Long time listener, first time caller.

First, truck is a 1993 F-250 with 7.3L N/A E4OD group 65 850 CCA batteries (as if that helps?) with Motorcraft/Beru GPs.
I bought the truck with a cold start issue where the GPs had to be cycled twice if cold (three times if quite cold) which improved greatly when I replaced the batteries with 850 CCA group 65 Costco Interstates and replaced GPs. Later had to replace mechanical fuel pump.
After all that work it would start and run great for needing some TLC, but eventually GPR death clicking hard start issues crept up again and so I tested GPR for voltage drop through the large lugs and decided to just replace it.
And so then when the key was turned the WTS light would kick on, the relay would click ONCE, the volt gauge would dip, and the WTS light would extinguish as the relay would click once more and the volt qauge would rise again.

Fast forward a year, now I have since learned that GP tip erosion is a sign of the IP being too advanced, or is tip erosion a sign of the relay being kicked on when it should not be?
Looking at the top of the relay, from the top-left large terminal is constant hot Battery +, the small lug top-right is the red wire from the GPC and a double set of Red/Light-green signal wires, then the last two lugs are the large lug for + 'switched' power to the GPs via the resistor strip with lastly the small lug being for the white wire from the GPR that allows the controller to cut the ground connection to the relay effectively disengaging it.

Am I missing something?

• Are the Red/Light-green signal wires going to the top-right small lug on the GPR 12 volts constant hot or is it switched on/off through the wiring harness to the ignition switch?
• The schematics I have seen show a 8-pin connector that is labeled as a Engine to Chassis connector, with battery feed occupying two pins on one end, but the location I have read for it is on the passenger side. Mine appears to be on driver's side and it is absent the battery feed wiring (1993 truck, so 1993 updated harness?)

I have not physically traced the Red/Light-green wires from the GPC/GPR to the connector I mentioned, but I do see two pins with that color wiring. I measured for continuity from one pin to the other, and from each pin back to the small top-right GPR lug, and the wires would appear to be connected, and when I had the ignition on I measured ~12.4-12.5 volts at that lug.


Slightly salty and slightly chaffed.

 

the Red/Lt Green originates at Fuse K in the engine compartment Fuse box.

 

Red/Lt-Grn should only be Hot when the ignition is in Run or Start then.
Then if Red/Lt-Grn is hot with the ignition off and the key out of the ignition, then that would suggest wires have chaffed and are touching together.
But if that is the case, wouldn't the fuel shutoff solenoid click when its lead is touched to the terminal, and when the engine is dead the cold idle solenoid should push the plunger up against the 'throttle' lever on the injection pump?

 

IF it is HOT with the IGN switch OFF then the Engine will not shut down, The Schematic I posted is For a 93 F-250 .. it most likely applies to other models too.

Fuse K should Only be hot in Run and Start position.

The Cold Idle solenoid and the Cold Advance would not necessarily engage IF Fuse K was Hot all the time because there is a Temp switch that controls them.. see the schematic. the Fuel Shut Off would always be energized IF Fuse K is always Hot.

 

Lonewolf, I greatly appreciate you posting the schematic, as that actually looks like the more correct one for the 1993 wiring harness!
When I turn the ignition to run my WTS light comes on but I cannot hear the GPR click at all, but if I connect a remote starter switch between the white wire small lug and a negative battery post I can activate the relay and it clicks on.

I have experienced volt gauge needle sweep and GPR click-click-click from bad glow plugs before, but will enough bad plugs cause the GPR to not activate when I turn the ignition?
I touched a 12 v test light to the male bullet terminal on all 8 and the light glowed readily without any dimming, but when I measured for continuity on a multi-meter some measured 0.000 k ohms (0.00 ohms) and the rest were showing .2 to .3 ohms.

Urgh.

 

individual GP resistance is between 0.1 Ohm and 6 Ohms .. most MultiMeters will not read Resistance in this range. You can search the Specs of the Plugs you have installed and Verify what the resistance should be for a Good Plug.

A common Mode of Controller Failure is that the Driver MOSFET in the control electronics will not Energize the Glow Plug Relay. I reversed engineered these controllers years ago because I saw lots of what I thought was Premature Failure... the wire harness itself is a Resistance element also you will find that it is Fuse link wire. The controller does get FeedBack from the plugs Via the Yellow and Green wire to the controller using the Buss Bar as a Shunt... the controller gets it's power from the Red wire and the White wire is what toggles the Relay.

Much easier to be done with the Crappy Controller and wire the Relay for Manual control. JMHO
IF you go a Manual system then Use 12 Volt Plugs

to make Measurements on Low Ohm resistance I use an Old Fluke 8520A with Kelvin Clips ... this is beyond the scope of these forums

 

I checked the fuse and it is still intact, and the circuit is hot when ignition is in the run position, but I also tried checking the resistance on the "Electronic engine control relay, Diode" in position 12 (position L?) and no matter which way I tested my DMM was saying it had high resistance.
Then the test procedures for isolating GPR or GPC as the issue will be the next thing I need to do, or replace the GPs and test?

 

are you speaking of the Diode in the PCM circuit ?

Do you have Automatic Transmission ???? IF so a dirty test is Pull the Diode and the OD Lamp will glow dim.
But still that diode will test when you put your meter in the Diode Test mode ... 2 K scale for most meters that don't have a Diode test mode.

