Fuel pump troubles

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HealeyBN7
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Fuel pump troubles

Post by HealeyBN7 »

Thought I would start a new thread as the original subject about breakfast is now several meals past yet there are parts of the morning that still linger on...

viewtopic.php?f=2&t=2356

So replacing all the fuel lines didn't work. Took a longer test run up a couple hills to see if I can keep fuel in the bowls. With the left pump I was able to drive smoothly for a few miles, switch on the right pump and it just starts to stumble. Took it home and rechecked all the fittings. Ran both pumps to ensure there was no air in the lines, then went back to the specs and took another look at the psi and volume. PSI is as it should be, yet I misread the volume spec. Should be 1.1 pints per minute. You can see below that I noted that they were the same.
HealeyBN7 wrote: Fuel pressure was 2.7psi exactly. Both pumps put out the same psi and volume. Dean
And they are nearly the same - 2.0 oz/min and 2.5 oz/min. The problem is they should be pumping almost 10 times that much volume or at least 18 oz/min. So yes they are the same, they are both under delivering. I would have to get over 60mpg to keep from starving the bowls - not likely. So this is why both pumps result in just about the same outcome.

They both have unrestricted access to fuel, so it must be something I did when I rebuilt the pumps... hmmm. Neither pump ticks fast. Both are slow and one is slower then the other.

The decision to save the old pumps probably wasn't a good one. I'll pull them out again and see what could be wrong. What ever it is, I did it twice. At least I made it back home this time:)

Dean
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Re: Fuel pump troubles

Post by Steve Simmons »

Sounds like your gas caps aren't venting. Have you tried running with them open?
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Re: Fuel pump troubles

Post by Larry Kluss »

Are you still getting air in the system? If so, and it's not pump the inlet lines/connections, perhaps the pumps have air leaks on the suction side?
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Re: Fuel pump troubles

Post by HealeyBN7 »

This morning I placed a call to the UK to see if the kit is correct for the application and explore any ideas on why the flow is so poor. "Air leaks and a blockage is what it comes down to. Find them and eliminate them..." ok.

After replacing the lines and compression fittings there is not much else I can do to address air leaks, so then it must come to blockage. Fuel quickly flows out of the tanks and hoses, so I am pretty sure the pumps have unrestricted access to fuel.

So what else is there? Could I have rebuilt the pumps incorrectly - sure, but how?

I started by comparing the parts I installed with the exploded diagrams of parts. Here is the generic parts diagram for a SU HP pump. Then I remembered a little spring that I reused and installed. Hmm. It is not in the picture.
tech_su_44a.jpg
Here is a parts diagram for a very early pump. Note the little spring "J" in the picture. It is really hard to see. It is the only pump type that I was able to find that used a spring, even though it is not a SU HP (1331).
su-pressure-pump.jpg
su-pressure-pump.jpg (27.15 KiB) Viewed 29082 times
I have one of these springs in each of my pumps, yet they were not provided in the rebuild kits. They put pressure on the valve. I don't see them in any other diagrams that I found.

Tonight I'll try removing the springs to see if has a positive effect in removing the "blockage".

What could possibly go wrong?

Dean
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Re: Fuel pump troubles

Post by Steve Simmons »

Do you want to borrow a spare pump and see if it makes a difference? I have a freshly rebuilt MGB pump here that should work, if the fittings are the same as yours.
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Re: Fuel pump troubles

Post by HealeyBN7 »

Thanks Steve, but believe it or not, I have two new pumps on the Peerless chassis that I could use. Of course now it is a matter of engineering pride...
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Re: Fuel pump troubles

Post by Larry Kluss »

Dean, a blockage causing low flow makes some sense, but you said when you did the flow test, you were getting lots of bubbles along with the fuel. Where are they coming from? Could the pump be airiating the fuel? Or is it pulling air thru one of it's seals to the outside air?

I guess you'll find out when you remove the "extra" spring.

Good luck.
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Re: Fuel pump troubles

Post by Steve Simmons »

Intake-side leaks can be incredibly invisible. You may not see or smell anything but there can still be enough of a leak to pull air into the fuel flow. This si normally accompanied by a fuel pump that won't stop clicking. The faster the clicking, the bigger the leak. A slow leak would produce a click every few seconds with the ignition on but engine not running.
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Re: Fuel pump troubles

Post by Larry Kluss »

Steve, I agree with the possible inlet-side leak, but not the clicking. Once the set pressure is reached on the outlet (carb) side the clicking will stop (key on, engine off). That is true even if the outlet line has air, because pressure is pressure, liquid or air. However it will take longer for the clicking to stop with air in the line because it has to compress the bubbles. Once at pressure, it should not click again until the pressure drops either by carb/engine fuel usage or an outlet-side leak. Because an outlet-side leak is under pressure, it would be accompanied by the telltale fuel smell and wetness.
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Re: Fuel pump troubles

Post by Steve Simmons »

Technically you're right, but the pump will sit and click as stated if it can't pull fuel because of an intake-side leak. I had this problem once. The leaky hose allowed air into the line and the car would randomly die. Eventually it couldn't pull fuel at all and sat there clicking away until I moved the hose, and suddenly fuel flowed again. It was then I realized there were micro-fractures in it that I couldn't see until the hose was removed and under a light on the workbench. I'll admit it was an odd scenario.
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Re: Fuel pump troubles

Post by Larry Kluss »

