Powerstroke 7.3 glow plug relay

[John T]

Just replaced my Glow plug relay for maybe the third time since I've owned the truck new in 95...

This time the hot wire post was getting smoking hot....
replaced it and all is fine again..

But,
I never liked the way the GPR stays ON for so long after the truck starts....
just watch the battery gauge.. it continues to draw big sometimes close to 2 minutes...

So tell me if I'm nuts,
Heres my idea...

I run a battery shut off switch through the firewall to the dash where I can reach it conveniently. cables go to the relay/battery wire.

start the truck:

switch ON relay power
turn key/wait to start
start truck

turn off switch.

OR,
switch ON power
wait to start...

turn off power so starter gets full power...
start truck.

either way, when the truck starts, you kill the power to the relay... possibly saving the GPR and the glow plugs un needed use.

If you happen to leave the switch on, no problem... the truck justs acts like it normally would.

I don't think the power wire to the PCM ? will know the difference...... it will just time out and shut off the relay like normal..


Do you see any flaws in my thinking here?

[Insaneride]

I have a dodge so it uses a fuel heater instead of glow plugs. I do believe the batteries get taxed and I wait for the timer before starting. I just put in new batteries but a switch couldn't hurt and less taxing on batt's.

The only flaw I see is the hi amp switch you show could bypass the solenoid altogether. A smaller switch should be used to energize the glow relay but then I don't have a ford so I'm armchair wiring.

Parking with grill facing the sunrise helps a little but not till noon.

[John T]

Hmmm
You just gave me an idea
Instead of running 2 big power cables to the dash of the truck

It would probably be smarter to run a second relay/heavy duty relay to the glow plug relay to a toggle switch on the dash


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[Insaneride]

Yep, a second relay.

[MetalMan23]

If it was me I wouldn't touch it, in the winter you're going to want the glow plugs to stay on longer, 7.3s don't like the cold.

[bigb]

Are you using the Motorcraft relay or the Stancor?

[John T]

Are you using the Motorcraft relay or the Stancor?

Motorcraft


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[TJS]

Why not just have a switch that removes the ground side of the coil side of the relay. You would interrup that ground circut with a switch. Once it starts open the switch and the coil side on the relay will open and remove the power from the output power side of the relay.

[John T]

If it was me I wouldn't touch it, in the winter you're going to want the glow plugs to stay on longer, 7.3s don't like the cold.

The relay and glow plugs will continue to stay on for as long as necessary in the cold weather

The only difference will be
I will have the ability to cut the power to the relay once the truck starts

Instead of driving down the road for a half mile with the volt gauge reading 10 V


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[jrb06]

The glow plug relay measures the resistance of the glow plug circuit in a series type circuit. Based on the resistance it measure's it controls the on time. Quick refresher of electrical, as something heats up the electrical resistance increase's so as the glow plugs heat up the resistance goes up. Once the pre determined amount of resistance/heat measured by the relay is achieved the relay shuts off. The main processor looks at ambient temp, oil temp, and coolant temp to determine when glow plug assist is needed and may command the relay to turn back on but it cannot control the amount of on time as that is determined by the measured resistance of all 8 glow plugs.

So more to the point what causes relays to burn out fast is this resistance thing. As glow plugs get older they naturally start to increase in resistance requiring more amperage to be drawn (remember ohms law volt and amp correlation) on the module which in turn causes more heat to be placed into the module since it is supplying the voltage and amps and the excessive heat burns it out. Now when a glow plug burns out in this circuit it causes more voltage and amperage to go to the reaming glow plugs which causes them to get hotter faster and reach the total resistance level faster and then will shut the glow plug relay off faster. It starts to create a domino effect as the higher amperage makes the glow plugs to hot to quick and then more burn from being over amped you might say. You notice this when the wait to start light goes off much quicker than before, and this will cause a hard start and a lot more white smoke at start up. I know you said it was staying on to long but your burn out problem may be related to glow plug drawing to much amperage. Glow plugs a re a maintenance item and anytime after 70,000 miles it may require replacement.

