Test to conduct before purchasing a second-hand vehicle
The sump compression of an engine must be negative. Pull out the dipstick while engine is idling, don't rev the engine. If there's any wind, gas or oil escaping the dipstick holder then the rings are worn. This condition is known as 'blow-by'.
White smoke from the exhaust indicates engine oil remaining on the bore that the rings haven't scraped off -loss of oil control. Black smoke from the exhaust indicates dirty fuel injectors on a diesel engine. Dirty fuel injectors aren't a serious problem. The rings gets progressively worn down. A slight escape of wind from the dipstick is the first stage of ring failure. It will get worse until gas and oil start escaping the dipstick holder. Reduced compression or blow-by on the rings has nothing to do with the condition of a diesel pump.
Reduced engine compression/white smoke are the result of the piston rings not sealing tight with the bore. 'Blow-by' on the rings results in less power transferred to the crankshaft. The compression gas that escape past the rings are forced out via the sump. This results in the sump leaking oil.
The dry/wet readings must be very close to each other. To do a dry test, unplug the spark plugs for petrol and remove the glow plugs on a diesel engine. Place compression tester inside glow plug and crank engine 10 times till the needle indicates maximum compression. Note this reading and write it down. Repeat test for remaining three cylinders. All four readings must be within 10% of the vehicle specs and very close to each other. Should a reading be out, insert 10ml engine oil into the glow plug and repeat compression test. The oil seals any faulty rings. Should the reading differ from the dry reading, it indicates a failing ring. Above sea level the compression readings on all four pistons must be within 80% of the specs.A mechanic must perform a compression test on any used vehicle before purchase. And don't use the mechanic next door to the retail outlet - ensure you obtain an unbiased opinion.If there's no air,gas or oil escaping the dipstick holder, but the compression readings are not correct then the cylinder head is cracked or there is a blown head gasket. Look for a white emulsification on the dipstick. It would indicate a cracked cylinder head, leaking engine coolant on the piston.Check the dipstick end for gear oil or engine oil. Car salesmen add SAE90 gear oil to mask faulty ring symptoms.
Prevent engine overheating
Replace water pump, thermostat and radiator hoses. Have radiator cleaned at a radiator workshop. Make certain that the radiator capacity is big enough for the engine. Diesel uses 3core, petrol 2core radiators for L D V. Remove radiator cap and check for oil. Oil in the water means a cracked cylinder head. This is major structural damage to an engine. Machinist shops test head integrity via a pressure test. There must be engine coolant in the radiator. Clear water in radiator indicates poor maintenance of engine.
Automobile Repair/Diagnostics
Diagnostic skills are not taught in automotive schools or books as much as in the past, for several reasons. First, it is often more efficient for a mechanic to remove and replace a part than to try to repair that part. Second, the parts themselves are not made to be repaired as much as in the past. Granted, the time it would take to repair a transmission may be far more than it would be to replace the transmission, so it may be a more efficient system overall. However, the modern way does have its disadvantages--one of them being less ability to diagnose. In one case, a customer was nearly charged $3000 to replace the transmission in a pickup truck when the problem was a bad spark plug (the plug was not firing properly so the engine computer would down shift looking for more power and would then be told to up shift again because the R P M's were too high). Knowing how to really track down the problem can save you a lot of money.
There are two approaches to diagnosing a problem: 1) using a repair manual, or 2) relying on your own analysis 3) using the experiences of others with the same problem. I suggest grabbing a repair manual until you know more. As you repair with the guidance of a manual, you will develop an 'intuition' that will guide you to problems. This process won't happen on its own, however--you have to be hungry for it.
The first step in any diagnosis is to gather information. Use your senses and ask questions: when does the car make that noise? What does it sound like? How does it feel? Where is the sound coming from? Does it happen at all speeds? Does the car do anything at all?
The second step in diagnosis is to grab a manual armed with that information and look for the troubleshooting charts. I believe that factory manuals have great information, but are not as novice-friendly as the manuals from the auto parts stores. For my own vehicles, I try to get the factory manual (for the most authoritative information) as well as the Haynes (or similar) manual. If you only get one, maybe just the Haynes.
Please note that advanced mechanics will often not need this step, as the problems will be obvious to them. After doing enough repairs, the different systems fit together and do not seem foreign, separate, confusing, or threatening.
Astra Engine temperature erratic usually low
This is usually caused by the thermostat stuck open. Either luckily or by design thermostats usually fail safe - open. On a C14NZ the thermostat is behind the camshaft belt casing and requires the camshaft belt and pulleys to be removed so it cannot be easily tested. New thermostats are remarkably cheap from generic parts supplier, and can be fitted in the upper radiator hose as an alternative to their proper placement. Haynes does not describe this procedure. Remember to fit the thermostat the correct way around,, that is with the longer piece facing the engine.
Astra Engine temperature high, electric fan not running
First check the fuse. Fuse # 11. Second test the Cooling fan thermostatic switch. Removing this will let all the coolant out, observe safety precautions described in the Haynes manual - cool engine and catch coolant. The switch often fails open circuit, use a continuity tester to check if switch closes when heated in a pan of water just before boiling point.
