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Discussion Starter · #1 ·
Starting to take short drives in my recently completed swap, and I'm running into a situation where about 50% of the time the truck will keep running for 15 or so seconds after I turn the ignition off and kill power to the VE solenoid. I am also experiencing very rough shut downs regardless of how long it takes. Any ideas what is causing this and how to remedy?
 

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Do you have an electric fan running at shut down? I've seen electricfans act as generator supplying current as they coast to a stop if there isn't a diode in the circuit.

Idk if the fuel shut off would slowly close if current was reduced tho
 

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Do you have an electric fan running at shut down? I've seen electricfans act as generator supplying current as they coast to a stop if there isn't a diode in the circuit....
This happened in my 4bt Grumman bread van. If both heater fans were running, shutdown took an extra couple of seconds. I do not seem to have the problem in my F150 (same engine). Next time, try a shutdown with the headlights on (extra load on the electrical system), see if the shutdown time is much shorter.
 

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Discussion Starter · #4 ·
Update... I just took the truck for its first real drive, about a 5 mile trip to the parts store and back. I let it idle in the parking lot, but when I got home I turned it off and the truck kept running. This time however it did not shut down after a few seconds like in the past, instead it just kept on trucking along. I popped the hood and took the wire off the shutdown solenoid removing any possibility of an electrical issue and the truck kept running. I had to remove the air filter and cut off air supply to kill it.

I am thinking there is some kind of fuel leak somewhere but have no idea how to diagnose this.
 

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I would be looking at the fuel shutoff solenoid,try killing it with the mechanical shutoff lever.
 

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Discussion Starter · #6 ·
A little more info...

I noticed when I turn the key off at least some of the cylinders are shutting down, but the engine will keep running on the ones that are still getting fuel. You can feel the cylinders kicking in and out by turning the key to run and back again. If I toggle the key from run to off a few times it'll choke the motor up enough to kill it.

I forgot about the manual lever, will try that next and report the results.
 

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Isolate it first to see if it's electrical or mechanical:

With the engine running, Disconnect the wire to the IP solenoid. If it immediately shuts down it's electrical. If it acts the same then remove the solenoid and inspect the plunger tip for damage.
 

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Another thing to check is whether it could be running on engine oil after the fuel is shut off. Possible sources of engine oil are leaking turbo seals, or crankcase vapour if that is put back into the inlet system, or possibly bad seals on inlet valve stems.
 

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Discussion Starter · #9 ·
Isolate it first to see if it's electrical or mechanical:

With the engine running, Disconnect the wire to the IP solenoid. If it immediately shuts down it's electrical. If it acts the same then remove the solenoid and inspect the plunger tip for damage.
I ruled out electrical when I pulled the 12v wire off the solenoid and it kept running. I ordered a new solenoid, so I'll give that a shot first.

If the engine shuts off with the manual lever, does that rule out running on engine oil?
 

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Discussion Starter · #10 ·
I put new shut off solenoid in this afternoon with mixed results. The bad news, is that it still does not turn off every time when they key is turned off. The good news it that now if I pull the power wire off the solenoid, it will kill it. So I'm thinking that I had a bad solenoid, and a wiring issue. Now I just need to figure out why there's still power being left in that wire when I kill the ignition.

Another thing that happened, is that the truck now idles a lot smoother than it did before. Not sure how a new solenoid could cause that to happen? That was the only thing I changed.
 

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Maybe your ignition switch needs adjusting or replacing. It's possible that power continues after turning to the off position. It can be adjusted up or down. IIRC, you'll have to lower the steering column to get to it. Some tell tale signs that it needs adjusting - dome light stays on or door chime continues after removing ignition key. On the other hand, if it needs adjusting - it can create a no-start condition.

Chris
 

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You're getting a 12v back feed into the solenoid circuit. Need to trace that wiring and find out if that same circuit is feeding another item. Seems like on the Dodges, the culprit is often the starter solenoid. There a diode fix for that one.
 

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Discussion Starter · #14 ·
I took the factory Bronco engine harness and de-pinned it to remove everything except for two run hot circuits and A/C wiring. One running hot circuit I didn't trace so I don't know what it used to operate, but I am using it now for my electric vac pump.

The second hot circuit that I kept from that harness was the power wire to the SBF ignition coil. This is the circuit that I am using to power the VE pump. I ordered a starter repair kit just to rule that out, but I am thinking I am going to try getting power from a different source, or adding a relay to that circuit to see if it changes things.

I've also been thinking about using the 3-wire FSS solenoid and connecting it to my manual shut off lever in place of a choke cable. Has anyone done that before and made it work?
 

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The second hot circuit that I kept from that harness was the power wire to the SBF ignition coil. This is the circuit that I am using to power the VE pump. I ordered a starter repair kit just to rule that out, but I am thinking I am going to try getting power from a different source, or adding a relay to that circuit to see if it changes things.
This should be a red/light green wire and is connected to the ignition switch. I would check to make sure you are not getting any voltage when turning off the ignition on the red/light green wire. It's a possibility that the switch is just slightly out of adjustment that it sometimes doesn't turn the power off.

Looking at the diagram, there is a noise capacitor on the same circuit (red/light green). Don't capacitors store energy? I am not very competent when dealing with wiring diagrams and electricity.

Chris
 

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Discussion Starter · #16 ·
This should be a red/light green wire and is connected to the ignition switch. I would check to make sure you are not getting any voltage when turning off the ignition on the red/light green wire. It's a possibility that the switch is just slightly out of adjustment that it sometimes doesn't turn the power off.

Looking at the diagram, there is a noise capacitor on the same circuit (red/light green). Don't capacitors store energy? I am not very competent when dealing with wiring diagrams and electricity.

Chris
Thanks for the info, I believe that they do and I hadn't even thought of that. I wonder where the capacitor is located because if it was after the big junction on top of the driver's side wheel apron then it's gone. I only kept a foot of so of the original wire from that point on out towards the engine. I'll investigate further this weekend and also check that ignition switch on the column. It never gave me trouble with the gas engine though, so again I didn't think to mess with it.
 

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If you have a capacitor in the circuit, it definitely stores energy. It might keep the solenoid energized until it bleeds down. Maybe swap the vacuum pump and solenoid wires and see if that cures it.
 

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I'm not a Bronco guy but I'd wager that the capacitor is not the culprit. It's purpose is to snub voltage spikes caused by voltage arcing between switching contacts. The most common cause of back EMF, in an automobile, is the alternator Field terminal. I don't recommend you unplugging this lead while running, rather disconnect first and then start/stop cycle it.
 

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Discussion Starter · #20 ·
So, I'm back to where I started with this issue. I switched power sourced, tried a relay, all without making any kind of a difference. I tried pulling the wire off the solenoid when it wasn't shutting off and it kept running without the wire. If I start it and shut it off in the driveway it shuts off fine, but after driving it any distance it will not shut off without me pulling the manual shut off lever.

To recap...

New shut down solenoid
Keeps running with the power wire removed
Shuts off with manual lever


I'm at a point where I think I am going to try and install a solenoid with a pull arm on the manual shut down lever and wire it up to my ignition switch so I can still kill the truck with the key, but it's bugging me not knowing what is causing this issue. I am thinking it has to be something with the pump, or that it's running on engine oil? What can I check first to see if it's running on engine oil?
 
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