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Mechanical Assistance: Engine Problems

Mechanics use a process of elimination to find faults which is how you should use the following information.  Carry out any of the checks you feel comfortable with, if you can't fix the fault you will  be able tell a mechanic what you have checked to help their diagnosis which could save you money.

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If you cant find a solution try our free online mechanical help and one of our engineers will help you with your car problems.

If you cant find the answers you are looking for on this page have a look through our past mechanical Questions & Answer pages

More mechanical engine problems & faults on page two

Free Mechanical Help
All the problems and possible solutions detailed below are provided by the experienced automotive mechanical engineers who carry out our vehicle inspections. The problems covered can be common to most vehicles but the list is by no means exhaustive. If your particular mechanical problem is not answered below ask our engineers for mechanical assistance here.

Engine turns over but wont start

Possible Fuel Problems.
Although obvious this is the most common cause for an engine failing to start. Your fuel gauge may show there is fuel present however the mechanical measuring devises can be flimsy and prone to wear or clogging from any contaminated fuel giving an inaccurate reading.

How to check For Fuel.
Locate the in line fuel filter and have someone turn over the engine and see if you can see fuel passing through the filter or fuel line or,
Take off the fuel cap and place your ear close to the opening and rock the car gentle from side to side and listen for the fuel sloshing around or,
A fool proof method, get a can of fuel and put it in the fuel tank!

Note: If there is fuel present but its low and your vehicle has been stood on an incline this can cause fuel starvation. If you have a primer pump in the engine compartment squeeze it three or four times until it stiffens up and try to start the vehicle again.


Click to view large imageIf your car has a fuel primer pump it will look something like this. They come in a verity of colours often quite bright if they have been replaced.
 

If it starts it may stop again when what was primed has run out so get a can and fill her up.

Fuel present but wont Start

Petrol cars:
Depending on the age and type of car you may have a carburettor or a fuel injection system. Either could be faulty or have blockages which is unlikely but never the less possible this being the case professionals will need to take a look as taking a carburettor apart to clean requires considerable knowledge and electronic fuel management systems can be tested quickly and easily with specialist electronic equipment.

Diesel Cars:
Diesel cars require heater plugs to warm the fuel to a temperature at which it can combust. Each cylinder has a heater plug and they are consumable items which perish with use. They can be checked by removing them individually and examining them visually. If they are disfigured or black with soot the chances are they need replacing.


Click to view large imageThis shows the difference between a worn glow plug and a new one, the latter being on the bottom. Click on the image to view a larger picture.
 

Any main dealer or auto parts retailer will stock them and they vary in price depending on manufacturer. It it's always recommended to buy genuine plugs for the make of your car as they last longer but expect to pay more.
 

Possible electrical problems
Modern cars have become more dependent on electronic management systems and as a result have become very complex. There is an upside to this however as computer diagnostic equipment can be plugged in to your car and for a cost of around 50 you can get an analysis which could in the past have taken hours and come with a hefty bill.

Electrical problems are more likely in a petrol engine as in order to run you need fuel, ignition and compression and a diesel needs only fuel and compression but does need electrics to initially fire.
 

Petrol cars:
If there is no spark there is no fire. Remove the spark plugs and check they are in good condition. They should be a light brown in colour, dry and undamaged. If they are white, oily or wet with fuel you could have fuel/air mixture problems and/or worn cylinders or piston rings and possibly leaking valve seals. This being the case a mechanic is a good idea as cleaning the plugs will only be a very short term fix.
 

Check for a spark
Obtain a spare spark plug you know is working and one by one so you don't mix up the plug leads disconnect a lead from a plug and insert the spare. Place the spark plug metal to metal somewhere on the engine to earth it and get a friend to turn over the engine. You should see a bright spark between the terminals at the end of the plug.
If all work then remove each spark plug one by one from the engine replacing the removed plug with the spare so you don't have an open cylinder and repeat the exercise.
 

No spark from a working spark plug
This could be the plug lead or the distributor/distributor arm. Remove the distributor cap and look to see if the the rotating arm contact point and contact terminals are worn this will be quite apparent if they are. They may also be corroded with a green oxide layer which can be cleaned with sand paper for a temporary fix. If the terminals and arm are worn then they may be no contact so replace them. Same goes for the plug leads, check for corrosion on the connections and if you have a circuit tester make sure current can pass along the lead.
 

