New plugs wont start now.

[Cainon]

Replaced all glow plugs couple weeks back. Last two days went back to hard starting. This morning just cranks and cranks. Wont start. IP, controller or relay maybe? Glow light comes on but stays on for about 20 seconds

85 f350 6.9l

 

[Cubey]

Do you have a working block heater? If so, try plugging it in for at least 2-3 hours, then try starting. That should rule glow plugs if it starts fine that way.

Are they new Motorcraft plugs? 20 seconds is way too long.

 

[nelstomlinson]

Do you have a clamp on ammeter that does DC? Check your current, if so. You should see starter levels of current on the big, yellow wires feeding the relay.

 

[Cainon]

Do you have a working block heater? If so, try plugging it in for at least 2-3 hours, then try starting. That should rule glow plugs if it starts fine that way.

Are they new Motorcraft plugs? 20 seconds is way too long.

Yes they are. Also block heater works. Before I changed plugs I had to plug it in to get it to start. So I put in new motorcraft plugs. None broken upon removal. Everything went smoothly. I have had a knock recently as well. Seems its fuel related knock and not the bearings.

I will plug it in tomorrow for a bit and see if it starts. I checked the connector at each plug and they are pretty loose. The old connectors do not clamp down like they did on the old plugs. And they are not broken. The tips of the plugs seem to be off.

 

[dgr]

Someone correct me if I'm wrong. Power for the light comes from the same post on the GP relay that runs power to the glow plugs. If that's the case, then the relay is working. Pull the plugs for all the glow plugs, turn the key to on and quickly check for power at the plugs

If there's power on the GP feed side of the relay then you need to trace the wires from it, across the valve cover and to the glow plugs. Common points of failure are fusible links and the wire harness plug on top of the valve cover.

 

[Cainon]

Thanks

 

[Thewespaul]

The light is triggered by the controller not by the relay, so the relay could still be bad. I sell replacement harnesses and conversion kits to upgrade from the stock glow plug setup that are worth looking into.
https://classicdieseldesigns.com/collections/electrical

 

[notenuftime]

^^^^ had a similar issue like this. Fixed it all up with CDD harness.

 

[bbjordan]

Hate to say this, but your new glow plugs might be burnt out already. The 6.9 Glow Plug Controller is notorious for failing in the closed or ON position. It is located at the back of the drivers side head. Pic below.

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You can convert it to a manual system by disconnecting the GPC and running a wire from the Glow Plug Solenoid/Relay to a momentary switch.

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[quickster]

Just for the hell of it, disconnect the fuel shutoff from the harness on top of the pump. Touch a test wire from the + battery to the fuel shut off. See if it's clicks. You never know when these electrical parts go.

 

[Cainon]

Hate to say this, but your new glow plugs might be burnt out already. The 6.9 Glow Plug Controller is notorious for failing in the closed or ON position. It is located at the back of the drivers side head. Pic below.

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You can convert it to a manual system by disconnecting the GPC and running a wire from the Glow Plug Solenoid/Relay to a momentary switch.

You must be registered for see images attach

Plugged the heater in for little over an hour. Fired right up first tap of the key. So it's not fuel. That's good. So control bypass and new relay?

 

[bbjordan]

That's what I did. Or you can upgrade to the new GP system used on the 7.3s.

 

[BeastMaster]

Really quick GP test... Take piece of wire, touch to one big terminal of GP relay, gingerly brush other end across other big terminal, as if you were seeing if a battery has any juice in it.

Expect Sparks.

If you did not get a healthy display, you have either no juice or all your glow plugs are bad.

Well, sometimes you don't have the voltmeter around. Just be careful and don't let the wire weld itself in place.

As always, be prepared for bits of molten copper, and shield your eyes.

 

[david85]

I had this happen to me years ago before I knew any better.

Your new plugs are toast, and your OEM style controller killed them. Likely all of them, since you're not even getting a kick from one or two of the cylinders while cranking.

For a Pre-1987 IDI, anything over 7 seconds of glow time is stressing the plugs. After 1987, the newer controller not only had more reliable operation, but it also had an inline resistor to allow the plugs to heat up over a longer period of time. This gives the prechambers more time to warm up, but also makes it easier to safely power the glow plugs.

 

[Cainon]

Thank you everyone