L300 glow plug trouble shooting

[AKcub]

I'm troubleshooting a cold start issue with my '92 Starwagon with the TD. Unless the temps are in Summer mode I always seem to get 30-45 seconds of grey smoke and clunky running before she smooths out.It helps to manually bump the idle up around 1100 rpm. Once it's past the initial roughness, she runs well with no smoke. The van has been modified with a manual glowplug control setup.
I assumed I had a bad plug or two so I bought new plugs. The year old plugs were the 6 volt style, even though the ECU has been bypassed. I replaced them with HKT 11 volt plugs.
I took some measurements before removing the old plugs and the 6 volt plugs all ohmed out at about 1.3 ohms. My bus bar voltage was right at 9.7 volts with the glowplug button pushed.
After the new glowplugs were installed (they all ohmed out at about 1.3 ohms as well before install) my bus bar voltage jumped to 10.7 volts. Still seemed low so I checked each plug individually from battery to plug and they showed battery voltage (13.3 volts).

The lead running from the switch to the ECU is a piece of primary wire (16 gage), I'm pretty sure it's only carrying power to the ECU to turn the solenoid on that gives power to the glowplugs or I would suspect that it's causing the voltage drop- Is that a correct assumption?

I only had a chance to make one start but it was a totally different experience than prior to plug swap- temps are in the upper 70's (20's for C inlined folks). I gave the bypass button a few seconds and cranked a few seconds with no sign of life. I gave it a long 5 count and when it came to life it was pretty smoky and ran did it's usual come to life dance. The smoke may have been from the initial cranking.

Any of this starting stuff sound familiar? If this is the way these things come to life then I'm good with it but want to make sure I'm not running a broken rig.

Anything I am missing in the glowplug troubleshooting? I have a pal with an '88 and the ecu and his comes to life without a snort or puff of smoke and seems to roll right into a nice 700 rpm idle.

Thanks for any thoughts,

Scott

[Growlerbearnz]

The voltage on the bus bar sounds about right- glow plugs draw a lot of current, so you'll get a bit of voltage drop. If you're reading above 12V then one or more of your glow plugs probably isn't working.

The 6V system (super-quick glow) has two solenoids. One of them powers the glow plug bus bar directly, the other powers it through a giant resistor. Your manual override should be connected to the spade terminal on the solenoid that powers the bus bar directly. You're correct: the 16-gauge wire is sufficient to power the solenoid, but nowhere near enough to power the bus bar. Then again, if that wire was connected to the bus bar I imagine your manual switch would have burst into flames by now.

With 11V glow plugs I'd give them about 6 to 8 seconds on a 15C day. 6V glow plugs (running on 12V) take about 4 seconds.

One thing you could test is holding the glow plug button on once the engine has started (for about 10 seconds or so, don't over do it). If the idle or smoke improves, you know your glow plugs are working.

It's normal to have to increase your idle speed for the first minute or so, even on an engine with perfect glow plugs. Letting it shake about at 500rpm while the oil is cold is not great for the bearings.

[AKcub]

Ok, thanks for the information. Looks like i'm ok here.

Is it possible to actually burn up a glow plug by using it?

Scott

[Growlerbearnz]

Oh yes. Keep them on too long, or when the engine is hot, and they can melt, crack, or burn out. I think the original Mitsubishi ceramic 6V ones are more susceptible to breaking than the aftermarket ones.

[Growlerbearnz]

Oh yes. Keep them on too long, or when the engine is hot, and they can melt, crack, or burn out. I think the original Mitsubishi ceramic 6V ones are more susceptible to breaking than the aftermarket ones.