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MG MGB GT V8 Factory Originals Technical - Fuel Tank Sender for F.I.
|I'm starting to run the fuel system for fitting of an aftermarket throttle-bosy EFI setup, and have a couple of questions. I'm sort of planning to use the later model sending unit with the pickup pipe on it in a baffle-less tank to fit a '68. The float, as mounted out to the side, will have interference from the support bracket inside the tank, keeping it from reaching anywhere near the normal bottom position. Can the gauge be recalibrated to compensate for that?|
Someone said to reverse the float, but then I don't see how you can fit the whole array thru the tank opening like that. And besides, then the float ends up coming down on top of the pickup filter, which is a similar situation where it never comes near the bottom.
Can some kind of compression fitting be used on the sender output pipe, to go to either a hard line, or woven line, to the 'first' pump? Thanks, Joe
|Joe, I've done this.|
Late sender with pick up in an earlier tank, that already has its own pick up.
The pick up on the new sender goes in a little then curves/bends down and locates closely up against the old pick up. The float as is will interfere with the existing "old tank" pick up.
At the moment it clips into a wire at the front end/ right hand side of the float and sticks backwards. You need to unclip it, turn it around (or move it to the right) and then clip it back so it sticks forward.
You can get it into the tank opening by a bit of jiggling and persuasion. If I recollect, I half unclipped it again, put it though, then fully clipped it back in place. I tied a bit of cotton to the other end of the float in case it got away during all this jiggling, then pulled the cotton away once the float was through the opening and securely clipped again.
From the new sender pick up, I ran a length of fuel line to a large (its about the size of a soup can) filter (Kmart $20) than connected that to a small "feeder" pump. This feeder pump supplies the larger bosh high pressure pump ($150). Which in turn feeds the injectors.
The large filter acts as an antisurge tank, an external "swirl pot". It is very effective and I have never noticed fuel starvation, even with <7 litres in the tank. Iíve had this set up for about three years and 50000 miles now. Never a problem.
The feeder pump is necessary because the high pressure Bosh (and any other brand) pump is a roller vane pump, that has lots of small vanes. Lots of little rapidly turning vanes make good pressure, but have rotten suction. It will not suction through a big fuel filter without cavitating, making lots of noise, wearing prematurely, and starving the injectors. Also petrol is not like water which siphons well. Petrol has a low surface tension and a high vapour pressure (approx 70 KPa at 38.7 deg C, Read method) and readily forms bubbles. Keep in mind the boiling range of petrol is around 15 to 100 degrees C. The engine compartment is much hotter than that. This is another reason why the petrol from the engine compartment has to go back though the main bulk of the tank. Much of the gas will redissolve, or be vented though the petrol tank venting system. Also the tank itself will get quite warm in Summer, so the problem will get worse then.
The pump is made by Peirburge, part Number 12001. Like the bosh pump, it is a roller vane pump and can keep up with the high pressure bosh pump, however the vanes are much larger, so it is much better at suction. It is less able to produce high pressure, because you need lots of small vanes to do that. Catch 22.
I have noticed since that Jaguars also run two inline pumps like this.
The fuel gauge may also be recalibrated via two slot adjusters in the back of the gauge. One sets the bottom end of the scale and the other sets the top end.
Paul Hunt has a very good description, see the MGB technical forum, question on petrol gauges
|PS, don't be tempted to run without a filter. I tried this and my pump failed within an hour. had to be towed home. An expensive mistake!|
By the way, the peirburge pump was around $95 Australian dollars, apply exchange rate to get an Idea. They are obviously German, readly availiable everywhere.
You can put the filter and pumps in the boot if you like. I carry a spare if ever the main Bosh pump fails. Easy to get at and change.
Thanks for the details; I gather that you just have to persuade the float and pickup into the hole when you reverse the float. Glad to know it can be recalibrated adaquately.
I hadn't thought of placing the filter/swirl pot first thing in line out of the tank, then using one pump to feed the other. My idea was to pump to the filter, then gravity-feed to the high-pressure pump. Seems like that can work, but calls for adding an outlet on the bottom of the filter, making more of a plumber's nightmare, and adding to the chance of a leak. The whole dual-pump thing is new to me, and I'm still feeling resistance to it, but it's clear that it works for a lot of people.
Seems like there was something in the archives about a magic Volvo or VW pump/swirl pot combo that would stand alone, so I guess that I need to investigate that as well.
I'll just take the new pickup into the local tubing/fittings guy and see if he can suggest something. Joe
|Volvo 240 TURBO, has to be the TURBO version. Filter is a big one, mounts on a plate with the pump.|
|Thanks, Jim, I'll check that out.|
The Volvo pump is supposed to be good. I havent used it . It is a larger version of the standard rover bosh pump and can suck a little better. But note, not all that much better and no where near as well as the peirburge pump. It costs a little more as well.
