Low fuel pressure problems Rotax 912 uls

[JUSTNUZZA]

Have you solved the problem yet ? I am having the same issues with mine.

 

 

[storchy neil]

justnuzza reply 25 appears to have identified the problem try what he has done

 

are the aircraft same make and model neil

 

 

[JUSTNUZZA]

Storchy, No I have a Roko NG4. Never had a problem until I installed the new pump. Post 25 says it is only 90% rectified.

 

 

[DrZoos]

No we havent solved it. We have reduced it by wrapping it in heat shield wrap, to the point where now it only occurs occasionaly in cooler conditions, but frequently when hot. Clutching at straws. Its definitely heat related. But so far all suggestions on how to fix it have been unapproved modifications, so we havent gone down that path in case we introduce a problem that results in more then an alarm. I think the logical first step is to replace the sender or relocate it. But i need approval or supply of the part to do so, which hasnt been forthcoming yet.

 

How long is your alarm activated or are you below 0.15? Your allowed 5 seconds

 

Also it might be worth letting floods know because they reckon we are the only one with the problem.

 

Floods it seems to me have no idea how to fix it, which is to be expected if it is a sender or isolated problem. Perhaps its just beginning to show now. Many dont run fp guages or have analogue ones and wouldnt notice .

 

Floods suggested chopping the fuel pump breather hose off a few inches inside the cowl. Made no difference. Now they want the breather re routed and placed in an overflow bottle.

 

Problem is i dont like being a test pilot. I bought a factory built for a reason.

 

 

[JUSTNUZZA]

Mine has been dropping well below 0.15 even registering 0.00 for up to 20 to 25 seconds in hot conditions.

 

Get the occasional low reading in cool conditions which seem to return to correct pressure range within the five second limit. I have also spoken to Floods who have told me I am the only one with the problem. Have also run the drain into a bottle with no improvement. I will try the heat shield.

 

 

[storchy neil]

ok to different aircraft get hold off the latest rotax installation manual and follow the directions given

 

heat shield as mutch as you can as recommended by rotax

 

is the motor showing any sighns of lack off fuel like running rough or lack of power

 

I had the opposite to mutch pressure neil

 

 

[JUSTNUZZA]

Storchy. The engine purrs like a kitten, just don't like seeing the low fuel pressure indication at rotation.

 

 

[DrZoos]

Same purs like a kitten.

 

Its definitely heat related. My dealer is chasing alpi for the fuel flow sender and pressure sensor as we speak. So id say i will have them replaced in a week or two and can hopefully say its a dodgy poor located pressure sender.

 

 

[DrZoos]

Nuzza have you tipped your plane to max climb angle and done a fuel flow test to be sure. Check your l/ hr just to be safe. Only takes about an hour and it will give you a lot more safety knowing you actually do have ample flow.

 

 

[JUSTNUZZA]

DrZoos,

 

I will try that and the heat shield. I doubt if the sender is faulty as my aircraft has done 400 hours on the old pump hassle free with a good steady fuel pressure indication.

 

 

[DrZoos]

Nuzza i dont have the info with me right now but on the fuel sender that distributes the fuel to its various sources, the tube that goes back to the tank is supposed to have some sort of jet / limiting hole to limit the amount of fuel going back to the tank. I may be wrong on this but that hole / jet would affect pressure and may be too big for the new fuel pump.

 

Im thinking out loud here so please anyone correct me if im wrong (im sure someone will).

 

The new pump causes a fuel pressure drop that is allowed to go below the lower limit of 0.15bar for 5 seconds max. If that whole was too big for the current fuel pump then this in my opinion could allow that fuel pressure to go longer then 5 seconds ?? However you would need to be very careful changing it as reducing that whole may well make the pressure too high and cause an engine out.

 

Ive come to the conclusion that because mine is under warranty, I dont want to be the test pilot and hence i want mine to be diagnosed , fixed and test flown by a qualiified person / LAME or the like. Because having to make the changes above may well cause what is now only a fuel alarm to become a life and death or aircraft destroying engine out. This also has huge implications for the insurance of my aircraft as well.

 

So before anything else is doen i want them to change my fuel flow transducer which is faulty and my sender, before they go pulling my plane apart and making unapproved modifications to try and fix it.

 

Id also say watch this space. As i think others may soon start having this problem when they go to the new fuel pumps. I was told by my dealer that Floods said we are the only one with the problem. So maybe they just havent put two and two together yet, or maybe the problem is in its infancy and some others will soon have it.

 

 

[DrZoos]

Nuzz another thing im trying is when i first wrapped it in heat wrap it caused all alarms to cease. I cant remember ambient temps. So i then wrapped it in more heat shield , tied it in place with cable ties and the problem partially came back. So im now wondering if the cable ties holding it in place allow vibration to affect it . So another step worth trying is to try and isolate it from much vibration.

 

 

[DrZoos]

I used this stuff initially that worked well

 

https://www.google.com.au/search?q=go+kartexhaust+sealer&rlz=1C1GGGE_en-GBAU451AU451&espv=210&es_sm=93&source=lnms&tbm=isch&sa=X&ei=kCupUqKKOI2TiQfA1IH4Dg&ved=0CAkQ_AUoAQ&biw=1366&bih=643#es_sm=93&espv=210&q=go+kart+exhaust+sealer&spell=1&tbm=isch

 

Then i added a second layer and some rotax exhaust header wrap that i bought from Autobarn and cable tied that to the original position. Its now questionably less effective then when i just first wrapped it and left it lose to test it. But the weather has also got hotter. So the jury is out at present on that.

 

 

[JUSTNUZZA]

Today I bled the fuel line at the pressure sender, wrapped the sender, gascolator and electric pump in thermal reflective tape, checked and used contact cleaner on sender electrical connections and flew for 1.2 hours hassle free with no low pressure warnings. Even in high pitch attitude practising stalls with idle thrust no low pressure warnings . Will now see what a hot day is like next as today was only 21 degrees.

 

 

[DrZoos]

Nuzz i tried feeding the pump vent hose into a plastic bottle made no real difference. So i cut those extra cable ties off to lower the vibration and haven't had an alarm since, but only 3 flights about 15 touch n goes. But just like you it has not been hot.

 

Glad your having some success.

 

I found the heat shield worked well till ambient temps got to about 28 - 29 C but my plane has small intake holes its built for speed. So on hot days my cowl temps are prob hotter then a lot of others. Yours seems like a speedster as well. Funnily though only one other alpi has had the problem and placing the pump vent hose in a bottle fixed it.

 

 

[DrZoos]

Still getting alarms but only when hot. Of a morning i can do 5 touch n goes before i get an alarm and they gradually become more regular and longer.

 

Alpi have no said to check the presence of and size of the return valve to the tank that its a size jet n 38

 

Im certain and have expressed my opinion to Alpi in Italy that its temperature related and that they should try a new pressure sender or relocate it.

 

They are "certain" its not a sender ... so i am at their mercy for a litany of other things to try first.

 

 

 

[JUSTNUZZA]

Have been flying last two days in 35 degree heat and no low pressure warnings since covering sender, gascolator and electric boost pump in the heat reflective tape. I do not have a return line to fuel tanks so I don't think that will be your problem DrZoos.

 

 

[DrZoos]

I have since taken my outer two layers of heat shield off and am getting less alarms with just the one layer. I think with three layers once it did get heated up it stayed hot.