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Old 09-30-2008, 02:51 PM   #1 (permalink)
amateur mech. engineer
Join Date: May 2008
Location: New York City
Posts: 112

Sporty Accord - '88 Honda Accord LX-i
90 day: 23.25 mpg (US)

Dad's Camry - '01 Toyota Camry CE
90 day: 22.81 mpg (US)

Artie's Camry - '98 Toyota Camry
90 day: 37.3 mpg (US)
Thanks: 0
Thanked 15 Times in 3 Posts
Here are a few engine problems that hurt fuel economy:

- missing or defective thermostat, causing low operating temperature

- clogged intake manifold exhaust crossover passage (for heating intake manifold)

- engine misfire caused by bad spark plug, ignition wire, coil, dist. cap or rotor

- late ignition timing

- bad vacuum advance unit (common in old cars)

- stuck centrifugal advance mechanism in distributor (needs oil occasionally)

- bad tension adjustment of centrifugal advance springs

- defective oxygen sensor (causes rich mixture)

- defective coolant temp. sensor for engine computer (causes rich mixture)

- worn timing belt (may cause rich fuel mixture in fuel injected cars with a MAP sensor)

- incorrect timing belt installation (timing marks should line up)

- sticking or poorly adjusted carburetor choke (causes rich mixture)

- dirty air filter on an engine with a carburetor (causes rich mixture at high power)

- clogged or defective PCV valve

- incorrect valve clearance (especially if too tight)

- high performance camshaft installed (not efficient at low power)

- worn valve guides (makes fuel mixture too lean at low power)

- vacuum leak from bad vacuum hoses or intake system gaskets (causes lean mixture)

- dirty fuel injectors

- bad fuel pressure regulator

- bad MAP sensor for fuel injection

- leaking intake duct between air flow sensor and throttle body

- too much alcohol in gasoline with old car (requires carb. modification for correct mixture)

- rusted or missing exhaust heat stove or pipe for heated air intake

- loss of compression pressure due to worn rings or leaking valves

- sticking EGR valve (causes rough idling and rich mixture on some engines)

- exhaust backpressure caused by clogged catalytic converter, muffler or crushed pipe

- stuck exhaust manifold valve for some V type engines. Intended for fast warm up.

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