Canadian Hummer Club Forums

Posted: **Tue Jan 12, 2016 8:45 am**

Now before injectors,----- you say you do not have fast idle....
That will be controlled by the temp sender and the computer. A malfunctioning temp sender will give a very rich fuel . The computer takes this info and sets your idle. If the sender is dead and reads -40, I am not sure you will get a fast idle. Not the gauge temp sender but the engine sender, there is 2 coolant senders

Posted: **Tue Jan 12, 2016 1:21 pm**

Hmmm, first off this board give crazy great info-!!!!

Well , I just went to Hamilton and filled up my main tank at a station where I see lots of trucks, (figured less chance of anything bad)

I went to Walmart across the street and picked up Lucas injector cleaner...just because ,lol

Drove back across the skyway bridge to Burlington , drove hwy, hopefully to clean out, seemed ok at speed,..I really couldn't see the haze, but was windy today,...,

Ok at a stop light it don't seem to smoke, but in Burlington city driving, (around 30-5km) part throttle , I see LOTS of smoke here and there, and sometime I get a little chugging, (not sure if anyone would notice, but I know my truck),...only worst with lower speeds and all warmed up, but sometimes can see any,

So I'll give it a few days before I start my crying routine, and relize is not the fuel...lol

When weather get a bit better I'll see where the cold sensor is, and see with that first, then ugggg will see..hehe

Posted: **Thu Jan 14, 2016 3:42 am**

Roy brings up a good point on the temp sender and it would totally explain the lack of fast idle.

Posted: **Thu Jan 14, 2016 12:01 pm**

It does make sense.

Fortunately the one on top by your thermostats (2 wire) is the one for the computer. It's easy to access and test/change. The tough one to get at on the side of the block is for your gauge.

Let us know

Posted: **Thu Jan 14, 2016 12:19 pm**

Lol yup .......I've been studying where that sensor was, and uggg has to a pain in the butt spot in the back passenger side,....lol nothing up front, on a plastic clip that says, "remove me ,and all will be great" lmao...,,,

See now I'm getting delirious ,,hehhe

It's covered in snow right now so in couple days I'll slide under and see maybe tomorrow as warming up today,..,, just so I know what I have to tackle for this job...,....

The more I think of it, the more I can see it being the switch ...I googled sooooo much and ya seems logical as well..

I'll fill ya in soon as I see it,.,,,

I'm sure this summer I have to do injectors/glows and timing chain,,,,it's super tired and needs a face lift,....it's the equivalent of 5 cups of coffee, and the truck motor will be peppy....

Posted: **Fri Jan 15, 2016 12:14 am**

Simply unplug the sender from the thermostat housing and note the difference in idle if any. Conduct this test when cold and when hot. The sensor on the back of the engine seems to be working fine because as you have indicated, your temp gauge appears to work!!
I would caution against just throwing parts and money at the problem. There is a well known issue with the DB2 pumps that should not be overlooked. The advance bore often becomes corroded preventing the plunger from moving. I would be more inclined to think that this is what may be going on and also causing your smoke. The temp senders are pretty reliable and i have never seen one go out, The advance bore is a very common issue with the DB2 pumps. The all-aluminum housing tends to wear out quickly where the steel advance piston is located. This causes excess return fuel and poor pump timing, which results in poor fuel mileage, excess smoke and low power.
See below
http://www.stanadyne.com/dealerportal/ssi/english/Service%20Bulletin/428.pdf

So based on this a proper diagnostic should be done to accurately determine the issue at hand. It would be a shame to throw a pile of money here and there only to find there is a more serious problem. The simple tests cost very little or nothing and will go a long way to finding out what for sure is going on.

Posted: **Fri Jan 15, 2016 12:56 am**

There are three timing advance mechanisms on the fuel injection pump:

An automatic advance system
A mechanical light load advance
The housing pressure cold advance (HPCA) solenoid.

