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Discussion Starter #1
Sorry in advance for the rehash. I have read posts and replies for 3 days and
am thoroughly confused with this glow plug relay problem.
I am working on the truck in my signature(420K mi.). Never had a cold start issue since the original
relay died about 10 yrs. ago.
I have done voltage tests as recommended.

What I've got:
Two different new relays- not stancor
Battery voltage to relay is good.
Batteries are good.
Other three terminals- 0 volts with key off.
KOEOff I have 0 volts on large lug out to glow plugs, & full battery voltage to both small lugs.
No discernible 'click'.

Questions: Will the relay activate with the engine warm?
How can I test for PCM failure to ground?
How do I test the sensors?
Obviously I have a good relay, so how do I best proceed?
Thanks!
 

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The relay will still activate with a warm engine. Note that the Wait-To-Start light has nothing to do with when the glowplug relay (GPR) is active (its more of a reminder). To check the GPR, measure the voltage drop across the GPR's large terminals. While the GPR is active (up to 1.5 to 2 minutes after the key is turned to Wait-to-Start) put your meter leads on the large terminals (one lead on one large terminal and the other lead on the other large terminal). The measures how much voltage is being "lost" across the relay. A reading of 0.3V or more indicates a bad relay. Also, check the relay’s control wires (smaller wires) disconnected from the relay for battery voltage at the Red/Light Green striped wire and ground (provided by the PCM) at the Purple/Orange striped wire (check both when the key is turned to Wait-to-Start).

If you are still having starting issues when cold with a bunch of white smoke and you know the relay is good (per the above) and the glowplugs are good, your injector poppets may be worn past specifications. Cheers!
 

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Discussion Starter #3 (Edited)
Thanks Patrick, as I said no voltage at all on second big lug with key on. And the voltage
drop test shows -12.00 ish...
I have Battery voltage to each of the small ones. This testing was done while the
engine is warm. I think I'll re-check everything in the morning with temps.
expected around freezing. I take it the lugs are all interchangeable??
More to come...
 

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You will have voltage to both of the small lugs when the key is on because the relay coil is just a length of wire. To activate it you need the ground signal from the PCM to activate it. The PCM gets its information for the ground from the engine oil temperature sensor along with the barometric pressure sensor that is located under the dash.

To accurately test the activation wires you need to disconnect them and look at them separately. If there is no ground when the key is first turned on then it could be a broken wire or something wrong with the PCM.
 

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Discussion Starter #5
Thanks Bug,
I'm a little weak on electrical so bear with me.
I understand that the PCM grounds one small lug to activate the GPR, but how do I determine if there is ground from the PCM?
 

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The ground will only be there for a short time, up to 2 minutes on a cold engine.

You need to look at it with a ohm meter when the wire is disconnected from the relay. However if the relay does not activate when the key is first turned on then odds are you are not getting that ground.

Now for a work around if there is a problem with the ground that other owners have done if they don't want to go through all the troubles of trouble shooting it or if they have a defective PCM.

You can run a wire from the relay control sided to inside of the cab and install a push button switch is is only activated when you push it. Then ground one side of the switch. Then for a cold start just push the button in and hold it for a count of 20-30 after you have turned the key on and then try to start. This will provide the ground to the relay and should activate the relay sending power to the glow plugs.
 

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Discussion Starter #7
Thanks Bug,
Just to clarify, to test the grounding from the PCM, I put the common lead on
battery ground and the positive lead on the PCM wire to the GPR?
How much resistance should I be looking for?
 

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That's it, just disconnect the wires first.

You should see close to a direct short to ground. I have never measured it or looked it up to see what it should be if it is even listed.
 

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Discussion Starter #9
Bug, I checked out the relay this morning (temp.30deg.) and sure enough,
the GPR works fine. Turns out it does not come on at all when the engine is warm.
The problem is I still have a cold start issue. Now on to check glow plugs via the
harness pins. I suspect I have more than one gone as they are original.
YT
 

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Discussion Starter #10
Update: I do indeed have at least 2 GP's dead. Did not check the harness under the
cold air intake..This may be a spring time repair. I'll plug in through the winter.

On another note: Does it make sense(other than cost) to replace injectors while I am
under the valve covers? No problems with them currently. Runs great and buzz test good.
Is there another test that I can run on the injectors?
 

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Injectors should be fine for a long time.

However since you have the glow plugs out when you are replacing injectors it only makes sense to replace them.
 

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If you wanted, you could check the injector armature clearance (checks for worn poppets). You do this by removing the injector solenoid (don't drop any of the solenoid screws!!!) and measuring the clearance between the square armature plate and the injector body. Under 0.002" is worn while new the clearance is around 0.004". When my 94 with 250k was having cold start issues (extended cranking with white smoke and good Stancor GPR and GPs), my armature clearance was less than 0.002" (some were around 0.0015"). Cheers!
 

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Discussion Starter #13
Right. Thanks Patrick.
That's gonna be a spring time job.
How do you rate the glow plug/injector job?
I have done all my own work on the peripherals of this truck(everthing but front end and flex plate), but have never gone under the VC myself.
Now on to my 99 F350..New Bilsteins and I found a small coolant drip:((
 

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Glowplugs … easy if you can wrench a little. Get a 1/4"-drive, deepwell 10mm socket for the job. 3/8" will have trouble clearing the rockers. Tape the socket to any extensions to make sure it doesn't fall off and down into the head passages (don't ask how I know this).
Injectors … also fairly easy, but read up on precautions such as getting the oil/fuel out of the cylinders to avoid hydrolocking the engine, torque specs, etc. You will need to remove the vacuum reservoir that's attached to the AC/Heater box on the passenger side of the firewall to get the back injector out.
Cheers!
 
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