Boost is a little low?

denver_whitest185 · Post by **denver_whitest185** » Wed Nov 28, 2007 3:21 am

So, im currently getting .4 bar of boost on my new gauge (approximately 6psi). i thought the stock boost was a little higher than that? i used a t-fitting on the vacuum line that comes off of the intake manifold and goes to the bypass valve, since that was the closest line to reduce the length of total tubing and also because it is the largest I.D vacuum line off of the intake manifold. BTW, vacuum is measured at 375-400 mm Hg (~14-15 in Hg), which is normal for this altitude and an older engine

most of the vacuum lines on the car have hardened, so i;m going to be replacing them all shortly, but im still wondering if thats normal.

BXSS · Post by **BXSS** » Wed Nov 28, 2007 3:50 am

It sounds low (8.7psi=target), for a car not running in "safe" mode, & high for a car running in "safe" mode which is wastgate boost - 5psi.

Not sure what these cars boost @ altitude ( I thought the boost target would not be affected by alt), but if the boost is low for your alt. maybe the boost solenoid is dying..?.....

denver_whitest185 · Post by **denver_whitest185** » Wed Nov 28, 2007 3:55 am

its not in safe mode to my understanding. i threw two engine codes awhile back, but thats all.
http://bbs.legacycentral.org/viewtopic. ... highlight=
they keep popping up when im on the highway cruising, but never intown.

vrg3 · Post by **vrg3** » Wed Nov 28, 2007 6:02 am

Yeah, it does sound like you're at the standard wastegate pressure. This could mean your boost control solenoid is not doing its job, or that the ECU has decided for some reason to limit your boost.

To get some insight into the first option, put the ECU in test mode (green connectors) and turn the ignition on. The ECU will cycle all the relays and solenoids on and off, including the boost control solenoid. If you listen carefully to it you should be able to hear it click on and off several times a second. If it doesn't make a sound at all, that's probably an indication it's dead.

To rule out the second option, reset your ECU's stored parameters. Doing the procedure to clear the codes should take care of that. If your oxygen sensor is still on the fritz, that won't work, so just disconnect your battery and press the brake pedal for a few seconds. Then, on your next drive, check your boost level the very first time you go on boost. If it boosts properly, the ECU must have detected excessive knock or something, making it limit boost.

If it is clicking and the ECU's not disabling it, then maybe there's a clog in the line between the solenoid and the intake resonator? There is a 2mm restrictor in that hose, so I suppose it could get clogged fairly easily.

denver_whitest185 · Post by **denver_whitest185** » Wed Nov 28, 2007 7:05 am

wow, your back. i thought you disappeared or something. BTW, thanks for the vacuum diagrams, they are extremely helpful.

I'll do those two tests this week. are boost control solenoids hard or expensive to get? i hope not. how about for the restrictor?

yeah, i need to just get a new O2 sensor already, so i can see if it makes the engine light stay away for good.

BTW, Vikash is there a wire i can splice my 12volt lead for the bulb in the gauge so that it will dim with the dash? that would be awesome. apparently your the electrical guy, and i don't know much about car electrical systems.

asc_up · Post by **asc_up** » Wed Nov 28, 2007 7:11 am

just by a manual boost controller if your BCS is on the fritz. that way it'll still get the same job done and you can adjust more or less boost...

denver_whitest185 · Post by **denver_whitest185** » Wed Nov 28, 2007 7:17 am

well, why would it be going off of a solenoid in the first place. shouldn't it be controlling boost off the actuator's spring? i know my alltrac only has a line between the actuator and the intake manifold, and then there is a line to a vacuum switching valve to lower boost in the first two gears when attached (i plugged mine off to get consistent boost in all gears), but thats all.

SemperGuard · Post by **SemperGuard** » Wed Nov 28, 2007 8:07 am

It has a solenoid so that the ECM can regulate boost based on more things than just manifold pressure/vacuum. Giving more consistent power than a simpler system.

vrg3 · Post by **vrg3** » Wed Nov 28, 2007 2:15 pm

Yeah, like SemperGuard said. The solenoid doesn't actually actuate the wastegate; it's just a valve that allows the ECU to bleed pressure away from the wastegate, increasing boost pressure.

Replacing the solenoid probably would be expensive, but like Aaron says, a cheap manual boost controller is not an unreasonable replacement. You do lose the protection of having the ECU reduce boost when it thinks things are going wrong, but it's adjustable and a lot cheaper.

The hose and restrictor probably aren't that expensive from the dealer, but you can just get hose of the right diameter and make a restrictor with a piece of rod and a drill.

Dynamic Entry · Post by **Dynamic Entry** » Wed Nov 28, 2007 6:40 pm

I don't know if you know or not Vikash but you have a veritable fan club on this board. You posting feels like meeting a celebrity!

Good to hear from you!

vrg3 · Post by **vrg3** » Wed Nov 28, 2007 6:48 pm

It's Coca-Cola Classic!

vrg3 · Post by **vrg3** » Thu Nov 29, 2007 5:09 am

Oh, and sorry I never answered your question about the dimmer... This page tells you what you need:

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

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Boost is a little low?

Boost is a little low?