To start out, I own a 92 F-350, 7.3l diesel, 5-speed, crew cab, dually. My problem deals with the electrical system. I see it happening whenever I start the engine. The voltmeter jumps between, I'm guessing, 12.5 to 14v. It can also be seen the lights - headlights, dome light and dash lights, getting brighter and going dim repeatidly. It usually only lasts until I start driving away. This problem also happens sporadically driving down the road. On a road trip to NE Ohio, with no trailer, cruising around 68 - 70 mph the voltmeter would sometimes do the dance between something like 12 to 14 volts. I could get it to stop by revving the engine and it would go away, but 10 to 20 minutes later do it again and then not again the rest of the trip. I don't know if there is a battery isolator or voltage regulator on the alternator. Any info would help, as this is the first diesel I have owned. It has 270k miles on the truck, but the drivetrain is less than a year old, so I'm hoping for another 270k+ miles of my own. Thanks

 

The problem that you are describing sounds like something electrical is firing up. When it happens do you hear a relay clicking. The reason that I ask is mine does just as you were decribing but only when first started and it's the glow plug controller heating the pre-chambers. I can hear the controller click even with the engine at idle. The glow plugs take if I remember correclty 40 amps to fire, which you will see on a voltmeter. I would suspect a loose connection, bad connection or something to the effect in the glow plug controller system. The reason that I say this is if I am not mistaken the Glow Plug System senses engine temp to determine if the glow plug is needed. I wonder if it's a bad connection that is causing the GPC to fire the Glow Plugs. Check all the wiring out and let us know what you find. This is an interesting problem.
Just my .02

1991 F350 CC Dually 7.3l, E40D, Soup bowl removed, K&N

 

I'll go and check the glow plugs. But I'm not sure if that is the problem, because it happens at times well after the truck has warmed up. I'll be driving down the road for a half hour and the voltmeter would jump around. I'm guessing that the voltage for the glow plugs will only occur during the warming up period or is it constant voltage. Thanks again, for I am new to diesels.

 

[font size="1" color="#FF0000"]LAST EDITED ON 28-Sep-01 AT 11:30 AM (EST)[/font][p]the glow plugs cycle, as in they are turned on for a second, then off for a sec, then back on, off.... you get the picture, when this is happening, watch your voltage meter, it will be dancing, notice your head lights, interior lights, anything electrical.. it will be dancing in sync, listen to the clicking, that is your Glow Plug Controller relay. It is supposed to do this when the truck is first started, becasue the engine is cold, and needs the help to burn the fuel. Then after the truck gets running and warms up a bit, the glow plugs are shut down, until the next time the truck is started. This is where I think the problem is coming in at, in the effect that the Glow Plug Controller system thinks that the glow plugs are needed again. I will dig out my manual and see if it uses a coolant sensor, resetable timer ( which I highly doubt ) or what to determine when the system is needed.

1991 F350 CC Dually 7.3l, E40D, Soup bowl removed, K&N

 

Hey Argve, you described excatly the problem I'm having. I can hear something, the relay, clicking on and off as the lights and voltmeter are dancing. If your manual says anything. That would be a great help. Thanks.

 

ok after wiping the grease off of it, ( in middle of doing rebuild on my diesel ) it's a haynes manual, so not much detail... but it does mention that the system "reads" the engine temp. The book does not break down the system in a diagram, but here is what it has to say...


To test the control unit...

engine and igintion off, connect test light to test terminal on GPC. ( it's the one with the strap connected )

then have someone turn the key on, then watch how long the test light stay on for, then compare to these guidelines.

temp of Glow plug controller ( not surrounding air temp )

-20F -- 35-70 seconds
0F -- 26-60 seconds
35F -- 15-35 seconds
70F -- 7-15 seconds
105F -- 3-5 seconds
140F -- 1-3 seconds

if it falls into one of these slots then they say that the controller is good.


1991 F350 CC Dually 7.3l, E40D, Soup bowl removed, K&N

 

Thanks for the reply. I'm heading outta town so I won't be able to check the controller. But that sure is going to help me. Thanks again.