hi, the interior standard boost gauge is reading wrong, its intermittant and isnt all the time but at the moment usually the gauge is nigh on permanently reading full boost, even when at idle.

i have changed the pressure sensor and the problem still is there, what other issues might be causing the problem? maybe a problem with the ecu reading wrong? there are no air leaks, the car runs fast as she always has but its annoying me something chronic.

any ideas?

dale

You've changed the most obvious culprit. The stock boost gauge is notoriously dodgy following as it does chocolate teapot design principles To eliminate the possibility of a sticky needle it might be worth trying another dash to see if that is the problem.

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Don
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1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

tried it again, the gauge is moving.... the tinyest bit, with no throttle after approx 5 mins or so it will settle down to around the 1/2 to 3/4 on the gauge, any throttle, and it shoots up to full again, stupid gauge!

will it have any input on the fueling etc? or is it litterally just for the boost gauge?

If the idle is smooth while gauge is reading near full boost, then I'd suspect the gauge. If the ECU were seeing that sort of boost it would overfuel like crazy. If the engine running OK with normal ecconomy ?

Looking in the wiring diagrams, the MAP (turbo pressure) sensor goes directly to both ECU and gauge. If the gauge is feeding out current, or drawing current, it could affect fueling. I would expect both gauge and ECU to be high impedance inputs.

I would suspect the problem is most likely at the gauge end, but could also be a bad earth.
Boost, fuel, tacho and speed all share an earth which says it's at the 'instrument panel brace LH'. Fuel sensor also shares this earth so may read correctly, and tacho & speed are pulses so may also read correctly.
The MAP sensor earths back to the ECU, which is earthed to the underside of the inlet manifold.
Therefore, any of the above earths, or the earth from body to engine could all cause this symptom.

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gah sounds like a few issues it could be. :S

she idles fine, starting idle is about 1k then when warm she idle at 750rpm and stays smooth no miss or anything.

although she does use a bit of fuel, but i always presume that they do, approx 30 pound(so 24l) to around 100-120 miles, this is short trips though, i work approx 10 miles from home so all short trips which could explain not so good fuel economy as she isnt even warm by time i at work so would still be on cold start so fueling more anyhow.

the rev counter is fine, the fuel gauge reads perfect, however the speedo is sometimes erratic, but this appears to have no effect on the boost gauge.

however i read that sometimes a bad connection to a speedo converter can give irratic readings? i.e a bump can make the speedo read say 40mph upto 70mph then back to 40 for arguments sake.

is the earth to the underside of the manifold hard to reach?

if so might it be easier to change the ecu to see if this will alter the problem? i have access to another st205 ecu in my brothers car so might be worth trying?

just dont want to cause any damage, it doesnt seem to affect the car, it still runs just as smooth and fast as it always has, revs all the way through to the red line, pulls extremely hard and doesnt smoke under boost or on idle.

sometimes she smells a little of fuel on long idle but i have no cat so i presumed that this is the cause of the smell?

thanks for the reply.

Fuel economy sounds a little poor but only slightly if its a JDM, they always seem to return poorer mpg than the UK cars.

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1996 ST205 UK

yeah its a jap import, last time she went on the rollers it was reading a perfect 11:1 under wot but the gauge wasnt quite as bad when it was on the rollers, was sometimes erratic, strange thing is.. once in a blue moon it reads right, could this mean that it is a loose earth? seems as of late its got worse, maybe the connection has become worse over time?

Dale I have had the same problem for a while I think its something in the cluster...if i hit the dash rite above the cluster just rite the gauge goes normal...I dont have any problems with the car while that boost gauge is going crazy, plus ive heard there not to be trusted anyway lol

ha, it seems the trusty old brute force method works then? haha

only reason i really asked is im sure i read somewhere that it can have effects on the fueling?

is there a picture anyone has of the earthing on the intake manifold so i can see exactly where it is, had a little look down the top this morning and only see vac lines.

too wet to get underneath this morning.