Ignition Failure Sensor
Overview of the IFS
The "Ignition Failure Sensor" is a small self-enclosed circuit which acts as a connection between the ignition switch and the coils, and also sends pulse signals to the ECU and Tachometer. The ECU uses these pulse signals to compare the ignition trigger signals it sends to the coils to the number of witnessed coil firings. Should the numbers differ, the ECU is intended to generate a misfire code for the corresponding cylinder.
Unfortunately, the IFS is a common cause of roadside breakdowns, as if the IFS fails (and it commonly can) there is no power provided to the ignition coils and therefore no spark.
Alternatively, sometimes spark will continue but the tachometer pulse signal will fail, resulting in the car operating but with no rev counter.
Why does the VR4 even use an IFS?
Whilst we cannot pretend to understand the reasoning behind the decision to use an IFS by Mitsubishi Motors, it is likely that at the time this EFI system was designed, there was no ability to directly monitor if coils are firing. Some more modern EFI systems are advanced enough to not only directly monitor if coils are actually firing without a separate sensor, but also monitor the health of the spark that is generated. Doing so requires much more processing power than is likely available in the VR4 ECU.
Can you buy replacement IFS modules?
Yes, these are still available from Mitsubishi as they were used on many vehicles. There are also knock-off units from China for very cheap however we cannot speak for their reliability. The price of an OEM sensor hovers around $60USD.
Recommendations for VR4 owners
All VR4 owners should do one of the following to ensure they are never stranded:
- Have the ability to bridge pins 3 and 4 of the IFS by the roadside if it fails
- Keep a spare known-good IFS in the glovebox at all times
- Permanently Remove/Bypass the IFS; OR
- Permanently increase IFS reliability by bridging wires 3 and 4 on the harness side of the IFS connector, whilst leaving the IFS connected.
Wiring of the IFS
The IFS has four wires connected to it in the following pin arrangement:
| Pin | Description | Purpose | Notes |
|---|---|---|---|
| 1 | Primary Coil ground | Monitors the ground circuit from the coils | Monitors the raw analogue voltage pulses seen on the ground wire for the coils. |
| 2 | IGnition Feedback (IGF) | Monitors current on the ground circuit (Pin 1) for the coils and generates pulse outputs for each coil firing | For each coil firing (analoge voltage) seen on Pin #1, the IFS generates a 5V pulse output on Pin #2.
This pulse output of Pin #2 is used by both the tachometer and the ECU (ECU Connector 35, ECU pin 58).
|
| 3 | IGN | Power output to coils from IFS | If the IFS fails completely, this output does not work, killing all ignition power to the coils. |
| 4 | +12V IGN | Power source for coils | When the key is in the ON position, this wire is always fed a +12V power feed from the ignition switch |
Managing IFS reliability issues
As the IFS is unreliable and its ability to detect coil failure is poor, the obvious question is why not bypass or remove it? The IFS can indeed be removed, and if you are using an aftermarket ECU (e.g. Haltech, Link) then it is redundant anyway.
You can choose to remove your IFS completely, or you can choose to increase the reliability of the IFS. Both are acceptable solutions.
Removing the IFS completely
To Remove the IFS completely, you need some way of generating a tacho signal and powering the coils.
Alternatively, you can purchase a pre-made IFS delete kit. These are available from Rob Vectose on Facebook Marketplace. https://www.facebook.com/marketplace/item/777577502770940/
Powering the Coils
Powering the coils is simple and just requires that we bridge the wires going to pins 3 & 4 of the IFS connector. You can choose to do this via any method you like - tapping and briding wires, or making a piece of wire that inserts into the pin 3 & 4 positions on the IFS connector. Both are perfectly acceptable but I recommend you include a 10 amp fuse inline. You can buy wires with an inline fuse from most auto parts stores. I recommend the Narva inlune blade fuse holder as it already comes with appropriate gauge wiring:
https://www.narva.com.au/products/54406BL
Generating a tacho signal
Generating a signal for the tacho is slightly more complex. Thanks to the efforts of James Borthwick, it was discovered that the green wire coming from the Crank Pulse Sensor also generates a 5V square wave signal which can be used by the tachometer. As a result, all we have to do is tap into that green wire and connect it to the existing white wire on pin 2 of the IFS. It is the tapping of this wire which is the hardest part of our job because this wire is inside the main engine harness sheath. Tapping existing critical engine sensor wires without damaging them is the key here, and it's something that you would not generally do. No plug and play harness exists yet and so at the current time you are required to perform this work yourself.
Once the green wire from the Crank sensor has been connected to the white wire at the "inspection connector" on the firewall near the ABS unit (or the white wire on the IFS connector itself), and pins 3 & 4 of the IFS have been bridged, your IFS is effectively deleted. The ECU will not throw any codes and you will not be at risk of the IFS failing and leaving you stranded.
Increasing IFS reliability without removal
If you do not wish to take the risk of tapping your Crank Pulse Sensor, but wish to remove the risk of a breakdown whilst keeping the IFS in use, you can just tap into the wires on the IFS connector and bridge wires 3&4. Use a wire with a 10 amp fuse inline for safety. This will halve the current passing through the IFS, reducing the risk of it dying whilst also ensuring if it does die, you will only lose your tacho signal but the car will keep running.
