Consider this scenario: Your diesel vehicle has been in the garage for a while, but now you want to start it. However, there’s one risk– cold starting it could cause excess wear. How do you crank the engine without it starting?
Here’s how to crank a diesel engine without it starting:
- Remove the glow plugs.
- Pull the pump fuse.
- Pull the coil wire.
- Unplug the injector harness.
- Disconnect the fuel cutoff solenoid.
- Pour oil into the oil supply port.
- Prime the engine.
In a nutshell, there are several ways to ensure oil circulates in your engine to prevent starting it while it is still dry. So, let’s walk through the steps together and get into the details. So, start your engines, and let’s get into it!
1. Remove the Glow Plugs
Glow plugs are small heating elements that warm up the fuel-air mixture just before it enters the combustion chamber of a diesel engine. Without glow plugs, diesel engines won’t start. Therefore, removing them is an easy way to crank a diesel engine without starting it up.
Here are the steps to follow:
- Locate the glow plugs (You will find them on the outside of the cylinder head, hidden in a recess protected by a metal cover).
- Unscrew the bolts that hold the metal cover in place.
- Remove the wires connecting the glow plugs to the engine.
- Remove all glow plugs from each cylinder head.
- Try cranking your engine by turning the flywheel manually.
Here’s a demo on how to remove glow plugs from a diesel engine:
Caution: Glow plugs are highly fragile, so ensure you handle and store them safely.
2. Remove the Pump Fuse
A diesel-powered car won’t start without a working fuel pump, so removing the fuse is a practical way to crank a diesel engine.
Here are the steps to follow:
- Locate your engine’s primary fuse box and open its lid.
- Remove the fuel pump fuse from the panel (you will find it connected to an electrical wire with a small clip or safety pin).
- Try cranking your engine by turning the flywheel manually.
Note: You can also remove the fuse that powers your ignition coil.
3. Pull the Coil Wire
A diesel-powered car won’t start without an ignition coil connected to the engine control unit (ECU). Removing its wire is another way to crank a diesel engine without turning it over.
Here are the steps to follow:
- Locate your ignition coil (It’s usually close to your fuel pump fuse or somewhere on top of your starter solenoid).
- Unscrew the bolt that holds the wire in place and remove it from the coil terminal.
- Try cranking your engine by turning the flywheel manually.
4. Unplug the Injector Harness
Modern diesel-powered cars use an injector harness to distribute electricity to each fuel injector of your engine. Without it, you can crank a diesel engine without it starting.
Here are the steps to follow:
- Locate the injector harness behind your rocker cover (It looks like a bunch of wires).
- Unhook its small electrical clip or safety pin.
- Try cranking your engine by turning the flywheel manually.
Here’s a video tutorial that may come in handy when unplugging your injector harness:
5. Disconnect the Fuel Cutoff Solenoid
Another easy way to crank a diesel engine without starting it is to disconnect its fuel cutoff solenoid. This small electrical component connects the fuel pump to the injector harness.
Here are the steps to follow:
- Locate your vehicle’s solenoid (it will be mounted on a metal bracket close to the fuel filter).
- Detach its wire from the bracket.
- Unscrew and remove both bolts that secure it in place.
- Try cranking your engine by turning the flywheel manually.
- Once you remove the fuel cutoff solenoid, your engine will keep trying to start but won’t be able to.
7. Pour Oil Into the Oil Supply Port
A diesel engine won’t start without sufficient oil pressure. You can trick it into cranking without starting by adding some oil to its oil supply port, raising the pressure.
Here are the steps to follow:
- Locate the oil supply port (it will be somewhere on top of your engine).
- Add 2-3 quarts of diesel engine oil through it until you see oil pressure registering on your dipstick. If there’s no dipstick, use a manual hand pump or refer to your owner’s manual to determine oil pressure.
- Try cranking your engine by turning the flywheel manually.
Note: This method works with most diesel-powered engines but isn’t as effective as removing glow plugs or disconnecting fuel cut-off solenoids.
8. Prime the Engine
If you’ve removed all components that prevent a diesel engine from starting and there’s still no oil pressure, try priming it to crank by hand.
To do so, pour about half a canister of fogging oil into your air intake filter and start cranking your engine until it starts running smoothly again.
Here’s an excellent primer on how to prime a diesel engine:
Note: Do not take apart or tamper with any other components apart from those described in this article. If you need professional help with your specific vehicle, contact a mechanic.
Also, note that your dashboard may show error codes once you’ve attempted most of these methods, so ensure you check and clear them once you’re done.
I recommend this Vgate iCar Pro Code Reader (link to Amazon) if you need a code reader. It’s Bluetooth compatible, works on most OBD apps, and comes in handy when you need to diagnose and clear error codes.
Frequently Asked Questions
Can You Turn a Diesel Engine by Hand?
You can turn a diesel engine by hand, but only if you use a decompressor. It’s a tool that allows you to turn compression into rotary motion and crank your engine by hand without starting it. However, avoid turning your engine by hand since that poses injury risks.
As this discussion thread highlights, you can only turn a diesel engine by hand using a decompressor lever. However, I highly advise against that since you could injure your wrists and hands and damage your engine in the process.
How Fast Does a Diesel Engine Need To Crank To Start?
A diesel engine needs to crank at least 150 revolutions before starting. It’s because you need to raise the temperature of its injectors and glow plugs to average operating temperatures (232°C/450°F) before it can start. If the engine doesn’t rev high enough, it won’t start.
Also, the cranking speed of a diesel engine is related to its compression ratio. The more powerful a diesel engine is, the faster you’ll need to crank it before it starts running (source).
Final Thoughts
A diesel engine won’t start without a working fuel pump, ignition coil, or injector harness connected to it. So, by removing the first two components or disconnecting the third one, you can crank a diesel engine before you force it into starting.
Adding oil into its oil supply port is an effective way to do this, too. Moreover, you can always try priming your engine to crank it by hand if all else fails. However, contact a mechanic for assistance if you’re not sure about what you’re doing or if your car’s engine is damaged.
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