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Discussion Starter #743
I'm getting some kind of stumble into boost. It's a new thing. It's almost like the car tries to fall flat and then picks up again like normal. Smoke tested it, no leaks. Hmmphf


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Discussion Starter #745
I was thinking that too, I did pull one and it looked ok. I have about 10k on these. I'm wondering what interval people are running for spark plug changes.


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I was thinking that too, I did pull one and it looked ok. I have about 10k on these. I'm wondering what interval people are running for spark plug changes.


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I like 30K intervals on 1 step colder spark plugs. Some people may even say to replace them earlier than that. I guess it all depends on what kind of power levels and abuse they deal with. I think if your getting a stumble while entering boost i think you should start there. I would also say maybe get a fuel pressure reading too.
 

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Discussion Starter #747
I'm thinking it's possible it's blow out. The car basically hesitate and then takes off like a rocket.


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Discussion Starter #750
This could be similar to the stumble user mentioned a week or so ago due to e85 gunk build-up? If so, it would be a super easy fix...
Just read it... interesting, and relatively cheap. I will try it either way, since I haven't had any 93 in the car for a little while now.

Ordered new plugs also. I did pull one, and while it looked ok the gap appears to have opened up to .034-35 (I had them at .030 IIRC, I will probably drop it to .028) soooo that would surely cause some issues. I left it for now since I didn't have the time/will to pull all 4. My hands aren't *BIG* by any means, but they also aren't small either LOL

I'm actually thinking it might be easier to do the plugs from underneath the car. :confused:
 

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Discussion Starter #751
So I got into it today, and I'm now fairly confident it's spark plug related. I have been hesitant to give it any real throttle but I attempted today, to get to the bottom of it, and it mimicked what I've felt spark blow out to be on prior turbo charged cars.

Now to find the time. >_<
 

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Discussion Starter #752
2 hours start to finish. Car still stumbles in boost. No knock. No misfires.


What.






The.





Fuck.


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Have you checked your fuel pressure yet while entering boost? Also get a fuel quality sample. You can never be to sure. Does this issue happen only under boost? Will it continue to get worse as you increase boost?

Im suspecting a fuel pump issue but i think you should really get fuel pressure reading at key cyle, idle, driving, and under boost.
 

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Discussion Starter #755
coil packs? bad gas? vacuum leak?
I was thinking coil packs are possible, but I'm not really seeing any misfire events. It's initially why I was skeptical on the blow out issue, but I figured maybe it's flukey.

I think I can rule gas out as this is now across 2 tanks. I have debated putting 93 back in to see if that changes anything, but I'll have to wait till I burn this tank off.

We did smoke test it, but the regulator is only a 3psi version so we are thinking about upping the pressure and seeing what happens.


Have you checked your fuel pressure yet while entering boost? Also get a fuel quality sample. You can never be to sure. Does this issue happen only under boost? Will it continue to get worse as you increase boost?

Im suspecting a fuel pump issue but i think you should really get fuel pressure reading at key cyle, idle, driving, and under boost.
I do have the fuel pressure logged, and it does seem to rise with boost. So we didn't look too closely at it, I will have to revisit it now that the issue persists.

Fuel wise, I think I'm good because I'm across 2 tanks, from separate stations.

It's funny you mention fuel pump, I briefly debated it but wrote it off. So today I did notice what seems to be a "hold back" while cruising around ~2500RPM. Almost like the car is being held back a little bit. Hard to explain, and I wouldn't call it a hesitation per-se because I'm just cruising, but there is something going on. So fuel pump is back on the table, or maybe something weird with the FPR. Idle FP is around ~24PSI (07 Sti FPR)

Essentially, what it feels like is upon entering boost the car will stumble, kind of fall flat, and then all of a sudden you get a kick in the pants and it takes off as it normally would. I typically don't pull it much past that. The other day, when I got a decent run in, is when it felt like blow out.

As much as it's going to pain me, I'm going to need to get a log of what's happening when I push past the initial hesitation. :(


All in all, the car runs well. Idle is smooth, no weird noises.
 

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Discussion Starter #756 (Edited)
So here is a small snippet of the log RPM/Boost/FP The red slash mark is ~1PSI. Boost curve looks smooth, I don't really see the "issue" present, but it did happen for this log.




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Discussion Starter #757 (Edited)
Different snip from the same log. Red line is begining of positive boost pressure. I do feel like the FP gets a little screwey and then all of a sudden it shoots up.

The very low red(FP) valley as the green(boost) rises is 25PSI vs 5PSI respectively.
B | FP | RPM
4.35 28.27 3958
5.27 28.27 4035
5.94 25.1 4025
7.07 32.67 4036
8.61 41.33 4234






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Discussion Starter #758
Since this is all I think about, I'm going to go out and test the regulator base pressure with no vacuum attached at lunch.

The fuel pressure can't be correct.
 

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Discussion Starter #760
Startup Idle fuel pressure sits at 36-37PSI fuel pump duty sits at 100%. About 20 seconds later the fuel pump duty drops to 33% and the idle fuel pressure drops to ~25PSI



Hmm
 
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