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Re: 92 9KT, base boost only, BCV fine, big boost w/W discon Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 6 Apr 2005 05:43:37
In Reply to: 92 9KT, base boost only, BCV fine, big boost w/W discon, Ed N, Tue, 5 Apr 2005 17:10:29 Members do not see ads below this line. - Help Keep This Site Online - Signup |
With the W hose disconnected, there is no limit on the Turbo boost, as you have found out. That you get full boost means that the turbo is working and that the ECU is responding just fine to increased boost.
The APC system commands the BPC to provide full, normal boost if it doesn't detect knock. If it detects knock, it reduces the boost to base boost by porting more pressure through the BPC to the W (wastegate actuator).
DO NOT ASSUME that base boost is due to an ECU problem. The first assumption should be that the engine is indeed knocking, and that the system is reducing boost for a very good reason. There is a lot of info on Base Boost - check the archives.
But in general, run a higher octane fuel if you can and see if that fixes the problem. Make sure you have the EXACT RIGHT NGK spark plugs - NO substitutions, gapped properly and in good shape. Make sure the the cruise control isn't on (base boost only with cruise on) or that the brake light switch isn't stuck on - base boost only if the system thinks the brakes are in use.
The reason to check for noise (as Ron J suggests) is that the knock sensor listens for knock. A noisy wheel bearing, rattly timing chain, or blown out motor mounts can increase the noise, and fool the knock sensor into thinking there is knock, and telling the APC to dial back boost.
I assume there is no Check engine light on.
If the APC thinks the engine is knocking, it will dial boost back to base. The reason to find out if you are knocking, even a little, is that knock under boost can punch a hole through a piston (or pistons) very quickly, and with little warning. And you may not be able to hear it. So the first approach is to make sure (1) the engine isn't knocking, followed by (2) things that may make the APC think the engine is knocking.
Lastly, a simple check. I believe that a '92 has the 2 wire APC solenoid. With the engine at idle, unplug the solenoid. You should hear it click. Check that there is 12 volts and ground on the pins. An energized solenoid gives full boost (assuming a good solenoid). If you aren't getting 12 volts (and ground!) at idle, start tracing back, because it is unlikely you are knocking due to boost it idle. But noise or a loose knock sensor may cause it.
posted by 192.249....
, Wed, 6 Apr 2005 05:43:37 <-- Viewing This Message
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