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Smoking engine/High oil consumption?

Discussion in 'Diagnosis/Help' started by Stig, Apr 17, 2009.

  1. Stig

    Stig ST162 Guru Donated!

    Diagnosing a smoking engine

    Black smoke (soot like) – Running Rich (too much fuel, not enough air).
    Black smoke is raw gasoline burning. A rich condition can be caused by a leaky/stuck or mis-adjusted float, a choke stuck shut, a bad oxygen sensor, a bad map sensor, a bad fuel pressure regulator, a plugged up air filter, bad timing or a bad injector. Typically, if you only get black smoke first thing in the morning, it has to do with the choke or the fuel enrichment portion of your fuel injection system.
    If you get black smoke all the time, get it fixed NOW. If you don’t, you run the risk of destroying the catalytic converter or worse, a rich condition causes “cylinder wash” – the oil gets washed from the cylinder walls by the fuel and causes major wear to the piston skirts & rings & bore and will lead to an engine seizure.


    Blue smoke is oil burning. The tailpipe will either smoke all the time or just once when cold. If you get blue smoke all the time it is a sign of impeding doom, ie Broken rings, worn out rings, bad pistons, piston rings “glued” by burnt oil & carbon, damaged cylinder walls, glazed bores – all high dollar items.
    Please note – some synthetic oils burn white.
    Blowby – Remove oil cap while engine is running, if blue/gray/white smoke is seen it is a major ring/piston problem.

    Smoke appears when:
    1) On starting – Valve Seals (allowing oil to travel down guides into combustion chamber)
    wait until you begin to see other symptoms of this oil usage or you start fouling plugs, wait until the oil consumption is greater than one quart every 1,000 miles. And never assume that seals alone will totally fix this problem, if the engine has 100k plus it’s an indication of overall wear.
    2) When accelerating – Worn rings (Perform compression test)
    3) When engine is de-accelerated – Worn Valve Guides

    On the other hand, if all you get is a puff or two when the engine is cold and never again throughout the day, then your problem is probably bad valve guides or guide seals. It will cost between $350-800 to replace the seals, $750-1,500 to replace the guides and seals, wait until you begin to see other symptoms of oil usage or start fouling plugs, the oil consumption is greater than one quart every 1,000 miles. Never assume that seals alone will totally fix this problem, esp if the engine has done 100k plus.


    Grey smoke can really be black or blue. You can usually tell which it is by the smell or by matching other symptoms you have to the colour of the smoke.


    White smoke (lingering) can be either the transmission shift modulator - allowing the engine to suck and burn transmission fluid.
    White smoke - Can also be Synthetic Oil burning!
    White smoke – Not very common, but if your brake servo is leaking, brake fluid is sucked into the intake manifold and burns white
    White smoke could also be coolant or antifreeze that is either leaking, or being forced into the combustion chambers and being burned, the exhaust will look wet and have a sweet smell to it.

    A bad head gasket (75% of the time), a broken head (15% of the time) or a broken cylinder wall (10% of the time) will be the reason your engine is burning coolant or antifreeze. The repairs start at $400 and go to $4,000.
    Pressure test cooling system and check all plugs. The “cleanest” plug is washed clean of all ash is often the cylinder with coolant leaking into it. White smoke will become worse when coolant is full and engine is at normal operating temperature.
    Check for combustion by products in coolant.
    Pressure test cooling system and inspect for coolant leaking into cylinder.

    White smoke (dissolving) – Steam, cold ambient Temperature, Humidity? Disappears as the engine is driven..Nothing to worry about.


    Using Oil
    Slow oil consumption (no smoke) – Worn oil control rings



    Engine Compression Test
    Check cylinder compression in all cylinders.
    Warm engine up, Remove all plugs, Disable fuel system and ground or disable ignition system, block throttle plates/pedal open.
    Install pressure gauge.
    Crank engine at least 3 times per cylinder and check reading on pressure gauge.

    If two adjoining cylinders are low, it could be a blown adjoining head gasket.
    If one cylinder is low, perform a wet test.
    If compression test shows high compression on all cylinders, it is due to carbon build up
    If compression test shows low compression on all cylinders it's possibly due to incorrect valve timing (jumped time)


    Wet Test –
    Add 2 squirts of oil to the low cylinder
    If cylinder readings increase on wet-test, its worn rings, if not, its either the intake or exhaust valve seating (or in rare cases a hole in the piston). Perform combustion leak testing.


