I have a 1997 F350 XLT, PSD. I have been reading through a lot of posts regarding glow plugs and cold starts. I am pretty sure my truck must have some glow plugs that are not working. When it is cold it takes a few attempts to get it to start, this is after a significant amount of time for the plugs to warm up. Then it will blow white smoke for about 2 minutes. I have notice the ammeter and it does show a draw when the key is turned on and then returns to normal after awhile. This leads me to believe that some of the glow plugs must be working and that the relay is still good. I tested the glow plugs the way the Chilton’s manual suggested. Using a test light connected to the positive terminal of the battery and with the key off touch the other end of the light to each glow plug terminal. If the light comes on the plug is good. All plugs checked out using this testing method. To me this test only checks to see if the plug is grounded properly, therefore is not an accurate test. I am leaning towards replacing the glow plug unless someone has a different solution. I also have four 4 pin connectors that lead under the valve covers going to the glow plugs; I believe the outside wires are going to the glow plugs. The outside wires are brown and that is the color the Chilton’s manual indicates is the glow plug wires. I hooked up my voltmeter (set on DC) to the negative terminal of the battery, turned the key on and checked the 4 pin harness to see if I had any DC current. No reading. Should it not have 115 Volts DC? One more question, where is the glow plug relay? In the main Fuse/relay box under the hood on the left side, I find 4 relays. According to The Ford operators manual none of these are the relay in question. I do have two more relays next to the box closest to the fire wall that I can’t seem to find in any of my manuals. Is one of these the glow plug relay and if so which one?

I do apologize for beating the subject of glow plugs to death yet again.

Thank you for all the Info,
Matthew Chonka

 

If you have a good ohmeter you can try and get a reading on each plug. If no resistance or open it's bad. A resistance, but it will be very low, would be a good plug.

On my 95 the glow plug relay is next to the fuel filter. It has two large posts -- one is hot all the time -- the other when the key is turned on.

 

First of all it should be 115 volts a/c. As far as the test lite your are correct it is looking for a ground which if a glowplug is good the lite will light if not the glowplug is bad or open. With an ohmeter it should read .6 to 1.8 ohms to ground. You might also want to check the relay and when you turn the key on you should have power 12 vdc on both sides of th big post of the relay.

 

One other thing to try is to cycle your glow plugs twice, depending on how cold it is out.If this doesn't help I would check the glowplug relay, I had one on mine that would make the volt meter drop on my truck, but it was no good. If these don't produce any results, there might be something deeper, such as a weak high pressure oil pump that is not delivering enough pressure to give your injectors enough fuel right away, causing a hard start situation or a rough start.

 

Will your truck start better when you have plugged it in at night? Are all of your connections on your glow plug harness ( into the valve cover gasket) sound. Any smoke on a warm start? Some of the things that were wrong with my PSD when the harness had burned connectors on it.

 

It seems to start better if I cycle through the glow plugs with the ignition a couple of times. No smoke on warm start ups. All the connections seem to be sound. I haven't checked the resistance of each plug yet, maybe today. I do want to check the relay but still having trouble locating it.
marspec where is your relay, your sentence got cut off.

 

On my 95 the relay is forward of the fuel filter under the cover. When the cover is up you have to look under the forward fixed part slightly to the passenger side. I have to take my cover off to get a voltmeter on it.

 

So if it does seem to start better with the block heater plugged in, does this indicate glow plug malfunction?

 

The only place you would have 115 VAC is at the block heater. If you are testing the glow plugs, you would be looking for ~12 VDC at the harness. If the ambient temperature is warm, or the engine is warm, the relay may not latch and energize the glow plugs. Its up to the PCM to make that decision.

 

Can anyone answer this question?

 

Normally, yes it does.

 

Mucho thanks.