Electric Fan After Heatsoak

Expanding on that idea, and given that a lot of people here are always looking for projects to do, what about making it so that when you push the button, it oscillates the signal to the injectors?

1 Like

What if pushing pushing the button started the circuit to fire off each injector in sequence around the firing order, maybe 2-3 times around? Would that provide enough bursts to clear the vapor out of the injectors, and would eliminate any overheating possibility of the injectors?

My point was that prior clearing the vapour, you still have vapour lock and as soon as the vapour is cleared, you have a torrent of unburnt petrol in the cylinders. You then proceed to cranking and add more fuel, so you’d end up with flooding. Since the engine is already hot, very little fuel needs to be injected at cranking, so the probability of flooding is high.

At 80’c, the cranking pulse width is in the order of 7mSec. It’ll crank at 120rpm, which is 2 revs per second, which is one engine cycle per second. That’s a duty cycle of 7%. Leaving the injectors 100% open is 140 fold too much fuel - much more than the ~7mSec needed during cranking after the lock is cleared.

If you are utterly sold on opening the injectors 100%, then what may work better is a short dose of “full injector on” to clear the lion’s share of any vapour lock, followed by a strategy of pulling the coolant and air sensors out of their sockets. This will mimic freezing cold conditions as far as the ECU can see, so it’d approximately triple the pulsewidth to 20% duty cycle. This will more quickly clear the lock than just cranking on its own and substantially reduce the risk of dumping fuel into the cylinders.

I have actually started a heatsoaked v12 by pulling the coolant sensor. It ran terribly when it started, but very quickly adjusted and restarted normally a few minutes later. The reason it failed to start was a heatsoaked coolant sensor. This made for a lean enough mixture to not let it light off.

kind regards

Why not modify that idea to something similar…such as… for what would seem to be a relatively simple circuit…a push button switch to short circuit the coolant temp sensor. Switch in the cabin. Just two wires and a button that activates a switch to temporarily bypass the CTS signal to the ECU. During a vapor lock scenario, both the ignition switch would be turned to start and the bypass button pushed. Button push duration ?? 1,2, 3 seconds. Trial and error.

Steps…1) Get in and crank…no start…suspect vapor lock
2) Key on to energize the fuel pump to clear the fuel rail
3) Key to start and bypass button pushed.
4) Vary the time the bypass is active until you find the sweet spot.


A short circuit of the coolant sensor is the exact opposite of what you want - that would indicate very hot. You want open circuit - i.e. a very very high resistance, e.g. ~20k ohms or more. (Bosch sensors:- 2k ohms = room temperature; 15k ohms = very cold; 100 ohms = very hot.)

Do step 2 before step 1 regardless.

Certainly. such a button would cut the cranking time to purge the injectors by a factor of three with less chance of huge overfueling. As soon as the engine is coughing, some of the injectors must be purged.

kind regards

I knew that…had too many thoughts going on and didn’t review. Tks. SD

1 Like

Once you find the sweet spot, instal a relay to open the circuit (infinite resistance) or connect in a 20k ohm resistor, which is operated by an adjustable time delay off relay (which you set to that sweet spot time).

Push button, (which pulls in the time delay off relay, which pulls in the second relay … the time delay off relay clocks down and releases the second relay, and also releases power to itself, so button can be momentary on switch), turn key.

And if you add a thermal switch triggered at a critical temperature at the fuel rail in combination with the delay relay, it all could be done automatically without a push button or any other intervenance.

1 Like