Glow plugs and changing engine operating noise

[lewis]

Hey guys,

Installing my aftermarket water temp gauge yesterday (which appears to be a dud (cheap and chinese hardly surprising i guess)) I found a wire unplugged that I think is related to the glow plug timer. I plugged it back in to see if anything changed, and instead of the glow plug light going for about 5s, it just flashes for like 1s. Since its pretty warm in Auckland now I cant tell if the glow plugs are working or not (all I know is that if its been sitting on the side of Ruapehu for 3 days in snow I had to crank it for like 1minute, so bought some engine start spray which sorted that problem) but besides that extreme situation its always a good starter and I have always waited for the glow plug light to go off.

The second and main changed I noticed was engine noise after plugging the sender in. It went from being to having nothing but that rattely diesel truck noise, to sounding much smoother and quieter (I can even hear the turbo now). However im leaving it unplugged since I dont know what its doing. So what I want to find out is how this is changing the engine operation and what peoples theories are as to why the lead has been disconnected by a mechanic at some stage in its life. Maybe with it plugged in the glow plugs are going the entire time as something is not working properly, which is making it run quieter? Maybe with that lead unplugged the glow plugs arent actually going at all?
There is no difference to operating temperature, or no difference in power noticible.

Cheers
Lewis

[dasnoboarder]

That wire goes to the temperature sensor for the cold start system.

It is supposed to activate the cold start when the coolant temp is under 5 degrees (or somewhere around there).

When under 5 degrees C, the system makes the glow plugs go for much longer (the 5seconds), and advances the injection timing to help the engine warm up.

When over 5 deg, the system runs the glow plugs for about half a second, and leaves the timing as normal.

That wire is supposed to be connected, and if the system is functioning correctly, the above should happen

When the wire is disconnected, it forces the system to think that the temperature is below 5 deg. Useful for fault finding and sometimes helps starting if the weather is cold, but not lower than 5deg.

Andy

[lewis]

Right, that is pretty much what I thought.
So my engine thinks its always under 5 degrees...
So the fact that the engine sounds different could be due to the timing changing? It definitely sounds quieter, less truck like, less rattely in the engine with that connected.
However if the timing was set when the belt was last replaced with the lead unplugged then maybe it has been set correct with the lead unplugged? But yeah I didnt really notice a difference in performance with it plugged in, just sound. Should it theroetically have more power with the timing advanced?

Should I leave it unplugged or keep it plugged in ?

Thanks

[dasnoboarder]

Not sure on that one, if the timing is set with engine off, the cold start system shouldn't have been activated.

Geeves has said in the past not to drive with the wire disconnected, any thoughts Geeves?

[lewis]

Oh of course what was I thinking haha.

Im sure its been disconnected for years so cant be doing major damage

Look forward to hearing what geeves thinks

Cheers

[geeves]

Hard question. I would be tempted to connect it but keep a close eye on the temp gauge. If the timing ends up retarded it will run hot. If not it would of had a fair knock going on before

[lewis]

Ok cheers geeves, its definitely noticably quieter/less rattley sounding with it plugged in so ill give it a go for a while, but dont think it was knocking in a bad way as such.

[geeves]

If I disconnect that wire one almost has to wear earmuffs which is why I said yours is a hard question. It might just be that the wire fell off and all is ok but without hearing it who knows.
If the timing is out either way it will overheat.
Do expect it to smoke a little more cold with this wire connected

[lewis]

Oh no way its nothing like that, the change is barely noticible when the engine is idling and I pull it out. Its just a bit quieter and sounds smoother when you are inside driving so yeah I dont think its 'knocking' cause it sure dosent sound bad (i listened to some diesel knocking clips on youtube)

I thought about recording the sound but Im not sure if the difference would be noticible unless the file size/quality of the sound was pretty good.

It was definitely running fine with it unplugged so im not sure whats been modified by a mechanic or isnt working or whatever in the system etc and has most likely been like that for years and years

Didnt overheat on a 10km drive with it plugged in but yep will monitor that

Always smokes when cold anyway

Thanks

[jackmech2]

Is there a way of testing the sensor/switch that activates the cold start system?
My 4jb1T sounds like a tractor all the time right up untill the temp gauge hits around 1/4, then it becomes allmost silent running, and there seems to be less power at low rev when running quieter.

[geeves]

See above pic for the sensor. On the 4jb1 it should switch at 5C so your might be faulty. Try earthing that wire and see what happens