1986 c7000 box truck 366 engine won't start

[primemover]

Electrical issue: For a few days, I had dash lightup when switching on ignition, engine rotation when switching to "start," but no fuel feed. Added gas to tank, changed a _very_ old filter, and tried again. Switch to "ignition," and everything lighted up; switched to "start," and I got maybe a second of starter action, then everything quit. No further electricity movement. I have power to the ignition (same voltage as at Battery). I figure it must be the switch or some fault after the switch. How do I diagnose this??

[VileZambonie]

check your battery connections

[primemover]

Positive and negative battery connections are firm. Correct voltage at battery, correct voltage at cowl junction. Correct voltage incoming at ignition switch. Nothing going through the switch. Are there other connections I should be aware of before the switch?

[Jon87V20]

Just out of curiosity, has it been sitting for a long time?

[primemover]

Oh, sure.

[Irish_Alley]

check your connections at the starter also. theres a chance that you may have contact to get 12v but a poor contact so it cant carry the amps

[primemover]

I wish my schedule would allow me to stay on this project until fixed:( Oh, well:), on we go!

I have 0.2 amp coming in at the ignition switch. i don't have the specs available, but that wouldn't seem to be enough. What has anyone found to be the right # of amps coming into the ignition switch?

 

[bd]

I have 0.2 amp coming in at the ignition switch. i don't have the specs available, but that wouldn't seem to be enough. What has anyone found to be the right # of amps coming into the ignition switch?

Are you confusing voltage with current?  Current flow is based on the electrical load that is operating at the time.  To clarify, describe how and where your meter was connected to the circuit and what you were attempting to measure.

More than likely the truck has connection problems or a damaged fuse link.  Base your diagnosis on voltage drop measurements while the circuit is operating.  For instance, check for voltage at the ignition switch while attempting to crank.  Did you check the battery cable end and its connection to the starter solenoid as suggested?  The cast exhaust manifold on MD trucks prior to the introduction of TBI concentrated heat in the area of the starter, baking the solenoid and its connections, causing them to gradually loosen with use.  Even a slightly loose cable connection at the starter can rapidly degrade and burn, severely limiting current flow.  Occasionally, there will be sufficient electrical connection to supply voltage down circuit until an electrical load is applied, causing the connection to instantly open.

[primemover]

Thanks, bd!

So, with current flow based on  the electrical load operating at the time, if I have no load operating, I can expect no current (or maybe something small, like 0.2 amp). Do I have this part right?

As the circuit will not operate, I can not measure any voltage drop while it _is_ operating (as, e.g., while attempting to crank.

I cannot (yet) reach the connections on the starter solenoid, as the heat shield is in the way and rusted in place, until I can get the nuts loose:( Therefore, I am only wishing (while I wait) to check those connections.

The MD truck heat concentration issue at the solenoid seems like a reasonable possibility for my situation. Twice, I have had this scenario. With appropriately charged battery, turn on ignition. Everything works that is supposed to. turn key to "Start." Starter turns over for a couple of seconds or less, and all power is lost, suggesting a connection supplying power was burned up or jarred loose. Working with the "burned up" assumption, I searched unsuccessfully for a burned wire or fusible link. Finding neither, now I working with the "jarred loose" assumption. Could the starter being jolted with an impulse to start from the ignition in "Start" position be enough to "jar loose" a bad connection elsewhere on the solenoid -- where the battery cable joins the solenoid and a wire that might supply power to the ignition switch?

[bd]

What type of ammeter are you using - inductive or series connected?  If a circuit is "open" there will be "zero" current flow.  Current indication on an ammeter means that either a circuit is connected and operating (even if not effectively) or the ammeter isn't zeroed, or it isn't stable and it drifts.  Avoid using an ammeter to diagnose this problem.  Use only a voltmeter and analog test light.

As the circuit will not operate, I can not measure any voltage drop while it _is_ operating (as, e.g., while attempting to crank).

As long as voltage is connected to a circuit, you can measure voltage drop.  You just need to understand what the measurement is telling you.  You measured B+ at the ignition switch.  Was that while attempting to crank the engine?

[primemover]

My Ammeter is the 10Amp function on a multimeter -- I assume that is series connected. Induction is the type that wraps around a cable, right?

Voltmeter and analog test light -- I will:)

What is B+? I was not attempting to crank the engine as it seemed that no power was going through the switch, either in "Start" or in "Run" (ignition switched on).

[bd]

You have a series connected ammeter.  Using a series connected ammeter for diagnosing power delivery problems imposes a high risk of blowing the internal meter fuse if there is any possibility that the circuit being measured can draw greater current than the selected scale of the ammeter - in this case 10 amps.  Had the starter solenoid actually engaged, in combination with ignition, etc, it probably would have blown the meter fuse.

B+ is battery hot, or 12.6 volts for a fully charged automotive lead-acid battery.

For a list of automotive acronyms see, Common Automotive Acronyms in our Technical Pages.

I was not attempting to crank the engine as it seemed that no power was going through the switch, either in "Start" or in "Run" (ignition switched on).

Retest using the voltmeter or a test light, probing all of the ignition switch cavities in turn while attempting to crank.  Include the red B+ wire that feeds power into the ignition switch when performing this test.  Post what happens.

[primemover]

Good to know that about the multimeter Ammeter function. That must be why I never tried to use it before now -- too scary!

I was afraid we'd get around (sooner or later) to probing connections. Seems simple, but I never did figure out how to do that. And I can't seem to figure it out this afternoon. I've poked a big paper clip down next to the terminal block connection on the ignition switch, but I can't seem to make contact. With the switch disconnected from the terminal block to expose the blade connectors, I do get 12.65 volts on the "BAT" blade, but, of course then I can't see if the switch will transfer that to the other blades connected to wires. Leaves me kinda stumped and feeling silly.

[bd]

...With the switch disconnected from the terminal block to expose the blade connectors, I do get 12.65 volts on the "BAT" blade, but, of course then I can't see if the switch will transfer that to the other blades connected to wires....

Not following you.  Post a pic of what you are doing along with the meter and its test leads.

[primemover]

Here are three photos of the ignition switch parts I'm working with. I have voltage to the hot wire connector from the battery, but I'm not getting any voltage to show up downstream through the switch or bypassing it. On any other vehicle that lost power through the switch, I've always been able to bypass the switch by pulling the terminal block off the back of it and making up a set of wires to leave the switch out of the stream. I can't seem to figure this one out.

I'm getting battery voltage from the BAT connector to the IGN connector on the terminal block but not to any other connector.