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LANE A START UP QUESTION

  • JUSTIN
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4 months 2 days ago #16563 by JUSTIN
JUSTIN created the topic: LANE A START UP QUESTION
Hello
I'm JUSTIN .Now,we have a new ROTAX 912is engine that have some trouble.Need your help.

1.Fuel pressure:Other aircraft's sensors show instantaneous changes when the fuel pump is turned on,but this engine fuel pressure is rising very slowly, waiting for 20-30 seconds to rise to normal(44-45PSI).We examined all of the external fuel roads (including change fuel pump,filter).But the results have not changed.
2.LANE A and LANE B:The engine cannot start when LANE A and LANE B are opened simultaneously;
Only opened LANE A,the engine produces sharp vibration.Dare not continue to force the start.
Only opened LANE B, the engine start and works very well.But,The engine produces sharp vibration and the RPM is significantly reduced when LANE A is turned on.After closing LANE A, the running is normal again.
LANE A 'sensor sensor shows normal and there was no warning.Then we exported the USER LOG-DATA.The data showed that EGT1 and EGT4 temperature were significantly lower than EGT2 and EGT3.We have replaced the spark plug, but we haven't solved the problem.We don't know how to do it,so please help us.
Looking forward to your reply.Thank you
JUSTIN
This is the USER LOG-DATA picture:

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4 months 2 days ago #16566 by Rob Seaton
Rob Seaton replied the topic: LANE A START UP QUESTION
What size orifice do you have on the bypass line? it sounds like you have a big flow between the inlet and return system.
Carefully check all the spark plug caps are on the correct spark plug, it sounds like 2 of them are switched to the wrong cylinder.

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4 months 1 day ago #16579 by JUSTIN
JUSTIN replied the topic: LANE A START UP QUESTION
We have five engines and the orifice size is 0.7 MM. The other four are normal, only this fuel pressure has a problem.
I checked all the spark plugs today and there was no mistake.And check the connection of the ignition coil but found no problem.Why is it that when I turn on LANE A the engine have obvious shake and RPM decrease?

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4 months 1 day ago #16580 by Don
Don replied the topic: LANE A START UP QUESTION
It seem that when you turn on Lane A , Cylinder 1 & 4 doesn‘t work, and then engine noticeable shake.

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4 months 1 day ago #16583 by Rob Seaton
Rob Seaton replied the topic: LANE A START UP QUESTION
First you need to find out why the fuel pressure is not rising, it could be you have a restriction or some other loss of flow.
Disconnect the fuel hose from the engine fuel RETURN fitting (at fuel regulator above cylinder #4). Connect a temporary hose to this fitting and place open end in a fuel container. Turn ON the main fuel pump for exactly 1 minute. Record amount in fuel container. It should be at least 6 liters.
Repeat for Aux pump.
Both pumps should provide at least 6 litres. (Max Take-0ff fuel consumption (26.8Lph) + 125%=60.3Lph)

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4 months 22 hours ago #16584 by Bill Hertzel
Bill Hertzel replied the topic: LANE A START UP QUESTION

JUSTIN wrote: We have five engines and the orifice size is 0.7 MM. The other four are normal, only this fuel pressure has a problem.
I checked all the spark plugs today and there was no mistake.And check the connection of the ignition coil but found no problem.Why is it that when I turn on LANE A the engine has obvious shake and RPM decrease?


Have you actually inspected the orifice on the suspect engine.
This is not a time to assume anything.

When operating on a single lane only 4 of the fuel injectors are used.
When both lanes are in service, the two injectors on each cylinder share the duty by injecting on alternate intake cycles.
If you have a bad injector, it may be one of the disabled ones when lane B is operating.

An Injector issue could also be related to the slow fuel pressure increase.

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4 months 7 hours ago #16593 by JUSTIN
JUSTIN replied the topic: LANE A START UP QUESTION

Rob Seaton wrote: First you need to find out why the fuel pressure is not rising, it could be you have a restriction or some other loss of flow.
Disconnect the fuel hose from the engine fuel RETURN fitting (at fuel regulator above cylinder #4). Connect a temporary hose to this fitting and place open end in a fuel container. Turn ON the main fuel pump for exactly 1 minute. Record amount in fuel container. It should be at least 6 liters.
Repeat for Aux pump.
Both pumps should provide at least 6 litres. (Max Take-0ff fuel consumption (26.8Lph) + 125%=60.3Lph)

We checked orifice first when there was the problem,then check the fuel return and fuel flow,finally changed fuel pump.You said the fuel flow we have checked, the main fuel pump and the auxiliary fuel pump are normal value.

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4 months 7 hours ago #16594 by JUSTIN
JUSTIN replied the topic: LANE A START UP QUESTION

Bill Hertzel wrote:

JUSTIN wrote: We have five engines and the orifice size is 0.7 MM. The other four are normal, only this fuel pressure has a problem.
I checked all the spark plugs today and there was no mistake.And check the connection of the ignition coil but found no problem.Why is it that when I turn on LANE A the engine has obvious shake and RPM decrease?


