02 2500 Hd 66 Lb7 Blue Smoke on Accelration

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• Forums
• Engine Discussions
• GM Duramax Engines
• 01-04 LB7

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Blue smoke at idle

• Thread starter HighSierra86
• Start date Jun 8, 2012

• #1

Ok guys, I need a few opinions here....

03 LB7 with 320K miles on the clock. Injectors have about 120K. I have been getting quite a bit of blue smoke at idle once the engine gets real warm, as in after running on the highway for a while. My first thought was injectors, but a balance test from the dealer showed all was well in that department.

They had suggested the turbo was becoming worn or the rings were nearing replacement as well. The truck dosent seem to burn much of any oil at all between changes, so I am a little skeptikal. Truck runs great with no other signs of a problem.

I know at this mileage there are alot of things that could be going on, but I figured that I would throw if out there to hear some of your opinions on the subject. Thanks in advance.

-Nick

• #3

Another thing it could be, especially after "getting the engine" warm, could be a plugged crankcase breather. How do the DMAX engines vent there crankcase? Is it a road draft tube? Valve system similar to to the CDR can on a 6.5L? High crankcase pressures can cause oil to blow past the seals on a turbocharger as the drain line becomes pressurized.

I say testing the turbo would be important as well. Take off your hot side and cold side CAC piping, check for excessive oil in the pipes. A light film or coating of oil is normal. Excessive amounts of oil can mean a failing turbocharger. If there is excessive oil in the piping, I recommend replacing the CAC as well. Usually it becomes full of oil from the bottom up and will reduces its efficiency.

• Staff
• #4

PCV reroute might be in order based on Jamie's thoughts. I'm not real familiar with the LB7 PCV though.

• #5

If its any help at all, the fact that your getting blue smoke AFTER the engine has had time to warm up is a good sign that the engine is physically in good shape. 9 times out of 10, worn rings will cause the engine to blow blue smoke COLD because clearances increase as things become cold, than as the engine warms up, those clearances return to an acceptable level as things warm up and expand and the blue smoke will either go away / disappear, or only show up under heavy load.

It could be early signs of an injector getting ready to take a crap, but I'd still say best place to start is with your turbocharger. Having that guy blow apart would certainly ruin your day

• Staff
• #6

Injectors, plain and simple. Balnce rates are almost pointless for testing injectors for wear, and I wish dealers would quit pushing it as a test as 9 times out of 10 balance rates will be good with junk injectors. Blue smoke sounds like injectors popping to early and giving a poor spray pattern. The PCV reroute does not apply to the federal LB7 as it is already an open vent to atmosphere through a filtered can(a MUCH better design than any of teh PCV reroutes out there on the market). Return rates are SO much more important than balance rates though, but most don't want to do a return rate test as it takes actual engine teardown and work to perform. They would rather let the scanner tell em, but in reality it isn't very accurate. And no test will tell you spray pattern in the truck, it requires pulling them and sending them out for testing to verify.

• #7

Blue or would it be closer to white? Is it continuous or more of a cloud while the engine is settling down and cooling some?
I'm thinking an injector that's getting close to sticking open wants to spit a bit when hot or the 300k+ engine is getting loose internally. Kind of like us old farts really...

Smoke is deffinetly blue. Usually after a long highway run when pulling up to a stop light, a large cloud of smoke will pass you by followed by a steady haze of blue afterwords. Now this isnt the usual smoke "haze" that we normally see with these trucks. It is deffinetly more than usual.

-Nick

• #8

Injectors, plain and simple. Balnce rates are almost pointless for testing injectors for wear, and I wish dealers would quit pushing it as a test as 9 times out of 10 balance rates will be good with junk injectors. Blue smoke sounds like injectors popping to early and giving a poor spray pattern. The PCV reroute does not apply to the federal LB7 as it is already an open vent to atmosphere through a filtered can(a MUCH better design than any of teh PCV reroutes out there on the market). Return rates are SO much more important than balance rates though, but most don't want to do a return rate test as it takes actual engine teardown and work to perform. They would rather let the scanner tell em, but in reality it isn't very accurate. And no test will tell you spray pattern in the truck, it requires pulling them and sending them out for testing to verify.

I always am hesitant to jump on the injector bandwagon. It seems people are quick to blame injectors on any LB7 problem..just as people are always quick to blame the injection pump on any problem with the 6.5L

But it seemed to me in this case thats what was going on. And with 120K on this set, it seems this is generally around when we have replaced them before. Interesting to hear your take on the dealers "test".

Now why is it that you see blue smoke with failing injectors? I would think a poor spray pattern, or excess fuel, would result in a black/unburnt fuel smoke. I know in the past when we have replaced injectors the truck would suddenly develop a no-start condition and then that was it.

Thanks for all the replies guys

-Nick

• Staff
• #9

Theer are several differrent kinds of LB7 injector failures. High balance rates was a sign of poor spray pattern if it was just 1 injector. High return rates is the most common where teh system cannot build enough pressure to start or will throw low rail pressure codes under power. Causes of this can be worn ball seats which causes it to return to much to the tank, and then there was the cracked injector bodies which was common with 01-02 injectors. High return rates was the only failure that GM approved of for the extended warranty policy, but dealerships turned it into an injector warranty. Blue smoke is normally from retarded timing or porr atomization from a low pop pressure though. It will be a dark rich blue smoke from injectors that can have a grey or white mixed in with it. Black will show up under power if to much is injected, and white will show up when one is hanging open. There have been quite a few people here lately who have doen engine work only to find out that there injectors were the problem all along, so make sure and check em. If you pull em out and they are wet on teh tips, that is an almost guarantee that it is bad(unless it has low compression on that cylinder).

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Source: https://www.thetruckstop.us/forum/threads/blue-smoke-at-idle.35639/

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