Discussion in '6.9L IH & 7.3L IDI Diesels' started by Isaac Ristow, Dec 6, 2020.
I wonder if you could put an inline resistor to trick the controller back into it's operating range.
I plan on putting the bosch 80034 into my truck, and will play with the controller to see if I can get it to function.
All you need to do is cut notches in the big Z resistor on the controller to increase its resistance and the controller will think it’s seeing a higher current draw then what the plugs are drawing. If you look at the Z resistor you will find a hole close to one of its ends, that’s how the factory “calibrates” the resistance.
For example, the big Z resistor is say 0.005ohms, the zd9 draw ~200 amps, the Z resistor will drop 1 volt across itself (200amps x 0.005ohms = 1 volt). Now the new plugs say draw 100 amps, you need to notch the Z resistor till it dropped 1 volt across itself or became 0.01 ohms (100 amps x 0.01 ohms = 1 volt). This way when the controller reads the voltage across the Z resistor it sees the same voltage and thinks the same current is flowing to the plugs.
Are those the actual values? 0.005 ohms and 200A?
If yes, then in theory it should work. The only catch is to avoid taking off too much material and over-correcting. Although a parallel resistor could be used to calibrate for glow time once you get it "about right".
It also means anyone can probably make this style of controller work with my ZD1a glow plugs.
At least with the 80034s, over correcting shouldn't be a problem, just call it assisted warmup.
Unfortunately the meter I have only reads down to 0.01 ohms so I can’t directly measure the Z resistor resistance but doing some calculations you can get fairly close. I’ve measured a few dozen zd9 glowplugs and they are all around 0.25ohms cold, take 8 of them in parallel and you get 0.03125ohms, now there is wire losses, connector losses, the Z resistor loss and battery voltage sag that you have to account for in calculations.
For example if I assumed the battery stayed at 12v and there were no wire/connector losses then the current flow would be (12v / 0.03125ohms = 384 amps) the glowplugs would use but realistically if you included the wire/connector losses and battery sag the plugs are getting 8-10v and your around 250-300 amps.
The easiest way to adjust the Z resistor is to measure across each end with a multimeter on the volts setting and see how much voltage you get at the beginning of the glow cycle and do same with the new plugs and try to match that voltage and the controller should keep the same glow time if you get it correct.
If you over shoot the notching of the resistor the plugs will stay on longer then needed and you will either have to replace the Z resistor, parallel wire across it or patch the Z resistor and slowly notch it again till you hit the target voltage.
Or live with it if its still in a safe enough range , some glowplugs/people like to afterglow. The 80034 sound like a proper 12V plug so you should be able to run them extended periods. didn't someone say they did 18 minutes before quitting here?
Great info guys!
Yeah, you would need a DRLO or "Ductor", which is basically a milliohm meter. Not something you tend to find at a low price. But you could probably get close enough with the method described.
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