Disabling Ignition System
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5th Gear
Joined: Oct 2020
Posts: 5
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From: Salem, OR
Disabling Ignition System
just bought a blue top steering box and had a question about the install process.
Im new to working on my own vehicle so just want to double check with the pros here.
it asks for me to disable my ignition system to perform a flush and bleed procedure on power steering pump.
whats the best way to go about this? I don't see anything about it in my Haynes manual.
Can I simply remove the coil to distributor wire?
thanks for the help
1985 F150 4.9L 300 I6 4x4
Im new to working on my own vehicle so just want to double check with the pros here.
it asks for me to disable my ignition system to perform a flush and bleed procedure on power steering pump.
whats the best way to go about this? I don't see anything about it in my Haynes manual.
Can I simply remove the coil to distributor wire?
thanks for the help
1985 F150 4.9L 300 I6 4x4
Lead Driver
Joined: Nov 2013
Posts: 7,158
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The safer method: At the distributor cap, remove and ground the center lead. Leave the other end connected to the coil.
This may sound backwards, but it's much easier on the coil to leave that end of the wire connected and ground the other end that connects to the distributor cap.
With everything connected as normal, the coil output only builds high enough to jump to ground, creating the spark (out at the plugs). But if no (relatively) easy ground path is available, such as via the spark plugs, the coil output will build and build to potentially damaging levels. In some cases, it may find a weak spot, such as marginal insulation inside the coil, and create a new ground path. But if you ground the coil output, the voltage harmlessly dissipates and can't cause any damage.
This may sound backwards, but it's much easier on the coil to leave that end of the wire connected and ground the other end that connects to the distributor cap.
With everything connected as normal, the coil output only builds high enough to jump to ground, creating the spark (out at the plugs). But if no (relatively) easy ground path is available, such as via the spark plugs, the coil output will build and build to potentially damaging levels. In some cases, it may find a weak spot, such as marginal insulation inside the coil, and create a new ground path. But if you ground the coil output, the voltage harmlessly dissipates and can't cause any damage.
Fleet Mechanic
Joined: Nov 2006
Posts: 1,664
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From: Northwest
I usually remove the positive cable from the battery... That would keep the engine from cranking over if something went haywire while you were under the hood..... Like your 5 year old son who "just wanted to help" and turned over the ignition switch.... LOL
Hobo
Hobo
Post Fiend
Joined: Feb 2008
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From: St Albert, Alberta
Pretty hard to crank the engine over when the battery is disconnected...
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5th Gear
Joined: Oct 2020
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From: Salem, OR
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Lead Driver
Joined: Nov 2013
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From the Department of Unsolicited Advice:
For safety, disconnect the ground cable instead when working under the hood. If disconnecting both cables, such as when replacing the battery, it's always ground first off and last on.
If you disconnect the positive cable, your wrench is now energized, and mere inches from the fender. While the initial sparks might be pretty, the subsequent flames typically are not. If you disconnect the ground cable first, there's no risk of creating a dead short with the wrench.
Note I keep saying ground cable, not negative. I was taught this particular phrasing years ago, and not just to be persnickety. If you ever work on classic cars, you may encounter positive ground. For example, this was found on most older British cars and even Fords before 1956. If you give directions to disconnect the ground cable, it covers all vehicles regardless of polarity, and is hopefully safer.
For safety, disconnect the ground cable instead when working under the hood. If disconnecting both cables, such as when replacing the battery, it's always ground first off and last on.
If you disconnect the positive cable, your wrench is now energized, and mere inches from the fender. While the initial sparks might be pretty, the subsequent flames typically are not. If you disconnect the ground cable first, there's no risk of creating a dead short with the wrench.
Note I keep saying ground cable, not negative. I was taught this particular phrasing years ago, and not just to be persnickety. If you ever work on classic cars, you may encounter positive ground. For example, this was found on most older British cars and even Fords before 1956. If you give directions to disconnect the ground cable, it covers all vehicles regardless of polarity, and is hopefully safer.
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Lead Driver
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I remembered why I said to pull and ground the center lead at the distributor cap. My voltage drop test guide was originally written for old Jeeps. Very early models (like my 1948) have the coil under the dash, not in the engine compartment. Access is a pain, and there was no separate fuse for the ignition system. The easiest method is to ground the high tension lead from the coil.
This is still applicable to any vehicle with a distributor. But of course, as you have suggested, it's even easier to disconnect the power connector from the coil. At least in most cases, or If working on a 1948 Jeep.
Although the voltage drop test guide is posted on a Ford truck forum, it's really for any vehicle.Whatever option is used to disable the ignition, the important thing is don't just disconnect the coil output without grounding it. That's when you might damage the coil, as discussed earlier.
[/hijack mode off]
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
That's the great thing about FTE, an almost cult-like devotion, an obsession if you will, with staying on topic. Almost never happens. 
I can envision disabling the ignition, in the procedure of which I'm not familiar to flush a power steering pump, but when did fuel injection start? How much cranking is involved here? Just curious. It might save wear & tear on battery and starter too, to remove the spark plugs, too. Heck, a cylinder compression test would be setup too.
I can envision disabling the ignition, in the procedure of which I'm not familiar to flush a power steering pump, but when did fuel injection start? How much cranking is involved here? Just curious. It might save wear & tear on battery and starter too, to remove the spark plugs, too. Heck, a cylinder compression test would be setup too.
Lead Driver
Joined: Nov 2013
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For bleeding the new power steering system, what's the purpose of disabling the ignition? Let's say the instructions say to crank the starter for 15 seconds (strictly a guess). Why couldn't you just idle the engine for the same amount of time?
The only difference that comes to mind is cranking speed is a little slower than idle. Is that it? Or was this just some clever lawyerly gambit so you'd be less likely to drive away without doing the full bleed and thus crashing into a bus full of nuns and orphans?
FTE Legend
Joined: Nov 2015
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From: Angier, NC
The trouble with motor running it would be cold so the choke and fast idle would be on.
The pump would then build more pressure and make a bigger mess.
Beside running the risk of running the pump dry and hurting it.
The flush & bleed was pretty easy following Blue Tops paper.
Dave ----
The pump would then build more pressure and make a bigger mess.
Beside running the risk of running the pump dry and hurting it.
The flush & bleed was pretty easy following Blue Tops paper.
Dave ----
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
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