Gasoline pump and LPG conversion best practices

Propane, Butane, LPG, GPL, C3H8, C4H10
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rack
Posts: 33
Joined: Fri Apr 20, 2012 7:28 am
Location: Sofia, Bulgaria

Gasoline pump and LPG conversion best practices

Post by rack »

Hello to everyone in the forum,
I have been away for a long time.

Recently I have very unpleasant accident, actually very dangerous one, with my car, 2004 Monte Carlo SS Supercharged with BRC vapor injection LPG system.
I bought the car from UK in 2014 as is, and since then I put some 25K km on it, mainly on LPG (95% may be).
Last summer, the fuel pump started to blow fuse occasionally. I put new fuse and everything is OK for a week or two. Lately, it started to blow it almost every day.
In the morning, I can clearly hear the pump primes the engine. I can do it many times.
Lately I noticed the problem starts when the car is hot.
I was making my mind on buying new pump when disaster strike.
I was driving when I smell burned plastic. Since I expect problems, I almost immediately pulled over to find this under the hood:
burnt_2.jpg
To be continued...

rack
Posts: 33
Joined: Fri Apr 20, 2012 7:28 am
Location: Sofia, Bulgaria

Re: Gasoline pump and LPG conversion best practices

Post by rack »

Then I went to the fuel pump itself.
After removing it from the tank I found these:
burnt_pump1.jpg
burnt_pump2.jpg
burnt_pump3.jpg
The whole cable from pump to body is burnt. I clearly see this is not the first time this cable was melting. The pump also smells burnt.

Anyway, I am lucky the car did not get on fire.

To be continued...

rack
Posts: 33
Joined: Fri Apr 20, 2012 7:28 am
Location: Sofia, Bulgaria

Re: Gasoline pump and LPG conversion best practices

Post by rack »

Now, I am putting it back on wheels...
I got "new" fuse box from ebay and going to rewire it.
Also, I also order used pump from supercharged engine and expecting it in two weeks.

I will also revise all LPG components and connections.

Here comes my questions:
What is the best practice to manage fuel pump with LPG system?
Should it be shut off when driving on LPG or left working?
Have in mind that, at least on paper, supercharger pump supplies 27g/s vs 18g/s for naturally aspirated engine.

Thanks for the help,
Ivo

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Gasoline pump and LPG conversion best practices

Post by storm »

I prefer to leave the fuel pump operational. Why? because it cycles fuel and this helps to keep the injectors cool and clean.

Also, and I'm not sure about all systems, some LPG systems switch back to petrol under full load so if you shut the fuel pump off and your system switches to petrol under full load you may find yourself starving the engine of fuel at the most inopportune and possibly dangerous times.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

rack
Posts: 33
Joined: Fri Apr 20, 2012 7:28 am
Location: Sofia, Bulgaria

Re: Gasoline pump and LPG conversion best practices

Post by rack »

You are correct, current setup switches back to gasoline at heavy load.
Actually it was switching before I changed vapor LPG filter. After that, I haven't notice switch backs.

When it blow the fuse for the first time last year, I changed the fuel filter. It was almost clogged. Running it with clogged filter may be make the pump to overheat, then cables and so on...

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Gasoline pump and LPG conversion best practices

Post by C3H8 »

Starting back in 1985 before LPG injection even became a product this question has haunted our industry. One side argued that leaving the pump running was a safety concern. The rational was that on propane a gasoline leak was undetectable and leaving the pump operating could drain a gasoline tank while operating on propane creating a dangerous situation in a vehicle left idling or in slow moving traffic. A normal gasoline vehicle in this situation would normally quit operating causing the pump to shut off. The other concern was that it was not wise to let a pump run with low fuel levels as the pump could run hot and overheat. The truly logical argument was why wear out a gasoline fuel pump not being used. Prior to LPG injection we adopted the practise of shutting down the pumps.

The other side claimed that leaving the pump running cooled the injectors and prevented varnish build up. They also claimed that when switching to gasoline the transfer was immediate without any hesitation or lag even if done a WOT.

Along came fuel injection for LPG and the same arguments prevailed but one thing was clear. We had more pump failures with the higher pressure pumps now being used although I have never seen a failure quite like yours. The key issue is that the gasoline is needed to start the engine and may switch to gasoline during heavy loads requiring the pump to operate. A taxi company that used BRC on smaller engines (V6 3.0L or smaller) in Toronto devised a timer system that allowed the pump to run a minute or two during start ups. The pump was shut down until the next start cycle using the timer. Switching to gasoline with the switch or automatically due to LPG pressure loss bypassed the timer reactivating the pump. Doing this allowed them to carry less gasoline without causing the pumps to heat up or the gasoline in the tank to heat up due to recirculation. Pump failures were non existent with this set up. The only concern was if the engine tried to switch over on its own the pump had to suddenly build pressure causing a lag or even a stall. This was rare since the smaller engines seldom exceeded the maximum capability of the LPG injection system.

Your case requires the pump to be left on. The size of your engine leaves it very susceptible to automatic switchovers. I would advise you keep a reasonable amount of fuel in your petrol tank to mitigate any heat build up of the pump and to allow the fuel to keep cool from the recirculating of the petrol. I would say at least 1/3 to 1/2 tank. Also considering the damage that occurred periodic inspections of the harness would be advisable to make sure it does not reach this point again.

rack
Posts: 33
Joined: Fri Apr 20, 2012 7:28 am
Location: Sofia, Bulgaria

Re: Gasoline pump and LPG conversion best practices

Post by rack »

Thanks for the info.

I will leave it operating.

I suspect previous owner was driving it with empty tank, because I keep it full almost anytime.
If the pump is gone bad, keeping it submerged would not bring it back. :D
I disassemble the pump assembly, it smells burnt.

I am waiting for parts to arrive and will put it together.
I will updated.

Thanks,
Ivo

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