My boost goes on and off in 3rd-5th gear
 

Hi you guys, My fd has a really weird problem. It runs fine in 1st and 2nd gear. I can slam on the gas pedal and it'll boost all the way to redline. But in 3rd 4th and 5th gear it like slows down. It usually happens at around 3-4k rpm. It'll go pssshhh(boost noise, sorry don't really know how to type out boost sound) then brr then pssssssssssssssh the brrrr then psssssh. The brr is when it stops boosting and wont accelerate. If i start tapping on the gas it'll start boosting but it will still make that noise and stop. My car is completely stock(except catback) and 120k miles no rebuild yet. Only things i have done to it is change oil, change transmission oil, differential oil, airbox filter, fuel filter, spark plugs, and spark plug wires. Basically just the maintenance stuff. What could be causing this problem and how do i fix it?

i had a 1G tsi that did that, it would boost 18psi then drop to 11psi then back to 18 then 11 then 18 then shift and all over again...
never did figure that out before i got rid of it
Good Luck with it

Oh that's soo weird. I really hope someone out there knows how to fix it. Thanks for the good luck. I really need it haha. I hope the fix won't be too expensive. I'm still in high school.

Boost leak test?

Get a cheap gauge, to me it sounds like fuel cut, which is somewhere around 12psi.

Do you have a boost gauge? Hard to know what's happening.

Sounds like a boost leak.

120k on an original motor is quite impressive.

My fd doesn't have a boost gauge. The only thing aftermarket on it would be the stereo deck and the catback. Do you guys recommend me get a boost leak test or compression test? Wouldn't fuel cut happen only if i have higher boost where stock fuel stuff would not be sufficient? Yeah I don't really drive it hard, only occasionally but this problem holds me back. Could it be the turbos?

In order to diagnose your car's problems you need to get a working boost gauge. It is likely that your stock car has a boost leak, or malfunctioning turbo control system.

Probably the best thing you can do is get a boost gauge and a boost controller.
With the boost controller you can eliminate potentially bad solenoids from the equation.
With the boost gauge you can check your sequential operation and narrow possible culprit issues.

If you have problems after installing a boost controller the likely culprits would be a boost leak, a bad actuator on the turbos, or the turbos themselves. These are all relatively simple to identify and rectify.

But without any of that it's really impossible to say more.

Have you replaced your vacuum lines yet? Maybe computer thinks the car is overboosting and is cutting fuel? Maybe car is overboosting... On a side note have you been running the stock precat this whole time? I am just curious for my own sake.

Okay i'll try to get a working boost gauge installed within this month. Is that the only way to diagnose this problem? And sc frontier I haven't replaced my vacuum lines( the rat's nest right?) I bought the kit but haven't started. So right now the main suspects are boost leak, actuator, and the turbos? I have an auto class at school do you think they could give me a compression test or something? The teacher isn't a rotary specialist or anything though.

Nobody mentioned the turbos because they are not the problem.

I wouldn't worry about the turbos or a compression test.

Unlikely low compression would cause this, but I bought a compression tester at autozone that had a stainless braided line and has worked well for many years. The craftsman (sears) tester lasted less than one year and no warranty.

Oh so it's either the actuators, fuel cut, or boost leak? Would the Rat's Nest contribute to the boost leak? I think I can probably get a boost gauge this week or next week for diagnostic reasons.

Having SORT OF a similar problem with my newly built engine. It happens in 3rd or 4th, and I've never really gone fast enough to really push 5th to past 6k RPM. But it happens very rarely. It'll boost properly (tuned for 12-13psi, boost pattern is 12/13psi - ~10psi - 12/13psi) 95% of the time, but occasionally when I go WOT, it'll only boost to around 7 or 8psi and there's a hissing sound (leak somewhere) and it won't boost any higher. If I let off on the gas, pop it in neutral and let it drop down to below boost levels, and then put it back in gear, it'll go away 100% of the time.

It sort of sounds like a solenoid or something somewhere that isn't working properly 100% of the time.

time to go into the rats nest

Sticky solenoids just like mine so this is where I am headed!

https://www.rx7club.com/group-buy-product-dev-fd-rx-7-269/custom-solenoid-rack-968956/

I recommend putting a pressure regulator on the line to your pressure tank and setting it to 8psi. 12-13psi is enough to stick just about any solenoid.

I had a similar issue. My car would break up from 3rd to 5th bad. Changed plugs and wires and still same issue.

Turn out that my map are all screwed up. I got a base map in the PFC and it ran perfect.

Since you are stock my issue has nothing to do with yours. I would def check your solenoids for the transition of the turbos.