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urgent help vy supercharged calais

1nonly

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I have a 2004 series 2 vy supercharged calais it has been boosted to 10 psi. I am having a major problem when i accelerate heavy in second and third gear the car sort of looses power and gains power and it becomes quiet jerky and doesn't gain much speed. When I had my dual 2.5inch catback exhaust on it would back fire when it happened. I have had it at the mechanics and he hooked it up to his scan tool and came up no engine problem and no transmission problems. And will take alot of work to diagnose which means alot of money. Please help me brainstorm some ideas as I am stumped. Whether it is injectors or fuel pump not putting in enough fuel for the air its bringing in or a vaccuum problem or worst case compression problem. Has this happened to anybody?
 

Big-Al

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no not really.
has it been tuned since you changed the pulley. what fuel are you running? Changed the fuel filter recently? Sounds like the ECU is pulling timing out due to detonation.
 

SV6SIDI

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Did it only happen after you did the pulley? Make sure you are only running it on 98 octane fuel. It could be the leads ,plugs or coil pack that need replacing .mine did something similar and it ended up being the plugs and leads.
 

1nonly

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I only ever run 98 and as I brought the car already boosted one would imagine it would have been tuned but the problem has only started happening over the last few months. Changed fuel filter last week and pump still had good back pressure. What would cause the backfiring?
 

1nonly

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And I thought plugs and leads cause the hesitation on take off not while your driving and accelerating
 

Big-Al

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sounds likely to be ignition based then. back firing would be caused by unburnt fuel reaching the cats. try changing the plugs, check the leads with a multimeter and make sure the resistance is within spec, try coil changing packs with known working units.
does it back fire at any particular RPM range? e.g when it hits 4,000rpm.
 

1nonly

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Its around 3 -4000 rpm in 2 and 3 gear. First gear is fine underload.
 

WogBoyz

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sounds like ignition problem, as it cant the handel load in the higher gears ect, as said id be changing plugs checking leads and coil packs and lastly the DFI which im pretty sure is under the coilpacks
 
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