Argh. I have a 1996 F350XL 7.3l gas in a commercial vehicle conversion to a lavatory service vehicle. So far this year, we replaced the steering column (ignition issue), the starter (damaged solenoid/intermittent ground issue on solenoid), and the fuel pump (out). Today I cleaned and replaced an end on the ground of the battery (discovered loose, but other employees tried to jump it last night and may have knocked it off).

The vehicle was working fine for about the last 60 days. Suddenly I have an issue that I think is ignition based but acts like a ground problem. Symptoms:

1. I turn the key to RUN and we have dash lights, headlights, turn signals, etc.
2. The fuel gauge is at overfull, indicating a possible ground problem
3. I turn the key to START and nothing happens, except a bit dimming of the dash lamps. NO crank or click.
3. If I bypass the start relay on the firewall with key in RUN, the starter cranks readily, but the vehicle doesn't start, indicating no power/ground to the fuel pump. This would also seem to eliminate any ground issue at the starter.

I used jumper cables to supplement/bypass ground cables to the block, frame, cab, just in case, but still nothing on the key/start. I'm an old 1980's mechanic, so not useless ( I did the steering column replacement, my first), but also not a pro. Mystified where to check next. I tested the fuses in the power distribution center, all have continuity. I'm wondering if there's a fusable link I'm missing, a relay that might be out somewhere, or if the wiring block/igntion assembly suddently went bad (the white block at the bottom of the column was transferred over in the swap).

No starter power, no fuel pump power, almost certainly related. Course of action, anyone?

Thanks
sirrobocop

 

Welcome to FTE!

I've moved your post to the forum for these trucks.

First, if you have a gas motor it must be a 7.5 or 460. The diesel for that year was a 7.3. But you have electrical issues, so the engine doesn't matter so much.

The starter is going to be grounded by virtue of being bolted to the block.

There are multiple grounds, with a frame to engine, block to head sometimes, head to firewall, body to frame, dash to firewall--just about everything that houses anything electrical has a ground from the supporting structure.

Start at the component, and work back until you find a gap or electricity. Or work the other way.

Good luck and watch for posts from folks who actually own one of these.

 

Please clarify details on the truck - is it gas or diesel? Single or dual tanks? Auto or manual transmission? The starting circuit is nearly identical between them except for a couple differences between the ignition switch and starter relay.

Others may have more specific ideas but from what I’m seeing on the wiring diagrams (looking briefly at both a gas and Diesel engine) the starter relay and fuel pump get power from different fuses. I can give you better details when I know for sure what set up your truck has.

Pull the small wire off the starter solenoid and have a helper turn the key to crank. Use a test light or volt meter to check whether or not there’s power getting to that wire when cranking.

I’d recommend getting a code reader and seeing if anything is stored for trouble codes - basic readers are available for about $30.

 

I'll work on the OBD code reader soon and post any result..

The 1996 F350 truck is gas powered, automatic, single tank. (I'll check the dash again on this since the truck is modified) Also, I'll check the energizing wire to the relay for voltage and get back to you. I examined wiring coming from the column thru the firewall to the power box for a meltdown or breakage, but nothing phyiscal is immediately obvious. Thanks for helping!

 

Below is the starter circuit. If you’re not getting power to the starter relay from the ignition switch, shift the truck into neutral and try again. If still nothing, trace the circuit back towards the ignition switch, first checking for voltage on both sides of the transmission range switch, then the clutch safety switch jumper, then at the switch.

If you are getting voltage to the small wire at the relay, it’s most likely the relay is at fault. You didn’t specify how you jumped the relay before, so I’ll just suggest leaving the small wire unhooked and then jumper B+ to the small terminal on the relay (fused jumper if you have it, just in case) - if it doesn’t click or crank, relay is shot.

Both the fuel pump and gauge ground at G108 which is on the left (driver) side of the upper radiator support. The fuel gauge shares power and grounds with other gauges in the cluster so if none of the other gauges are showing problems it’s not likely an issue with the cluster.

I was also curious about the general condition and age of the battery - if it had to be jumped recently, has there been any charging system problems? A parasitic drain? Nasty/corroded terminals and cable connections? In terms of age, 5-6 years is about the limit. I’ve seen a few beyond that in well maintained customer cars but we’re usually replacing them around 5 years, especially this time of year when the cold starts killing them.

 

We've been busy and haven't had time to check it all out yet, but the schematic will help.

There's no power to the small wire on the solenoid during start. To test starter for crank and overall battery level, I used a screwdriver to bypass the starter relay completely. The starter is less that 60 days old, wanted to eliminate it as the problem.

The battery is almost new - after we installed the steering column, it wouldn't start, and I swapped the batteries with another vehicle that had a new one to eliminate that as an issue. Turned out to be a problem with the solenoid on the starter (bad ground, loose post/cap).

I'll get back after I check the ground and trace some of the circuits.

Thanks!

 

Update: Using the schematic information - the Red / Lt Blu start wire under the steering column has power when the key is turned. No power at starter relay. Based on the circuit you sent - I'm thinking that the Neutral Sensor is stuck in a gear position (it's an automatic), but I'll test the input there for power first. If I'm on the right track feel free to lemme know lol

Thanks!

 

Yep - that’s where I’d be looking too.

If you have power going into the range sensor (white/pink wire) but nothing coming out (red/light blue wire) the range sensor is probably at fault. The only other thing I would check is the state of the connector and terminals - unplug it to inspect - corrosion can obviously be an issue but so can terminals that are spread out/fretting.

The range sensor can be ohm tested but I don’t recall the specs.

You can also bypass the range sensor by unplugging it and jumping the white/pink wire to the red/light blue wire and attempt to start - if it cranks that would verify the range sensor being the problem.

 

The neutral switch was swapped out but had no effect. The ground at the radiator seemed a bit dirty so i I wire brushed it, also no effect. What's left? Trace the power thru the firewall? I can't see any obvious damage under the hood or at the sensor to the wiring.

 

Did you verify power to and from the range sensor?

Power from the range sensor but not at the relay indicates an open/high resistance in the circuit between the range sensor and the starter relay.

You said there was power at the ignition switch with the key in the crank position, so no power getting to the range sensor indicates an open/high resistance in the circuit between the ignition switch and the range sensor.

 

I am thinking you have problem at the column and power not leaving the ignition switch when it is turned to the start position.

Attachment 282544

Note there is a red/lt green wire going to the ignition switch also.


/

 

The OP states in post #7 that there is power at the ignition switch on the red/light blue wire with the key in the start position.

I’m not saying it’s necessarily the only reason the truck won’t start, but figuring out why it won’t crank should be resolved first. Having spark and fuel (or lack thereof) makes no difference if it doesn’t crank.

 

Agreed, but I think they're related since both happened at the same time. I'll examine the schematic just sent and try to test the wiring under the column.

When I have time. Grrr.

Thanks for the help, I'll keep working on it.