Question about Cars & Trucks
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Posted on Jan 02, 2017
Black smoke means "fuel not being combusted" or "runnig rich". I have no doubt you have gasoline. Your spark may not be burning the gas. Is there a check eng lite? If EGR was sticking, you would probably get a check engine light for this. If your truck has a Vortec design, I would find out if you need a new "spider". What is your mileage? Are you due for a tune up? What spark plugs are you using? Vortec? "Not all the time" sounds like intermittent. When was the last time you changed the fuel filter? Can't hurt to change this. This would be the actaul starting point for me. I would change the fuel filter which is under the driver under the chasis. You will need a 16MM and a 20MM. USE ONLY LINE WRENCHES. You may need a fuel line disconnect kit too depending on your model. Notice it only happens on acceleration? that is when you are forcing even more fuel thru the system, but not enough of a fuel stream make cause sputtering and when the fuel comes thru too rich that would be the black smoke. It sounds like you have the 2 extremes. is there afuel regulator on your vehicle? If so, you may need to change that too. Good luck.
Posted on Sep 10, 2009
Once you are able to identify the EGR, you simply unbolt the valve and ant other obstaructing part. Clean its surface of carbon. Repalce the gasket if worn. Any sticky bolt/nut that you encounter could be removed by spraying some WD-40 around them. Also disconnect the negative wire of the battery first. Diesel do run hot, so get ready for some hard bolts to loosen.
Posted on Oct 21, 2009
SOURCE: I replaced egr valve on
Are you in California. Did you put aftermarket exhaust on the truck?
California Duramax are configured differently and if you mess with the
exhaust it trips an EGR code that will turn the SES light on. Now, on a
truck configured for Minnesota or Iowa changing the exhaust trips a
code but it wont turn on the SES light. So, do you have any mods?
The LB7 EGR valves are vacuum operated, unlike the LLY,LBZ,LMM which are electrically controlled. This is why a finger stick does not work with LB7's.
The most likely cause is the belt driven vacuum pump which is mounted below the belt tensioner. These do go bad and stop pumping vacuum. Usually they make a knocking noise when bad. You need to pull a vacuum hose off on top of the fuel filter the runs to the vacuum pump and check it for vacuum with the engine running. Should have at least 15 inches. If this is not the problem the it gets a little more complex from here.
P0404 - Exhaust Gas Recirculation Circuit Range/Performance
The EGR (Exhaust Gas Recirculation) system's purpose is to redirect exhaust gas back into the cylinders. Since exhaust gas is inert, it displaces oxygen and fuel, thereby lowering cylinder temps, which, in turn, lowers oxides of nitrogen emissions. For that reason it needs to be carefully metered into the cylinders (via the EGR valve) so as not to adversely affect the engine's performance. (Too much EGR and the engine won't idle).
If you have a P0404, then the EGR valve is likely an electrically controlled EGR valve instead of a vacuum controlled EGR valve. Also, the valve will usually have a feedback system built into it that informs the PCM (Powertrain Control Module) what position the valve is in; open, closed, or somewhere in between. The PCM needs to know this to determine whether or not the valve is operating as needed. If the PCM determines that the valve should be operating, but the feedback circuit shows that the valve is not open, this code will set. Or if the PCM determines the valve should be closed but the feedback signal indicates that the valve is open, this code will set.
Symptoms: There may be no symptoms of a P0404 DTC other than the MIL (malfunction indicator lamp) or check engine light. However, Exhaust Gas Recirculation systems are inherently problematic due to carbon buildup in the intake manifold, etc. This normal buildup can lodge in an EGR valve, holding it open when it should be closed. If this is the case, the engine may idle rough, or not at all. If the valve has failed and is NOT opening, then symptoms would be higher combustion temps and as a result, higher Nox emissions. But the latter symptoms aren't going to be noticeable to a driver.
Causes: Usually this code points to either carbon buildup or a bad EGR valve. However that doesn't rule out the following:
* Open or short in the 5 Volt reference circuit
* Open or short in the ground circuit
* Open or short in the PCM controlled voltage circuit
* Bad PCM (less likely)
1. Using a scan tool command the EGR valve to open while watching the actual EGR position (it will probably be labeled "desired EGR" or something similar). The actual EGR position should be very close to the "desired" EGR position. If it is, then the problem is likely intermittent. It may have been a lodged piece of carbon that has since dislodged, or it could be a bad EGR valve winding that intermittently opens or shorts as the valve temperature changes.
2. If the EGR "desired" position is not close to the "actual" position, then unplug the EGR sensor. Check for a good 5 Volt reference voltage to the connector. If it doesn't show a reference voltage, repair an open or short in the 5 Volt reference circuit.
3. If there is a 5 volt reference voltage, activate the EGR with the scanner, monitor the EGR ground circuit with a DVOM (Digital Volt/Ohm meter). It should indicate a good ground. If it doesn't then repair the ground circuit.
4. If there is a good ground, then check the control circuit. It should indicate voltage that varies according to the percentage that the EGR is open. As it's open more, the voltage should increase accordingly. If it does, then replace the EGR valve.
5. If the voltage doesn't increase incrementally, then repair open or short in EGR control circuit.
Keep us updated.
Posted on Jan 25, 2011
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