Burning out glow plugs

[ClockwerkRat]

This has probably already been answered somewhere, but when I search the results are nothing to do with the specific issue I am having.

Truck is a 1984 F-250 with the 6.9 IDI and manual transmission.

Only modifications are aftermarket air cleaner, slightly advanced timing, and a momentary switch to replace the factory glow plug controller.

The issue I am having is that the glow plugs keep burning out. When I bought the truck it had new glow plugs in it, and after a few months those burned out. I replaced them with Motorcraft ZD1A glow plugs, and after about a month those burned out as well.

I hold the momentary switch down for a maximum of 10 seconds at a time, and a couple of times the glow plug light on the dash stayed on after the momentary switch was released, a couple times for upwards of 20-30 seconds.

This is leading me to think that the relay wired into the momentary switch is sticking, but was curious if anyone has had a similar experience, or any advice.

Thanks in advance!

 

[Comptech]

I'm not absolutely sure but I believe they draw around 80 amps when all eight are working. That's a pretty good load on a small relay.make sure yours is size properly and it sounds like you're on the right track. Depending on battery condition, voltage drop can affect those amp readings pretty dramatically. Ohm's law says amps equals voltage divided by resistance.so when you're working with a 12-volt system that voltage drop of a couple volts means a big difference in amp draw if you do the math. You might be frying the contact shut.

 

[DrCharles]

The inrush current is quite a bit more than that figure, too... remember the resistance increases as they get red hot (and the controller senses the drop in current so it knows when to turn off the WTS light). If you are using the common "ice cube" style relay, they have contacts rated for 30 or at most 40 amps.

 

[ClockwerkRat]

I'll have to doublecheck, but I believe it has the controller replacement kit installed which has a relay similar to Ford starter relays. The big round unit that normally mounts to the fender.

 

[IDIBRONCO]

You don't need that relay or the kit itself. All you need to do is put power to the terminal that the purple wire plugs on to on the factory relay on the passenger's side fender. A push button works just fine. This method will also not put very many amps through your button. I think mine has a 15 amp fuse (I'd have to look to be sure) and the wires are about 16 gauge. That big of a fuse is probably overkill with wires that small.

 

[IDIBRONCO]

Another thing. Yes 20 to 30 seconds is too long for your glow plugs to stay on. Whatever is causing that is most likely the cause of your glow plugs burning out.

 

[The_Josh_Bear]

The GPs pull over 200amps, I measured it a few weeks ago myself!

I've had manual GPs for years and she fires up great at 30*. I also haven't had them burning out so something is wonky with your setup.
Do you have the OEM relay or a different one?

 

[snicklas]

Is the factory controller still in the picture? The one that is screwed into the back of the drivers head. If it is still connected to the relay on the fender, it can still try and run the plugs. This type of controller is known to fail "on" and burn up plugs.

 

[IDIBRONCO]

Is the factory controller still in the picture? The one that is screwed into the back of the drivers head. If it is still connected to the relay on the fender, it can still try and run the plugs. This type of controller is known to fail "on" and burn up plugs.

I thought about that too. I just forgot to mention it. Even if there's a "bypass" kit on the truck. Somebody may not have known to leave it unhooked.

 

[ClockwerkRat]

That was a great suggestion, and honestly something I hadn't even thought of.

I went out and checked, and the factory controller has been removed completely.

There is a wire running from the drivers side battery positive to the momentary switch in the dash that then runs back out to the hot side of the low amp circuit on the relay. It goes through the relay to the purple wire that would normally go to the controller, but in this case they have spliced in a wire to the Glow Plug light in the dash then back out to an orange wire in the same harness. I am assuming this then goes to ground.

Looking at all of this, the only things that make sense to me are that the momentary switch is internally sticking, or that the relay is sticking.

The momentary switch has good action, and to be honest they are so simple that I would be surprised if it was the issue.

I'm thinking my next step is to replace the relay, all 8 glow plugs, then cross my fingers.

Any thoughts or better ideas are welcome.

Thank you,

Joe

 

[riphip]

Update to the new Glowplug Controller if you are replacing all 8 GPs. You will be glad you did. Save lots of $$$ in the future with a system that works consistently.

 

[IDIBRONCO]

but in this case they have spliced in a wire to the Glow Plug light in the dash then back out to an orange wire in the same harness.

That's funny. My glow plug lights have worked just fine without an extra wire running to them.

 

[Thewespaul]

If its not an electrical issue burning out your plugs its likely a fueling issue. Too advanced timing will burn out plugs, and an injector hanging open can do it as well

 

[IDIBRONCO]

and an injector hanging open can do it as well

I had that issue with the wonderful rebuilt injectors that I had before i bought my Moose Jr. and BB's from Mel.

 

[ClockwerkRat]

That’s a good suggestion, I do have the timing advanced slightly to cure a white smoke issue I had when I got it.

The only reason I keep going back to electrical is because of the several times the glow plug light in the dash stayed on with the switch off.