boost spike 4th gear

mello · 07-22-2008, 01:56 AM

G'day Guys,

Am getting boost spike in 4th gear, usually as i get to 5000rpm. Had the car tuned yesterday after getting a vf34, top mount and pump.

It is fairly consistent too, of about 5 times working thru 4th gear i lost power 4 times. I have read it is common with the 2.5s, but i have a cat in the down pipe and have had it tuned properly.

After the first spike i went back to my tuner and after some mucking around he was certain the problem was fixed but a few hours later i noticed problem wasn't fixed

. My tuner has no idea what it is yet.

Any ideas or any1 else had the same issue with the 06-07?

cheers

newtothegame · 07-22-2008, 05:02 AM

Are you still using the stock BCS or even have the stock resrictor pill in there? If so, chaning to a 3 port (stock is 2 port) BCS or replacing (via new pill or drilling it out) the pill might solve the problem. Might also (not sure) be a problem with your wastegate.

mello · 07-22-2008, 07:15 AM

yeah that is all stock still.

I actually disconnected the battery for a while, thought resetting ECU might do something, anyway it hasn't spiked in 4th (after 3 runs) but it did do it in 5th on the last run....

Can you tell me more about the restrictor pill? just found in another post about buying larger one from a dealer or drilling. Are they hard to replace?

Longshot · 07-22-2008, 08:13 AM

CobbTuning.com - Service Bulletin: 07 WRX/STi Overboosting with Catless Exhaust

Resetting the ECU won't fix the problem as it's a mechanical issue. Changing to a different bcs such as a 3 port as newtothegame suggested will help to hold boost better (must be retuned for). You can port the wastegate which seems to help solve this issue with the 2.5L engines. As for the restrictor pill, you can see in a diagram in the link above that it sits in the vac line from the T fitting to the turbo compressor housing. It's a little brass pill with a small hole in it designed to help hold stock boost levels. COBB recommends when you upgrade the turbo to drill it out to a certain size, but I recommend a 3port bcs and retune to start.

newtothegame · 07-23-2008, 04:50 AM

Thanks for finding that link Mike, I couldnt find it for the life of me yesterday. I now have it save. I too would also look more toward the 3 port BCS, but that kind of depends on financial state. The wastegate or the restrictor pill will be the cheaper and easier fixes.

Longshot · 07-23-2008, 07:38 AM

Quote:

Originally Posted by newtothegame

Thanks for finding that link Mike, I couldnt find it for the life of me yesterday. I now have it save. I too would also look more toward the 3 port BCS, but that kind of depends on financial state. The wastegate or the restrictor pill will be the cheaper and easier fixes.

You're welcome, but come one you can get a gm bcs for like 30 bucks. A solenoid is very inexpensive when compared to what it does for you.

newtothegame · 07-24-2008, 03:09 AM

You can get the BCS for cheap, but what about a tune on top of that? Im not trying to argue or discredit anyone or anything. You can change the whole line for like $6 and be done, but it might not solve your problem. If I were in this spot, I know I have the cash and would be looking for the best fix, thats the 3 port with a tune.

dumdum · 07-24-2008, 09:33 AM

Quote:

Originally Posted by mello

G'day Guys,

Am getting boost spike in 4th gear, usually as i get to 5000rpm. Had the car tuned yesterday after getting a vf34, top mount and pump.

It is fairly consistent too, of about 5 times working thru 4th gear i lost power 4 times. I have read it is common with the 2.5s, but i have a cat in the down pipe and have had it tuned properly.

After the first spike i went back to my tuner and after some mucking around he was certain the problem was fixed but a few hours later i noticed problem wasn't fixed

. My tuner has no idea what it is yet.

Any ideas or any1 else had the same issue with the 06-07?

cheers

Are you getting a CEL?Sounds like it is just hitting the boost/fuel cut.You tuner could just raise that limit alittle or try tunning boost for 4/5th gear instead of 3rd.

mello · 07-25-2008, 02:40 AM

thanks for the help guys.

Yeah have spoken to my tuner and he is going to work on it , he is confident he can fix it without getting an aftermarket BCS.

Yeah was getting the CEL and flashing cruise light, is jsut the ECU doin its bit to save turbo and engine.
After the first time it happened he did raise the limit a little, but wasn't enough.

Unfortunately cant get it tuned in a hurry due to logistics so will being taking it easy for the time being.

midniteblack · 08-08-2008, 12:15 AM

i assume you're running a high flow d/p? spike is from a small turbo and WG. When theres all of a sudden a big load hitting a small turbo(such as in 4th 5th or 6th gear), it's going to cause it to spool really quickly, too quick for the wastegate to open. But as long as the boost comes back down relatively quickly you should be fine.