I have a 1986 F250 with a 6.9 that runs great. My problem is that it has to be plugged in to start. I did some research and I put a manual switch in for the controller and I have traced all the electric from the switch to the harness plug and everything is working fine however my truck still won't start without being plugged in.

I used a test light to check my plugs as they are all only 3 months old but I am not sure I am doing it right. When I touch the light to the spade of the glow plug it doesn't light but when I touch the base of the glow plug it does light. It is this way on all 8 of the plugs. Are my glow plugs all bad or am I doing something wrong? Or is there some strange reason that my plugs would be conducting at the block but not at the spade? Thanks all

 

When you test them, hook the clip on your tester to the postive post on one of the batteries. Then pull the connector off the first glow plug and touch the tip of the tester to the top of the gp. If it lights its good. Rehook the connection and move on to the next one.

 

What brand of plugs did you use? If anything but Motorcraft- Beru is not good. If the test light is not lighting when the spade is touched the plug is probably bad . Replace with Motorcraft ZD1A plugs.

 

Sounds like all your plugs are bad to me if you had checked them with the lead to the +plus side of the battery and probed the spade connector. No light means no connection inside.
I would now suspect you either held the button on too long, 10 seconds is more than enough time, and/or may not of wired your switch correctly and they were stuck on all the time.
Double check your wiring before hooking up the new ones.

 

Or if they are not motorcraft beru's you may have not done anything wrong.
I don't how many reports I have read ac's autolites boch etc. ect. only lasting 1 or 2 starts.

 

ZD-1 glow plugs for $9.99

6.9 Liter Diesel Motorcraft Glow Plugs - Ford 6.9 Liter Diesel Motorcraft Glow Plug

 

Thanks everyone. I kind of suspected the plugs were bad. I will get a set of Motorcraft.

 

That seems to be a good price on those glowplugs compared to what my local dealers are telling me, so awesome link. I was about to crap my pants after trying to look on ebay for a deal. I do not think allot of sellers on ebay these days are in touch with reality

I am new to diesels and got a 1985 6.9 a couple weeks ago. It was actually starting fine. Never had to crank it more than 5 seconds in 30 degree weather, and this is with whatever stock glow plug controller(which i am going to bypass asap).

Anyways the previous owner obviously didn't take care of it, I just went outside to test them all, and I see different types of plugs. I have no idea what the "good" ones are, I am not even going to touch those.

But I found that 1 is bad, one had the blade tip broke off, and another one has the whole nut broke off with the rest of the threads, etc. still inside the engine! oh boy, yet another project now

Its kind of interesting to read these forums though as far as the starting/glow plugs things go. One of the reasons we got the beater truck we did is because it was cold and we started it right up and test drove it around the freeway, etc. Truck has all sorts of things wrong with it as I look things over but it starts, pulls great with our load, drove at freeway speeds empty pretty good, and barely spits out any smoke.

 

with some TLC, that 85 will turn into a very dependable truck.

 

MTgoldnchampagne and damac,
Welcome to FTE and the IDI diesel forum.

When you do manual glow plugs, use a momentary switch only.
Regular switches can get bumped to on, and since they stay where ever they are put, your glow plugs can be toast when you need them.
With a momentary switch, even if you bump it on, it springs off again.

Also you need to leave the relay in the circuit, glow plugs draw almost 200 amps when they are heating.
So the switch and wire would have to be huge to handle the load.

 

When you mention such high amps, aren't we talking about larger wiring then is in that bundle, and wires larger than the battery cables???

That would be needed along with a switch that can handle 200 amps @ 12 volt???

 

nope. the relay handles the high amps. the switch is a low current trigger for the relay. and the wires to the glow plugs are small because they only need to carry around 25 amps each at full draw with new glow plugs..

 

ok cool. should the line going to the switch have any inline fuse with it?

 

it cant hurt to have it in there if you want to put one in.

 

Most of the glow plugs are 6 volt glow plugs.
That is why they can get so hot so fast.

The stock glow plug harness runs one 10 AWG wire for each head from the battery supply to the glow plug relay ands then on to the cylinder bank.
Each wire is carrying 96 amps.

Yes that wire is to small for the amps it is carrying, but that causes a voltage drop between the battery connection and the glow plug connection, which makes the glow plugs last longer.

A while back someone rewired the glow plug harness and used a 6 AWG wire for each head.
And he was burning up glow plugs with the stock 7.3 controller.
Running larger wire changed the resistance (lower) so they were staying on to long and the larger wire was also getting to much voltage to the glow plugs.

If I remember right, he did a manual conversion and only holding them on for 5 seconds before he stopped burning up plugs.

That said, if you wanted to put a 200 amp switch in the dash and eliminate the relay, look at how much extra wire you will have between the battery and glow plugs.
The length of the circuit also changes the resistance (voltage delivered) and how much current is lost/converted to heat in the wire.

Some of out equipment has 12 volt glow plugs.
Normal glow time is 20 to 30 seconds.

This is just like the constant duty glow plugs that come up from time to time.
12 volt glow plug, longer glow time, so now the timing circuits are out of whack.
The glow plugs are not hot enough for the engine to start like it should in the time the timers allow.

The stock system should have fusible link protection in the main power wires and in the harness at each glow plug.

I just saw that fusible link size the other day on a schematic, if I remember right each bank is protected by a 12 AWG fusible link.

Don't remember what size the links at each glow plug are.

The glow plug wires are not that small just to cut costs, they are also engineered to not deliver to much current to the glow plugs.
The most common failure that was not engineered very well is the engine to chassis connector.
The glow plug wires in that connector usually get a little corrosion on the connectors and melt the connectors.
And that is why that is usually in my post to anyone having glow plug problems.

Yes it takes 10 or 15 years to show up, the connector on my 86 died 8 or 9 years ago.
But now that 10 or 15 years is also including all of the IDI engines.

The engines and trucks last longer than the wiring does.