Stancor relay 586-902 vs OEM GPR warning........Maybe??
 

IMO you need to be careful with the larger Stancor relay, it may melt the GP's if you treat your rig like me....ie. drive away with the GPR still active or use the AIC for warming the engine.

FSM quote:Verify this by increasing the engine RPM w/the GPR active....watch the battery voltage dip up and down....or the head lights go bright and dim. This is the GPR being switched on/off by the PCM.

This does not happen with the STANCOR relay #586-902 no matter how high you rev it.

Anyone else notice this?? or did I screw up....again haha

A relay is a relay. The stock GPR should act just like the Stancor GPR if both are wired correctly. The only difference should be the amp carrying capacity of the contacts and the quality of the unit.

I have never noticed the glow plugs being switched off and on with a Powerstroke, just off after "x" time but maybe I am just not watching close enough? My son's 92 IDI switches them rapidly once they reach a given temp.

While doing some trouble shooting for cold start issues I wired an indicator light to the switched side of the GPR. I noticed that after it started up the light did flash off & on. about 3 sec. off/3 sec. on. I could also notice the off/on cycle on the volt meter.

I agree. A relay is a relay. If the pcm is switching on and off the stock one it would be switching on and off the stancor as well. I dont understand how the pcm knows how much voltage the gps are using because I don't think there is feedback from the glow plugs to the pcm at least nothing I know of?

Maybe your alt is starting to go bad? Or your stock gpr had a bad contact inside?

The PCM could be reading what voltage the alternator is charging at and cycle the GPs if that voltage reaches a certain point. I don't know. Just sayin'

Jim, it's possible if the PCM is monitoring current draw through the GPR coil. Different relays would have different coil resistances thus different current draw. It would be interesting if you could measure the actual coil resistance on the "Stancor" relay and compare that to OEM coil resistance.

In any case, good observation.

If that was the case and the stancor was sending more voltage through to the glow plugs wouldn't the pcm shut off the stancor more so than the stock one?

Except on cali trucks PCM has no idea how much voltage is actually going to the glow plugs. I suspect a higher "contact" rated relay might have a higher resistance coil. No proof, just speculation based on Jim's observations.

I would think the current draw for the coil would remain constant whether the engine is running or not. I don't think this parameter would be used by the PCM to trigger the ON/OFF cycling of the GPs.

Jim makes an excellent point. Granted a relay is a relay. Either works or not. But the efficiency of different relays is the question. I am of the impression that the PCM sends ground to the relay until oil temps reach a certain level. That may not be correct but that is my assumption. Like the IDI engines and coolant temperature.

If you fired up and went to high idle immediately I can see the higher voltages coming into play. Even though for a very short time.

Gonna have to do some more thinking on this one.

Actually, it's a good design practice to monitor the voltage/current at the device you want to control. Stancor web site indicates it is rated at 12volts @ 8 watts. A little math indicates the relay coil resistance is about 18 ohms.

@ 18 ohms and 11 volts current = .61 amps
@ 18 ohms and 14 volts current = .77 amps

If OEM relay was 15 ohms (don't know, again just speculating) then ...

@ 15 ohms and 11 volts current = .73 amps
@ 15 ohms and 14 volts current = .93 amps.

If - when it stops raining hard I'll go out and measure my OEM GPR coil resistance.

I dont have mine shut on and off, but when the Relay is on, oh man does it pull on the alternator.
Winshield wipers are useless if the GP's are on in my truck too. They go at the speed of slow, even if i'm driving and the GP's are on, they still don't function right till the GPR turns off.

I've never had mine turn off and on.
And far as my knowledge goes, relay is a relay.
But Jim's got the right idea up above us here.
I'd go out and measure my old GPR, its still .... no wait, I just took it to the scrap yard. It was bad anyways.

Thanks for a good topic of Discussion Jim.

Good stuff guys.....I think Hussler has it right (cali model)......That darn shunt never made sense to me. Electrical ain't my strong suit....can you tell haha

Every PSD I've ever seen will turn off the GPR when you rev the engine.......just like the quote from the FSM above. FYI: The dual alternator models deactivates one of the alternators when the GPR is on, most likely for the same reason.

For now, I'm just letting the engine idle until the GPR goes off. No need to drop a GP tip into the cylinder.....

EDIT: I found this in the FSM about the cali engine.

DTC P1395 or P1396 will set on the bank that is reading less than 39 amps.
Does this mean the PCM monitors the amp draw vs voltage??

Hmm. Mine doesn't shut off when you rev while GPR is on.....

I plan on doing the shut off wiring.
No reason to use GP's when the motor is hot.
That stuff is just silly.