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Old 06-29-2007, 16:28   #1 (permalink)
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code 556: vacuum leak, EGR or fuel pump?

after replacing my IAC, PFE and EGR Vacuum ergulator, I cant figure out why I now have part throttle stumble. It feels like a vac leak; but the codes say Fuel pump primary circuit failure. I've checked the vac lines and dont hear or see a leak. The Throttle body "elbow" was removed and cleaned as well.

Under load (uphill) the car stumbles with a rough idle until I hit the passing gear, Then it seems better; but still underpowered.

anyone have an idea of what I want to try next?

EdPDX

92 merc Grand Marq. 4.6
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Old 06-29-2007, 17:28   #2 (permalink)
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cool Re: code 556: vacuum leak, EGR or fuel pump?

Quote:
Originally Posted by EdPDX
After replacing my IAC, PFE and EGR Vacuum regulator, I cant figure out why I now have part throttle stumble. It feels like a vac leak; but the codes say Fuel pump primary circuit failure. I've checked the vac lines and dont hear or see a leak. The Throttle body "elbow" was removed and cleaned as well.

Under load (uphill) the car stumbles with a rough idle until I hit the passing gear, Then it seems better; but still underpowered.

Anyone have an idea of what I want to try next?

EdPDX

92 merc Grand Marq. 4.6
Check the fuel pressure. It should be at least 30 psi. If it isn't then you may have a bad fuel pump. Slim possibility you may have a wiring issue.
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Old 08-10-2007, 07:26   #3 (permalink)
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Re: code 556: vacuum leak, EGR or fuel pump?

Well after lots of reading and testing with a multimeter I have not come up with the current demon. I have now replaced the:

O2 sensors
MAF
Temp Coolant Sensor
EGR
EVR
PFE
IAC

The hoses were checed for vac leaks- 2 Found:

EGR tube replaced for a split in the corrugated elbow.
PCV lower hose to intake manifold- the infamous "rubber 'T'" was bad and replaced.

Contacts have been cleaned and replaced at every connector that was disconnected.

PCV valve seems to shake freely.
TPS was tested as good

Past codes include:332 542 543 556 176 177. All have cleared with changing of various parts above.

Emmisions test at the state inspection station yesterday produceed expected results X NO PASS X Hydrocarbons and carbons too high.

Help... I'm about ready to see if changing the floor mats will help.

Thanks,

Ed
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