frank marriott Posted April 25, 2014 Share Posted April 25, 2014 Has anyone experienced this: Fuel starvation at full power with only engine pump working. Switch on electric and all comes good. Installed new fuel pump no improvement - starvation at slightly lower rpm. Type 2 pump with the 74mm pushrod. Checked main jet - clean with no obstructions. With normal operations with electric pump on, the only other thing in play is the mechanical pump, at least to my knowledge?? Link to comment Share on other sites More sharing options...
Bob Llewellyn Posted April 25, 2014 Share Posted April 25, 2014 Has anyone experienced this:Fuel starvation at full power with only engine pump working. Switch on electric and all comes good. Installed new fuel pump no improvement - starvation at slightly lower rpm. Type 2 pump with the 74mm pushrod. Checked main jet - clean with no obstructions. With normal operations with electric pump on, the only other thing in play is the mechanical pump, at least to my knowledge?? Speaking generally - I don't have a Jabiru - the engine should have been shown to develop full power with either pump out of action; so is there a fuel wasp's nest in the line, or a collapsing inner or something? Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 Bob, Both pumps are in series and use the one feed. I have run out of ideas. Link to comment Share on other sites More sharing options...
Camel Posted April 25, 2014 Share Posted April 25, 2014 My advice is change fuel filter. The mechanical pump has to suck fuel where the electric pump pushes fuel through filter. I have seen filters causing problems like this in cars that suck through filter. The Z15 filter is a paper element and I would change it very regular no mater whether it looks clean. 2 Link to comment Share on other sites More sharing options...
Bob Llewellyn Posted April 25, 2014 Share Posted April 25, 2014 Bob,Both pumps are in series and use the one feed. I have run out of ideas. Yes, the idea is that the valves on either pump will allow fuel to pass through even if that pump ain't active. Fuel hose is normally made with an outer, a robust string-reinforced body, and a liner. I have had happen to me twice (once car, once U/L); and heard of several times; the liner comes loose from the body. Now, if the liner between the engine pump suction and the elec pump outlet did this, with elec not running the suction partly closes the fuel line; and the elec pump pressurises it back to full size. To test this, get a length of line - the cheap clear not-really-fuel-resistant stuff is ideal - and run it through the cab, or on the ground outside, from the elec pump outlet to the engine pump inlet. Then ground run the engine. If it works fine under test, you've got yourself a good spare engine pump! - and the pleasant job of replacing the std fuel hose with something of at least equal quality... (as far as I know, NO lined fuel line is immune from this problem, ocassionally) Link to comment Share on other sites More sharing options...
Bob Llewellyn Posted April 25, 2014 Share Posted April 25, 2014 My advice is change fuel filter. The mechanical pump has to suck fuel where the electric pump pushes fuel through filter. I have seen filters causing problems like this in cars that suck through filter. The Z15 filter is a paper element and I would change it very regular no mater whether it looks clean. If the filter is between the pumps, definitely try that first. Link to comment Share on other sites More sharing options...
Camel Posted April 25, 2014 Share Posted April 25, 2014 Actually the filter is before electric pump too but is very close to it ,the filter is between the header tank and electric pump. I still would change filter first no matter what. Link to comment Share on other sites More sharing options...
Bruce Robbins Posted April 25, 2014 Share Posted April 25, 2014 Frank, We have also had a faulty electric pump cause a similar problem. The two pumps are in series, and Jabiru do not plumb in a bypass line. In this case it was Boost pump off - ops normal, pump on - engine faltered. Replacing the electric pump solved the problem. Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 The electric pump provides 60 ltrs/hr as it should. It is a straight swap to a new engine. No problems with supply to old engine. Filter fairly new and does not obstruct the 60ltrs/hr electric (tested flow rate) Runs normal on engine pump up to just below full power. All indications ( to me) was it must have been a faulty engine pump even though it was new - replaced with another new one but problem continues. Runs perfectly, full static revs and climb out with electric on. First discovered the problem on test flight when the electric was turned off. Link to comment Share on other sites More sharing options...
RKW Posted April 25, 2014 Share Posted April 25, 2014 Could it be that the fuel pump is not getting sufficient lift from the cam lobe. Is the cam lobe worn or damaged? Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 RKW, new engine including pushrod to the cam. Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 Thanks for the input. I was just hoping someone may have struck the problem before. I guess I'll have to wait until Monday and see what the factory has to say? Link to comment Share on other sites More sharing options...
