JX re-starting problem when shut down quickly from hot

[windy]

My JX engined syncro has an annoying habit of occasionally not wanting to re-start hot, but only in a certain set of circumstances.

If the engine has been working fairly hard, and for instance I come to a road junction & stall it, when I try to re-start it turns over fine but wont "catch".

Same thing happens if I forget to let it idle for a few moments after a long run & then go to re-start within a few minutes.

If I then leave it to cool for 15mins it starts fine, although if I've been trying to unsucessfully re-start it will initially belch smoke from the unburnt fuel that has accumulated.

So in a nutshell;
engine works hard & left to idle for a few moments before being switched off= re-starts normally
engine works hard & switched off immediately= won't start until left to cool for 15mins

I realise its good practice to idle the engine for a while before shutting off, but occasionally I forget & in a stall situation its unavoidable.

Any ideas?

[windy]

Bump

[windy]

No-one ever had this before then?

[JonB]

I had something similar on my old van if I wanted to restart just after it was turned off. The pre-heater yellow indicator led on the dash wouldn't come on and the engine wouldn't start. Leave it a short while and everything worked fine.

I found a thread somewhere describing adding a 4.7k ohm resistor in the glow plug heater wiring (from memory on the blue/black wire from temp sensor). This basically forces the glow circuit to be on for an amount of time regardless of engine temperature.

I made the change using spade connectors so could easily revert and didn't have a problem after that with restarts.

I've looked for the thread but not had much joy. It's either on here, brickyard or the Samba.

Sent from my Nexus 4 using Tapatalk

[windy]

Thanks for the reply Jon.
My yellow pre-heater indicator light doesn't come on when the engine is hot, so it sounds like the same problem.
Sounds like these engines need the glow plugs to come on at start up even when the engine is already quite hot then?

[ghost123uk]

I'm no Diesel expert, but to test that, you could temporarily fit a switch to manually activate the glow plug relay, just to see if that helps it fire up.

[windy]

That sounds a good idea but I probably have a 4k7 resistor knocking around (ex electronics engineer ) so its probably easier to just do the mod.
The problem is it doesn't happen that often, but when it does it can be very awkward, like when I stalled it trying to pull out of a sideroad onto the busy A5 in third instead of first gear

[ghost123uk]

That sounds a good idea but I probably have a 4k7 resistor knocking around (ex electronics engineer ) so its probably easier to just do the mod.

Good point.
I am an ex electronics engineer as well

[windy]

The more I think of it the more it makes sense, because normally after a run the hot engine coolant from the cylinder head circulates past the glow plug thermal sensor on the rear of the head for a few moments, but if the engine stops suddenly the very hot heat soaked coolant from the head just sits there, so the sensor would also sense that heat, causing the glow plugs not to come on.

[ghost123uk]

Maybe a bit odd though that this issue does not seem to have cropped up on here with other JX users as far as I know.

[windy]

Agreed. It looks like even with a hot engine it should be getting some pre-heat, which its not, so I'll measure the hot glow plug sender resistance against the temperature gauge sender one (think they are the same part number?) & if thats ok look into the timing circuit of the relay. Could be a capacitor on the way out maybe?

[Oldiebut goodie]

Are you getting heat soak due to the auxiliary water pump not running on to cool it down after switch off?

[windy]

If it was failing to restart after a minute or so I would have considered the aux pump, but this is a failure to restart immediately after shutting down, so I can't see it being that. Thanks for the suggestion & I will investigate it if all else fails though

[colinthefox]

4k7 is too much resistance. 470 or 600 ohms is the usual value. I haven't heard of it being used with a JX before, but might do the trick.

[windy]

The 2 sender resistances measured quite similar so I'll check the timer relay components next. If they are ok I'll try the resistor mod with Colins recommended values, as 4k7 does seem too high.