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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #61  
Old 28th June 2015, 10:13
phil.coyle phil.coyle is offline
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Hi Robin,
I feel like I'm becoming the Harbinger of Doom, but the LP must have failed for a reason as most pumps go on for years. Are you sure there is no obstruction of the pickup pipe in the tank, certain that the pickup pipe isn't touching the bottom of the tank and therefore covering the end of the pipe which in turn will cause premature failure of the LP and the snowball effect on the HP.
I'm beginning to feel I should be there to help you as I am becoming as frustrated as you in solving this problem.
Phil
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  #62  
Old 28th June 2015, 13:46
8 Valve Ed 8 Valve Ed is offline
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If the HP pump could drag sufficient fuel to run the engine at all then the suction pump can't be that restricted. Normally a suction pipe is cut at an angle to prevent that sort of blockage. Reasonable point though. Is it possible to peer inside the tank or pull the dip pipe? Gently blowing on it should say if it's restricted... Does it have a filter on the end?

In order to check the flow it should be a simple matter to run a temporary pipe into a container and run the pump for say one minute, then measure the fuel?

My mind keeps coming back to this being a temperature related fault. The symptoms occur when the engine has been running for some time on a warm day and it has been gradually getting worse?

I think it's important to keep that at the top of the mental whiteboard.

This is the first concrete fault that has been discovered, until it's rectified no further solid conclusions can be drawn.

Having eliminated most if not all of the electronics, we seem to be left with the fuel system components and perhaps the fuel.

Given the pump seems to be US, why not slice it open and try to establish what has happened inside. That might be good info for us all, I think many of us rely on these Facet pumps, although I have fitted two, not trusting these new fangled things!!! The SU's were notoriously unreliable. That said, my understanding is that the Facet pumps work in exactly the same way just that they don't have the mechanical contacts. A plunger is pulled by magnetic pulse against a spring. The spring pressure presses on a diaphragm and pressurises the fuel through a one way output valve. So the pump shouldn't be overloaded by being unable to suck fuel, it should just lie idle, or pulse normally, as though trying to suck fuel, that shouldn't overload or over load the windings or circuit.
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  #63  
Old 28th June 2015, 17:23
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GreatOldOne GreatOldOne is offline
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As Robin has already stated, the sportster fuel tank is very basic. There is no pick up tube - just an outlet but welded on to the bottom, and a return slightly higher up the wall of the tank.

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  #64  
Old 28th June 2015, 20:03
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MartinClan MartinClan is offline
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I can catagorically state there is no blockage in tge tank - the rate at which the petrol pissed out when I disconnected the LP pump is testiment to that lol.

I agree its unusual for a LP pump to fail specially as its a genuine facet. Its completly open circuit so its the electronics that have failed. I am in the process of taking it to bits but it is very well made and seems to be filled with some potting compound.

I am using a sytec swirl pot. I have stripped it and its clean as a whistle.

New pump arrives Tuesday. Just in time for the heat wave :-)

Cheers, Robin
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  #65  
Old 28th June 2015, 22:47
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Sytec told me that their HP pumps will burn out their vanes in seconds if they are allowed to run starved of fuel (the petrol acts as a coolant): so though your HP pump may run, it would be a good idea to test the pressure it puts out after you have fitted your LP feeder.

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Originally Posted by MartinClan View Post
I can catagorically state there is no blockage in tge tank - the rate at which the petrol pissed out when I disconnected the LP pump is testiment to that lol.

I agree its unusual for a LP pump to fail specially as its a genuine facet. Its completly open circuit so its the electronics that have failed. I am in the process of taking it to bits but it is very well made and seems to be filled with some potting compound.

I am using a sytec swirl pot. I have stripped it and its clean as a whistle.

New pump arrives Tuesday. Just in time for the heat wave :-)

Cheers, Robin
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  #66  
Old 2nd July 2015, 09:45
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MartinClan MartinClan is offline
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I have fitted the new LP pump. And - what a surprise (not) - the HP pump is much quieter in that you can no longer hear it. (Just as when I first built the car.) Fuel pressure looks healthy - as one of my efforts in diagnosing the problem I have a tee fitted for a fuel pressure gauge. I hope I haven't damaged the HP pump as I already replaced it once when first starting to trace the problem.

So far the damage to the wallet has been:
HP pump, filter and non return valve ()
Crank position sensor ()
Coil (Borrowed from Peter)
ECU () actually would have been () but I bought the wrong one first time - oops.
HT leads and distributor cap ()
LP pump ()

I discovered the LP pump problem just after I bought the HT leads and distributor cap which is a bit of a bugg€r. I haven't fitted them yet so they could well end up on Ebay.

On the plus side I found the coolant leak that I have had since the car was first commisioned, and the coil is now mounted in a far better (cooler) location. And the new fuel pump had a big note with it saying it was E85 compliant.

Drove to work this morning. I didn't experience the big missfire but I still not convinced things are 100%. As I started to suspect, and the reason for it being so difficult to diagnose, there may have been two problems. Which means there still is one....

Tomorrow I have a longer run planned - weather permitting.

Cheers, Robin

BTW - I checked the old LP pump (4th time!) and it is definitely US. This time I just did it the simple way of wiring it to a battery. I checked the new pump before I installed it and I discovered a continuity check is a waste of time as the electronics in the pump means you don't get any sensible resistance readings. Indeed in one direction it is infinite. I guess the pump has an internal blocking diode to stop damage if wired the wrong way round.
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  #67  
Old 2nd July 2015, 13:23
phil.coyle phil.coyle is offline
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Sounds good, and a nice ride out in the rain never hurt anyone. I have had a read through the previous posts and notice that your plug leads are quite old, or have you changed them, I would get out the old multimeter and check the resistance of all the leads, copper ones seem to last a lifetime but the carbon leads break down with age.
If you have new leads take them for a run out, and if the problem starts again swop the leads and see what happens. Your manual will tell you the ohms for the leads.
Phil.
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  #68  
Old 4th July 2015, 12:24
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MartinClan MartinClan is offline
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My trip out yesterday went without a hitch. Round trip of about 60 miles in temperatures up to mid upper twenties. So I think I can conclude that the major issue was the low pressure pump. Only time will tell if there is/was a secondary problem but right now I intend to start enjoying it again!

Phew....

Robin

PS - thanks to everyone for their input :-)
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  #69  
Old 4th July 2015, 17:33
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Good news!
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