Wrong compression
Its best to leave compression testing to the professionals as you will need specialist equipment. And if there is a compression problem it may be a major fix such as replacing piston rings or a head gasket.
 

Diesel Cars:
If you have already examined the heater plugs as described above and found them to be in good shape you can test them by removing the plug. Making sure the plug is still attached to the connection wire place the thread used to screw in to the cylinder head on a metal part of the engine. Keeping the element clear of anything in the surrounding area (including your hands they get hot! Use pliers or vice grips) have a friend turn the ignition to the on position but not all the way. You don't want the engine turning over with an open cylinder. If the plug is working properly it will glow beginning at the tip and moving upwards. Switch off the ignition and repeat the exercise with the remaining plugs.
 

Heater plugs working but not glowing
This could be a result of poor connections or a faulty heater plug timer relay which controls how long the plugs receive current. Remove the inline connecting wire and clean the connection points and when replacing ensure the connection nuts are secure. Using a circuit tester on the wire will fitted will help trace the problem back to the timer relay.
Remove the timer relay from its connection point and check the terminals are clean. Use sand paper if they are corroded or replace it with a new one.

In the case of both diesel and petrol cars check the fuel filter and air filters are clear and free from build up. If they are dirty or contaminated replace them. An engine starved or air will run rich and be inefficient both in performance and economy.
 

Incorrect timing
All internal combustion engines require a host of events happening in the correct sequence at the right time controlled by a timing belt or chain. If a timing belt or chain becomes loose or worn it can slip or jump if this happens the sequence of events required for an engine to run correctly will will be out of step. The same result will obviously occur if a belt or chain is fitted incorrectly. Setting the timing will require a manual to find the settings and is best left to a qualified mechanic as if it is set out of time too far you can cause engine damage such as bent valves which can become expensive.

Have another question? Ask our engineers for mechanical assistance here.

Engine doesn't turn over

Check battery
If there is no effort made to turn the engine remove the caps on the battery (if possible) and have a friend attempt to start the car. If the battery fluid has bubbles in it whilst the ignition is turned all the way the battery is shot.
 

Battery fully charged engine turns over too slowly
Too much compression will stop the engine from turning over at a speed needed to start. Too much compression can caused by water leaking into the cylinders from a failed head gasket. Check the colour of the water in the radiator if it appears milky then oil is present indication a failed head gasket.

Turn the ignition key and hear only a click

Faulty Starter Motor
If when turning the ignition to start the car the dash lights dim but don't go out its likely the starter motor is stuck. This can happen when dirt and grime build up in the starter mechanism as a sliding cog has to move freely to engage the cog assembly which turns the engine. Starter motors are relatively inexpensive items and can be exchanged for a reconditioned unit. Check your local directories under Car Electrical.

Engine starts but splutters and cuts out

Fuel - Compression - Ignition
As an engine needs fuel, air, correct compression and in the case of a petrol engine a spark all timed correctly to run properly this problem could be caused by failure or poor performance by any or all of the above. Check the section above titled engine turns over but wont start as a spluttering engine can be a result or similar problems to a vehicle which wont start at all.

Engine stopped with no warning

Check the section above titled engine turns over but wont start as an initial starting point. If all the checks reveal no obvious flaws you may have something more serious.
 

Cambelt Failure
As mentioned in the engine turns over but wont start section the timing of an engine is essential to its running. If a timing belt or chain (or cam belt/cam chain) snaps which does happen, an engine will stop running immediately.
If this happens it's likely you will have an expensive repair on your hands. When the engine stops combusting due to a snapped timing belt or chain the momentum the engine is carrying keep the pistons moving up and down without the camshaft allowing the valves to retract out of harms way and as a result they can get damaged and bent sometimes even damaging the piston head. Its for this reason that regular servicing and changing of a cambelt is essential.
 

Failed big end bearing
Pistons are attached to con rods and con rods are attached to the engine crank via a bearing call the 'big end bearing'. These bearings are fed with oil from small oil ways which can become blocked if regular oil changes have been neglected. If the bearing is starved of oil it will fail and if this is the cause of your engine stopping you will almost certainly need the crankshaft removing to be reground as well as replacing shells, gaskets and bearings. It can be done with the engine in situ but has to dismantled from the underside so best left to those in the know with a pit, lift or ramp.

