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vacuum leak or dirty maf? misfire& day dependant boost levels

1723 Views 3 Replies 2 Participants Last post by  SebastianLeCrab
good evening all,
first off i have a 2004 AWM 5spd, no performance mods yet

a few days ago i installed a new south boost gauge, everything went fine, testing it that day ran numbers like 10-11 from low revs and ~8 at high revs

same with the next day.

day after that it would only boost till 8psi from low and ~5-6 from high revs.
looked at the T fitting and the gauge end was a little off, pushed it back on, tightened the 3 sides. boosted to the norm rest of the day

yesterday...same problem, max psi was 8. tried fiddling with the whole nylon hardline of the gauge for about 20 mins and it didnt seem to be stuck on anything. everything seemed fine. wouldnt boost past 8 or 7 for the rest of the night.

this morning, while driving to school, same thing, wouldnt boost past 8. then an engine light came on. immediate fault was the "cooling system performance" that ive been getting everyonce in awhile(ill get to it later :p) and a 'pending fault' for a cylinder 2 misfire :icon_eek: . so this made me think it had to be a vacuum leak somewhere,
got to school and checked the L hose and anything else i could, didnt fix anything that i knew of.

when i got back to my car(in the rain) and drove home...its boosting till 10 again, whole way home. wtf?

whats going on, im pretty positive i didnt push anything tighter together, and i dont want to bring it to a mechanic , cause my luck it'll boost normally when i do haha.
could the MAF just be dirty? or need replacing? or any rain-dependant vacuum leak?
any help would be awesome

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worked fine last night and 10 mins driving this mornings. remainder 20 mins it wouldnt go past 7 or 8.

any info on where to look besides the L shaped hose would be great.
You could try putting together a boost leak tester (do some searches for how) and see if you've got a leak somewhere.

Swap the #2 coil with the #4 coil and see if the misfire moves along with the coil. If it does, you've got a bad coil.

If you're doing consecutive WOT pulls you may be heat-soaking the side mount intercooler. Next time boost drops, try driving conservatively (stay out of boost) for a while to cool things off then see if it starts boosting back to the higher pressures.
thank you!

i havnt gotten another misfire yet which is great. i was plannin on doing the boost leak test today, as all of friday(~50 miles) is was not full boosting,
however saturday (~100 city miles) i was boosting wonderfully, as well as today! its like it doesnt want to be found haha
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