raw fuel smoke

[Greg Marshall]

I have a few questions reguarding injectors and glow plugs. Last winter I started experencing hard starts when cold duh glow plugs, so I replaced the set and seemed to fix the prolbem. Then this spring whiel I was towing, I started to experence a coolant loss from the coolant tank, no overheat just loos of coolant. To make a long story short the prolbem was a combination of bad pressure tank cap (would not hold any pressure at all) and a slightly stuck thermstat.
Durring this I started to see upon cold start a lot of whit or blue smoke at start up the after about 5 sec. or so it woudl somth out and be fine. I just last week replaced all of the injectors had the old ones checked at the local diesel shop and saw for my self that they were all bad. THought that would cure my smoke prolbem,WRONG. I still get a raw fuel smoke at cold start runs great on road so here is my question, I understand that I col dhave had a glow plug bad. How do you test them on the truck and can a leed in wire go bad we had to replace the end of one of the wires on the passenger side so I am guessing in the dark dont think it is much as the injectors have really helped it also by the way first set of injectors on it at 150000. :confused:

[DmaxMaverick]

That smoke you are seeing may not be fuel at all. Sounds more like steam, or water vapor.

The white smoke you see now, but not before, could be caused by repairing your cooling system. Before, there wasn't enough pressure in the cooling system to force coolant into the cylinders from whatever cause (head gasket, head crack). Put on a new radiator cap and fix the stuck thermostat and up goes the pressure. Enough pressure to force coolant into the cylinders when you shut it off, which will be there when you do a cold start. You didn't mention hard starts, rough idle, or power loss. If there is none, I would bet on that white "smoke" being from coolant, not fuel.

You can check the glow plugs on the vehicle easily with an ohm meter, or test light. All you need is to check continuity of the spade connector on the plug to ground. You could check the resistance, but that never really got me anywhere. 5K - 10K ohms, I think, is the correct neighborhood. If the circuit is closed, the plug will (should) heat. That simple.

Disconnect the glow plug wire at the plug spade connector. Ground one probe of your meter, and touch the spade with the other. It should show closed (short circuit). With a test light, connect the alligator clip to bat + and touch the probe to the spade, just like with the meter. If the light comes on, the plug will heat.

You can also check voltage at each plug wire connector while it is in a glow cycle. Depending on your system, anything near 6 or 12 volts

[eracers999]

Try this little test, cold eng preferably in the morning, unplug the coolant temp sensor then get in and start it, normal routine. Report your results.
Kent

[charliepeterson]

Try this little test, cold eng preferably in the morning, unplug the coolant temp sensor then get in and start it, normal routine. Report your results.
Kent


Great idea. When you do this the ECM thinks the water temp. is veeerrrry ccccooold. The glow cycle is twice as long and the engine should start easy with no smoke.

[eracers999]

Charlie;
There is 2 other sensers that share the same ground path as the coolant senser so the glow plug time should be pretty close to the same maybe a little longer, the main reasone is the pump timing advances and should start instantly. If there is a question of a/f being burned then it should still smoke. I have a little battle going on with mine now that the weather is warmer, if you try to start it in the morning it will imediatly start then die and then when you do get it started it smokes and bucks like it has a few glow plugs that are bad. If you unplug the coolant senser it pops right off with no smoke and runs perfect. Been too busy to get to deep in this problem and if anyone has any ideas feel free to speak up. Coolant senser, intake air temp senser are new, the truck has no codes and runs perfect after a short time. Starts warm with no glow plug time just fine.
Kent

[charliepeterson]

Kent:

With the extra glow cycle when the coolant sensor is unplugged do you think one or two GP's could be dead? On a normal start the GP's don't get much of a burn and if one or two are missing you will definitely feel and see it. On the extended burn the other GP's could get the cylinders up and running smoother with or without a bad plug on a warm day.

[tom.mcinerney]

Kent--Not sure just how the glow relay works, but pretty sure there are mechanical contact points. I'm guessing you have low voltage thru worn/burnt points, this requiring extra dwell to warm the g-plugs.
I'm basing this on similar experience (of worse starting performance in moderate spring temps in a VW diesel, with known poor g-relay contacts). This assumes you do see indication that there is an appropriate moderate glow duration for the moderate weather. Varying condition of contacts can significantly change output from relay.

[tom.mcinerney]

DmaxMaverick -
Like most of your posts, from which i've learned a lot, the above is worthy. But,only half of this:

>>You could check the resistance, but that never really got me anywhere. 5K - 10K ohms, I think, is the correct neighborhood.

Like incandescent light bulbs, glow plugs have a very low resistance cool (off), but a high resistance when warmed-up. As a consequence, the 'inrush current' for bulbs and g-plugs is quite high, it subsides after the filament attains red heat(or white). If the G-plugs output 100 watts [each] when warm, and the circuit voltage is 10-V, the resistance of each g-plug would be about 1-Ohm. The resistance of each plug would be a fraction of an ohm cold.
Power=Current(squared)X Resistance; P=I(2)X R.
Power{assume 100watts}also=Volts{assume10} X Amps.

Moondoggie has aptly suggested the better test for glow plug operation is a current meter. But the sophisticated controllers used on 6.2/6.5 are easy on g-plugs, so a test lamp is adequate for quick check...

[eracers999]

Tom;
When it wont take off after a couple of tries and just 1 cycle on the glows, i can go out and unplug the coolant sensor and it pops right off, no missing and no smoke. Go out and plug in the coolant sensor and all is well. I have all but ruled out the glow plugs and relay. They OHM out good and it draws hard on cycle. The proper GM way of checking these with a OHM meter is to set the OHM meter on the 200 scale, measure, less than 1 ohm good, more than 1 OHM bad. Right now the truck is out 16 hrs a day and other than that runs flawless. It will hot start all day with just starting it like a gasser. One of these days of maintenence i am going to get to the bottom of it. Will report.
Good day to all.
Kent