Knocking sound from the engine

Failing big end bearing
Knocking coming from the engine is not normal apart from some diesels when started on a cold day until it warms up then the knocking should disappear. Depending on how loud the knocking is it could be a number of things. A failing big end bearing or bearing shells could be the cause and should be checked ASAP to ovoid the result in the above 'engine stopped with no warning' section. If only the bearing shells are the problem you may have saved yourself a large expense as replacing just the shells is a relatively easy job.
 

Incorrect timing
As mentioned at the end of the engine turns over but wont start timing puts every aspect of an engine's running in the right place at the right time. If the timing belt has jumped far enough out of position the pistons could be hitting the valves however if this was the case its likely the knocking would be accompanied with a misfiring engine lacking in power.

Water leaking from the engine block

Core plug failure
Surrounding the engine is a network of waterways that carry the flow of water which keeps the engine cool. Some engines have core plugs which are a deliberate weak point should there be any excessive build up of water pressure. They can be prone to corrosion and the seal they provide can become compromised and be the cause of a water leak.
 

Gasket Failure
Gaskets within the engine come under constant pressure from combustion and as a result can wear around the water ways causing leaking. Depending where the gasket has failed, the engine could be using water and need constant refilling without any visual external leakage. See the section below for more information.

Excessive white smoke from the exhaust when starting engine

All diesels when starting from cold will produce some white smoke from fuel that hasn't ignited in the cylinder. Large clouds or plumes of smoke is not normal and can be caused by a number of problems.
 

Diesel Engines
If the engine is reluctant to start and then when eventually it fires you get the excessive smoke you could have worn out heater plugs. Stand outside the vehicle and have a friend start it from cold. If the fumes smell heavily of diesel then the chances are the heater plugs are the problem. It could be that one or two have failed and the others are fine which is why it actually will start however when replacing heater plugs its wise to replace them all as they will most likely have been fitted all at the same time and it will not be too long before the others also fail.
 

Head Gasket Failure

Diesel & Petrol Engines
Another cause of excessive white 'smoke' could be head gasket failure. If the gasket fails the cooling system will pressurise due to gasses leaking in from the combustion chambers. When the engine is stopped the excessive pressure in the cooling system will force the water into the cylinders where it will sit until the engine is started. The eventual combustion will then turn the water into steam which will exit through the exhaust and look like smoke.

There are two easy ways to check for head gasket failure. The first is to check the colour of the water in the radiator, if it has a milky appearance it will have mixed with oil from the engine and will almost certainly be because of the head gasket failing. The second is to check the cooling system pipes that lead to the radiator for excessive pressure. With the engine running after a short journey squeeze the pipes taking care they are not too hot to handle. You should be able to flex the hoses, if they are hard then you have a pressurised cooling system. In short if you have milky water, excessive pressure and white smoke head gasket failure is a near certainty.

Providing the engine has not suffered any intensive overheating changing the head gasket is not a difficult job if you have some mechanical ability and a manual is always a good idea. The important things to remember are marking any cables you remove and the position of the timing belt, replace all head securing bolts with new ones and tighten to the correct torque settings and tighten in the correct manufacturer approved sequence.

If the engine has suffered intense overheating the cylinder head may have become warped and be unable to provide a good seal when fitted. In this case the head may need skimming on a milling machine by an engineering company. If you do have the head skimmed you will need the appropriate replacement gasket. Take the old gasket with you so the engineer can check for indicators in case the head has previously been skimmed. A good engineering firm will be able to provide you with the correct thickness replacement gasket to compensate for the material removed from the head to maintain the correct tolerances in the engine.

Constant excessive white or black smoke from the car exhaust

Oil in the cylinders
This can be caused by engine wear or damage which allows oil to enter into the cylinders and burn during combustion. There are many ways this can happen from worn piston rings to cracks in the engine block or pistons. If a turbo is fitted the oil seals could have perished or become worn allowing oil to be fed into the air intake via the turbo and in extreme cases the engine may rev highly uncontrollably running on the unregulated oil. If this happens whilst driving it will be like a stuck throttle and can be dangerous.
 

Worn Turbo
Signs of a worn turbo before excessive smoking occurs can be indicated by a whining from the engine in the higher rev range. It will be quite distinctive and alien to the noise you usually hear but can take some time to develop and be subtle in the initial stages.

More mechanical engine problems & faults on page two
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