My 1999 7.3 PSD (165,000 miles) died on the highway the other morning when it was -20 F. Fuel gelling was the likely cause. Dummy forgot to add anti-gel before fueling the week before. I got the truck to restart and ran it missing and sluggish to get off the pavement. Now it will note restart.


Here is the situation currently:


Plugged in block heater.
Added 911 Red to the tank.
Added 911 Red and diesel to the fuel filter bowl.
Filter bowl drains and refills. No gum, crystals of junk in filter.
Replaced Glow Plug Relay.
Cranks but will not start.


SO, I want to check if the GP Relay is getting orders from the PCM. Here is the question about trouble shooting this.
I remove the two small wires from the GP Relay,
With jumper wires, apply voltage from the battery across the two small terminals. If the voltmeter reads voltage on the big output terminal the GPR is OK and the problem is in the PCM circuit that tells the GPR to activate. Right?
I do not understand what "apply voltage from the battery across the two small terminals" means exactly. What do I actually do here? Does this mean run a wire from the battery to one of the small terminal and then connect to the two small terminals with a jumper? I do not want to screw this up and damage the relay.


If the GPR is activating then the next step it to test the GPs at the connector.

If anyone can make this a little clearer I would appreciate it. Thank you for any advice.

 

The two small lugs on the relay are the power to the coil. One is positive and one negative. The positive wire from the truck should be hot whenever the ignition is on. The other wire should carry ground while the PCM is commanding the glow plugs on. If you want to power the relay independent of the PCM, remove both wires from the small lugs and connect one to +12vdc and the other to -12vdc. The lugs are isolated from the case and each other, so as long as both of the truck wiring harness wires are disconnected it doesn't matter which lug gets positive and which gets negative. Do not connect the small lugs to each other.

 

Thanks.


I wanted to be clear on this and did not know what the small terminals were exactly.


The GPR tests hot with the ignition switch on so the starting problem may be the glow plugs themselves. They were replaced 87,500 miles ago and may have failed with my repeated attempts to start while stalled on the road side.


I wish the GP pin connector was more accessible for testing!


Thanks again!

 

I guess I can test each plug at the plug. Resistance should be less than 1.0 ohms and grouped together.


I sure hope that plugs are the problem. Cam sensor was replaced about 60,000 miles ago.


I guess I will have to move on to the fuel injector?

 

I would jump the relay with a big screwdriver. If you get a hot spark when making the connection you have a decent glow plug draw. This is not a calibrated test but it is a start. If you get a good spark hold them jumped for a while and see if it will start. If it does there's a good chance that the GPR is the problem and that's an easy fix.

 

A new glow plug is between 0.6 and 2.1 ohms. Testing them together isn't likely to tell you much. The easiest place to test them individually is at the valve cover gasket connector. The front and rear-most 2 pins are the glow plugs. They'll be the largest 4 pins in the connector.

 

Just for kicks, it may not be a bad idea to check your engine oil level

 

You made a good point. The dip stick showed low by a quart plus. Topped it up. Is there a sensor reset or something else I need to do about this?

 

No, there's no sensor for oil level. A quart low won't keep it from starting.

 

Sorry if I missed it, but did you get your truck into a warm garage? If the fuel gelled the only way to get it moving again is to warm the whole truck up.