[mike837go]

Why not just have a switch that removes the ground side of the coil side of the relay. You would interrup that ground circut with a switch. Once it starts open the switch and the coil side on the relay will open and remove the power from the output power side of the relay.

Good idea electrically. No new heavy-duty parts needed. But I would worry that the PCM would start throwing a Glow Plug Relay Coil Fault code when it starts seeing the open circuit.

Personally I'm with you John, I hate it when the engine has started and the glow plugs are still on. Give me a heavy-duty switch to run the glow plugs manually any day!

[John T]

Why not just have a switch that removes the ground side of the coil side of the relay. You would interrup that ground circut with a switch. Once it starts open the switch and the coil side on the relay will open and remove the power from the output power side of the relay.

I suppose that might work
But that wire runs to the PCM
And also to the wwait tostart light

I'd rather not mess with that

I like my way better

LoL


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[John T]

This particular relay is isolated

It does not ground to the truck


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[John T]

The glow plug relay measures the resistance of the glow plug circuit .

Ummm
NO



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[BaTu]

If you have a simple relay (GPR) then the PCM knows nothing about GP resistance. BUT if you have a GPCM (Module) it does. I'm guessing you have the GPR.

As for your plan

No, No, and NO!

First, you Need the plugs on after it starts to run smoothly. The cly temps aren't up to what they should be (especially with split/shot injectors where just a tiny amount of fuel is initially introduced). The PCM decides on how long they're on based on temperature. The only time they would be on for 2mins would be in the Very cold and that's the Max the PCM is programmed for. Also, there is No relationship between the WTS and GP function. The WTS is a dumb timer, it's on when the plugs aren't and often off when they're on.

The idea of switching the Battery power to the relay is way too expensive and complicated. Controlling the relay would be a much better thing to do. When the PCM decides to energize the GPR it simply completes the path-to-Ground to the relays coil (mostly bases on Engine Oil Temp) and all you'd have to do is to interrupt that wire to break the path and shut the relay off.

But what you should do is to leave the whole system Alone and let it do what it's designed to do

[mike837go]

I=E/R Georg Ohm is spinning in his grave.

If voltage stays constant (E=12 volts) and resistance increases (R goes up) then current (I) decreases. Total power consumption will therefore decrease.

Correct in your scenario, except when a heating coil (glow plug) heats, the resistance decreases and therefore the current increases. Heating the resistor until thermal runaway; To the limit of the power supply.

I did the research on how a manual glow plug system is supposed to work when I rebuilt the electrical system on my Diesel compressor.

An additional heating element "Glow Plug Indicator" is placed between the heavy-duty momentary switch (or relay) and the glow plugs.

Once activated the glow plugs heat up, dropping resistance and calling for more current. The Indicator (big-azz-heating coil) glows when the glow plugs are drawing maximum amps. At that point, stop heating and spin the engine. Running engine within 10 seconds.

[TJS]

If you have a simple relay (GPR) then the PCM knows nothing about GP resistance. BUT if you have a GPCM (Module) it does. I'm guessing you have the GPR.

As for your plan

No, No, and NO!

First, you Need the plugs on after it starts to run smoothly. The cly temps aren't up to what they should be (especially with split/shot injectors where just a tiny amount of fuel is initially introduced). The PCM decides on how long they're on based on temperature. The only time they would be on for 2mins would be in the Very cold and that's the Max the PCM is programmed for. Also, there is No relationship between the WTS and GP function. The WTS is a dumb timer, it's on when the plugs aren't and often off when they're on.

The idea of switching the Battery power to the relay is way too expensive and complicated. Controlling the relay would be a much better thing to do. When the PCM decides to energize the GPR it simply completes the path-to-Ground to the relays coil (mostly bases on Engine Oil Temp) and all you'd have to do is to interrupt that wire to break the path and shut the relay off.

