Glow plugs on when it's warm?

[andrewroudny]

Hey all,

Received a good bit of help with my other post about engine not starting - thanks - but I would like to know definitively one thing:

Do the glow plugs come on even when it's warm outside (like warmer than 70 degrees)? And if they don't come on, does that prevent other things in the engine from working (fuel pump, fuel shut-off valve, etc.)?

Thanks!

[JohnC]

Anything 94 and later will have some glow cycle no matter what. This is an effort to reduce visible smoke on start.

Glow plugs won't prevent other things from working, but, since the glow plugs are controlled by the PCM, whatever is keeping them from coming on could also cause other problems. I guess the first place I'd look is the fuse box and the second place the cluster of ground wires in the right rear of the intake manifold. Of course, check al the battery connections too, tlthough you said it turned over OK. Do the dash lights self test correctly?

[Robyn]

Every time the key is cycled on and off (start then run then stop and then restart) the glow circuit works.

Now that said the cycle time is short when things are warm.

The older engines (mid 80's 6.2) had a glow inhibit switch that stopped the glow system from working when the engine temp was over about 120F or somewhere in that range.

The idea was sound but in practical application the switch would fail and leave a poor hapless soul with no glow and no start.

Happened to me on a cold winters day up in Spokane Washington.

Came out from the motel and NO GLOW :eek:

I was not familiar with the inhibit circuit at that time. I simple used my Jump cables (had zero tools in the rig) and I jumped the glow plug side of the relay to the battery.

Poof 10 seconds and up and going.

Now to answer the rest of your question.. The glow circuit will have no effect on the Lift pump or other goodies from working right.

The glow timer is regulated by the Coolant temp switch and the ECM.

Hope this helps

Robyn

[andrewroudny]

So it looks like should be getting that "wait to start" light regardless of temp. And I'm not. But what I don't understand is if the engine is turning over and getting fuel, it should start up in warm weather.

My battery connections are good. I've replaced a cable (the one that leads from the battery to one side of the glow plug relay) and the glow plug relay itself as well.

So I'm gonna try the fuel shut-off valve first, and then if that doesn't do the trick, I guess I'll start looking at the wiring from the key to the relay.

Thanks again for the help.

[JohnC]

But what I don't understand is if the engine is turning over and getting fuel, it should start up in warm weather.

Yes and no... It'll still be quite hard to start a cold engine with no glow plugs even in the summer. However, the reason they are not comming on could be a symptom of a bigger problem, like a failed PCM or a wiring problem with the PCM.

You stated that the PCM is sending the "on" signal to the relay. Are you sure? If so, your problem could be a simple as a failed relay. You could try jumping the relay for 5 or so seconds with a heavy jumper wire (plan for 80 -100 amps) with the key off, then see if it'll start.

[trbankii]

It would also help to add your vehicle information - year, model, etc - to your signature line so that people can focus on what may be wrong with the components that your vehicle has.

[andrewroudny]

Just to clarify: The signal to turn on the plugs is NOT there.

I'll add it to my signature, but I have a 2000 Chevy Express 3500, 6.5L Turbo.

Looks like I have a wiring issue. But also the fuel cutoff may be a problem because I don't smell diesel when I crank the engine.

[JohnC]

Just to clarify: The signal to turn on the plugs is NOT there.

Then all bets are off. Figure out why.

[enormiss]

I'll add it to my signature, but I have a 2000 Chevy Express 3500, 6.5L Turbo.


Needed info, as some of our stuff is located differently.
If your trying to see if you have other issues besides the glo signal then Jump it like Robyn or JohnC mentioned above & see if it'll start.

[andrewroudny]

Again, thanks.

Does anyone have a wiring diagram of the glow plug circuit which includes the ignition (key)?

Cheers,
Andrew