Hello,

New to the forum and hoping for some help. Been researching for about a week. Lots of people with similar sounding issues, but nothing definitive.

Car starts, and runs fine until boost gets in the neighborhood of .8 to 1 on the Factory gauge. Then it pops and sputters, loses all power (unable to accelerate at all). Pop sounds like air to me, and with every occurrence, the boost gauge spikes 30-50% of whatever the pressure was.

I rigged up a cap to test for leaks. I disconnected the airbox, and capped the intake hose, and pressurized with air compressor. I did take oil cap off based on a video I watched mentioning I could blow my cam seals off without doing that. I did cap with my hand a couple times to let pressure build, but found no leaks.

I also tested that the wastegate responded to pressure. I do think it was opening a bit early, but that wouldn’t seem to explain the symptoms. I was more worried it was randomly shutting somehow.

Saw something about TGV causing this, but research and visual inspection tells me a JDM in my year doesn’t have them anyway.

Where do I go from here? Seen some coilpack, wires, plugs, and injector type posts, but that doesn’t seem to cause the spike I’m seeing on the gauge?

I need some help folks.

It was not showing a CEL. I was about to hook it up to my code reader anyway, but my wife accidentally took the key with her on a trip for the next 2 weeks.

I did start working on it some more though. It has the stock turbo inlet on there, which wasn’t in great shape. Not 100% if that’s the cause though. It had two little tears, but that might have been from the violence it took to remove. I got it out (huge pain). Having trouble deciding on a good replacement though. 98 JDM STi EJ20 is pulling up some stuff that I’m not sure is going to fit right.

I saw a little oil in the inter cooler, so I am going to replace PCV as well? Is that it screwed into the intake manifold just under the throttle body? What is the 3 way thing? Do I need to replace both?

just an extra question while I was working: why are there two throttle cable guides?

Since last post I’ve replaced the stock turbo inlet, which was worn quite a bit; and I’ve replaced the inter cooler hoses as well. I replaced Mass Air Meter, and it’s still stock airbox. All back together, but still pretty much same issue.

I’ve pulled all plugs and done compression test. I was 120psi in all 4 cylinders, letting engine turn twice. I only hand tightened my tester, and did not have throttle body open; so I’m considering that good since they are so even with each other.

3 of four plugs show a little bit of dry carbon on the outer ring, but otherwise very normal. The 4th (from number 4 cylinder is almost the same, except the insulator has the same build up on just one side. Dr. Google tells me that’s slightly rich on 3 and a bit more rich on #4.

I’ve ordered new plugs and wires. Debating if I should do coil over plug while at it, because those wires aren’t cheap!

But what does all this tell me? I’m thinking wires or coil pack, but I’d prefer not to just keep replacing things. I was ok with the hoses and MAM because those are good maintenance. Plugs is fine, I also did a new fuel filter. Help me guys!

Here is a video of it running a couple days ago with the issue. If you watch a bit you can also see its intermittent.

Im obviously going to keep working on it myself, but I’d certainly appreciate some feedback if anyone else has seen this issue.

hi mate
i had a similar issue recently and I did plugs leads etc and it was low fuel pressure
looks like the lock off nut on the regulator had come loose and turned down itself (faulty reading on the gauge)
worth a look and good luck

Just an extra note that New plugs are in. I passed on wires for now, since I’m probably going cool over plug conversion if it goes that direction.

Car fired up, but issues remain. I listened to all injectors with screw driver and did not hear anything different between them.

Im probably going to rig up a smoke test when I get back from a business trip.

On the fuel pressure regulator; does a stock 98 STi have one? I had the whole intake manifold off and didn’t see one? Wasn’t really looking either though. Also, does this car have a nozzle to check fuel pressure with, or do I have to rig up something inline after the filter?

found the regulator. That doesn’t look fun to change now that it’s all back together.

Will installing and fuel pressure gauge after the fuel filter allow me to diagnose? I’ve got no problem swapping it out, but would like to confirm somehow.

I have the boost gauge on steering column and fuel pressure, voltage and temperature in center console; all stock.

I’m not aware of the boost gauge having a fuel pressure connection. I believe it is just T’d with vacuum line off the turbo and wastegate.