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Old 09-04-2015, 11:37 PM   #1
Minorthreat7171
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Default Warm Start Misfire Help

Hello, I've done the research and have read the "similar threads we found" before posting this. The only reason I'm making this thread is my mechanic has asked me to get on the forums and ask what people think and have done to fix this before we start throwing money at a problem.

07 WRX catted turboback exhaust, Cobb SF intake, kartboy leightweight crank pulley (still using factory fly wheel) and tuned for said parts.

I've been getting misfires in cylinder 3 and occasionally 1 on warm starts.

I have changed the sparks and coil packs, cleaned the grounds and added the "big 3", put in a new MAF sensor, have no boost, intake or vacuum leaks and have had a compression test done.

Compression is showing 120 all the way around, which is low but to my understanding isn't uncommon with 7+ year old cars with 110k miles.

We've cleaned the throttle body, top end cleaning and ran pure injector cleaner.

At the moment we're thinking it's a leaking injector. Any other thoughts?
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Old 09-04-2015, 11:58 PM   #2
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What does the fuel pressure read when this happens? It should hold some residual fuel pressure.
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Old 09-05-2015, 12:06 AM   #3
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Not sure what the actual pressure is but he said it drops 11% after 5 minutes, 14% after 10 and 16% after 15
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Old 09-05-2015, 09:47 AM   #4
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Have you tried to change your fuel filter? Something else to look at.
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Old 09-07-2015, 11:47 PM   #5
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Is it for sure a dead miss or does it just seem to run rough? Also im assuming you have ruled out the quality of the fuel. Is it only when the vehicle has heat soaked or do you notice it any other time at all. Does it have any other noticeable driveability issues? Have you recently changed anything prior to the issue no matter how insignificant it may seem? How long does it take for it to smooth back out after restart? Sorry for all the questions.

Last edited by mbtech764; 09-07-2015 at 11:48 PM. Reason: more questions
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Old 09-08-2015, 12:03 AM   #6
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Quote:
Originally Posted by mbtech764 View Post
Is it for sure a dead miss or does it just seem to run rough? Also im assuming you have ruled out the quality of the fuel. Is it only when the vehicle has heat soaked or do you notice it any other time at all. Does it have any other noticeable driveability issues? Have you recently changed anything prior to the issue no matter how insignificant it may seem? How long does it take for it to smooth back out after restart? Sorry for all the questions.
Dead miss but since cleaning the top end, throttle body and injectors it seems to be just a rough idle, it goes back in tomorrow for more testing.

Doesn't matter where I fuel up at it still happens.

Yes, only when it's a heat soaked start. No misfires while driving or idling at a red light.

Just the standard 100k-120k maintenance: water pump, new pulleys and timing belt and added a lightweight crank pulley.

At most 20 seconds to smooth out.
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Old 09-08-2015, 11:14 PM   #7
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Did you put the plugs in after the misfire problem started or before while you were doing the maintenance. Also do you have any kind of heatshield on the hot side of the turbo or dp. Do you still have the old plugs around and know which cylinder each came from to attempt to read them.
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Old 09-08-2015, 11:21 PM   #8
Minorthreat7171
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Changed the plugs after the misfires. I do have a heatshield but it's securely held in place.

I no longer have the old plugs but when my mechanic removed the new ones for the compression test. 3 was black and 1 had a small amount of black. Which is why we're thinking its an injector issue.
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Old 09-09-2015, 12:34 PM   #9
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The only reason im not thinking injector is because i would seem to think that you would have the issue every time you restart not specifically when hot. It is possible though. Have you checked the o2 sensor values.
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Old 09-09-2015, 05:28 PM   #10
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Was also thinking about this while at work today. I know you said you ran a compression test on the vehicle and the numbers seemed lower than expected but okay. Was curious because as the engine gets hotter the valve lash gets tighter, im wondering if your valve clearances are set too tight and youre only noticing an issue at hot start. A lot of people dont realize valve lash gets tighter over time due to the fact that typically the valve face and seat wear before the cam or lifter does. Just a thought, i know it seems unlikely as you dont seem to have any other driveability issue.
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Old 09-25-2015, 10:58 PM   #11
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After my mechanic had it for a week running tests, taking notes, swapping senors etc. he's concluded that mechanically everything is fine other than its running too rich on idle.

So next week I'll get a hold of my tuner and see what he thinks.

Thanks to mbtech764 and bush57 for your input.
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Old 09-26-2017, 02:40 PM   #12
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Quote:
Originally Posted by Minorthreat7171 View Post
After my mechanic had it for a week running tests, taking notes, swapping senors etc. he's concluded that mechanically everything is fine other than its running too rich on idle.