The automatic advance mechanism advances and retards the start of fuel delivery. This mechanism starts working as the engine speed increases to ensure that the injector nozzle opens just before the piston reaches top dead center, when compression is at its highest point. Otherwise fuel wouldn’t be injected before the piston had started moving downward on it’s power stroke.
The mechanism comprises a power piston, servo valve, servo spring, servo piston and a cam advance pin. The cam advance pin connects the advance mechanism to the cam ring. When the power piston moves, it rotates the cam ring so that fuel is delivered earlier.
<img height="186" src="http://www.motormayhem.net/wp-uploads/2009/10/IMAGE0066.JPG.jpg" width="243" alt="IMAGE0066.JPG.jpg">
Housing pressure and transfer pump pressure behind the power piston influence the action of the servo piston. When the engine is cranking, the fuel behind the servo piston is at housing pressure, and the power piston is seated against the housing. As the engine speed increases, transfer pressure rises and the subsequent increase in transfer pump pressure forces fuel into a chamber behind the power piston.
When transfer pressure in chamber behind the power piston exceeds housing pressure, the servo piston acts against the servo spring, and the power piston pushes the cam advance pin which rotates the cam ring in the opposite direction to the distributor rotor’s rotation and so the rollers contact the cam lobes earlier and injection timing is advanced.
When engine speed decreases, transfer pressure drops, the cam ring rotates in the other direction retarding injection timing.
A light load advance mechanism provides advance when the engine is operating at low speed or under light load, when the transfer pressure is too low to move the advance piston.
The light load advance is actuated by an external face cam and rocker lever assembly when the throttle shaft rotates (on the 6.2L and 6.5L engines, this mechanism is on the passenger side of the pump). The lower end of the rocker lever pushes on the end of the servo advance plunger.
As the throttle shaft rotates, the face cam pushes on the rocker lever using a “see-saw” action, which depresses the servo plunger and advances the timing through the power plunger’s linkage to the cam ring. At a predetermined angle, the face cam flattens out, so that additional throttle movement does not affect the servo.
After the light load advance mechanism ceases to act on the servo plunger, advance action is regulated by transfer pump pressure.
<img height="164" src="http://www.motormayhem.net/wp-uploads/2009/10/IMAGE70776.jpg" width="290" alt="IMAGE70776.jpg">The housing pressure cold advance (HPCA) solenoid is one of three solenoids that affect the operation of the injection pump. The HPCA solenoid makes it easier to start a cold engine by reducing housing fuel pressure in the advance mechanism.
The HPCA solenoid is located under the fuel return outlet, under the pump housing cover. It is activated by the coolant temperature switch, which is mounted on the rear of the passenger side cylinder head. When coolant temperature is low the temperature switch is closed, energizing the HPCA solenoid (rear pump terminal connected with a green wire), which lifts the check ball off its seat in the return outlet. This reduces housing pressure to near zero, so that the transfer pump pressure behind the power advance piston can easily advance the cam ring.
In addition to the housing pressure cold advance (HPCA) solenoid, there is a fuel shut-off solenoid (front terminal connected with a pink wire) located inside the pump housing cover that stops the engine by cutting off the fuel flow.
The fuel shut-off solenoid moves the governor linkage, which in turn rotates the metering valve.<img height="231" src="http://www.motormayhem.net/wp-uploads/2009/10/IMAGE0038.JPG.jpg" width="255" alt="IMAGE0038.JPG.jpg">
When the ignition is off, the solenoid is no longer energized and the return spring pulls the shut-off rack to the “OFF” position, which through the governor linkage rotates the metering valve to cut off fuel.
The minimum/maximum engine speed governor, located under the governor cover maintains idle speeds under varying engine loads and limits the maximum speed of the engine.
The governor assembly comprises weights, the governor arm, low idle spring, idle spring guide, main governor spring, main governor spring guide, and the guide stud.
<img height="181" src="http://www.motormayhem.net/wp-uploads/2009/10/IMAGE0071.JPG.jpg" width="183" alt="IMAGE0071.JPG.jpg">The governor weights are rotated by the drive shaft. Their centrifugal force controls the metering valve at minimum and maximum engine speeds.
At idle speed, the governor weights don’t exert much force, so the spring on the governor keeps the metering valve nearly closed.
At high engine speeds, the centrifugal force of the governor weights moves a pivot arm, compressing the spring, and rotating the metering valve to an almost closed position.
At engine speeds other than idle or maximum, the driver directly controls the metering valve through the accelerator/throttle linkage. At those engine speeds the force of the governor weights and the governor spring tension are balanced, so that neither can influence the metering valve.
A pressure regulator protects the transfer pump from excessive output pressure caused by high engine speeds or because of a restricted fuel return line.
When the valve is closed during normal operation, the valve spring holds the piston forward, blocking the regulating slot in the valve thus rendering it inactive.
As output pressure increases, the valve opens. High-pressure fuel pushes the valve piston, which compresses the spring. If the pressure is high enough to overcome the spring’s force, the piston will be pushed back, uncovering the regulating slot in the valve. This will allow fuel to flow back to the input side of the pump, thus relieving output pressure.
A viscosity-compensating device maintains the constant fuel pressure, so that fuels with differing viscosity levels due to composition or temperature may be used. The compensator is part of the design of the pressure regulator mechanism.

Posted: **Fri Jan 15, 2016 1:04 am**

Here is the opposite to your issue https://www.youtube.com/watch?v=0HxQjav1Lik

Posted: **Fri Jan 15, 2016 1:17 am**

Yet another excerpt from the HML Worth pointing out you have not confirmed fuel pump/ fuel pressure yet which is the first step in this.

As others have mentioned, the first troubleshooting is to determine that you have 12 volts on both wires (green I think) when cold. If not, look at the wiring or replace the temp switch. The fast idle solenoid is on top, you can measure the stoke to see if it's working or listen for a click when you apply 12 volts with a jumper wire. BTW, the usual failure for the fast idle solenoid is the very little wire that connects to the spade terminal breaks off and can be soldered back on. The advance mechanism won't necessarily work if there is 12 volts. They stick inside the pump when they fail. To check the cold advance, when it's cold, start it up, then quickly and carefully remove the lower green wire on the passenger side of the injection pump and see if the engine sounds different and quieter and maybe rougher. If yes, then it's working. If not, when the engine is cold again, start the engine and use a jumper wire to apply 12 volts and see if the engine sounds different and louder. It should, and if it doesn't, either your timing chain is stretched to the point that the timing needs to be adjusted, or the advance mechanism is sticking. I think this requires pump replacement. Have the timing checked before replacing the pump. Also make sure the lift pump is functioning properly and the filter is clean before replacing the pump. Always start with the lift pump and filter function first. Many injection pumps have been replaced unnecessarily. All of this is correct for NA engines (DB2 injection pump) for sure. I don't know if the details are the same for the electronic pumps (DB4 pump) on the turbodiesels.

Posted: **Fri Jan 15, 2016 9:27 am**

Such good advice. What a great community!

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