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Fg Xr6 Turbo runs fine till gets up too operating temp then sounds like it has no compression upon start up


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hey guys a bit of a headache here, car runs fine when its warming up, once up to operating temp starts to run a bit shit and progressively gets worse till the point of stalling. when trying to start again it sounds as there is no compression. im thinking the intake cam is getting stuck open but once it gets flashed with the sct there is no issue. here is the tune if anyone can shed some light it would be amazing if someone had some help


info on the car also-

e85 10.5-1 compression 

atomic pistions and rods

stainless o'ring headgasket 

0.05 over inlet and exhaust valves 

mild port job

hoontune ht2 cams still retaining vct


v8EATER SP1 & SP2.tec

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  • EddieKepper changed the title to Fg Xr6 Turbo runs fine till gets up too operating temp then sounds like it has no compression upon start up

Do a compare to the SCT tune. What differences do you see?

There are literally hundreds of things that could be wrong. Personally I would start tuning the car entirely from first principles.

Eg ensure your injectors are dialled in with stock cams.

Lock the cams in the software and tune each speed density row one at a time.

Tuning cams properly will take you a solid 1-2 weeks of R&D. Throwing in higher compression and porting etc means you have a big job ahead of you as none of the standard tables will work. You will need to redo all of your speed density and spark maps. This means you need a dyno.

How have you dialled in the speed density tables to start with?

Are you working with injector data that is known to be good on that motor? Eg without cams, are you confident the injectors would result in a less than +-5% trims?

Has the VCT system been modified to support the higher ramp rate of the camshafts? If not are you getting a large VCT cam error? If you are getting a large error you will need to either modify the VCT system or lock the cams.

If you don't have your injectors dialed in with a stock motor, then you have no way of knowing which is out, the speed density or your injector data. You will be chasing your tail for months (literally months) without this.

Finally you say it sounds like it has no compression. Have you done a hot compression test? Maybe the VCT system is failing.

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I had a bit more of a think about this and it sounds like a VCT system problem. If you log your cam angle and cam error at idle I am willing to bet it is large hence the car dropping compression and running terribly as the oil pressure has dropped off when warm.

I'm not sure where you are located but if you send us an email I can give you the contact of some workshops who have tuned big cams with a modified VCT system and can most likely help you out. The issue will most likely be with oil supply in the head or with the VCT actuators themselves.

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