rpms dropping while on boost

TurboSubie · Post by **TurboSubie** » Mon Feb 14, 2005 6:27 am

I have a stock 94 turbo Legacy, was runing perfect until I took out the resignator box and intstalled a K&N panel filter, took it out..didn't feel like it ran any different. went in and came back out to drive it. The turbo was spooling really loud, has plenty of power and the BOV got pretty loud. ONly problem is that it doesn't like to hold boost for really long at any throttle. taching 4 grand for maybe a second then dropping to two and trying to boost again with the same thing happening again. The n I took it to 5 grand and it jumped down in rpms again. what could be wrong...before it jumps down in rpms it pulls fairly hard. Any help is appreciated. also no Check engine light on.

Nomake Wan · Post by **Nomake Wan** » Mon Feb 14, 2005 2:19 pm

I could be wrong in this, but you have a 4EAT in that car. The automatic transmission doesn't like to run at high RPMs unless in Power Mode (mashing the pedal to the floor quickly). Usually it'll top out at 4k before shifting up, thus causing the rev drop you're experiencing.

Try using the numbered gears, i.e. start in 1, shift up to 2, shift up to 3, etc. If this rev-drop still happens, then I'm utterly wrong.

But if I'm right, there are ways to make your tranny run more like you want it to. Use the forum's search feature to find posts by "ciper" in the Drivetrain forum. Or check this thread out.

free5ty1e · Post by **free5ty1e** » Mon Feb 14, 2005 2:22 pm

do you have a boost gauge? If the line came off that feeds the wastegate, then your turbo is overboosting (20+ psi pretty much immediately), which on a stock car would pull really hard and sound really loud but after 2-3 seconds of 13+ psi your ECU decides you're overboosting and cuts fuel. So it could be the auto tranny thing or it could be fuel cut.

Nomake Wan · Post by **Nomake Wan** » Mon Feb 14, 2005 2:23 pm

Isn't it an ignition cut?

free5ty1e · Post by **free5ty1e** » Mon Feb 14, 2005 5:06 pm

might be, i thought it was fuel. If it isn't, the "fuel cut defend" mod is quite ill-named.

vrg3 · Post by **vrg3** » Mon Feb 14, 2005 5:51 pm

It's fuel cut, not ignition cut.. Dumping raw fuel into a hot catalytic converter is something few carmakers will do.

Both Chris and Nomake Wan's suggestions seem plausible, TurboSubie... You need to tell us more. Are you monitoring boost pressure? Does it do this even when you prevent the transmission from shifting? Does it seem to happen only after 3 seconds of sustained boost?

TurboSubie · Post by **TurboSubie** » Mon Feb 14, 2005 7:27 pm

it does it even when I manually shift the gears. I can get the rpms up a little higher than 4 even when I manually shift or when its in drive. it never makes it to redline without doesing the wierd boost cut. I am not monitoring boost, just got the car and haven't had a chance to buy a gauge. hopefully this will give a better clue to what is wrong.

vrg3 · Post by **vrg3** » Mon Feb 14, 2005 7:39 pm

Well, it could be some kind of misfire also.

Does it seem to happen after about 3 seconds of sustained boost? Cuz if it's overboosting that's what you'd see.

My scan tool could help you figure out whether or not it's fuel cut.

TurboSubie · Post by **TurboSubie** » Mon Feb 14, 2005 7:46 pm

when I just went out for a test drive, when I got on it I heard a popping from under the hood like a misfire, but it doesn't do this all the time. this is the first I noticed it. I have had a miss on my n/a before. The fact the BOV is so loud (can be heard outside the car) kind of scares me. What is this scan tool you speak of? The fact I put the intake back together took it for a spin and it ran fine, then later it does this. so I don't think a vaccum line popped off. I still need to do a tuneup to this car. The previous owner said he replaced the plugs/ wires recently...but then again who knows if he actually did.

free5ty1e · Post by **free5ty1e** » Mon Feb 14, 2005 7:56 pm

The scan tool, along with all kinds of other useful info, can be found at the world-famous website of Mr. V. Just look here:

http://www.graphics.cornell.edu/~v/

You'll be there for a while. It happens

TurboSubie · Post by **TurboSubie** » Sun Feb 20, 2005 6:52 am

measured boost at the manifold...20 psi...all vaccum lines look good. any other ideas?

vrg3 · Post by **vrg3** » Sun Feb 20, 2005 7:01 am

Woah. That ain't right.

