1 Burst Of Boost [Archive] - SaabCentral Forums

: 1 Burst Of Boost

28th September 2005, 10:30 AM
Hi guys,

'91 SPG, 75,000 miles, all original, no mods. I recently had a front motor mount replaced and did the belts on the front (back!) of the engine. It's probably just coincidence, but since then, I get 1 good burst of boost first thing in the morning when the engine is just warming up. The APC will go all the way to the right side of the orange & the car really pulls (just like it should). However, after that, I only get about 1/2 way up the boost gauge for the rest of the day, even if the car cools completely. What do you think? I'm wondering if I've got a boost leak somewhere? The rest of the driveability is just fine, BTW. I'm still seeing up to 28mpg with steady highway driving. Just no boost consistently.



28th September 2005, 10:41 AM
on full boost your car should be half way in the red and not half way in the orange, which would indicate you're only driving at base boost.

check for vacuum leaks to start with...

Oh, and if you want to preserve your engine and turbo: don't boost before the engine is fully warmed up! ;)

28th September 2005, 10:44 AM
on full boost your car should be half way in the red and not half way in the orange

not sure about that - can anyone else confirm? I always thought full 'standard' boost was as described in the first post.

28th September 2005, 12:35 PM
A standard motor should Boost up to the end of the Orange & not go into the Red ;)

its only once they have been modified that they will go into the Red

HTH Paul

Sleeper baby, no show & all GO........................

28th September 2005, 01:08 PM
I can also confirm that.

It sounds like your getting rich fueling at warm up which can give better boost and then maybe its leaning out? just a guess.

Have you cleaned you bits and bobs and made sure everything is in good working order?

28th September 2005, 01:31 PM
on touch into the red on 94 octane is normal on stock cars too.

28th September 2005, 01:54 PM
Hi guys,

Sorry about the color confusion, but I get 1 full blast at the top of the orange (not into the red), then the rest of my day I'm just getting to the middle of the orange at best.

The car is recently tuned with all new ignition stuff: plugs, wires, cap, rotor. It DID give me full boost regularly, just recently something changed. I have a Turboed Miata and the usual culprit is a bad coupling between turbo pipes but everything looks ok here on first inspection.

28th September 2005, 05:01 PM
on touch into the red on 94 octane is normal on stock cars too.

Normal situations the charging pressure shouldn't exceed 3/4 bar above ambient pressure, ie the intersection between orange and red.

18th October 2005, 12:13 PM
There is some APC wiring to the solenoid valve at the front of the engine bay, above the front engine mount. Perhaps some of that became disturbed, giving intermittent boost.

Try putting the old HT leads back on the car to test. Electrical interference from crap/old HT leads can mess with boost control (seriously).

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