The main problem we have with MGBs is that there is nowhere around the tank that you can put a fuel pump or filter. Youve got an exhaust, springs or handbrake cable on three sides.
This means you must run a fuel line up and over something, be it spring or axle. Petrol doesnt siphon all that well. When it gets warm you tend to get little bubbles, which make the pump very noisy. There is also the whole antisurge tank aspect. Without a constant supply of fuel the pressure drops at the injectors and the engine stalls. When you brake or accelerate the uptake pipe may become dry for a moment. As you know the injectors don't so much inject, but are on/off valves that need pressure behind them.
Ideally a fuel injection pump should be in the bottom of the tank inside a swirl pot, or antisurge baffle. However if you do that then you need to have a new MGB tank altered which means you are using an expensive non standard tank that cannot be replaced in a hurry . I have had to do this twice!
The VW golf has a removable swirl pot and pump combo that has been used in MGB tanks before. I looked at one and it seems very possible. You would need to weld in some sort of hatch in the tank.
Another approach is to set up an external swirl pot. A swirl pot is a small container with two outlets and two inlets. An outlet in the top that leads back to the main tank. An inlet toward the bottom that is fed by a low pressure pump from the tank. Another half inch out let in the bottom of the container that connects to the high pressure pump that supplies the injectors. Another inlet toward the top of the container that the fuel from the engine compartment returns to. The petrol in this container will get quite hot and will form bubbles of gas, which will stall your motor when enough accumulates. The outlet on the top of the container is a way of getting rid of this gas back to the main tank. This means that the pump that supplies the swirl pot needs to run continuously to keep the petrol gas free.
In other words you still need two continuously running pumps, and you also need to buy a swirl pot. Some people use a motor boat fuel filter as a swirl pot. These are screw on filters that attach to something that looks just like the remote oil filter on V8s. Two separate inlets two outlets. If I were to use a swirl pot, that would be the approach I would use.
You cannot just use a big filter with a T piece at the top and at the bottom. Ive tried this!. The bubbles of gas get by and make lots of noise the moment the fuel warms up a bit.
I initially thought I would try the two pumps in line without the messy swirl pot. I figured I could always go get the swirl pot later it I needed it. Since I still needed a reliable supply pump no money would be wasted. I figured that my SU fuel pump could not be relyed on to run continiously.
It worked very well and was very quick and easy to set up. Joined it all up with fuel lines and hose clamps then threw it in the boot. A few hours work, and relatively cheap.
Anyway, whatever your approach , good luck with it. The fuel injection is great. Starts every time, instantly, and runs perfectly (except when you dont have a filter that is!)
|Here is the Jag one about half way down the article.|
My filter and two pumps are in or around the boot and a bit easier to get at.
Thanks for taking the time to make the detailed explanation. The 'filter' that I was planning to use would double as an external swirl-pot. I have a large Aeromotive spin-on, mountable filter that I was planning to use. Your talk of vapor and bubbles has driven home the complexity of this type of setup, which is similar to. what some off-roaders have used in order to prevent losing fuel supply when climbing hills. The fact that you've tried the filter, suction pump, pressure pump setup, and it works, is reason enough for me to give it a try. So much simpler to layout and build, it's worth the effort, for a try, at least. It doesn't seem possible to gravity feed the filter from the tank, due to the arrangement of the pickup, so I have to "assume" that the suction pump will pull through the filter, and keep it full? Much thanks again, and I look forward to sharing my success in a future thread! Best, Joe
|Pulls though the filter no problems.|
The info sheet that came with that pump said that it was good to one meter above the tank. I tried this (with big filter between it and the tank) and it pulled to about a meter.
However that is with fuel at around 25 degrees.
The petrol tank can get very warm during the summer in peak hour. Up to 40 degrees C I've noticed. I would not have the pumps much above the top of the tank level, ie the boot.
I initialy had the pumps and filter just pushed into the corner of the boot. Later I moved them into a small box in that space behind the rear right wheel, just under the corner of the boot. Just to be neat and tidy. I also wrapped a bit of foam rubber around the pumps.
Any high volume suction pump should do the trick. The Jag' supply pump appears slightly different to mine, so there must be at least two brands around.
Just in case you can get them locally, the feeder pump I use is made by Pierburg in Germany and is called an "Auto-suction vane cell pump". stock no. 12001. it can deliver 0.5 bar when used as a primary pump. It cost $95 Australian (apply exchange rate to get an idea what it might cost locally) and for the people in Melbourne can be got from Petro-ject 03 98737006.
The main high pressure pump is a Bosh one pt no 0580464070 and cost $140.
This thread was discussed between 31/08/2007 and 03/09/2007
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