The obvious way to know of a wiring loom failure is through a misfire (not a backfire) when accelerating. The problem is caused through engine oil contamination to the injector plugs inside the rocker cover. The engine oil soaks the injector plugs the whole time the engine is running. The oil will then pass all the way along the wiring loom to the ECU, and then drip out into the ECU/battery tray. When this happens, you need to replace the loom. It’s a very simple process, so there’s no excuses!
You will need:
- 8mm Socket
- Philips Screwdriver
- 10mm Spanner or ratchet
- 13mm Spanner or ratchet
- Brake Cleaner
- Injector Wiring Harness
Before you begin, as always with any vehicle repair work, you need to disconnect the battery. You will need your radio code.
Next, remove the 3M8 (13mm) bolts that hold the acoustic engine cover on. Place this somewhere safe.
With your pliers you can compress the retainer on the camshaft breather pipe. Now unscrew the 13 flanged head screws (M5 – 8MM Spanner) on the camshaft cover and put them aside for reuse later, ideally in a money bag, self-seal bag or magnetic bolt tray.
Then lift off the camshaft cover, again keeping it safe as you will need it later. We recommend you replace the gasket, but you will need to note the year of your vehicle as the early 10p is different from the later 15p engines.
Next to come off is the Injector Loom. Start with the plug at the front of the engine, this should be an oil tight seal. Squeeze the plug on both sides from underneath the rocker. Then, unplug all 5 of the injector plugs; these have a squeeze inwards clip to release them. The old loom can then come out, ready for the new one to go in.
Connect each injector by pressing the plug down hard until it clicks in place. Work from the back to the front, apply a small amount of grease to the two O-rings, and press it into place on the end of the housing. Keep it in place and connect the plug from underneath – it will click when it’s fully located. Be aware that the guide rail might not sit in the housing on its own at this stage.
If not done so already, clean and fit the new gasket to the camshaft cover. Keep an eye on the injector loom guide as you put the cover on your engine. Take your 13 M5 flanged bolts and start bolting the cover down. Do not over tighten these, only go to 10NM (7ft lb). Replace the acoustic engine cover with 3 M8 bolts.
Check the ECU (red plug) for signs of oil.
For this, you will need to remove the battery cover. Take out the jack next to the ECU. You will find a Philips screw that retains the ECU in the battery box – remove it. Once removed, lift the ECU until it clears the cover. You should be able to remove the red plug. If you find oil inside, give it a good squirt of brake and clutch cleaner. Shake off any excess and reconnect the plug. Check it again after a few days of driving, making sure to repeat this cleaning process until no oil is visible.
On the Defender, your ECU is under the driver’s sea, but the cleaning is just the same. As the ECU is further from the engine, it is less likely the oil has got this far, but it’s not impossible.