loud bang. repeatable. WTF situation.

[zedicus]

at about 8psi i get a loud pop that sounds like an intake coupler popping off.

i have boost leak tested, changed basically every coupler on the intake, changed the intercooler, changed the BOV. smoke tested, boost leak tested again.

there is a MBC installed but it was in place for one of the boost leak tests and had no issue.

car is set up with MBC to run 16psi. walbro 190 pump, this is my 95 2g car. stock injectors and a 14b.

turbo does not whine, spools good. car runs great and boosts up to about 5 psi perfectly, then from 5 psi to 8 psi is a bit of a struggle then POP! and power loss but engine still sounds fine.

it HAS to be a weird boost leak at pressure but i am out of places to look. the confusing part is boost leak test was done at 28psi and that is over what i am running by a fair amount, so could it be turbo related?

also vacuum at idle looks good on the gauge, boost looks good right up until the pop sounds then the gauge goes nuts until i let off the gas pedal. then everything goes back to normal, rinse repeat.

thoughts?

 

[Joe Gekko]

Just spitballing- but maybe wrap a single layer of blue painters tape over the joins, and see if anything is blown off after you hear the 'pop'?

Also, have you checked out your wastegate? Have you tried bypassing your MBC and just running spring pressure to see if you still get this issue?

 

[zedicus]

Just spitballing- but maybe wrap a single layer of blue painters tape over the joins, and see if anything is blown off after you hear the 'pop'?

Also, have you checked out your wastegate? Have you tried bypassing your MBC and just running spring pressure to see if you still get this issue?

i was thinking of light spray painting all the joints but i like the blue painters tape idea.

yeah removing the MBC is the very next thing i am going to try, in fact i will be pulling it out in the parking lot at work in 45 minutes. ( i get weird looks messing with my car in slacks and a polo, in the work parking lot. its not the first time, gotta love owning a car older than half the people on the forum now)

 

[zedicus]

o.k. making progress.

replaced the stock side mount with a TDI VW side mount. (similar to supra side mount but not quite as large. and does not require cutting a new chunk out of the engine bay.) the stock intercooler looked like swiss cheese due to age and 16psi. the stock intercooler did not leak 1 month ago as i was smoke checking the intake for another issue.

my used evo 8 BOV was bad. again 1 month ago it was functioning normally. now at 8 PSI it pops open and or leaks.

also the valve cover had worked itself loose. i normally tighten the valve cover bolts every oil change but must have forgotten last time. i can not make them stay tight, so i just check them every oil change. must have spaced it out last time.

the only 1 of these that caused a vacuum leak was the intercooler, it was found and replaced first. the other 2 items were less easy to find and actually they even held 28 psi at a boost leak test. i assume they held during the boost leak test due to volume of air being moved. only a small volume can make it through the tire valve so it very slowly and easily works its way up to the psi i have set during a boost leak test.

for those keeping score at home that is 1 bad intercooler (stock sidemount had popped the welds holding the upper mount bracket), 1 bad evo 8 BOV, and loose valve cover.

this all caused 1 symptom, just in 3 different places. and it all happened at the same time.

 

[PlanZero]

Just an FYI I use both lock washers and regular washers on my VC and exhaust manifold and they never loosen, after having the problem for years. Plus it helps prevent over tightening. Also, make sure if you get another evo BPV its the aluminum one from late 9 or X. Glad you're not poppin anymore.

 

[zedicus]

Actualy it ran right ONCE after fixing all that and is now doing the exact same thing. I am at a loss.

I am going to add some of those toothed lock washers to the valve cover at some point.

 

[Ryan4dc]

Have you checked spark plugs? What is your gap?

 

[Archer Fabrications]

Fuel cut?

 

[zedicus]

Plug gap is .028 just checked them all. One was a smidge high so i adjusted it back. No change.

Compression is 160 across all 4. Almost no variance.

Changed injectors, maf, complete intake, filter, tightened every nut, bolt clip, fitting, etc.

I did find i tiny drip of oil coming out between the turbo housing. But not enough it makes me think it is an issue. And no shaft play. However if i drive around in slight boost for a while the entire intake tract becomes scorching hot.

The turbo only has maybe 5000 miles and came from a reputable builder here on the forum but i am out of ideas.

It also does not feal like fuel cut, and this car has never had issues with fuel cut before.

 

[Archer Fabrications]

So is your car completely stock then?

 

[zedicus]

I need to add my 2g to my profile....

95 talon tsi
Reman head
14b
Walbro 190
Timing and maintenance up to date
But really stock-ish

Due to the issue i have since swapped the parts listed also. Currently the injectors are evo 560 with a 482 MAF to accomodate. But the original injectors were refurbed OEM.

and when i pulled them tested the OEM injectors and they function normally on my bench.

I am trying to imagine if a turbo shaft seal could cause an issue like this or what inside the turbo could be happening. Even the wastegate seemed to operate in the boost leak test.

 

[zedicus]

so i worked on checking the wastegate actuator with an air compressor and somewhere the actuator is bleeding pressure off slightly.

so working theory is the bad actuator caused the turbo to be overworked and ruined the internal turbo seal. (this would explain the puddle of oil i just found under the old intercooler. and the actuator could explain the terrible boost and popping.)

i shall be yankin the turbo for deeper inspection next weekend.

 

[zedicus]

turbo was blowing oil, rebuit turbo, added new wastegate actuator also. this made the popping sound go away. car still has no power.

compression test again. apears to have blown headgasket now. probably between the cylinders, its not mixing coolant and oil, its not burning anything abnormal. just struggles to make boost/power. also could be a valve issue but it has a stock rebuilt head that is only a few thousand miles old.

long story short, im calling it quits for a while. i am older than the vast majority on here and i have a number of other projects i would like to finish.

mass purging of all DSM related parts including 1000cc injectors and link v3 to come. (started FS thread now.)

 

[Archer Fabrications]

Head probably wasnt decked flat properly dont give up

 

[1990TSIAWDTALON]

Yeah I saw your ad. I'm in the same situation with too many projects and age but its a nice little fun car. Mine has been down most of the summer and just now getting things back to working order. Hang in there man.

 

[1990TSIAWDTALON]

Simple motor rebuild.