But what you should do is to leave the whole system Alone and let it do what it's designed to do

See post #8. However the PCM sends the ground and if interrupted it may kick a code. So I would say then create an interupter switch from the ignition 12+ switch(12+trigger to the coil side). You could also hide this swtich and possibly use it as an antitheft, albeit there are many other ways for anti-theft.
T.J.

[mike837go]

Is the heating element a ceramic? All true metals have a positive temperature coefficient (some exotic alloys are nearly constant resistance with temp). Ceramics can be made with negative tempcos (thermistors being one example).

When dealing with classic parts (metallic heating elements, most with metallic covers), 12V batteries, as few relays as possible and no "electronics" there is only 1 temperature coefficient to worry about.

[BaTu]

See post #8. However the PCM sends the ground and if interrupted it may kick a code. So I would say then create an interupter switch from the ignition 12+ switch(12+trigger to the coil side). You could also hide this swtich and possibly use it as an antitheft, albeit there are many other ways for anti-theft.
T.J.

It's a "dumb system" all the PCM knows is that it's semiconductor inside is switched. You're not going to set a code. In fact, this is a mod many people have done for the Opposite reason. That is, a PCM that isn't activating the GPR (because something's wrong) has been bypassed by adding the sw to supply the Ground path manually (and those people can tell you if it's switched to "open" as soon as the engine starts, it runs rough and makes white "smoke" at the tailpipe from unburned fuel).

Since the engine will start without working GPs, not gonna be much of an anti theft though.

I did read your post, I was agreeing with it, didn't mean to ignore your contribution

[jrb06]

Ummm
NO

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Never mind. You apparently are a certified Ford Diesel tech my bad. My explanation was a basic understanding of how the system operates not a in-depth engineered process that goes into detail. You cannot just assume how a system works hell you want to bypass something that was designed to work a certain way.

[TJS]

It's a "dumb system" all the PCM knows is that it's semiconductor inside is switched. You're not going to set a code. In fact, this is a mod many people have done for the Opposite reason. That is, a PCM that isn't activating the GPR (because something's wrong) has been bypassed by adding the sw to supply the Ground path manually (and those people can tell you if it's switched to "open" as soon as the engine starts, it runs rough and makes white "smoke" at the tailpipe from unburned fuel).

Since the engine will start without working GPs, not gonna be much of an anti theft though.

I did read your post, I was agreeing with it, didn't mean to ignore your contribution

Ha. Maybe you could follow the smoke screen the wanna be thief leaves.

[John T]

Mission accomplished.

I interrupted the power wire from key switch power / to relay. ran it to a toggle at the dash.

works perfect.

flip the toggle, turn key and start as normal. (wait to start light)

when the truck starts, Flip the toggle off and the volt gauge jumps right back up to normal.

works for me.

carry on...

PS:

here is what the GPR looks like. (Genuine FORD parts)
if you are not familiar.

[John T]

Never mind. You apparently are a certified Ford Diesel tech my bad. My explanation was a basic understanding of how the system operates not a in-depth engineered process that goes into detail. You cannot just assume how a system works hell you want to bypass something that was designed to work a certain way.

Thank you, Doctor Science.

[bigb]

The only reason the glow plugs stay on after starting on the Powerstroke of the era we are discussing is to reduce initial startup smoke. That's all. They stay on for an extended period of time up to two minutes depending on the EOT. That's from the FSM.
A lot of Powerstroke owners use the White Rogers Stancor relay which is more robust and lasts a long long time. It fits where the OEM one was with a little coaxing. Mine's been in there for about 8 years now.

I don't recall my system voltage dropping as low as what yours does once it's running, I'll have to check that. Wonder if you need a new alternator or batteries?

[Michael ray]

You might be able to upgrade to an ambulance alternator and then you could run accessory lights and such cold and still make plenty of power. My 7.3 is in a warmer climate...I fire it up and glow plugs almost immediately turn off. It still has the factory relay