Got a '94 7.3 IDI with aftermarket turbo that's developed this annoying habit of blowing the 20 amp Maxi fuse responsible for the glow plug circuit. I can replace the fuse and get a few starts out of the truck before I no longer get the WTS light.

GPR was already on it's way out, so I've replaced that. Measured glow plug resistances and got some variations ranging from .7Ohms down to .2Ohms. I don't trust my digital multimeter due to the fluctuations in static resistance between 0 and .3Ohms. However, will measure again.

Does anyone have access to a wiring diagram specific to the glow plug circuit so I can begin tracing wires and checking components? Can glow plugs out of wack cause such voltage fluctuations to pop the fuse over a matter of hours?

 

20 amp fuse sounds kind of small for glow plug circuit.
glows draw close to 200 amps when working.

 

Not a clue what it should be, that's just what was in there and I've replaced. It's been in there for years, apparently.

Put a working 30 Amp fuse in and nothing. Popped in another 20 and I get the WTS and the truck will start and run.

 

hmmmm.. just a thought. try disconnecting the fuel heater on top of the fuel filter housing, tape the wire end off, and put a new fuse in to see if it works.
if the fuel heater shorts out it will blow the fuse and cause issues. i don't know the 92 and newer trucks that well, but it may be something as simple as a bad fuel heater element.
mine on the 88 has been bypassed since 1990.

 

You're on to something!! The heater had a leak from the plug, so my buddy took care of it and mentioned he may have broken the heater in the process. I will do just that!

 

Well, disconnected the fuel heater element (that single pol plug up top), popped in a new 20A fuse, and it blew immediately. 30 doesn't blow, but doesn't allow the circuit to work. 20A was the factory one, so it shouldn't require any higher, meaning something else is causing the issue.

 

Found a diagram among the forum resources, so I'm gonna play around with that.

Saw the DIY tach sensor too, which is something else I'm gonna do.

 

good luck, i hope you can find a simple solution.

 

Nothing is seeming to be simple on this green giant, but I'll figure it out.

 

yea that is the way it goes with these trucks until you finally figure it out, and then it is a smack the head moment with the following why didn't i think of doing it that way months ago thought.

 

I feel that's me with any project these days.

Ironically, this wasn't an issue until someone else tinkered on it about a week ago after I finished the clutch replacement!

 

 

So you're saying not to use this 100A fuse burning a hole in my pocket?? The 30A was never meant to be a permanent solution. The cabling on that circuit would likely tolerate no more than 35-40A before running the risk of starting a fire. Again, I'd no intentions of using higher than a 30A for the express purposes of testing. I've seen what using ridiculously uprated fuses can do in a circuit with wiring not meant to handle such amps. If you catch it early enough, you'll just have that awful burnt rubber smell.

I'm seeing lots of solenoids, wondering if one is sticking. I'll attempt to test and isolate the parts.

What's odd is that I get a few cycles out of the gpr when attempting to start the truck before the fuse eventually blows; it's not a case of where you put in the new fuse, turn key to on (or start), and the fuse pops right away. A sticking solenoid could be causing the problem after prolonged starting attempts.

I'll check it out in the morning. The diagram I found from the tech thread here has those parts listed. Any suggestions on just testing each individual solenoid by applying power through a fused connection?

 

So far, minus testing the cold timing advance solenoid and the thermal switch straight to the battery, the tests have proved inconclusive. I tried with the starter circuit 20A fuse out of the way so I could better see the condition of the fuse, turning the key to the ON position and connecting each component one at a time while examining the fuse after each plug in. I repeated the same tests with the starter circuit fuse in place and got the same results. Fuse still OK.

I've not tried to start the truck yet, but will be doing that shortly after checking all wiring once more.

I'm not entirely sure what could have gotten messed up when the filter leak was addressed, which is why I wanted to do that myself as the truck started and ran fine before that. It's been hard to start for years, but always started and never blew any fuses before. Could the stress of repeated starting attempts be causing the fuse to begin "cooking" slowly before it just gives up the ghost and pops?

I tested the plugs again and get a consistent reading across all between .5-.7Ohms (cold, obviously). Much wiring is hidden under wrapping as well as wire loom tubing, but none of it shows signs of heat damage. At a loss here. This really came out of nowhere after the filter housing leak was addressed. Fuel heater remains unplugged and I disconnected the "Water in Fuel" sensor just to be sure.

With a fresh fuse, WTS light comes on for 8-10 seconds, so nothing unusual there. I will try cycling the key between off and on a few times to see if the fuse will give out; I'll know when the WTS light no longer illuminates when the key is turned to ON.

 

Or in other words,conclusive to narrowing it down to one of these as the issue..........It's all in the perspective.