How To: Simplified Glow System
The HJ60 Cruisers came out with three different glow (aka preheat) systems. There were two versions of the 'fixed delay' glow systems, and then there was the 'Super Glow' system.
This writeup is as installed on a 1983 HJ60 with the Super Glow System. The same general theory can be applied to the fixed delay glow systems.
Super Glow System
It is important to understand how this system works, to make it easier to fault find and to also understand the limitations and complexity of it.
On turning the key to the glow position, the Preheat Timer energises the primary glow plug relay and therefore to the glow plugs, via the glow plug current sensor. There is resistance over the current sensor that reduces the voltage to the glow plugs. Depending on the condition of the battery and the wiring connections, the voltage measured at the glow plugs will typically be around 6-9 volts. This primary glow lasts for a period of time, usually around 5 seconds. The key is then turned further and the engine is started.
At the same time that the Preheat Timer de-energises the primary glow relay it energises the secondary glow relay. The secondary glow relay supplies power to the glow plugs via two resistors screwed into the intake manifold and the glow plug current sensor. This cuts the power to around 3-4.5 volts, again depending on the condition of the battery and wiring connections.
The glow plugs remain energised until a coolant temperature sensor in the head heats up and then sends power to the Preheat Timer, de-energising the secondary glow relay.
The Super Glow system uses 6V glow plugs. When a higher voltage is supplied the glow plugs heat up very quickly.
The idea of the secondary glow is maintain some heat in the glow plugs to help eliminate rough idling and white smoke, especially in cold conditions. This secondary glow is also known as 'afterglow'.
Strangely enough the glow plug warning light is not indicative of when the glow plugs are energised. This light is also supplied with power from the Preheat Timer.
The Super Glow system is actually very clever but can be problematic due to the fact that it is quite complex and there are a number of components that can fail.
Click on the full wiring diagram below for a magnified view. The diagram on the right is an exploded view.
Things You Need to Know - Before You Start
What – Replace the Super Glow system with a simple momentary switch and energise the glow plugs manually.
This write up uses the momentary switch to energise the primary glow relay and therefore the glow plugs. This is the simplest and cheapest method as it reuses most existing components.
Why? – To simplify the glow system. Once components in the Super Glow system begin to fail it can be quite expensive to replace them with genuine Toyota parts.
Check Your Glow Plugs! – Remove the bus bar (the aluminium plate connecting the glow plugs to each other). Using a multimeter check the resistance of each plug. The resistance of all 6 plugs should be the same. If the resistance of any of the plugs is OL (out of limit) or high then the glow plug has failed and needs to be replaced. In cold conditions even having one glow plug fail will result in very poor and rough starting.
A momentary push button switch. This Jaycar switch #SP0716 is perfect.
3mm wire - ideally 3 different coloured insulation. Like this Supercheap Auto 3mm wire.
How Long Will It Take?
Around 2-3 hours if you have the equipment and tools at the ready.
1. Locate the Preheat Timer behind the passenger side kick panel. Remove this (two bolts) and disconnect the two plugs. The Preheat Timer is no longer needed.
2. Remove the instrument cluster (5 screws), disconnect the speedo cable off the back of the speedo cable and mover the cluster to the right hand side as much as possible.
3. Solder two wires onto the momentary switch, pick a spot on the panel to the left of the steering wheel, drill the hole in the panel and fit the switch.
4. Run one wire from the switch to a positive feed, ideally a positive feed that is active only when the ignition is turned on. Don't actually connect this wire just yet.
5. Cut the two wires from the glow plug warning light. Insulate the cut ends that go back into the loom. Join a new wire to one of the light wires and connect to an earth. It doesn't matter which wire you use.
6. Join the second wire from the light and the second wire from the switch to a new 3rd wire. In the photo below the '3rd wire' was spliced downstream.
7. Cut the black/red wire at the primary glow relay.
8. Join the '3rd' wire to the black/red wire going into the primary glow plug relay.
9. Connect the wire to the positive feed located in Step 4.
10. Press the momentary switch and the glow plug warning light should come on and the primary glow relay should click. With the help of a mate measure the voltage at the glow plugs. You should be getting 6-9 volts here. The wiring diagram on the right shows the new wiring and switch in red.
Ensure all joins are insulated! The photos above show where the wires have been soldered. All of these joints were insulated with heat shrink.
DONE! Before starting the engine press the new glow plug switch. It depends on how cold the engine is and the ambient temperature as to how long you should hold it in for. Start with 5 seconds and go from there. If the engine begins to idle roughly and or blow white smoke after starting press the switch for a couple of seconds to add some glow. On really cold mornings you may have to do this a couple of times to ensure that engine idles smoothly.
You can go a little further than the above write up and remove the 'glow plug current sensor' and the 'current sensor plate'. This should be done anyway if these components are in bad condition. This will eliminate another couple of potential trouble spots and also allow full voltage through to the glow plugs.
The 6V glow plugs will burn out very quickly at this voltage so the glow plugs should be replaced with the 10.5V glow plugs available for the HJ60 (Bosch Glow Plug - GPT-218).
1. Remove the 'glow plug current sensor' and the 'current sensor plate'.
2. Disconnect the cable from the 'outlet' side of the primary glow relay and run a new cable from here (at least the same diameter) to the first glow plug/bus bar. The wiring diagram to the right shows the new wiring in red.
Anything Else? You can of course choose not to use any of the existing components. Some people use a completely new heavy duty solenoid and run a new power feed from the starting battery. It's a personal choice and it achieves the same result.