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?
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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
Marek
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.
SD
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
Marek
I knew that…had too many thoughts going on and didn’t review. Tks. SD
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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.
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I want to pick up my thread about heatsoak and my poor/low idle after starting from heatsoak. You can read the volume of theories and tries beforehand that seem to affect a lot of us.
In the end, i think i found a solution. Well, more of a treatment.
There are positive/negative wires to my extra air valve on the A bank. The 12V is live with ignition on. The ground is controlled by the timer relay, which completes circuit for 45 seconds only after car is started, and then shuts off. This is Jaguar by design.
So i tapped into these two wires, ran them to a simple relay, and hooked up the relay open/closed circuit to my full throttle vacuum switch nearby.
So everytime I start car, a little extra air PLUS a little extra fuel (i believe full throttle switch is +10% rich?) is introduced. During my heatsoak starts, this is now giving me an acceptable idle. When the 45 seconds are up, idle of course drops a bit, but it is good enough at this point.
Cold starts and normal starts are fine. Yeah, idle is a wee bit higher, but nothing crazy. Maybe +100rpm?
I understand this circuit is also controlled on my car by A/C if compressor turns on. But i have no A/C and doubt i ever will. If i do, i could put in line some heat sensor so it’s not enriching fuel all the time the A/C is on.
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So, if I understand correctly, the 45 sec timer triggers the Full Throttle vacuum switch via the relay for 45 sec every time you start?
Smart!
Why is your idle higher? Cause of the 10% fuel enrichment?
You can do this with a diode.
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Yep. At morning cold start, the engine likes the richer idle. At a restart with no heatsoak, i get a slightly higher idle than normal. Maybe 850rpm instead of 750rpm. But only for 45 seconds. 
Mine does too, but it’s the Extra Air Valve that does it.
Isn’t your’s connected to the 45 sec timer?
I thought you were saying that it was 100 rpm more than with the Extra Air Valve activated.
You’re right…I didn’t take exact measurements, I should.
Then I may be seeing 900-950rpm for 45 seconds on a normal start. Not unlike a cold start with AAV wide open.