Changing the timing belt can be a complicated process on some engines. It can often involve removing lots of plastic covers and some engine components to get to the timing belt. Sometimes when everything is put back together the car won’t start.
As a general rule, if your car won’t start after a timing belt change this is usually because the engine timing has not been set properly. It can also be caused by a lack of fuel pressure, a problem with the spark plugs or a problem with the starter motor.
It can be difficult to pinpoint the reason why a car wont start with a new timing belt fitted. The very first thing you should always double-check is that the engine timing is set exactly right.
Make sure when fitting a new timing belt that the engine is set to top dead center (TDC) so that the piston in the first engine cylinder is at its highest point in the compression cycle. This is usually done by aligning the crankshaft and camshaft with their respective marks on the engine block.
6 Reasons Why A Car Won’t Start After A Timing Belt Change
There are lots of opportunities for error when it comes to changing the timing belt. The number one reason why a car won’t start after a new timing belt has been fitted is because the engine timing is off.
It’s important to go back over each step and double-check everything if the car won’t start after the new timing belt has been fitted.
Reason 1. Timing belt fitted incorrectly
Probably the most common reason the engine won’t turn over is that the timing belt has been fitted incorrectly. This means that the belt is too loose, too tight, or is not positioned correctly on the teeth of the camshaft/crankshaft.
Most modern vehicles have an automatic timing belt tensioner. This means that you don’t need to worry about making sure the belt is tight enough when in position. It is however important to ensure that the tensioner is also replaced when the timing belt has been replaced.
Tensioners can lose their ability to hold the belt in place and this can lead to the belt jumping a tooth or coming off completely. If it’s an older vehicle then you may need to tension the timing belt manually before starting the engine.
It’s also important that the timing marks on the belt are lined up with the marks on the crankshaft and camshaft. If the engine has a double overhead camshaft then the belt must be fitted so that it is not too tight or too loose across the top of the camshafts.
Reason 2. Starter motor not re-mounted properly
Sometimes you may need to remove the starter motor to change the timing belt. If it is not refitted properly then this can prevent the car from starting.
When changing the timing belt it’s usually necessary to lock the crankshaft pulley in position so that the crankshaft bolt can be removed. The crankshaft on most cars is also used to turn the auxiliary belts that run components like the water pump or the air conditioning.
To get at the timing belt it may be necessary to remove the crankshaft pulley bolt. The best way to lock the crankshaft in place is to lock the flywheel. This can be done by removing the starter motor and holding the starter ring gear in place using a flywheel lock tool or a large wedge such as a screwdriver or metal bar.
Reinstalling the starter motor can be tricky and it’s important that the starter bendix lines up with the ring gear on the flywheel so that it can engage properly when the starter is fired. It’s also important to double check that that positive and negative leads are fitted correctly and all connections are tight.
Reason 3. Ignition coils not reconnected correctly
Although not always essential, it’s often necessary to remove the ignition coils or spark plug leads to allow access to the timing belt. Newer vehicles usually have indiviual ignition coils (COP – coil on plug) for each spark plug, while older vehicles will have a distributor with spark plug leads going to each spark plug.
The order of the wiring however is very important. When it comes to coil packs, the wiring for each ignition coil is usually only long enough to go to the correct coil, so it’s difficult to get it wrong. If your vehicle has a distributor pack and spark plug leads then it is possible to mess it up. Make sure to mark each lead before removal so that you put it back onto the right spark plug when reinstalling.
Reason 4. Lack of fuel at the correct time
The timing belt is repsonsible for the timing of the ignition and firing sequence of the spark plugs. If the timing belt has been fitted incorrectly, fuel will not be delivered to the combustion chambers at the right time and this will stop the car from starting.
The position of the crankshaft and camshaft also determines the flow of fuel and the operation of the fuel pump. If the timing of the engine is off then the ECU will be getting conflicting information from the crankshaft and camshaft sensors causing the engine to misfire.
Reason 5. Problem with the spark plugs
Another very common reason why a car won’t start after replacing the timing belt is because of a problem with one or more spark plugs. As outlined above, it’s often necessary to remove the ignition coils or to disconnect the spark plug leads in order to access the timing belt. It’s therefore vital that everything is put back together in the right order and securely so that each spark plug can fire properly when necessary.
Reason 6. Sensor left unplugged or are damaged
It’s usually necessary to unplug sensors or wiring as part of the timing belt replacement procedure. As outlined above, the ignition coils usually need to be removed. You may also need to unplug the camshaft and crankshaft sensors or other sensors such as the mass airflow sensor (if you need to remove the air filter box for access).
If possible, run a diagnostic to see if there are any engine error codes stored in the ECU that may point to a faulty sensor. P0340 is a common camshaft sensor error code, and P0335 can mean that the crankshaft sensor is not working properly.
Car won’t start with new timing belt? What next?
If you’ve fitted the new timing belt, and you’ve refitted any parts or sensors that were removed, but the engine still won’t start, then you’ll need to do a few simple checks to ensure that you haven’t overlooked something. Here are a few things to check to help narrow down the cause of the problem.
- Check that the timing is set properly. This is the most important step when fitting a new timing belt. Double check that the new belt has been fitted correctly. Ensure that it has been fitted in the right direction and that the belt is positioned squarely on the camshaft and crankshaft sprockets. Rotate the engine clockwise to top dead centre and ensure that all of the timing marks line up exactly with the new belt. You should also double check that the belt is tensioned properly and that there is nothing impeding the smooth movement of the belt.
2. Check the spark plugs. Check each spark plug is fitted properly and that the correct ignition coil is connected to the right spark plug. If the engine is older, make sure the distributor is refitted properly and that the spark plug leads are fitted tightly. If everything looks ok but it’s still not firing up, you will need to remove and clean the spark plug lead contacts and spark plugs before refitting.
3. Check for fuel pressure. Another reason why your car may not start is a lack of fuel pressure at the fuel rail. If you have moved one of the fuel lines or removed the fuel filter or injectors to get better access, then you may need to prime the lines again to restore fuel pressure and to remove any airlocks. If you suspect there is a problem with fuel reaching the fuel rail then you’ll need to hook up a diagnostic tool to measure the fuel pressure and to pinpoint where the pressure is dropping off. P0087 and P0193 are common fuel pressure-related engine error codes.
4. Check the starter is refitted properly. If you removed the starter motor to lock the flywheel then you may need to double-check that it has been refitted properly. Check that the starter is seated properly and mounting bolts are tight. Ensure that the wiring has been refitted correctly and that it is tight. If the starter is not rotating at all, check the battery is charged and has been reconnected.
5. Check all other hoses. If you’ve removed any other hoses such as turbo or vacuum hoses, check to make sure that they have been reconnected tightly. A significant vacuum leak can prevent the engine from starting or may cause it to cut out soon after it starts. There are usually a few vacuum hoses fitted to engines, and they will vary depending on the model.
It’s also a good idea to double-check the air filter is refitted properly, and any hoses or pipes to and from the air filter box are reconnected properly.
I recently changed the timing belt on my car as per the instructions, but now my engine won’t start. I double-checked that the engine timing is set correctly, but I’m not sure if the problem lies with the spark plugs or the fuel pressure. How can I diagnose whether the issue is with the spark plugs or the fuel pressure without taking my car to a mechanic?
After attempting to replace the timing belt on my car, it now refuses to start. I want to ensure I’ve gotten everything reconnected correctly, especially since I had to remove a few components to access the belt. Could issues with ignition coils not being properly reconnected cause my car not to start, and how can I check if they’re correctly reconnected?