I reset my learning, I had a A/F Learning (correction???) of 4.68%. So, I smoke tested the system. Had a couple leaks. Leak at the turbo inlet, AOS hose going into the block by turbo, Bypass hose going into the turbo inlet hose. Leaks all fixed, reset ecu learning, gave it a try no difference. Then I unplugged MAF, idle was perfect. A/F was pegged at 14.7. Took it for a drive with MAF unplugged (stayed out of boost). A/F started bouncing rich to lean when I came to a stop and idled eventually it smoothed out within 14 on A/F ratio. So, I decided to buy a new Denso MAF, No difference. i don't know what's wrong with this pos. I guess my next step is replacing the wideband. I have zero leaks and no codes.
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Old 06-20-2023, 03:55 PM   #43
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I'm no export but what you are describing does sound at least partially like symptoms of a failing O2/AFR sensor. The video I linked earlier in the thread has some details about that - the poster ended up unplugging his primary O2 to test it before springing for a new one.
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Old 06-21-2023, 09:16 PM   #44
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Just ran into the same exact problem a week ago... turns out it was a bad head gasket and a cyl 3 misfire, which was pushing coolant high up into the reservoir, which caused the factory radiator hose on top to rupture a few weeks prior... take it to a reliable mechanic and have him take the motor apart, then you'll know for sure.

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Old 06-21-2023, 09:29 PM   #45
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Also, replace your timing belt gears, they are worn. Do the entire service. #trust
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Old 07-06-2023, 11:12 AM   #46
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OP checking back in here. Still trying to figure out what is going on. Since last update I've done a compression test which check out fine (spark plugs looked good also) and also replaced the MAF just to rule that out. No change in the bogging behavior.

I will do my best to update this thread if i can figure out what the problem is.
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