LLY: Diagnosing smoke under acceleration

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CheMathSec

New member
Sep 21, 2016
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Hi all,

I know this has been covered before, I've read several threads detailing similar issues, but I need some things cleared up. I'm new to the diesel world and know very little about cars/trucks in general. I'm getting there, but you must bear with me...

So here's the situation:
I bought my truck back in March with about 213000 miles to be a daily driver and pull my fifth-wheel. First time out with the camper, the problems started. Power steering pump and hydroboost died - had those replaced, hitched back up and blew a turbo hose off (somewhere behind the front driver's side fender well, only took the mechanic 10 minutes to get back on). Since then, I've noticed a good amount of black smoke whenever pulling the camper, especially going up hills. And now I've started noticing smoke under moderate acceleration (passing, highway on-ramps) without the camper. This smoke is sometimes white-light gray and sometimes black. It blows consistently until I let off the gas. It's also got a pretty loud knock around 1700 rpm, but that could just be regular Duramax sounds, I wouldn't know.

From everything I've read, there are a ton of things that could be causing this. I cleaned the MAF sensor and air filter, I have not replaced the fuel filter. I know that bad injectors may be a possibility and that I need to check the balance rates to get an idea, but I would need help figuring that out. I just picked up an OBD2 WiFi scanner and hooked it up to my iPad, but the numbers mean nothing to me.

I'm really just trying to get a reasonable diagnosis without dropping my truck off at a shop for multiple days. It is my daily driver and I have to get to work and school.

Thanks in advance for any help!
 
Burn Down

Burn Down

Hotrodder
Sep 14, 2008
7,093
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Boise Idaho
The duramax normally doesn't have a loud knock to it... I would ck the ficm harness behind the alternator. It likes to rub through at the top of the ficm where the factory zip tied it and could cause issues like you described. Look into ice picking #2 and #7 injector pig tails.

What do you mean by cleaned the air filter? Guessing it is a K&N style?

Can you get the balance rates on your scan tool?
 
C

CheMathSec

New member
Sep 21, 2016
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Thanks for the reply. I'll look for the harness.

The air filter is factory, square paper-style. AC Delco if I remember correctly. I just took it out, beat some dust out of it and ran a vacuum hose over it a few times to clear some of the dirt and dust. It looked brand new when I pulled it out, but I figured it couldn't hurt.

I just picked up the scanner yesterday, so I'm not sure. What should I look for under PID?
 
Dozerboy

Dozerboy

Well-known member
Jun 23, 2009
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I would assume you would be looking for Balance Rates for all the individual cylinders.


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trashygasman

trashygasman

Slowly but Surely
Dec 18, 2008
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If you blew a hose off and someone else put it back on, I would be looking for a boost leak causing your black smoke. It may look like it's on there all the way, but a small leak can cause a lot of smoke. Ask me how I know?:)
 
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CheMathSec

New member
Sep 21, 2016
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North Carolina
trashygasman said:
If you blew a hose off and someone else put it back on, I would be looking for a boost leak causing your black smoke. It may look like it's on there all the way, but a small leak can cause a lot of smoke. Ask me how I know?:)
Click to expand...



Well that would be an easy fix. It wouldn't explain the lighter smoke I'm seeing though, correct?
By the way, what does the stock boost usually run? I was seeing about 2psi just putting around, 5-6psi at highway speeds, and I peaked around 14-15psi with 3/4 throttle.

Oh, and..how did you come by this information? I'd love to know!


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Dozerboy

Dozerboy

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Jun 23, 2009
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Way too many variables to tell you how much boost you should see it what time for sure. But your numbers don't seem out of line. Wide-open throttle I believe our trucks are like 22-23 stock


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C

CheMathSec

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Sep 21, 2016
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Dozerboy said:
Way too many variables to tell you how much boost you should see it what time for sure. But your numbers don't seem out of line. Wide-open throttle I believe our trucks are like 22-23 stock


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Click to expand...



Good to know. I was keeping an eye on all the numbers while driving around the past couple of days, but they don't mean anything to me yet.


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CheMathSec

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Sep 21, 2016
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North Carolina
I found the balance rate PIDs, but I'm going to need some help interpreting the data and verifying that I gathered it correctly. Here's what I did: I drove around on and off for about an hour (had some errands to run), parked it at the house, shut off the A/C and lights, let it idle for a few minutes and then checked the numbers.
Here's what I got:

Fuel rate: 0.16 gal/hr
Fuel Rail Pressure: ~4300 psi
Engine temperature: 189 F
MAF: 3.63 lb/min

Balance Rates
1) -1.3
2) 3.8
3) 1.6
4) -2.4
5) -1.1
6) 4.7
7) -2.5
8) -2.6

I found this post about "The proper way to check balance rates" (http://www.dieselplace.com/forum/63...b7/576505-proper-way-check-balance-rates.html), but I don't know how accurate it is. There were as many people claiming this to be legitimate as there were otherwise. One problem I have is my fuel rate in units of gal/hr is not comparable to units of mm^3, unless I have the pulse width. So Should I just use the numbers as-is? I've read that GM spec for this engine is -2 to 2, which would mean I've got 5 injectors out of spec??

If anyone has any insight here, I would really appreciate it.
 
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CheMathSec

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Sep 21, 2016
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Here's what I got. Not sure if it matters, but I was on a 1/4 tank for this first set.
9bc47f57903f16b7095bc46efdae484f.jpg

3f210aab22eae2cc342260a06886eda7.jpg


Then I filled up, started the engine, and put it in gear with my foot on the brake again for another check on a full tank.
60bdd3aac336cd8b3e417b4f58ef1154.jpg

dfb8fa379c3951c38c8007de3b870011.jpg



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Burn Down

Burn Down

Hotrodder
Sep 14, 2008
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Boise Idaho
looks like a couple bad injectors... Other test need to be ran such a injector return rate test, rail pressure test, and a compression test.
 
C

CheMathSec

New member
Sep 21, 2016
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North Carolina
Thanks guys. I'll try the fuel filter, as that should be pretty easy. Hoping it's not bad injectors, any more than one would push me way over budget for this truck. I'm already into it for more than it's worth. But hey, I could use an excuse to buy a new truck.
 
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