Glow plug troubles... again

[firehonomichl]

Ok guys so I have an 89 f250 7.3 with a ZF5 and The glow plugs are about 8 months old I tested them over the weekend and the glow plug harness is new and I put a glow plug relay on Sunday and still the WTS light comes on for about 2 seconds and click click click click for a bit and it’s hard starting... am I missing something?!

 

[franklin2]

The only thing left is the controller. I have the exact same truck that you have. I went to the dark side years ago and put a manual pushbutton on mine. Much better than that controller.

P.S. Have you checked your plastic wiring plug over near the pass side valve cover? It's famous for melting and giving a poor connection to the glowplugs. I had to cut the wires out of my plug and remake them up.

There are two fat yellow wires that feed the glowplug system running through that plug. It's sort of in front of the A/C coil sticking out of the firewall.

 

[firehonomichl]

Thanks I’ll have to look at that!

 

[BeastMaster]

Do you have an electric fuel pump? Can you hear it during the glow plug cycle?

Mine noticeably changes pitch when the glow plug relay kicks in and out. If you get the glow plugs to light off by force, that is manually routing battery to the plugs by whatever means, make a mental note of how much the pitch varies. That may help you in knowing if your battery and plug circuit are normal.

Note I have a noisy Carter vane pump. I don't know if other pumps make as much whine as mine does. It's done this for years. It was my prime evidence of glow plug relay contact failure when the main contacts failed to make, and I was getting a click, but no juice. The pitch didn't change like it had done in the past.

Dead giveaway the plugs weren't getting juiced.

 

[aggiediesel01]

P.S. Have you checked your plastic wiring plug over near the pass side valve cover? It's famous for melting and giving a poor connection to the glowplugs. I had to cut the wires out of my plug and remake them up.

There are two fat yellow wires that feed the glowplug system running through that plug. It's sort of in front of the A/C coil sticking out of the firewall.

For the brick nose trucks one of the best things you can do for your GP system is to get those two wires out of that plug and replace them with a single heavy cable going directly to the GP relay from the hot post of the starter relay (where the yellow wires start now). Ford did exactly this in ‘92 with the body style update, much better reliability for such a high current connection. After this many years and start cycles those pins have almost no capacity for handling that much current anymore. Every one I’ve come across has lost its temper, the pin and socket are soft and flex too easily to maintain a good electrical connection.

 

[firehonomichl]

I have just to OEM fuel pump

 

[franklin2]

For the brick nose trucks one of the best things you can do for your GP system is to get those two wires out of that plug and replace them with a single heavy cable going directly to the GP relay from the hot post of the starter relay (where the yellow wires start now). Ford did exactly this in ‘92 with the body style update, much better reliability for such a high current connection. After this many years and start cycles those pins have almost no capacity for handling that much current anymore. Every one I’ve come across has lost its temper, the pin and socket are soft and flex too easily to maintain a good electrical connection.

I have heard you guys talk about Ford doing that. How did Ford protect that wire? The two smaller wires had two fusible links, one for each wire. Do they make a fusible link large enough for the one large wire?

 

[79jasper]

Iirc, it still has the 2 fusible link wires, but then ties into one larger wire.

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[chillman88]

I have heard you guys talk about Ford doing that. How did Ford protect that wire? The two smaller wires had two fusible links, one for each wire. Do they make a fusible link large enough for the one large wire?

Regardless of how Ford did it, I've been using a large inline fuse (GM used them inline with the alternator on some vehicles). You can get a universal housing and fuse relatively cheap. If you want, I can look them up and post a link for you.

 

[franklin2]

Regardless of how Ford did it, I've been using a large inline fuse (GM used them inline with the alternator on some vehicles). You can get a universal housing and fuse relatively cheap. If you want, I can look them up and post a link for you.

I know what you are talking about, my 99 tahoe has one up at the radiator shroud. Am I remembering right and it's 150 amp? What size are you running that holds without blowing?

 

[chillman88]

I know what you are talking about, my 99 tahoe has one up at the radiator shroud. Am I remembering right and it's 150 amp? What size are you running that holds without blowing?

I'd have to look. It's either 175 or 200. The 150 lasted about 2-3 starts

 

[79jasper]

Initial amp draw can be 200 amps, then tapers down. So that's what I would aim for.

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[aggiediesel01]

Please don't add a "let's see if this doesn't blow" fuse to your glow plug system.

You can get the fusible link wire from a number of sources but this seems to be the most commonly available packaging.

https://www.oreillyauto.com/detail/...-fusible-link-universal/flc14bp/4414532?pos=3

The wire in the package is labeled 2.0 sqmm

For the GP system Ford used two 4-5" runs of the 2.0 sqmm fusible link wire that was soldered onto maybe a 4awg wire headed to the GP relay.

Your GP system shouldn't pull more than 80amps for a short duration I think? Maybe even less I can't remember off the top of my head. Fusible link protection is almost purely for short circuit protection, not "overload" protection (yes a SC is an overload but it's protected against differently). Inrush current is pretty high but that drops pretty quick for what we are discussing here. A 200 amp fuse in this kind of system is going to suport 200 amps of current for a long duration. So if you put that much fuse inline it's best to make sure you have cabling that can also continuously support that much current. If you don't, and say your relay welds it self closed, then you've got full current being drawn continuously (again maybe 80amps). That's going to get that wire pretty hot but probably not cause a wire in good condition it to melt and SC. Now we add 20 years of heat and vibration to our wire and now the relay welds it self. Now we've got a hot wire with weak insulation and chaffing that say leads to a melt through and a small current leak. With the already loaded system it won't take much of any kind of additional current bleed to ground to overload the fusible links and they melt away and the circuit is opened and safe. Maybe even the damaged section of the wire can be repaired. If you have replaced the fusible links with a 200 amp fuse, that fuse is going to allow up to 200 amps to pass through a wire that is not capable of supporting that load increase in an already loaded system. You will have significantly more damage to that wire as well as every wire that it touches as it runs through the harness. I would not recommend using a fuse for the glow plug system vs the fusible links unless you know how to select the correct style of fuse for this application. It's not just picking one capable of handling the max inrush.

 

[aggiediesel01]

Here are a few pics of the wires

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[firehonomichl]

Awesome thanks for the great info! I’m gonna year back into it Saturday