I was at the track today(this happens on the street too) my best was a 15.3sec 87mph in the quater and i hit fuel cut in 2nd and kept going. So i launch the car by holding the rpms at 3500rpms while i slip the clutch i stuff the gas to the floor and the boost goes to 10psi and right when it gets there drops to 6 - 7 in first. At 6300rpms i shift into 2nd and the boost hits 13psi bam fuel cut, the car bucks and pauses for a second and the check engine light comes on, and the boost drops to 6 - 7 psi again and keep accelerating. i shift at 6300rpms against into third. no fuel cut and the boost goes to 11psi and drops to 10psi. and right at 6200rpms im crossing the finish line. I tested it on the highway back to my house, 4th goes to 10psi and sits there. then 5th gear goes to 11psi and sits there. I baught the stuff to make a boost leak tester, but lowes had the stuff miss labeld so it was to big and tommarow im gonna by another 2 3/4 pvc pipe w/ end cap, tire valve, and a 2 3/4 coupler. im still confused as to whats goin on. anyone know? i happend quiet similar situation on all 6 passes, cept i played around with the boost controller and my launches and time were different.
sound like a boost leak or something else?
- Thread starter NeoJester
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Actually this is pretty normal...you hit fuel cut...that is one of several fail safe modes the ECU has to protect the engine. Code 34 is Turbo Pressure Signal, what everyone calls fuel cut...it literally cuts the injectors off. When that happens, your boost is going to fall (like it did) until the ECU senses the over boost is abated. That's why you were able to resume boosting after you shifted to 3rd and subsequent gears.
The drop in psi for 1st gear sounds more like a controller issue. The boost produced by the turbo is related to engine load...you were able to build to 10 psi with the clutch slipping, but it dropped on clutch release. It should have built back to the 10+ psi range as you went to the 6300 rpm shift point...especially since a launch is when the motor is under the heaviest load. Sounds like the controller is allowing the wastegate to open or you have a solenoid allowing excess pressure to reach the wastegate actuator doing the same thing. If it's an MBC, the valve is letting excess pressure to reach the actuator. Could be a wastegate actuator problem too.
What's strange about your problem is a boost leak usually manifests itself across the gears. That's why I'm thinking it's more of a controller issue. It won't hurt to check for leaks, but I would take a good look at the controller and wastegate.
The drop in psi for 1st gear sounds more like a controller issue. The boost produced by the turbo is related to engine load...you were able to build to 10 psi with the clutch slipping, but it dropped on clutch release. It should have built back to the 10+ psi range as you went to the 6300 rpm shift point...especially since a launch is when the motor is under the heaviest load. Sounds like the controller is allowing the wastegate to open or you have a solenoid allowing excess pressure to reach the wastegate actuator doing the same thing. If it's an MBC, the valve is letting excess pressure to reach the actuator. Could be a wastegate actuator problem too.
What's strange about your problem is a boost leak usually manifests itself across the gears. That's why I'm thinking it's more of a controller issue. It won't hurt to check for leaks, but I would take a good look at the controller and wastegate.
NeoJester said:
That's easy...take the MBC out of the loop and do a test run. Your boost will be lower, but what you are looking for is consistent boost as you shift through the gears.
NeoJester said:
that is basically same problem I have ... thru 1-3 gears it drops a bit ... the highier the gear less the drop ... and on 4th and 5th it holds good ... I got Voodoo MBC and 11ps set. It drops like crazy from 11 to 6 psi when in first ... like there is a LEAK but when in 3rd or 4th the drop bare noticable. I had every clap replaced and hose checked before installed ... turbo is not perfect but it rolls nicely ... no smoking or any other issue ... My guess is poor MBC or WG acting up and in need od shimming till new turbo
Mike
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