Since I don't know what Meter you are using I cannot tell you how to use it Properly.

 

Yes, the diode in the PCM circuit. I didn't think about that setting on the multimeter, D'oh.
Truck has the E4OD, and a quick and dirty test works as my DMM is a decent copy of a Fluke meter but it does the job well enough, though an O-scope would be killer cool...

My WTS light does come on, but after reconnecting all the wiring I had disconnected now the dummy volt gauge not longer moves or sweeps. It just touches the 'N' in Normal, whereas it used to 'function' a lot more and would dip when the relay was energized and rise back up when the glow plugs had finished heating.

Wouldn't the GPR click repeatedly if there are glow plugs that are not within specifications?
Or would it not activate at all if enough are just dead?

 

IF the VOLT indicator in the Truck don't dip... then either the GP Relay is not Closing or the GP's are open, and the controller will not Qualify the Relay....

BUT you said you tested the individual plugs with a test light and they all tested good SO that means the controller is not Grounding the small White wire on the relay since you don't see a VOLT drop on the OEM VOLT indicator the Relay is not being energized.


BTW as a Hobby I restore old Tek Scopes and I also post help in the Tek Groups ... if it ain't a Tek then it ain't a Scope

don't be Cornfused by the new CHIT Tek Produces under the Fluke name it's all Chinese Tek sold out and no longer exists they are pretty much Crap nowadays

anyway they are owned by https://www.danaher.com/ and their crap is Chinese

Danaher Setra-ICG (Tianjin) Co. Ltd.
China

 

These past few days I had new negative battery cables made and had a local auto parts store print out the GPR and GPC testing procedures.
Yesterday I installed the new battery cables and I swear I have never seen the headlights GLOW that BRIGHT!

1. new cables for engine block to both battery '-' post
2. new driver's side battery to chassis ground wire
3. new passenger side engine block to frame ground

On the relay I measured Battery '+' at the large Hot terminal to be ~12.5, tested the relay and it would only close if I jumpered the small terminal with the GPC white wire to a ground, however there was absolutely no voltage going through the relay to the Busbar.
So I put the original GPR back on the controller and repeated the test and the relay closed/buzzed, but this time there was voltage at the large terminal where the Busbar connects at, oh, 9.something volts.

lonewolf, you had said : And:
"IF the VOLT indicator in the Truck don't dip then either the GP Relay is not Closing or the GP's are open, and the controller will not Qualify the Relay"
Actually, the volt indicator isn't even budging or moving anymore, just sits in the same spot touching the N in Normal. I pulled the 4 rear GPs and threaded new ones in today, and the relay still did not try to close when
the ignition was in Run. But the relay has internal resistance that is dropping the voltage when I jumper it closed.

BUT you said you tested the individual plugs with a test light and they all tested good SO that means the controller is not Grounding the small White wire on the relay since you don't see a VOLT drop on the OEM VOLT
indicator the Relay is not being energized.
But an incandescent test light can test a glow plug as good as long as its resistance isn't too high, which the correlation between its internal resistance and a dead cold temperature would allow just enough power to flow through GPs to light it, or the GPs have shorted out internally??How would the GPC react if the GPs are shorted internally?


Finally close to feeling like I am going to enjoy my truck once again.

 

Of course the Test light is not a 100% good test for the GP BUT these GP's normally go Open when the Fail, I rarely find one that shorts to Ground. SO the Test light is a pretty good Go/No Go test, but the only way to really know is connect to Power and Monitor Current Per the Glow Plug Specification.

IF your Truck Voltmeter doesn't Budge or move then Maybe the Meter is Bad ???

 

@lonewolf_
I jiggled and re-connected the terminals on the alternator and the volt indicator is moving. And I finally had a day with cooperative weather and enough uninterrupted time that I was able to go through the testing procedures.
In doing continuity and voltage tests the GPR seemed to be the culprit, so I installed a Motorcraft relay DY-861 (as per Diesel Hub' website saying that is the proper part #, though the one I was sold has the terminals 'clocked' different than the original...).
Then with a new 'proper' relay I turned the ignition to run to hopefully hear the GPR click and see the voltage indicator move but the controller still was not closing the relay!

I returned the Motorcraft DY-861 and the first replacement relay back to the store and ended up buying a whole new controller.
Finally now when the ignition is in run the volt indicator moves up to ~N in NORMAL and the relay clicks on and then will click a few more times, with the volt indicator dipping then rising on each click.
I'd say it is working correctly now and fixed, just need to give the batteries a good charge today and try to start the engine finally!

 

so Obviously the old controller is Toast as was mentioned in Post #6

Generally Most just Bypass the controller and use a Manual Push Button.

I have done some Mods for a few that wanted a Timer and installed the Rodgers Relay and a Modded CUCV board

 

Yeah, bad controller.
Those dagmned relays are cheaper to swap, but alas it was the controller. And better than tossing more expensive parts in and getting the same "cannot recreate error on ground" effect.
I find it funny that for the longest time I wanted a cheap excuse to replace the whole controller and lo and behold it has probably been causing some issues along the way, until it finally quit functioning correctly.

Have you done any upgrades to the wire/cable that brings Battery + to the Always Hot + large lug on the GPR?
Could a slightly larger wire with new environmentally sealed heat-shrink tubing and fusible links lower resistance and 'speed' power inflow?