Thirdly check that 12Volts is being supplied to the fan motor, if not, broken wires can be the cause. Lastly prepare to replace the fan assembly, remove it and check it before buying a new one.
Astra Engine misfires at low revs
Symptoms such as misfires and stalls until engine is running at > 3000 RPM and even then runs rough. Firstly check the spark plugs for excessively large gaps, eroded electrode or dirt. Replace if necessary. Otherwise on the C14NZ engine this is often caused by oil in the distributor cap. The distributor is mounted horizontally on the end of the camshaft and the oil seal allows small amounts of oil into the distributor that then causes short circuits. This can be cured during the early stages by wiping the inside of the distributor cap with a clean rag. Later stages of deterioration burn carbon tracks in the cap and these can be cleaned off, but a new cap is required. If a lot of oil leaks into the distributor the whole unit has to be replaced, it is not possible to buy component parts of the distributor.
Astra Engine falters or stalls
The C14NZ engine may run for long periods and then it falters and perhaps stalls. In many cases it will restart and run normally for a while. This fault is infuriating if the period between failures is weeks since you can never be sure that the problem is fixed and it can be caused by numerous faults. First check the failure mode, if the rev counter drops to zero before the engine stops it is most likely to be the Engine Control Unit or the crankshaft position sensor. The C14NZ E C U is pretty robust and the CPS is more lightly to fail. Surprisingly the CPS can be intermittent, but it will eventually fail completely. It is simple to change, but cannot be bought as an individual component. If the counter continues to reflect the engine speed the problem is in the High Tension circuit, most likely the plug leads.
Astra Engine misfires under full throttle
Engine runs normally under light load but misfires at full throttle. Firstly check the condition of the spark plugs. Then look for signs of a rich mixture, check fuel consumption. An over-rich mixture can be due to a broken Coolant Temperature Sensor or wiring. The sensor operates the dashboard temperature gauge, check readings are sensible. A broken sensor failure is the equivalent of running with the choke on. The E C U thinks the engine is cold. The sensor connector is exposed and rather insecure. The sensor should read about 1600 Ohms at room temperature. See Haynes manual for replacement procedure.
Astra 5 speed manual gearbox, cannot select 2nd gear
Usually caused by a worn gear linkage. Inside the engine compartment, the top side to side link is made of plastic and seems to be the "weak link". With an assistant in the car, have them try to select 2nd gear, if there is side to side play replace the link. This is not described in the Haynes Manual - details follow.
The sump compression of an engine must be negative. Pull out the dipstick while engine is idling, don't rev the engine. If there's any wind, gas or oil escaping the dipstick holder then the rings are worn. This condition is known as 'blow-by'.
White smoke from the exhaust indicates engine oil remaining on the bore that the rings haven't scraped off -loss of oil control. Black smoke from the exhaust indicates dirty fuel injectors on a diesel engine. Dirty fuel injectors aren't a serious problem. The rings gets progressively worn down. A slight escape of wind from the dipstick is the first stage of ring failure. It will get worse until gas and oil start escaping the dipstick holder. Reduced compression or blow-by on the rings has nothing to do with the condition of a diesel pump.
Reduced engine compression/white smoke are the result of the piston rings not sealing tight with the bore. 'Blow-by' on the rings results in less power transferred to the crankshaft. The compression gas that escape past the rings are forced out via the sump. This results in the sump leaking oil.
The dry/wet readings must be very close to each other. To do a dry test, unplug the spark plugs for petrol and remove the glow plugs on a diesel engine. Place compression tester inside glow plug and crank engine 10 times till the needle indicates maximum compression. Note this reading and write it down. Repeat test for remaining three cylinders. All four readings must be within 10% of the vehicle specs and very close to each other. Should a reading be out, insert 10ml engine oil into the glow plug and repeat compression test. The oil seals any faulty rings. Should the reading differ from the dry reading, it indicates a failing ring. Above sea level the compression readings on all four pistons must be within 80% of the specs.A mechanic must perform a compression test on any used vehicle before purchase. And don't use the mechanic next door to the retail outlet - ensure you obtain an unbiased opinion.If there's no air,gas or oil escaping the dipstick holder, but the compression readings are not correct then the cylinder head is cracked or there is a blown head gasket. Look for a white emulsification on the dipstick. It would indicate a cracked cylinder head, leaking engine coolant on the piston.Check the dipstick end for gear oil or engine oil. Car salesmen add SAE90 gear oil to mask faulty ring symptoms.
Prevent engine overheating
Replace water pump, thermostat and radiator hoses. Have radiator cleaned at a radiator workshop. Make certain that the radiator capacity is big enough for the engine. Diesel uses 3core, petrol 2core radiators for L D V. Remove radiator cap and check for oil. Oil in the water means a cracked cylinder head. This is major structural damage to an engine. Machinist shops test head integrity via a pressure test. There must be engine coolant in the radiator. Clear water in radiator indicates poor maintenance of engine.
