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Old 25-10-2009, 09:06 PM
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Gibbmodoll Gibbmodoll is offline
Join Date: Oct 2009
Location: Madley in Herefordshire Uk.
Posts: 482
Thumbs up Audi A4, 1.9 TDI diesel, x plate, eng: code AJM.

Customers complaint of, poor power at times.
Codes P1556, charge pressure control negative deviation (intermittent fault)

We checked and found that the turbo boost rod was not pulling fully up, if you find this check the vacuum at the turbo boost pipe, this needs to be min: 20 Hg, and 15 Hg to work the rod to fully close the gate.

At turbo the vac: was found to be only 4 to 5 Hg, if you see this do a quick of the m/fold butterfly valve, blip the throttle and switch off the motor, check the m/fold valve goes closed, if not you have a vac: supply fault, and you will need to check for leaking vacuum pipes and pump.

We found the vac: at the pump to be ok, but the vacuum supply pipe running round the engine bay, was found to have a small hole in it, this had been rubbing on a bolt within engine bay.

Sometimes sucking up to the bolt and blocking the leak, and turbo working, and sometimes pulling away and leaking, and the turbo not working.
Gibbins Motors Technology Uk

The more you know the less you know!!
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