Date: Sat, 19 Sep 1998 18:14:03 -0700 From: Justin VanAbrahams <jvanabranopsamnet> Subject: Re: 900T16S Intermittant Boost Problem
James Borden wrote: > > I have an 88 900T16 S which has developed a really annoying problem. > Sometimes it only boots to half way, or less. The next time I drive it, it > may be OK and fully boosting again. My garage has replaced the APC control > box, but this has not solved the problem. Does anyone have any ideas? > > Thanks in advance. This seems to be coming up quite a bit lately... Check (in rough order): o All vacuum lines, everywhere o Your knock sensor - remove it from the engine block, tape it somewhere safe, and drive around o Your APC solenoid - first try unplugging it - you should get basic boost *all* the time. If you don't something else is wrong. Listen (with the engine running) to it before and after the engine the engine is hot - if it is clicking, you need a new one. Also, get a 12v (9v should work) battery, and connect the poles of the battery to the pins on the solenoid - with voltage applied across the pins, the solenoid should click once. If it shudders or makes many noises, it's shot. o Your cruise control - if the cruise control 'ECU' is acting up, it might cause the APC to go into basic boost mode (normally, while the cc is on, you are limited to basic boost). Also check all the vacuum lines to the cc unit in the fender. o On the same note, check the two pressure switches above the clutch and brake (one per pedal) to make sure they aren't leaking vacuum. Ideally, remove them and check that they are not permanently shorted; if they are, you'll get basic boost. o Your turbo itself (VERY unlikely) - unplug the vacuum line between the turbo wastegate and the APC solenoid and drive around for a *tiny* bit - you should get uncontrolled boost (limited to ~15psi by the fuel cutoff). If not, there may be something amiss with the turbo o Finally, some cars (I don't remember what years) will go to basic boost when you hit the brakes. So, check the brake light switch above the brake pedal and make sure it's working properly. If it's not, BTW, your brake lights will be on all the time. Good luck... -Justin
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