Hey everyone, I just purchased a 1985 F350 two wheel drive with the 6.9 diesel and a four speed. It has 263,000 miles on it and runs great. The only problem is the hard start, even in 100 degree Dallas weather. It has a switch on the dash bypassing a bad relay. I have done some research on this site and that seems to be acceptable. I flip the switch and the glow plug light comes on, I keep it on for about 10 seconds, turn it off and crank the engine for 10-15 seconds, let off 10-15 seconds and it usually goes on the second try. Would everyone agree the first step is to check the glow plugs? I appreciate any help and have really enjoyed searching this forum the last few days.

 

First if that is for the GPs.......use a momentary/push button switch or you will burn out the GPs. 10 seconds is a long time above 30F.... I would drop to 5 and 5.

Yes check the ohms of the gp with the wire disconnected....... Resistance spec for GPs = .5 to 1 ohm cold. Depending on the ambient temp in your area it may be slightly higher.

 

If the relay is bad, and the switch is replacing the relay, I hope it is a big switch.

Glow plugs draw about 200 amps when they are heating.
Use a momentary switch to trigger the relay.

Are you sure the relay is bad, or was the controller bad?
My relay on my 86 lasted for 440,000 miles, just had to replace it last winter.
However the controller has been dead for years, and I also have manual glow plugs.


To wire the relay for manual control, supply power to the controller terminal when you want to heat the glow plugs.
Don't need to be a big wire or switch, you are only triggering a relay.

Best way, find a terminal in the fuse panel that is only hot when the key is on.
Use that to supply power to a momentary switch.
Then wire from the momentary switch to the relay controller terminal (purple wire opposite the small terminal with the black wire on it)
Done with the wiring.

To operate, turn the key to on, push the momentary switch for 8 seconds, start the engine.

Having the switch on the keyed power source prevents someone from activating the relay and killing the glow plugs or batteries accidently.

Look on the passenger side inner fender.
Near the dip stick look for the connector circled in red.
In this picture, the large orange wires on the bottom of the connector carry glow plug power from the relay to the engine.



Inspect the connector on the end with the large orange wires for signs of melting.
Very common problem, if the connector looks like it has been hot and started to melt, you are not getting full power or possibly any power to the glow plugs.

The only option is to splice the wires around the connector.

 

Sorry about that, the switch is replacing the controller and not the relay. The relay appears to be new. I will change out the switch for a momentary switch this weekend and check the glow plugs and the connector. I have owned and repaired a lot of vehicles but this is my first diesel so I have a lot to learn. Thanks for the comments.

 

If it's been hard to start since you got it, I'm imagining the PO burned out the GP's with that switch.

I did the same thing back toward the beginning of the summer...held the switch a little too long and killed almost all the GP's.

But, I put in a new set of Motorcrafts and it works good now...and I also found out there was an Autolite in there from the PO, glad to be able to pitch that POS.

 

When I first did my manual switch, I also used a switch.

One day I was out wearing insulated coveralls and accidently knocked the switch on.
Needless to say, it did not start that evening with glow plugs.
Fortunately, I was at the top of a large hill, so I was able to get it started before I hit the bottom.

So that night, all new glow plugs and a momentary switch were installed.