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Old 06-30-2008, 11:21 PM
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insulating wire connections in fuel tank

The fuel pump inside the tank of my 87' vette went bad and I found a small problem when I went to replace it today. For some reason the harness plug that connects to the fuel pump inside the tank was semi-melted. I'm replacing the pump with a walbro that comes with a harness to adapt the GM style plug to the walbro pump connection. Since I think it's probably unlikely that I could find a new GM style harness plug to replace the melted one, I think the easiest fix is to solder the Walbro plug to the original GM wiring. That eliminates the melted plug problem, but what do I insulate the bare wires with that will resist deterioration issues from being in constant contact with fuel. I considered crimping on new generic electrical plugs but I don't know how resistant the rubber or plastic insulation on those would be either. Really not trying to make a simple fix complicated, I just want to do it the right way once and forget about it.

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Old 07-01-2008, 07:17 AM
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The short wiring harness from the fuel pump to the sending unit is available. You should be able to get one from just about any part store.
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Old 07-01-2008, 08:20 AM
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I would slip some heat shrink over the connections, solder them then shrink the tubing, that is all that's needed.

Vince
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Old 07-01-2008, 11:09 AM
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I found some PTFE heat shrink tubing. Took a butt connector, slid the center metal piece out, and soldered the two ends into the metal piece, slid the plastic butt connector insulator back over the metal and put heatshrink over the butt connectors. Maybe a little overkill, but it would take 10,000 volts to arc through all that. When the thing burns to the ground I'll know it didn't come from that connection! Thanks
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Old 07-02-2008, 09:03 AM
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Marine heat shrink tubing has an adhesive in it that completely encases the termination. For all intents and purposes, it's bulletproof. The type without the adhesive will wick fuel in this case or if it's under the car will wick water. The water anyway will (eventually) destroy the connection and the wire for several inches due to corrosion.

You can get marine heat shrink at marine stores or on the web at places like Defender.
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Old 07-02-2008, 09:12 AM
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Much is being made of this supposed problem. Truth is there is actually very little needed in the way of insulating those connections. It matters not if gasoline infiltrates the heat shrink, it cannot cause a fire or explosion. Submersed fuel pumps burn out all the time and do not cause a problem.

Vince
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Old 07-02-2008, 10:40 AM
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I had a thread not too long ago about a KIA fuel pump I replaced that had completely melted the wiring to the pump/sending unit, not just the insulation but the wire! The thing had lost ground to the fuel pump due to a VERY poorly designed connection and for whatever reason it became grounded through the light 20 ga wire to the gauge sender, with predictable results! Probably has nothing to do with your question but this sort of thing must happen sometimes, I am sure this is not the only case, and there does not seem to be a rash of fires from it.
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Old 07-02-2008, 11:25 AM
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I can't tell you how much money I've made from repairing poor installations, either from "value engineering" or poor workmanship. I usually err on the side of robustness and if I'm doing connections one way on a car or a boat, I'll do all of them that way, mainly because I'm in that mode and have that type of material on hand. Cutting back quality sometimes bites one in the posterior.
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Old 07-03-2008, 01:23 AM
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Quote:
Originally Posted by 302 Z28
Much is being made of this supposed problem. Truth is there is actually very little needed in the way of insulating those connections. It matters not if gasoline infiltrates the heat shrink, it cannot cause a fire or explosion. Submersed fuel pumps burn out all the time and do not cause a problem.

Vince
I totally understand what your saying. Wires submersed in fuel will not ignight the gasoline. My main 2 concerns were 1. What insulator would be resistant to the gasoline and not be deteriorated 3 years from now, falling to the bottom of the tank, leaving an uninsulated connection to short out another pump. an 2. Suppose there was a quarter tank of gas, and 3/4 a tank of combustable fumes. I suddenly get a spark between the deteriorated connectors, dead center of the fumes, could possibly be a problem. Not likely, the ratio of gas vapor to oxygen has a very narrow margin of creating an explosion. But hey, crazy stuff happens to me all the time, Things like exploding gas tanks. My main concern was really to prevent burning up another pump.
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Old 07-03-2008, 08:15 AM
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Quote:
Originally Posted by DaSouthWon
For some reason the harness plug that connects to the fuel pump inside the tank was semi-melted..
I have heard but not experienced that running a car with an in tank fuel pump with 1/4 tank or less most of the time will cause the fuel pump to over heat and fail. Fuel helps cool the pump, maybe the pump got hot and the draw, amperage went up and melted the plug as the pump died. Not all at the same time mind you, but the two could be connected.

