spdrcrpete

'97 TQM, K04, GIAC, 5 bar FPR, stock injectors/SIMC/plugs, Borla cat-back

I've had a longstanding misfire issue under load that seemed to get worse last week to the point I could only build 1-2 lbs of boost. I built the home-brew pressure tester shown in tons of threads and found 2 significantleaks,and repaired both. After that could still only get 5lbs of boost. Replaced plugs (stock) and no major improvement. I ran out of time to mess with it myself, and took it to my go-to guy for repairs. They replaced the #4 coil pack (probably cause of longstanding misfire) and repleced my N75J valve with stock N75 and replaced my ancient leaking TurboXS diverter valve with stock. The car runs great now, no CEL, no misfires, but ouly builds/holds about 14lbs of boost (used to be anywhere from 17-21).

The only other known issue with the car is a seeping valve cover gasket (oil buildup around top of plugs noticed when swapping).

Any ideas what could be the reason for the reduced boost?

Nate (ETKA+Scumbag)

o-rings are quite tired and should be replaced.

You say stock plugs, so are they Bosch plugs then? When were they last replaced?

Between those two and your leaky VCG, I'd say that's where your boost is going.

Just my 2ยข.

DVS27t

Did they check the wastegate lines themselves?

spdrcrpete

Probably, but I can do that tonight as well. My previous experience has been that if the wastegate line is messed-up, you get erratic boost and surging. This is rock-solid at about 14lbs.

spdrcrpete

OK, Plugs just replaced as I mentioned.

Nate (ETKA+Scumbag)

Right, okay.

SBGTi96

are you running a MAF from a later car?

spdrcrpete

Yes. Had to make that change shortly after K04 software install.

SBGTi96

Ok good. Well, I would take a look at what was mentioned below and go from there I suppose.