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Hi all, some help needed on my st170, in any gear when the engine gets to 4000rpm it starts to hesitate like hitting the limiter and wont go any further. Its not a misfire as doesnt do it under load on low revs(new coil pack and plugs fitted and leads recently) and have checked the inlet manifold flap which is ok. Having it checked soon for fault code no engine light on? Seems like a fueling problem??? Fuel pump??? Any help much appreciated thanks.

Rik
 

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hi this is an issue with the st170 there has been many firmware updates for the ecu to resolve this issue as it used to be really bad. if you run the car on normal unleaded fuel 95 ron then the problem is really bad and is also not alot better on 97ron. the best way to eliminate this issue being as bad is to run it on super unleaded or minimum 99 ron like you would get at tesco but tesco would be the last fuel i would like to use in my own cars but some people dont mind.
on all modern cars there is a sensor called a knock sensor and what this sensor does is when you put diffrent grades of fuel like 95ron then the sensor basically detects how the knock in the engine and adjusts the timing to allow the engine to run on this fuel when you put 97ron in then the sensor detects this and again adjusts the timing. as this engine is a variable valve performance engine it needs a higher octane fuel as said b4 99ron minimum is better as the timiming advance is correct and this eliminates the issue that you are having.
no fault codes will be present as the engine is trying to look after itself due to the fuel you use.
try using bp ultimate or shell v-power and see the diffrence.
mark
 

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My ST170 had a simialar issue. It had no fault codes, but just seemed to be a bit sluggish and was not revving as freely as it did. Turned out to be the lambda/hego sensor which is a very common problem on the 170's. Once changed it was like a different car.
I would however change the fuel filter first if you don't know when it was last done.
 
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