Bob Llewellyn Posted April 25, 2014 Share Posted April 25, 2014 Thanks for the input. I was just hoping someone may have struck the problem before. I guess I'll have to wait until Monday and see what the factory has to say? Worth asking - but unless I missed something, a collapsing inner would still fit the bill? Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 Yes, will look into that as well. Would be unlucky for that to happen right on changeover, but not impossible. I "think" the line is clear tube to the firewall and then rubber hose but will have to check that as well. Any suggestions are good as I have run into a brick wall. Link to comment Share on other sites More sharing options...
Bob Llewellyn Posted April 25, 2014 Share Posted April 25, 2014 Yes, will look into that as well. Would be unlucky for that to happen right on changeover, but not impossible. I "think" the line is clear tube to the firewall and then rubber hose but will have to check that as well. Any suggestions are good as I have run into a brick wall. Brick walls are not good for flight! Ummm - it couldn't be vapour lock, could it? If you mix fuels, and as they age, you can get vapour lock surprisingly easily... Link to comment Share on other sites More sharing options...
cherk Posted April 25, 2014 Share Posted April 25, 2014 Yes, will look into that as well. Would be unlucky for that to happen right on changeover, but not impossible. I "think" the line is clear tube to the firewall and then rubber hose but will have to check that as well. Any suggestions are good as I have run into a brick wall. not something ...like carby float level ?? Link to comment Share on other sites More sharing options...
Bob Llewellyn Posted April 25, 2014 Share Posted April 25, 2014 not something ...like carby float level ?? I've had the little rubber seal on a float valve needle disintegrate, causing blockage and yuk, but that was on an ooooold carby... and I'd think you'd notice the rich behaviour if the float sunk? Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 No fuel mix - straight avgas Don't think float level, bowl full when removed. Link to comment Share on other sites More sharing options...
Bob Llewellyn Posted April 25, 2014 Share Posted April 25, 2014 No fuel mix - straight avgasDon't think float level, bowl full when removed. I'd put 2 bob on it being s fuel line liner problem, because I can't imagine any other possibility to match the symptoms Link to comment Share on other sites More sharing options...
SDQDI Posted April 25, 2014 Share Posted April 25, 2014 not something ...like carby float level ?? I'm not overly mechanically minded but if you have just changed the engine and the problem started seems that the existing fuel line shouldn't be the problem unless something got into the line during the changeover, I'd be more inclined to suspect the new bits put on. 1 Link to comment Share on other sites More sharing options...
turboplanner Posted April 25, 2014 Share Posted April 25, 2014 Might pay to try to blow though the electric pump when it's turned off, could be a valve is sticking shut. Also check polarity of electric fuel pump wires, could be current holding the solenoid. 1 Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 No fuel pours through the electric pump when turned off just by gravity Link to comment Share on other sites More sharing options...
turboplanner Posted April 25, 2014 Share Posted April 25, 2014 OK in summary: Engine starves when the fuel pump is switched off New mechanical pump fitted Both pumps in series with one feed Fuel filter upstream of both pumps - does not restrict 60 lt/min electric pump flow Possible inner fuel hose collapse Next I would try bypassing the electric pump and filter Then bypassing the filter only If the electric pump in the off position is not blocking or partially blocking the line, then my thoughts are: (a) line collapse which Bob suggested, perhaps sucked in on itself by mechanical pump, then expands again when the engine stops (b) a batch of dirty fuel has left residue on the filter/gauze inlets. Link to comment Share on other sites More sharing options...
JabSP6 Posted April 25, 2014 Share Posted April 25, 2014 Frank, Just something else to think about. There were 2 different length pushrods for the jabiru supplied mechanical fuel pumps depending on which type of pump you use. If you have the shorter pushrod in with the pump that requires the longer pushrod then you might have the problems you are describing. Especially with the system performing ok prior to the engine swap. The new motor may have mistakenly been fitted with the wrong pushrod and you swapping pumps making no difference would be right if the pushrods is wrong. Jabiru can give you the dimensions of the correct pushrods for the pump you have. Might be worth looking at if the fuel hose inner liner isn't the issue. Safe flying Andrew Link to comment Share on other sites More sharing options...
frank marriott Posted April 25, 2014 Author Share Posted April 25, 2014 JabSP6 Type 2 fuel pump with the 74mm pushrod fitted (type 1 has 72mm) Link to comment Share on other sites More sharing options...
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