I have seen a connector fail/melt, before a motor failed from the over heating, which in time took out the motor.
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Old 07-03-2008, 01:41 PM
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Quote:
Originally Posted by DaSouthWon
Suppose there was a quarter tank of gas, and 3/4 a tank of combustable fumes. I suddenly get a spark between the deteriorated connectors, dead center of the fumes, could possibly be a problem. Not likely, the ratio of gas vapor to oxygen has a very narrow margin of creating an explosion.

Some time back there was a discussion about this possible problem resulting from sparks from a faulty gauge sender. There seems to be the idea floating around that there would not be enough air in the tank (displaced by fumes) to cause an explosion if the sparks occurred, from whatever source be it sender or pump connection. This IMHO is pure non-sense and sparking inside a gas tank would be EXTREMELY dangerous and would lead to an explosion in most cases. Common sense should dictate that Oxygen would be present inside a partially filled tank and an explosion would be probable. By using the displaced Oxygen theory one could then assume that welding on a gas tank would be safe but history proves this not to be true! Accidents resulting from fire near a gas tank are not all that uncommon, unfortunately, but if sparks inside could not cause a fire then sparks from the outside would not either but that obviously is not the case. Sparking inside a gas tank would be very dangerous and I think that should be obvious! You are right to be concerned about this but the good news is that it should not be at all hard to get a decent connection that will not be capable of causing a spark.
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Old 07-03-2008, 03:16 PM
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The movie industry has been very good at dropping lit cigarettes into spilled gasoline and the resulting explosion and fire. We all know this is not the case and has been proven many times that a lit cigarette cannot ignite gasoline.

On the other hand wasn't faulty wiring inside the center fuel tank of that 747 that went down off the coast of New Jersey to blame?

Vince
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Old 07-03-2008, 03:18 PM
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The ignition source has to have enough energy ie heat value and the correct amount of an oxidizer. A tank with a failure like this will not generally cause an explosion or fire because the oxygen level is too low. Conversely, the amount of combustible vapors is too high.

When welding on a tank, you are introducing additional oxygen into the tank and that is not the closed vessel a normal tank is in service.
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Old 07-03-2008, 05:14 PM
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Quote:
Originally Posted by bluesman2333
The ignition source has to have enough energy ie heat value and the correct amount of an oxidizer. A tank with a failure like this will not generally cause an explosion or fire because the oxygen level is too low. Conversely, the amount of combustible vapors is too high.

When welding on a tank, you are introducing additional oxygen into the tank and that is not the closed vessel a normal tank is in service.

Not at all, accidentally hitting a tank with a torch or welder will not induce oxygen inside the tank and I know of two instances where this has happened, once from sparks welding while doing body work and no one had been doing anything to the tank. Open the cap to fill the tank and air containing Oxygen will enter, how long before this would be displaced if the tank was not filled to overflowing? Come on there certainly could be times when there may not be enough air in the tank to cause a problem but most of the time that will not be the case. When the fuel level drops, especially in a gas guzzler, the fuel level will drop a heck of a lot faster than fumes from the gas could compensate for it and air will enter, it is a known fact that if a tank vent fails the tank will either collapse or the fuel flow will stop (happened a lot on older cars). Believe what you like but there IS air in that tank and quite often it certainly can be well within the right mixture range to explode!



302, A few years ago a buddy and I were ribbing another guy about smoking while cleaning parts with gasoline, his response was "Hell if I throw it into the gasoline it will just put it out"! To prove it to us he did just that and sure enough it did put it out, which is what we all expected. Later that day after he had finished he innocently threw another cigarette butt onto the gasoline soaked ground where it had splashed out of his cleaning pan and there was a violent flash as first the gas soaked ground ignited then the remainder of the gas in the pan flared up! No one was injured but the carburetor he had been cleaning was reduced to a molten pile of junk and the door on his pickup was badly damaged. It just depends on the situation but ANYTIME you have sparks and gasoline/gasoline vapors there is a potential for explosion and to say there will NOT be enough air containing Oxygen in a gas tank is ludicrous.
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Old 07-03-2008, 11:31 PM
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This is getting out of control. For a vapor cloud explosion there is a minimum ratio of fuel vapor to air below which ignition will not occur. Alternately, there is also a maximum ratio of fuel vapor to air, at which ignition will not occur. These limits are termed the lower and upper explosive limits. For gasoline vapor, the explosive range is from 1.3 to 6.0% vapor to air.

It's the same as an engine running too rich or too lean. But in an extreme sense. Fuel burnt in a cylinder is in liquid form. Fuel vapor is sublimated liquid fuel. Those fuel droplets sucked or sprayed into the engine are sorta like the molecules in the vapor.

Somebody call "Mythbusters", or better yet, has anyone seen that Mr. Wizard dude. He's like 140 but is still showing kids how to blow up and destroy things. I think he kicks it with Bob Barker on the weekends.

Last edited by DaSouthWon; 07-03-2008 at 11:45 PM. Reason: additional info
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