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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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Hollow tapping from fuel rail Duff FPR?Views : 1600 Replies : 30Users Viewing This Thread : |
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Apr 12th, 2018, 11:56 | #21 |
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I agree Eric, it could be any number of things connected with the fuel rail, I may just have to live with it!
Strange that there's so little info out there about the impulse inhibitor thing on the fuel rail inlet pipe! |
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Apr 12th, 2018, 12:09 | #22 |
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YOu may well find when you sort that wastegate/blow-off valve the problem disappears.
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Apr 12th, 2018, 12:32 | #23 |
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Hi Dave, I reconnected the control rod as soon as I discovered it was disconnected, it now boosts as it should and the wastegate does it's 'pa-shoosh' thing but the drumming is still there on tickover once the engine warms up.
If I unplug the MAF it appears to stop! Plug it back in and it's there! |
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Apr 12th, 2018, 12:52 | #24 | |
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It's certainly an odd one either way!
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Apr 12th, 2018, 19:46 | #25 |
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Unplugging the maf gets rid of the noise but as you say it's in limp mode, cleaned the maf and reconnected, cleared the error codes, the noise is still present, cleaning the maf has improved performance though!
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Apr 14th, 2018, 08:44 | #26 |
ericbeaumont
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What is this 'pa-choosh' sound? If I haven't heard it all these years, perhaps I ought get one. I feel like I'm missing out on something.
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Apr 14th, 2018, 09:12 | #27 | |
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As you accelerate through the gears, the turbo spools up and builds pressure. The wastegate limits that pressure to the normal maximum boost level say 10psi for normal use. When you let go of the loud pedal and stand on the clutch pedal to change gear, there's suddenly an excess of pressure between the turbo and the throttle butterfly. This can stall the turbo resulting in shattered impeller blades and other nasty things. This is where the dump valve or blow-off valve comes into play, releasing that excess pressure to prevent the turbo stalling. Usually on production cars it is silenced by dumping into the air intake system on the turbo intake side but a lot of people modify them with an external dump valve so they hear it in action at every gear change.
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Apr 15th, 2018, 11:01 | #28 |
ericbeaumont
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Thanks, Dave. Guessed it was along those lines. If, on my 97 LPT (178k) I hear no 'pa-choosh' is there a fundamental malfunction? Or was the 'pa-choosh' not fitted at the factory?
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Apr 15th, 2018, 11:40 | #29 |
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You would have had a "pa-choosh" fitted at the factory but as i mentioned earlier, it would be one of the silent variety. Also to be able to hear it, you need to be giving it the beans and even then, a factory one would be hard to hear.
If you're fairly gentle on the loud pedal you're unlikely to hear it and especially if you have an auto. Going back about 20 years, i had an MG Montego Turbo - one of the fastest production saloons of its time - and even giving that the beans i never heard the dump valve/ "pa-choosh". If you wander along to where your local boy racers meet up in the evenings, you're bound to hear a few dump valves which would be the aftermarket variety.
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Apr 15th, 2018, 18:58 | #30 |
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That's weird! I have a '97 LPT as well and there's definitely a 'pa-choose', ok it's not as loud as the boy racers with external dump valves but still there after pulling reasonably hard in the mid rev range then releasing the accelerator. Or am I hearing something else???
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