Okay, first thing to do is go pick up a short length of 1/4" vacuum hose and connect the wastegate actuator directly to the nipple on the turbo's compressor outlet. Use good zipties or hose clamps to secure them.

If boost drops down to about 6 psi, then the problem is somewhere in the other boost control vacuum hoses or in the boost control solenoid.

TurboSubie · Post by **TurboSubie** » Sun Feb 20, 2005 7:07 am

approx how many feet of this hose do you think i'll need? Im hoping this leads me to the problem.

vrg3 · Post by **vrg3** » Sun Feb 20, 2005 7:08 am

One foot will be more than enough. These two nipples are right next to each other.

TurboSubie · Post by **TurboSubie** » Sun Feb 20, 2005 7:20 am

Allright, I will give a shot in the morning. I hope this works. Its frustrating not being about to hit the gas above 4,000 rpms without that turbo launching you. The gas mileage kinda sucks too. really hope this works(fingers crossed)

Thanks,
Eric

vrg3 · Post by **vrg3** » Sun Feb 20, 2005 7:31 am

Not to mention the damage that so much boost can cause to your engine.

Let us know what happens.

free5ty1e · Post by **free5ty1e** » Sun Feb 20, 2005 2:19 pm

well, so much uncompensated boost on the stock turbo can cause damage to the engine.

I believe the EJ22T can take over 20 psi of raw pressure. It's just not a good idea without lots of support mods

Anyway, with the turbo compressor outlet connected directly to the wastegate you should end up with ~6 psi of boost. With the stock boost control in place (and 93 octane gasoline in the tank) you should be running ~9psi of boost. 20psi means your turbo is spooling unchecked by the wastegate. Something not right in that area...

TurboSubie · Post by **TurboSubie** » Mon Feb 21, 2005 4:19 am

Fixed, found the a vaccum line off between the wastegate control and the turbo, right where the little plastic union is. hooked this back up and she's running back to normal. Thanks guys.

vrg3 · Post by **vrg3** » Mon Feb 21, 2005 3:16 pm

That'll do it. =)

TurboSubie · Post by **TurboSubie** » Sat Mar 05, 2005 7:26 am

Have another turbo problem. When I hit boost one time it almost sounded like metal on metall so I let off. The next time I went to boost the turbo was REALLY loud...but no boost...it wanted to stall whem boost would hit. It has stalled a few times. did I blow the turbo? or could it be something stupid. I would say the turbo is blown..but woiuldn't it seize up and make no sound at all? The turbo was louder than usual these past few days. It was always sorta loud since ive owned the car the..sorta like a mid pitched whistle...now all you hear is air...like someone using a hairdryer..

vrg3 · Post by **vrg3** » Sat Mar 05, 2005 4:01 pm

It's hard to judge just from that description... Can you describe the metal-on-metal sound some more?

As the turbo's bearings start to go bad, the turbo does get louder and louder. I hope not, but it's possible the all that overspeeding of the turbo hurt the bearings.

It's also possible that you just have a boost leak. Maybe a hose popped off or something? Or maybe all that pressure created a crack in the plastic tube between the compressor and throttle?

TurboSubie · Post by **TurboSubie** » Sun Mar 06, 2005 3:36 am

Its a reall wierd sound, its not a metal on metal sound anymore..it was only one time...then it stopped getting boost. It is possible a hose popped off. I will have to check tommorrow. Will a blown turbo make any noise at all..this one almost sounds like a giant air leak. like a real loud shhhhhhhhh sound.

vrg3 · Post by **vrg3** » Sun Mar 06, 2005 3:43 am

If it sounds like a giant air leak, I'd say there's a good chance it is a giant air leak. The unlimited boost you were running is a lot more than this stuff was built for.

I don't know exactly what a "blown" turbo sounds like. I would imagine that depending on how it blew it could sound like different things.

TurboSubie · Post by **TurboSubie** » Sun Mar 06, 2005 7:34 pm

I am now getting large amounts of carbon buildup in the muffler tips..I mean alot. I'll clean them and a mile down the road...its covered again..

vrg3 · Post by **vrg3** » Sun Mar 06, 2005 11:09 pm

...almost as if you were running overly rich...

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rpms dropping while on boost

rpms dropping while on boost