Automobile Repair/Diagnostics
Diagnostic skills are not taught in automotive schools or books as much as in the past, for several reasons. First, it is often more efficient for a mechanic to remove and replace a part than to try to repair that part. Second, the parts themselves are not made to be repaired as much as in the past. Granted, the time it would take to repair a transmission may be far more than it would be to replace the transmission, so it may be a more efficient system overall. However, the modern way does have its disadvantages--one of them being less ability to diagnose. In one case, a customer was nearly charged $3000 to replace the transmission in a pickup truck when the problem was a bad spark plug (the plug was not firing properly so the engine computer would down shift looking for more power and would then be told to up shift again because the R P M's were too high). Knowing how to really track down the problem can save you a lot of money.
There are two approaches to diagnosing a problem: 1) using a repair manual, or 2) relying on your own analysis 3) using the experiences of others with the same problem. I suggest grabbing a repair manual until you know more. As you repair with the guidance of a manual, you will develop an 'intuition' that will guide you to problems. This process won't happen on its own, however--you have to be hungry for it.
The first step in any diagnosis is to gather information. Use your senses and ask questions: when does the car make that noise? What does it sound like? How does it feel? Where is the sound coming from? Does it happen at all speeds? Does the car do anything at all?
The second step in diagnosis is to grab a manual armed with that information and look for the troubleshooting charts. I believe that factory manuals have great information, but are not as novice-friendly as the manuals from the auto parts stores. For my own vehicles, I try to get the factory manual (for the most authoritative information) as well as the Haynes (or similar) manual. If you only get one, maybe just the Haynes.
Please note that advanced mechanics will often not need this step, as the problems will be obvious to them. After doing enough repairs, the different systems fit together and do not seem foreign, separate, confusing, or threatening.
Astra Engine temperature erratic usually low
This is usually caused by the thermostat stuck open. Either luckily or by design thermostats usually fail safe - open. On a C14NZ the thermostat is behind the camshaft belt casing and requires the camshaft belt and pulleys to be removed so it cannot be easily tested. New thermostats are remarkably cheap from generic parts supplier, and can be fitted in the upper radiator hose as an alternative to their proper placement. Haynes does not describe this procedure. Remember to fit the thermostat the correct way around,, that is with the longer piece facing the engine.
Astra Engine temperature high, electric fan not running
First check the fuse. Fuse # 11. Second test the Cooling fan thermostatic switch. Removing this will let all the coolant out, observe safety precautions described in the Haynes manual - cool engine and catch coolant. The switch often fails open circuit, use a continuity tester to check if switch closes when heated in a pan of water just before boiling point.
Thirdly check that 12Volts is being supplied to the fan motor, if not, broken wires can be the cause. Lastly prepare to replace the fan assembly, remove it and check it before buying a new one.
Astra Engine misfires at low revs
Symptoms such as misfires and stalls until engine is running at > 3000 RPM and even then runs rough. Firstly check the spark plugs for excessively large gaps, eroded electrode or dirt. Replace if necessary. Otherwise on the C14NZ engine this is often caused by oil in the distributor cap. The distributor is mounted horizontally on the end of the camshaft and the oil seal allows small amounts of oil into the distributor that then causes short circuits. This can be cured during the early stages by wiping the inside of the distributor cap with a clean rag. Later stages of deterioration burn carbon tracks in the cap and these can be cleaned off, but a new cap is required. If a lot of oil leaks into the distributor the whole unit has to be replaced, it is not possible to buy component parts of the distributor.
Astra Engine falters or stalls
The C14NZ engine may run for long periods and then it falters and perhaps stalls. In many cases it will restart and run normally for a while. This fault is infuriating if the period between failures is weeks since you can never be sure that the problem is fixed and it can be caused by numerous faults. First check the failure mode, if the rev counter drops to zero before the engine stops it is most likely to be the Engine Control Unit or the crankshaft position sensor. The C14NZ E C U is pretty robust and the CPS is more lightly to fail. Surprisingly the CPS can be intermittent, but it will eventually fail completely. It is simple to change, but cannot be bought as an individual component. If the counter continues to reflect the engine speed the problem is in the High Tension circuit, most likely the plug leads.
Astra Engine misfires under full throttle
Engine runs normally under light load but misfires at full throttle. Firstly check the condition of the spark plugs. Then look for signs of a rich mixture, check fuel consumption. An over-rich mixture can be due to a broken Coolant Temperature Sensor or wiring. The sensor operates the dashboard temperature gauge, check readings are sensible. A broken sensor failure is the equivalent of running with the choke on. The E C U thinks the engine is cold. The sensor connector is exposed and rather insecure. The sensor should read about 1600 Ohms at room temperature. See Haynes manual for replacement procedure.
Astra 5 speed manual gearbox, cannot select 2nd gear
Usually caused by a worn gear linkage. Inside the engine compartment, the top side to side link is made of plastic and seems to be the "weak link". With an assistant in the car, have them try to select 2nd gear, if there is side to side play replace the link. This is not described in the Haynes Manual - details follow.
No comments:
Post a Comment