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Could bad Glow plugs give low compression

N

Nowaydude

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Hi, I'm having an issue with white smoke all the time. Smoke smells like unburnt diesel
2000. Gmc 6.5td. 61k miles.
Changed all injectors with new bosch.
Checked rocker buttons.
It had 1 bad lifter when I bought it, wasn't able to see it run before I bought it.
I Was able to replace it with out taking off the head.
Fuel filter is clean.
New intake gasket.
New ECS.
It fires right up and Idles perfectly.
It cranks like it has good compression.
Number 6 and 8 cylinder don't have much change when cracking the injector lines.
It sat for awhile before I purchased it.
It sounds fine when running,just smokes even at higher RPM, and up to temp, no miss fires.
I was going to do a compression test, I started taking out out the glow plug got the first 2 out in no time numbers 2 and 4, got to number 6 and 8 and I can't get them out, 2 hrs later. They un thread but I can't pull them out, they must be swollen inside .I ordered a tool to remove them and new glow plugs from Leeroy diesel. Any Idea if bad swollen or cracked glow plugs could leak compression,causing low compression? Just a thought. Thanks mike
 
If the GP's were compromised to the point of a leak, something tells me that it would show as soot around the hole and probably expect to hear it as an extra cyclic noise.

The white smoke might point to coolant getting inside the combustion chamber.

FWIW, if you have access to software (example: Autoengenuity), it is possible to turn-off one cylinder at a time through the OBD-II port rather than mess with the injector line(s).
 
No, I don't have access to that, would be nice, I'm new to diesels, i don't think it's coolant, it smells like diesel and its not loosing coolant,but I guess it could be.

When I changed the Injectors, they all had the same soot color on the end, like they all were burning the same, if coolant was present wouldn't there be a color change? Thanks. Mike
 
Continue with the plan of extracting glows, and doing compression test.

Double check your fuel injection lines are all in proper order. This would be equivalent to mixed up spark plug wires on a gas engine. The 2 dead cylinders would be suspect. Mixing them up could easily happen when doing the rocker buttons and lifter.
 
Thanks for the reply, I didn't remove the fuel lines, was able to lift them out of the way gently to get valve cover off. The bad lifter was on the other bank. Its odd that the 2 back cylinder #6&#8 would have glow plugs that won't come out? Is there a hot spot where coolant doesn't travel thew that part of the engine properly? Is it possible to use a fiber optic scope threw the injector hole to look in the two back cylinders? Its odd to have 2 dead cylinders right next to each other.I guess when I had the valve cover off I should of cycled the engine to see the valve train working properly. The Previous owner had the intake and pass side valve cover off. Hack of a mechanic, he didn't take the last bolt out of the intake manifold and snaped the last ear off over # 8 cylinder. l Wonder if something could of got stuck in a valve with intake off? Just a thought. I found a couple of sockes in there under intake. Thanks. Mike
 
#8 in the block is a known weak spot, but when if fails- you wont guess- it is obvious and consumes a lot of coolant, engine overheats right away, etc.

Yes valve train issues could do it.
Possibility of blown head gasket between the two cylinders.
Also the leaking injectors could be bad and coincidence they are next to each other.
 
Injectors are new bosch, did the exact same thing, I'm guessing compression test will tell me something. How do i tell if it's a valve or head gasket? Thanks, Mike
 
First do all 8 compression test & write down.

Then crank the engine until that cylinder is on compression stroke with piston at top. Use glowplug adapter that was used in compression test and do a cylinder leak down test.
The backyard method is just hook air compressor hose to the adapter and see where the air is leaking out. Into the pan/ valve cover area is ring blow by. Out the exhaust pipe is bad exhaust valve. Out the intake manifold is bad intake valve. Air hose hooked to cylinder 6 and air coming out cylinder 8 is gasket.

This doesn’t always show up as cylinder pressure is 8-10 times that of an air compressor. But if it shows up- time to pull a head.
 
if you have a helper you can put a stiff wire down the injector hole and then bar the engine over, DON'T use the starter. very little room at the top of the compression stroke so you might have to turn the engine back and forth to find TDC. let the piston push the wire up slowly might have to play with it a bit to keep it from wedging from the odd angles
 
Ok, I was able to remove the glowplugs intact, tool worked great. I did a compression test on the suspect cylinder side, drivers side which i thought # 6 & # 8 cylinders were bad, but they have higher pressure #8-420, #6-475, #4-380, #2-360, i did this 2 times, to make sure readings were correct.only issue was i couldn't shut off fuel, I pulled the fuel pump relay and glow plug fuse. Would that screw up the readings having fuel in cylinders? Would it be like doing a wet test? I couldn't get the compression gauge adapter for the turbo side to work, it hits the exhaust manifold . Do you know if they make a flexable hose adapter that will work for the turbo side? It doesn't seem like its a compression issue though from those readings. Just a thought, could the injection pump control module be bad causing a timing issue? Thanks. Mike
 
turbo side is 2,4,6,8 non turbo side is 1,3,5,7 this is important to know for timing check comparing which injector lines go where.

yes fuel coming out injectors can mess up readings. can be deadly by causing the gauge or tester line to the gauge to explode. pull the wire to the fuel solenoid.

the difference between cylinders is out of limits. doesn't mean you cant run it, just expect issues.

get the fuel shut off, and with all plugs out crank the engine for 10 seconds minimum before re reading them. Check w/ local auto parts stores for a different adapter.
 
I don't think i can see where the lines connect to injection pump. I thought # 1 cylinder was on the left standing in front of engine? Hummm! Thanks. Mike
 
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