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Glow Plugs - 5v vs. 7v
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=85408		 Page 1 of 1
Author:  thesameguy [ Tue Oct 11, 2016 1:25 pm ]
Post subject:  Glow Plugs - 5v vs. 7v
Is there any reason you can't use a multimeter on the glow plug module to determine if you've got a 5v vs a 7v system? From looking at the wiring diagrams and reading the FSM, it seems the ECM produces a 5v or a 7v high-amp output via PWM (which is why it's a programmable voltage) which hits the module at terminals 9 and 10, and the module (fancy 12v relay ;) ) then switches that to terminals 1,2,3,4 out to the glow plugs. <5v at 1,2,3,4 is a 5v system, >5v at 1,2,3,4 is a 7v system. Is that fair?

(I do realize the bands on the plugs can indicate the voltage, but I can't see any, so I'm looking for an alternate method that doesn't involve taking things apart :) )
Author:  thesameguy [ Tue Oct 11, 2016 5:16 pm ]
Post subject:  Re: Glow Plugs - 5v vs. 7v
Meh. Nevermind. Just pulled #1 out.
Author:  mass-hole [ Tue Oct 11, 2016 5:55 pm ]
Post subject:  Re: Glow Plugs - 5v vs. 7v
thesameguy wrote:
Is there any reason you can't use a multimeter on the glow plug module to determine if you've got a 5v vs a 7v system? From looking at the wiring diagrams and reading the FSM, it seems the ECM produces a 5v or a 7v high-amp output via PWM (which is why it's a programmable voltage) which hits the module at terminals 9 and 10, and the module (fancy 12v relay ;) ) then switches that to terminals 1,2,3,4 out to the glow plugs. <5v at 1,2,3,4 is a 5v system, >5v at 1,2,3,4 is a 7v system. Is that fair?

(I do realize the bands on the plugs can indicate the voltage, but I can't see any, so I'm looking for an alternate method that doesn't involve taking things apart :) )


I think you would need a pretty decent scope to see the actual voltages. I know you can see that there is a voltage but it doesnt neccesarily correlate to what the glow plugs are doing. The whole purpose of the PWM to allow it to output a certain voltage based on a constant input(12+V) from the battery? I guess I assumed that if you have a 12V input and you only have it on for 7/12's of the time then you get an effective 7V amount of power(heat). Either that or maybe there is a capcitor in the fancy relay which has a known charge and discharge rate and they can use the the square PWM output to create a sinusoidal like signal out of the capacitor that hovers around 7V.
Author:  Ceearedeedriver [ Wed Oct 12, 2016 9:19 am ]
Post subject:  Re: Glow Plugs - 5v vs. 7v
The plugs are rated for RMS voltage so failing a scope a true RMS voltmeter will tell you what you need to know. Bear in mind that there are different phases of the startup sequence where different voltages are applied by varying the PWM control signal.
Author:  thesameguy [ Wed Oct 12, 2016 12:53 pm ]
Post subject:  Re: Glow Plugs - 5v vs. 7v
I have both, but ultimately it ended up not too bad to pull the #1 plug. The big hangup was the connector, which I could not reach and didn't want to break. Ended up using a valve stem seal removal tool, which worked like a charm.

The cavity seals on the back of the glow plug module are seated very deeply and I didn't feel like piercing them or the insulation and introducing a vector for moisture, so the plug had to come out.

Found this:

Image

I grabbed a similar-diameter metal rod and gently let it down the glow plug bore. What you see in the picture is that I have about 6 3/8" depth before the rod makes contact with anything - I'm going to assume that's the piston. I can only believe the glow plug crumbled into the exhaust and got blown out on the highway somewhere. The "break" on the plug is the same color & texture as the rest of it, so I am pretty confident it didn't break on removal and has been broken a while.

It's an original 7v Bosch plug, which I was pretty sure I was going to find based on the original module's part number (AA vs. AC). I ordered a new set from idparts - if one broke they're probably all in bad shape. Here's to hoping they all come out cleanly.
Author:  joelukex4 [ Thu Oct 13, 2016 9:59 am ]
Post subject:  Re: Glow Plugs - 5v vs. 7v
Why did you go searching? Did you have a code for the #1 glow plug?
Author:  joelukex4 [ Thu Oct 13, 2016 10:10 am ]
Post subject:  Re: Glow Plugs - 5v vs. 7v
Sorry, found the answer in your other post
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