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Discussion Starter · #1 ·
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.

Thanks,

John
 

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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! ;)
 

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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

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

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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?
 

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on touch into the red on 94 octane is normal on stock cars too.
 

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Discussion Starter · #7 · (Edited)
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.
 

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woywitka said:
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.
 

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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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