#3 and #6 cylinders...

[Mark Rinker]

...same bank? Adjacent?

Buddy stopped by and replaced the #6 glow plug that has been setting a code recently. This morning, after resetting code and SES, I have same message - but now for #3.

Arrggghhh. :mad:

Wondering if its coincidence, or if a wire might have been knocked loose in the process. (pronounced PRAH-sess, for most stateside folks, PRO-sess for northern Minnesotans and Canucks.)

[DmaxMaverick]

Opposite banks, not adjacent. The odd cylinders are on the passenger side, and the even are on the driver side, 1 and 2 at the front. #3 is the second from the front on the passenger side. #6 is the third on the driver side. The only thing they have in common is the harnesses plug into the same relay assy. So, no correlation between the two failures. Unless.....you had/have a sticky relay. In this case, look for the others to quit soon. ....Or not.

[Mark Rinker]

Is there any way to isolate or test the relay?


...or just throw another glow plug at it?

[DmaxMaverick]

Yes, on the test. The relay is a solenoid, with open/closed contacts. You can read the impedance of both (circuit must be closed/energized to test the contacts). However, intermittent problems are the bear. If the relay is weak, or slow to engage/disengage, you should be able to tell with a bench test, but not always. Otherwise, you'll have to use a Tech II to command the GP's on/off, and watch for a delay, if there is one. Unfortunately, you have no way of knowing if/when this is happening, be it hot, cold, damp, dry, etc. The relays are not expensive (if you don't get them at the dealership), and can usually be swapped with another circuit with the same relay (like the starter, etc.) for testing. The relays are well marked, so if the numbers match, they are the same. I don't know which relay is used on the 2006 GP, so you're on your own there. I'd just look in the box, then swap it with another in the underhood distribution box.

In the end, GP's will get expensive. If you have another blow, I'd replace the relay, regardless.

[Mark Rinker]

Thanks, we'll follow your complete advice.

[cabletech]

Elect diagram for an 06. Hope you can read it. If not let me know and I can send you the full size image.

Jay

[Mark Rinker]

Try sending the fullsize image to mark_rinker@hotmail.com please. Thanks!!!

BTW - one clue that I left out - when the SES first illuminated, indicating #6 GP was bad, the glow symbol on the dash would illuminate when you cycle the key, but would not go out, no matter how long you waited.

Realizing this might be leaving seven other glows getting TOO hot, I would simply start the truck after a three or four seconds, not waiting for the heat indicator to go out. Don't think I ever left the others to 'bake', but can't speak for other drivers on the truck - even though they were informed.

Is this a normal symptom when a single glow is out? Might it be further proof that the relay is to blame? Now that I think about it, it sure sounds more and more like the relay, or whatever controls the glow cycles...

:confused:

[DmaxMaverick]

The PCM "controls" the glow cycle. Logic is involved, and engine, air and ambient temps are valued inputs, and the GP's are commanded accordingly. If you think the "control" end is the problem, the PCM is shot, or an input value isn't what it should be. You'll need a scan tool to see what the PCM "sees", and compare with actual values. Otherwise, it's likely a sticky relay.

[Mark Rinker]

Thanks - we'll follow your tips, most likely replacing relay and #3 glowplug, in that order.

[cabletech]

The PCM "controls" the glow cycle. Logic is involved, and engine, air and ambient temps are valued inputs, and the GP's are commanded accordingly. If you think the "control" end is the problem, the PCM is shot, or an input value isn't what it should be. You'll need a scan tool to see what the PCM "sees", and compare with actual values. Otherwise, it's likely a sticky relay.


No true. With the Bosch ECM, Glow plugs are not controlled by the ECM at all. They are controlled by the Glow Plug mod only. The Glow plug mod is a CAN bus device just like the ECM & TCM.

Mark
There is a recall for reprograming the Glow plug mod. Has it been done?

Jay

[cabletech]

GLOW PLUG/CONTROLLER

The glow plug controller is a solid state device which operates the glow plugs. The glow plug controller is connected to the following circuits:
The fuel heater ignition 1 voltage circuit
The battery voltage circuit
The CAN communication circuit located between the engine control module (ECM) and the glow plug controller
The engine ground circuit
The glow plug supply voltage circuits located between the glow plug controller and the glow plugs.

The glow plug diagnostic circuits are directly monitored individually by using a separate transistor to control current to each glow plug. Individual diagnosis is thus possible for every glow plug.

[JohnC]

Mark: the recall was to address glow plug burn out. Make sure it was done!

BTW, the cylinders are numbered based on the position of the connecting rod on the crank, starting at the timing end.

[Mark Rinker]

No true. With the Bosch ECM, Glow plugs are not controlled by the ECM at all. They are controlled by the Glow Plug mod only. The Glow plug mod is a CAN bus device just like the ECM & TCM.

Mark
There is a recall for reprograming the Glow plug mod. Has it been done?

Jay

Not that I know of - I'll call and check tomorrow. It hasn't been in much - and this problem didn't start until ~125k so it would see like normal physical componant 'burnout' rather than logical programming problem...

[Mark Rinker]

Mark: the recall was to address glow plug burn out. Make sure it was done!

BTW, the cylinders are numbered based on the position of the connecting rod on the crank, starting at the timing end.

Will do.

Makes sense. Wonder why gassers are numbered by firing order, rather than by crank position? What is the firing order of the Duramax?

I first learned the importance of firing order - the hard way - when replacing the timing chain and ignition system on an 1980 Firdbird (turbo) T/A, using a Chilton's manual from my '79 Camaro...:eek: (Later, I learned the importance of leaving wastegates set that their factory settings, unless you know what you are doing...and that too much of a good thing doesn't = great.)

[DmaxMaverick]

Will do.

Makes sense. Wonder why gassers are numbered by firing order, rather than by crank position? What is the firing order of the Duramax?

I first learned the importance of firing order - the hard way - when replacing the timing chain and ignition system on an 1980 Firdbird (turbo) T/A, using a Chilton's manual from my '79 Camaro...:eek: (Later, I learned the importance of leaving wastegates set that their factory settings, unless you know what you are doing...and that too much of a good thing doesn't = great.)

I think you misunderstood him. The Duramax cylinders are numbered with the exact same method as GM V8 gassers and previous Diesels. The #1 cylinder is the first cylinder on the crank, 2 is the second, etc. Not the "firing order". If you look at the front of the engine from the side (and can see both valve covers), you'll see the passenger/right side is slightly forward of the other. This indicates the forward side has the odd (1-7) cylinders. If you do the same on any other GM V8, it will be the same, except the leading bank will be on the driver/left side.

Still, on a Duramax, #3 is on the passenger side, second from the front. #6 is on the driver side, third from the front.

[Mark Rinker]

I get it now...I think.

On second read - I think I confused myself...the Pontiac firing order is the same as a Chevy (1-8-4-3-6-5-7-2)...I think it was Pontiac's counterclockwise distributor rotation that goofed me up so many years ago.

...or maybe it was all the beers me and my buddies were drinking at the time...or both... :)

So what is the Duramax firing order?

[DmaxMaverick]

Duramax firing order: 1 - 2 - 7 - 8 - 4 - 5 - 6 - 3

It's been a while for me, too. The BOP cylinder banks may be opposite from other GM's (which makes them similar to the Duramax). It just hasn't come up in a decade, or two, or.....

Still, the method of cylinder location is the same. Whichever bank is forward, has the #1 cylinder at the front.

I have a Pontiac 350 here (from a '70 T/A, in a '68 GMC stepside). Just looked, and the cylinder locations are the same as the Duramax (opposite Chevy). The lead bank is on the passenger/right side.