Restricted boost in low gears

[Ginger pig]

All,

Took my SE out for a drive the other day and noticed that in the lower gears even at higher revs the boost gauge only read around 0.2/0.3 max. In 5th gear I could get to about 0.6 which I believe to be about right.

Before I start blindly rumaging around; does anyone have any suggestions of where to start and why it would only seem to affect the car in the lower gears (just not getting that rush)?

The marks on the boost gauge do not seem to add up either......from memory it shows 1.2 at the extreme but when I count back the marks on the gauge I cannot seem to get them to add up.....I take it that when the needle points directly upwards it is indicating circa 0.6?

Thanks for your anticipated help!

[jonwat]

Unlike the V8 the 4 cylinder ECM has no way of knowing which gear your in so you really need to get Freescan running before you start pulling things apart.

[andydclements]

Keep in mind that for a given engine speed under acceleration you tend to have the throttle open further when in high gears as you so easily whip through the rev range in low gears, so if the throttle isn't as wide you'd not expect the ECU to go for as much boost.

[Ginger pig]

Thanks guys.......I suppose what I would like to know is what should the boost gauge be showing in those lower gears as it barely gets past the 2nd marker which I would imagine is around the 0.3 - 0.4?mark

[Vulcan Grey]

ECU has no ability to restrict boost below the mechanical limit of the wastegate which is ~.65bar.

If your boost isn't building at least to that level, then you have a problem, something like an exhaust restriction or intake hose collapsing. Could be a coupling hose is loose, but you didn't complain about a sudden high pitch sound.

first thing to check is the EBP valve just below the catalytic converter. If that is closed, then you aren't going anywhere fast.

[Ginger pig]

Hi Travis,

Not heard a high pitch sound!

The EBPV was replaced by a spacer when I pulled the engine out several months ago to do the cambelt/water pump/seals/etc. I wedged an allen key in the loose hose which was left.

Having looked at several threads just recently it would appear that maybe the first few gears do not get much boost but I certaintly remember a real sudden rush when I first had the car up and running which I am not getting now!

It feels a little gutless low down which a friend of mine will testify was not the case 4 weeks ago when I took him out in it and he was screaming obsenities at me as soon as my foot touched the accelerater!

[Vulcan Grey]

No restriction in lower gears, especially not that low. Ecu doesn't have control below .65bar!

The waste gate spring may be broken or maladjusted, but that is not a normal boost restriction.

The allen key in the vacuum hose isn't good enough, you need to make sure there is no vacuum lost from the system, since that is where the brake booster gets its vacuum.

[ramjet]

Best thing to use to block the EBPV vacuum hose is a plastic golf tee. They're tapered so they jam in there real tight. Just tape it up after you've stuck it in.

[Artie]

Even if the spring in the wastegate was broken the minimum boost the turbo would make is .65. The wastegate flapper will be wide open and allow only enough exhaust bypass to make .65. Perhaps the studs/bolts holding the turbo to the manifold, or the exhaust manifold to engine gaskets/bolts have worked loose and allowing exhaust to leak and never reach the turbine housing at all. This seems most logical to me.

Artie

[sailorbob]

If the spring in the wastegate capsule is weak or broken and allowing the wastegate to open prematurely you would loose boost.