So next week I'll get a hold of my tuner and see what he thinks.

Thanks to mbtech764 and bush57 for your input.
Did he actually pull the valve covers and measure the lash on the intake and exhaust valves? If so, what was it?

After everything else you did, if that was not done, I can almost guarantee you that's what the problem is. It did not show up in a compression or leak down test for me.
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Old 11-23-2019, 07:45 PM   #13
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Was this ever resolved? I have the same problem on my 06 STI. Did you ever change the AVCS solenoid?
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Old 11-24-2019, 09:36 PM   #14
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Was this ever resolved? I have the same problem on my 06 STI. Did you ever change the AVCS solenoid?
Sorry. I gave up, got a second vehicle and started saving towards an IAG Performance short block and motor build.
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Old 12-07-2019, 10:39 PM   #15
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Quote:
Originally Posted by Minorthreat7171 View Post
Sorry. I gave up, got a second vehicle and started saving towards an IAG Performance short block and motor build.
Damn I wish this problem was solved. Im having the same issues on my built 06 STi. Only happens when I start the car shortly after being turned off ie gas station fill up. If the car is allowed to sit and cool off then started no misfire. Driving me crazy because car runs great but it makes me second guess whenever I want to flog it.
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Old 05-22-2016, 12:55 AM   #16
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Update: though I'm sure no one cares but it annoys me when people post problems, then never mention what the solution was.

Three days ago I changed the FPR and hoses. I've noticed warm starts are getting smoother each time and I haven't gotten a check engine light.
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Old 06-04-2016, 03:47 AM   #17
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Another update:

After a week the misfires came back under the same circumstance. After more research I've found it could be the AVCS solenoid and this is a stretch but Intake Manifold gasket

Also, during this past week I've been running Cobbs stage 2 economy tune (realtime) and the codes vanished on their own and didn't come back.
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Old 08-26-2016, 08:17 PM   #18
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Have yet to do anything since the FPR was replaced.

Back on July 3rd my transmission went out and since it was replaced I haven't had the misfire, rough idle or check engine light come back.

I don't see how that would fix anything but oh well.
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Old 09-02-2016, 05:48 AM   #19
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Well poop.

This happens to my 07 WRX as well. It will only do it on a warm start above the 2nd line on the temp gauge. At or below that line and there's no problem. I've changed coil packs, I've changed injectors(first for same type OEM and now for ID1Ks) and I've changed plugs. We've cleaned the maf a few times, checked function of my o2 sensors, cleaned the TB, etc.

But my transmission is still in there until I buy an 07 STi that's been wrecked and go 6 speed... So guess I'll see if that helps
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Old 09-02-2016, 06:02 AM   #20
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Quote:
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Well poop.

This happens to my 07 WRX as well. It will only do it on a warm start above the 2nd line on the temp gauge. At or below that line and there's no problem. I've changed coil packs, I've changed injectors(first for same type OEM and now for ID1Ks) and I've changed plugs. We've cleaned the maf a few times, checked function of my o2 sensors, cleaned the TB, etc.

But my transmission is still in there until I buy an 07 STi that's been wrecked and go 6 speed... So guess I'll see if that helps
I'll check my receipt later to see if he did anything else while he had it to let you know.

Just had it come back 2 days ago but I'm thinking bad gas because a few people I work with filled up there the same day and are throwing misfire codes as well.
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Old 10-10-2016, 06:25 AM   #21
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@91_Rugby_Subie
My bad, I did check the receipt last month and there was nothing but transmission work.


Since then I've filled it up several times at Sunco and Shell and still misfires.

Going to try new fuel pump and filter. Only reason I'm thinking this might be the problem, is the other day I went WOT to pass someone hogging the left lane and I had, what felt like, a fuel cut but not like the one that happens when you have a over-boost issue. More like a hiccup than the sudden jerk.
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Old 05-15-2017, 08:45 PM   #22
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Finally got around to doing the fuel pump. Car runs smoother but I'm still getting these heat soaked misfires.

However, it has drastically cut the time in takes for it to smooth out and idle normally.

So other than Seafoaming everything and getting it retuned, I'm not sure what else to look into.
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Old 05-15-2017, 10:27 PM   #23
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Did you ever add a few grounding straps from the manifold to the frame?
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Old 05-16-2017, 12:10 AM   #24
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Did you ever add a few grounding straps from the manifold to the frame?
Yeah. Cleaned the factory grounds as well.
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Old 09-24-2017, 02:23 AM   #25
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Was this ever resolved? I am having the exact same issue on a new build and it's making me crazy.
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