Have you actually inspected the orifice on the suspect engine.
This is not a time to assume anything.

When operating on a single lane only 4 of the fuel injectors are used.
When both lanes are in service, the two injectors on each cylinder share the duty by injecting on alternate intake cycles.
If you have a bad injector, it may be one of the disabled ones when lane B is operating.

An Injector issue could also be related to the slow fuel pressure increase.
This is the new engine, what's the probability that the injector is broken?As far as know that new parts need to be replaced after the injector is removed.But we don't have any spare parts at present, we need to buy additional.Could there be other reasons?we get rid of the other possibilities,finally remove the injector after purchasing the parts.Thank you for your reply.

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4 months 1 hour ago #16595 by Rob Seaton
Rob Seaton replied the topic: LANE A START UP QUESTION
I think you should look at the most likely cause: There is a very, very low probability of the injector being broken as all the engines are thoroughly test run at the factory. But the chance of introducing contamination from the newly constructed aircraft is very high.
Did you test the fuel flow?

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3 months 4 weeks ago #16600 by JUSTIN
JUSTIN replied the topic: LANE A START UP QUESTION

Rob Seaton wrote: Did you test the fuel flow?


Rob ,Thank you for your advice! We checked fuel flow at fuel regulator. Only turn on Main fuel pump is 0.9l/min. Turn on both pumps is 1.7l/min. We repeated it on another engine, is 1 litres when turn on Main fuel pump. Maybe the fuel flow is normal .The fuel pump capacity is approx.120l/h (912is installation manual).

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3 months 3 weeks ago #16633 by JUSTIN
JUSTIN replied the topic: LANE A START UP QUESTION
Why is it that when I turn on LANE A the engine have obvious shake and RPM decrease?Only opened LANE B, the engine start and works very well.Have some relevancy between them(LANE A & FUEL PRESSURE)?

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3 months 3 weeks ago #16637 by Rob Seaton
Rob Seaton replied the topic: LANE A START UP QUESTION
The fuel pressure is controlled by the mechanical regulator so it has not relationship to just Lane A.
Lane A controls half the injectors and half the spark plugs. So you have a plugged injector or a ignition issue.
-Start the engine on Lane B
-Note the EGT numbers
-Turn on Lane A
-Turn off Lane B
-Look at the EGT's the bad cylinder will have a dropping value. That is the cylinder with the injector or ignition problem.

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3 months 3 weeks ago #16647 by Bill Hertzel
Bill Hertzel replied the topic: LANE A START UP QUESTION

JUSTIN wrote: This is the new engine, what's the probability that the injector is broken?...

When I wrote that the Injector may be "Broken" I meant to say that it not Operating as Intended in the general sense, not necessarily specifically meaning that it is defective.

The Low fuel pressure and the Lane "A" problems are likely separate problems with a common root cause.
Both problems could be caused by debris in the Fuel system.
If the input to a fuel injector were blocked and the regulator was unable to close completely, that would explain both problems.

As Rob explained when the engine starts missing, the problem will show up as an EGT change.
If you get the engine running smoothly, the fuel pressure problem may still exist. Don't ignore it!

It is highly unlikely you have two problems at the same time unless they both have a common cause.

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3 months 3 weeks ago #16668 by JUSTIN
JUSTIN replied the topic: LANE A START UP QUESTION
Why is it that when I turn on LANE A the engine have obvious shake and RPM decrease?

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3 months 3 weeks ago #16674 by Bill Hertzel
Bill Hertzel replied the topic: LANE A START UP QUESTION
I would guess that you have 2 fuel injectors both operated by Lane A, CYL#1and CYL#4 with reduced flow.

The RPMs Drop, The MAP Increases, The EGTS Drop, The Fuel increases.
The ECM sees the cold EGTs and the MAP increase, the dropping RPMs and starts to add fuel to compensate.
It thinks that it is increasing the fuel flow, but does not know the bigger squirts are not actually happening.
The Reported Fuel flow is what the ECM "Thinks" it is delivering, Not a true measurement of the actual flow.

Lane A operates 4 of the injectors.
Lane B operates the other 4.
Operating only lane B removes the 2 bad injectors from the Loop. Good!
When you add Lane A to the Mix the engine runs on 2 cylinders but only on every other cycle. Bad!
When you remove Lane B from the Mix and operate Lane A ONLY, the engine runs on only the 2 good cylinders. Worse!

Is operating on Lane A ONLY, worse than operating on BOTH A+B?

The Rough running along with the Fuel pressure issue both indicate a fuel flow problem.
Contamination is the most probable culprit.

It is time to remove the fuel injectors and the fuel regulator and give the fuel lines a good flushing and the parts a good inspection and cleaning.

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