Come to think of it, at least on some pumps, the outlet-side is supposed to slowly bleed back so it doesn't stay pressurized during non-use. I can see that causing the pump to keep ticking slowly while energized, keeping the outlet pressure up. An inlet-side air leak (on its own) should not cause the pump to run if the outlet-side is up to pressure.
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Re: Fuel pump troubles

Post by HealeyBN7 »

So last night I started from scratch again and rechecked the fuel pressure. Both pumps build pressure to 2.7psi then shut off.
IMG-20130706-00347.jpg
IMG-20130706-00347.jpg (115.16 KiB) Viewed 29058 times
I removed both "J" springs on the first check valve and tested the flow again. It improved 100%, but a 100% improvement from 2oz/min is only 4oz/min. Still not enough to keep the bowls full.
IMG-20130708-00366.jpg
IMG-20130708-00366.jpg (131.55 KiB) Viewed 29058 times
Next I tried removing the first check valve flap, thinking that just the second check valve above it would be good enough. That didn't work at all. Pumps just ticked over, but didn't move any fluid. oh well.
IMG-20130708-00368.jpg
IMG-20130708-00368.jpg (120.8 KiB) Viewed 29058 times
With the fuel lines disconnected from the pump to the tank, I hooked up a temporary line from the output of the pump to a catch bottle. Filled the 30oz jar in 30 seconds. Both pumps performed the same. At that rate I could push enough volume to power the Range Rover.

I found the problem. Any guesses?
Last edited by HealeyBN7 on Tue Jul 09, 2013 9:58 am, edited 1 time in total.
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Re: Fuel pump troubles

Post by Steve Simmons »

Larry, the little square facet pumps have a bypass but I'm not aware of any SUs with that.

Dean, did you try the same thing at the carbs? Could be a kinked line somewhere.
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Re: Fuel pump troubles

Post by Martin Keller »

HealeyBN7 wrote:I found the problem. Any guesses?
From the photo of the two pumps the one pump was canceling out the pressure of the other pump at the t-fitting.
:drive
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Re: Fuel pump troubles

Post by Steve Simmons »

I missed the part where you solved it. Are you missing the check valve so whichever pump is active is pushing half of its fuel back into the opposite tank?
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Re: Fuel pump troubles

Post by HealeyBN7 »

Martin Keller wrote:
HealeyBN7 wrote:I found the problem. Any guesses?
From the photo of the two pumps the one pump was canceling out the pressure of the other pump at the t-fitting.
:drive
Good guess, but the t-fitting and routing of the lines is odd indeed, but it is original and not part of the problem.
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Re: Fuel pump troubles

Post by HealeyBN7 »

Steve Simmons wrote:I missed the part where you solved it. Are you missing the check valve so whichever pump is active is pushing half of its fuel back into the opposite tank?
Another good guess. The pumps build pressure at the carbs and stop ticking, yet just a small amount of fuel was reaching the fuel bowls.

One pump draws from each tank. With the in-pump check valves, fuel is not pushed backwards through the pumps into the opposite tank.

All check valves are in place and working properly.
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Re: Fuel pump troubles

Post by Martin Keller »

Fuel filters installed backwards maybe or not enough voltage going to the pumps making them run slow and not producing enough volume under pressure.
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Re: Fuel pump troubles

Post by HealeyBN7 »

Martin Keller wrote:Fuel filters installed backwards maybe or not enough voltage going to the pumps making them run slow and not producing enough volume under pressure.
:drive
Voltage is good to the pumps. Both pumps are able to draw the necessary amps. Fuel filters are installed in the correct orientation. hint hint
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Re: Fuel pump troubles

Post by Martin Keller »

Fuel filters clogged or ones that you did not know about.
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Re: Fuel pump troubles

Post by Steve Simmons »

The pumps have filter screens inside that you can't see without opening them up.
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Re: Fuel pump troubles

Post by HealeyBN7 »

Martin Keller wrote:Fuel filters clogged or ones that you did not know about.
:drive
Bing Bing Bing - Exactly!!!!

There is a sediment bowl on the left side near the front wheel. I thought it was an open drop bowl, but it has a very fine screen on the top. Of course you can't see it since the bowl is below the certerline of the wheel. I removed the glass part a couple times and cleaned out a few particles.
IMG-20130708-00367.jpg
IMG-20130708-00367.jpg (107.41 KiB) Viewed 29031 times
After removing the glass part of the bowl again and blowing the lines, it was evident that there was still something still blocking the fuel.

Reaching my hand under the lid of the bowl, I found this screen full of dirt.
IMG-20130708-00365.jpg
IMG-20130708-00365.jpg (108.59 KiB) Viewed 29031 times
Had I know is was there.... I could have cleaned it out on the way to Larry's house and avoided a week of head scratching and all the tow truck drama.

The little things we learn.
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Re: Fuel pump troubles

Post by Steve Simmons »

I bet it's the sediment bowl. There's a screen in the lid.
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Re : Electric Fuel pump " Fun "

Post by VWNate1 »

Dean ;

Thank you for this most excellent thread .

I am always asked about E Pumps , I like them and have run into most all the difficulties you mention here .

Siphon is on of the very first things I check as it's easy to check and so often there's some weird little thing like a dented fuel pipe between the tank and the pump or a 90° bend that's built up sediment , a clogged / rusted closed fuel cap vent.....

The bit about no filter before any pump is really important and so few seem to get it , like the idiots in Marketing @ Facet who insist on installing intake filters , closed , non viewable ones no less ! those crappo things are almost guaranteed to cause problems and pump failures when used in the average old car and that's where 80 +% of Facet pumps go . in klunkers .
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