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1997 Pontiac Grand Prix Loss of fuel economy

Tiny
BRANDI1975
  • MEMBER
  • 1997 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 150,000 MILES
I have experienced a significant loss of fuel economy. Egr valve is good, mass air flow is good, no fuel leaks, fuel pressure regulator is good, fuel pressure is good. Smoke tested and removed oil filler cap, found that the intake manifold was leaking.
Replaced intake gaskets, still no improvement on fuel economy.
Help!
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Wednesday, January 21st, 2009 AT 2:54 PM

4 Replies

Tiny
MMPRINCE4000
  • MECHANIC
  • 8,549 POSTS
Are you getting any error codes?

Sensor failure will cause the engine to run rich, like coolant temp, TPS.

Have PCM scanned at any autoparts store for any error codes or pending codes, this is free.

Other possibilities are leaking injectors, Fuel pressure should not drop for 2-3 minutes after fuel pump is off, if it drops fast, most likely an injector or FPR.
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Thursday, January 22nd, 2009 AT 10:13 AM
Tiny
BRANDI1975
  • MEMBER
  • 3 POSTS
No codes, no pending codes, fuel pressure is good across the board
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Thursday, January 22nd, 2009 AT 10:15 AM
Tiny
MMPRINCE4000
  • MECHANIC
  • 8,549 POSTS
Check fuel pressure regulator vacuum line, if gas is present, then the FPR diaphram is ruptured and will need to be replaced.

If OK, then try to borrow/rent a scanner and hook up to car and go to live data mode, compare readings of all sensors to range limits.
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Saturday, January 24th, 2009 AT 9:05 AM
Tiny
BRANDI1975
  • MEMBER
  • 3 POSTS
Have had it hooked to a scanner, but not sure about the FPR vacuum line, will have that checked. Thanks
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Saturday, January 24th, 2009 AT 9:46 AM

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