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St185 std boost gauge goes to full boost on ignition.
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Author:  Diceman [ Wed Nov 30, 2016 8:25 pm ]
Post subject:  St185 std boost gauge goes to full boost on ignition.

A bit of a wierd one this. Suddenly the boost gauge in the instrument cluster goes up to full boost on turn of ignition key and stays there.

Anyone had this before? I suspect it is just a an instrument cluster issue as the car runs and doesnt fuel cut!

Battery voltage was low and I've seen instrument oddities before due to alternator issues so maybe linked?

Author:  Sirius [ Wed Nov 30, 2016 10:12 pm ]
Post subject:  Re: St185 std boost gauge goes to full boost on ignition.

I have heard of this before and it being alternator related. Might be time for a trip to Burghfield.

Author:  Nibbles [ Wed Nov 30, 2016 11:19 pm ]
Post subject:  Re: St185 std boost gauge goes to full boost on ignition.

I've had the boost gauge go erratic on my 205, sometimes indicating full boost as above, sometimes working correctly. Again, engine operation was fine so not a sensor issue.

Check the alternator voltage with a multimeter to see if that's the problem. I suspect it's more likely a poor connection or gauge problem, maybe the instrument cluster earth.

Author:  Diceman [ Wed Nov 30, 2016 11:25 pm ]
Post subject:  Re: St185 std boost gauge goes to full boost on ignition.

Alternator appears to be outputting a steady voltage of around 13.8V.

The problem seems to have gone again now after a bit more charge and startup again after a couple of hours. Maybe it didn't like the jump pack?

This has kind of coincided with a start of sporadic speedo failure (then it gets better again!) so I will pull instrument cluster and check as well.

Author:  emicen [ Thu Dec 01, 2016 6:00 pm ]
Post subject:  Re: St185 std boost gauge goes to full boost on ignition.

Subscribing in case there are any eureka moments in this thread

My ST205's OEM boost gauge is still inverse reading.

Author:  Nibbles [ Thu Dec 01, 2016 8:13 pm ]
Post subject:  Re: St185 std boost gauge goes to full boost on ignition.

I never bothered sorting my 205, though I suspect the gauge itself as all other things work ok.

Author:  audiodjmp77 [ Thu Dec 01, 2016 8:15 pm ]
Post subject:  Re: St185 std boost gauge goes to full boost on ignition.

Just a thought. Could there be some form of capacitance, that if the battery is very depleted, cause false readings ?

Emicen, could you have a connector the wrong way round ?

I am ready to be shot to bits, as said before I am just thinking

Hopefully it all sorts out the faults

Sent from my Nexus 9 using Tapatalk

Author:  Diceman [ Thu Dec 01, 2016 10:45 pm ]
Post subject:  Re: St185 std boost gauge goes to full boost on ignition.

As I understand it the MAP sensor has a 5V feed from ECU and returns a voltage between 0-5V with circa 4.2V being around 17psi and low voltage being vacuum.

As such if you stuck 5V up the dash boost gauge it would think it had "mega-boost" so is possible if somebody has been ahem fiddling with wires. I guess there are other cocked-up scenarios that would cause a similar issue but you'd have to get a multi-meter on the dash cluster to measure the voltages.

If the ECU was seeing the same voltage it would fuel cut unless sombody had installed a fuel cut defender.

My theory is that it must be an issue dash cluster end or an anomaly with low battery.

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