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Holding Boost on Closed throttle....

581 views 2 replies 2 participants last post by  Gatton_GU 
#1 ·
As most of you would know I had the full top end of the engine replaced 2 months ago, complete Head and all new valves, springs, exhaust manifold, I have noticed that the fuel consumption is a lot higher than when I first bought it but I have also noticed that it is holding boost eg 10 -11 psi on a closed throttle. example driving at 100kph I have my boost at 16psi when I lift off it stays at approx 9 - 11psi on closed throttle. the boost does drop as the rpms decrease on closed throttle. EGT is 280c at 100, the turbo makes full boost by 1800rpm.

It's a strange one that goes against all I know.
 
#2 ·
When TPS is fully up, and therefore below 0.5V, fuel is cut if RPM is higher than 850 RPM : your motor just runs on "its inertia". This is almost always the case when pedal is "up" , except when you depress the throttle, and let the car go down to almost zero km/h). In that case, at some point in time fuel injection is resumed or your motor would just never restart, and would just stop. Fuel injection is always resumed when TPS is down again ( TPS > 1V roughly). Hence the little lag you can feel sometime.

No fuel, means no exhaust gaz, means no boost at all ( or almost none ).

In your case, I would first check your boost gauge.
Second, the TPS voltage, as if the boost stays that high, your IP might be continuing to be sending fuel to your injectors which the ECU ask it to do when it sees TPS > 0.5V.

btw, 16 psi at 100km/h looks very high to me ( on a flat road with no wind ).
And with full boost at 1800 RPM, I suspect you have a one needle - one dawes (or Tillix) arrangement for boost control. I would love to know your MAF voltage at 1800 RPM. You can certainly get a much better arrangement running. But that is another story.
 
#3 ·
I do have the full tillex set up, 1 needle and 1 Valve, I have checked the needle seats and cleaned them out, The boost gauge appears working as I can pull the line from it and it holds and drops reading with pressure. I may clean the Pedal sensor and MAF tomorrow. Failing that I may contact Caboolture Exhaust and politely asking if they can cast an eye over it... Paying for the time of course.
 
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