    Combustion leak testing
    Bring cylinder to TDC
    Install leak tester
    have someone hold the engine (johnson bar and 3/4 socket @ the crank pully) while you pressurize it or it will just spin backwards and possibly jump time.
    pressurize
    Listen for leak

    If air is heard coming out of the header/tail pipe, it is an exhaust valve-sealing problem (seating problem)
    If air is heard coming out of the throttle plates, it is an intake valve-sealing problem
    If air is heard out of the dipstick or the oil cap, its rings or a bad piston
    If bubbles come out of radiator, it’s a blown head gasket.


    Engine Makes Noise

    (Step 1) Check oil level and condition. If oil looks old or poor (black/white) change oil and filter with correct type.
    If oil is “too full” and “milky” the head gasket has failed and coolant is mixing with the oil.

    (Step 2) Figure out, when and where the engine noise happens.
    If noise happiness when engine is:

    Drive/Neutral – Engine may not be the problem, transmission, or flexplate or clutch may be issue.

    Cold/Warm Engine - No Load - High RPM (2000)
    A piston (wrist) pin knock. Loose piston pins will generally knock louder when the engine is not operating under a load. A piston pin knock is sometimes mistaken for a connecting rod knock although the pin knock is not as loud.

    Cold/Warm Engine - No Load - Higher RPM (3000-4000)
    The connecting rod knock is caused by excessive clearance between the connecting rod bearing inserts and the bearing surface of the crankshaft. It makes a loud, sharp knock while the engine is running at a constant speed without a load. You can detect the faulty connecting rod bearing by disconnecting and connecting the spark plug leads one at a time. When you disconnect the lead from the cylinder with the loose rod bearing, the knock will go away or at least change a great deal.

    Cold/Warm Engine - No Load - Low RPM (Idle)
    Loose main bearings on the crankshaft cause a heavy, dull, thud type noise which is usually worse with the engine loaded. Loose connecting rod bearings or main bearings will usually cause low oil pressure. This low pressure will be more noticeable at slow engine speeds. This is because the oil pressure leaks off past the loose bearing, and at slow engine speeds, the oil pump turns too slow to pump enough oil to maintain the proper pressure. At higher speeds, enough oil is pumped to overcome the leak and build up the oil pressure. If we have a sharp knock or a dull thud sound and the oil pressure is low, the connecting rods or main bearings are worn.


    Noise when Cold - Then Goes Away Once Warm
    A piston slap usually sounds off only when the engine is on a pull. Like the connecting rod, disconnecting the spark plug wire to the affected cylinder will generally stop the knock. Pistons have been known to knock quite loud when the engine is cold, then the noise completely disappears after the engine warms up. Also the water pump, oil pump, idler and tensioner can sometimes make light clicking sounds on startup and dissappear when warm, only way to find it is to get the cambelt off and check each one.
    A loud screaming sound which goes away can be either the alternator bearings or water pump bearings.

    Location
    Top of engine – Valve Train Noise, Camshaft, Valves, Lifters, Springs, Rocker Arms
    Lower end of engine – Connecting Rods – Main Bearings
    Front/side of engine – Timing Belt rollers, distributor, water pump or oil pump

    Perform Oil Pressure Test
    Install Oil Pressure Gauge.
    Warm Up Engine.
    Run Engine at 2000 RPM – Oil pressure should be about 25-30 PSI or more is OK.

    If oil pressure is low –
    Weak oil pump
    Worn Main or Bigend Bearings
    Damaged Camshaft caps
    Clogged Oil Pickup (screen)
    Low oil
    Head gasket leaking - blue smoke, 1 plug clogged
    Wrong Oil (too thin)
    Stuck OPEN oil pressure relief valve (weak or broken)
    Aerated oil (bubbles/whipping)
    Oil leak (internal or external)

    If oil pressure is too high -
    Stuck oil pressure relief valve
    Wrong Oil (too thick)

    Engine Runs Rough (constantly missing cylinder)

    Perform Power Balance Test to determine the dead cylinder
    Once dead cylinder has been identified, inspect fuel injector and spark plug and wire to cylinder.
    If both fuel and injector seem good, perform a compression test.
    If plug is fouled with oil, the cylinder has a major oil consumption problem (rings or damaged piston)
    If plug is washed clean it is a head gasket or valve leak.
     
    Last edited: Aug 20, 2015

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