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-   -   Old wren help (https://www.rcuniverse.com/forum/rc-jets-120/11643238-old-wren-help.html)

Larrythelathe 11-27-2017 01:39 PM

Old wren help
 
Hi I brought a secondhand model with a old wren in it. I thought he had serviced it but I am having trouble and need help!

So I will try and exsplain what happens. Its a wren 54 gas start. I have set the gas valve to one and half turns out as per the manual. However I don't get the pop until about 2.5 turns out. The glow plug is strong and nicely pulled out. So at 2.5 turns it starts up with a god lot of blue flame. The turbine increases in speed to the ramp point. Then it seems to slow some and the. Flames out saying low RPM.

I am stuck anyone?

siclick33 11-27-2017 02:15 PM

We need a lot more info to be able to help (ECU settings etc).

The first thing I would check is that you don’t have the gas and fuel lines reversed.

Dave Wilshere 11-27-2017 02:22 PM

Pull the glow plug coil out further.
Check the pump is not stuck by jumping it on a battery for a split second

Larrythelathe 11-27-2017 02:23 PM

Ok
 
So stock settings as per wren 75 manual. I can not copy and paste the PDF part for some reason.

Lines are correct. It will occasionally do a start. Runs fine then

Larrythelathe 11-27-2017 02:24 PM

Plug
 
Plug is at max its straight U its OK so much. Fuel pump is ok

ira d 11-27-2017 02:25 PM

Sounds like its not switching over to Kero after lighting off on gas, could be a weak battery or something not right with the fuel pump or valves. I would use the test mode to test fuel flow to insure pump and valves
are working with no obstructions in any lines, also check to see if the temps are rising after a light on gas. A word caution do not start the engine to much on gas if its not getting kero because that will destroy the bearings.

Larrythelathe 11-27-2017 02:27 PM

Heat
 
Ye that's why I am trying understand it. It all works in tests. Its like I need the kero sooner

siclick33 11-27-2017 02:29 PM

Does the ECU show ‘fuel ramp’ before the low RPM? Does it light on the kero and not ramp, or not transfer over to kero at all?

What temp does it get to? Are the RPM indications correct?

ira d 11-27-2017 02:29 PM


Originally Posted by Larrythelathe (Post 12386787)
Ye that's why I am trying understand it. It all works in tests. Its like I need the kero sooner

What type of battery and are you sure its a good battery?

Larrythelathe 11-27-2017 02:34 PM

Batt
 
Hi. Yes its a optipower 3500 2s.

ira d 11-27-2017 02:49 PM

Seems that battery should start it, also check the things that slick 33 suggested. I assume you have purged the fuel lines and fuel is right at the engine and you should be able to see the fuel in the line and observe if
the fuel starts to move as soon as the engine lights of on gas, if not it would suggest the ECU is not seeing a temp rise although I would think it would indicate low temp but it could also be a fuel pump or valve issue.

I dont own a Wren but I have a friend that has one and I am thinking when you check the pump in test mode it receives more power than when at start up and a tight pump may not run but will in test mode.

Si_B 11-27-2017 03:09 PM

If you take the glow plug out and look into the hole, can you see a pipe passing across it?

Simon

jason 11-27-2017 04:07 PM

sounds like the gas is getting cold and not 'gassing off' any more and/or the pump start ramp needs adjusting.

joeflyer 11-27-2017 05:39 PM

What are your values of PUMP START POINT and PUMP START RAMP parameters?

First make sure that the thermocouple extends about 1/8" to 3/16" into the exhaust cone. If it's not in far enough it won't see enough of a temp. increase and switch over later then it should.

PUMP START POINT - A good default value is AUTO+2. If it's less than that increase it. This sets the pump speed when it first turns on. A higher value will increase pump rpm, lower is slower. If you're getting a yellow flame when the pump first starts then lower the value.

PUMP START RAMP - A good default value is 6 . This parameter sets the pump rate of increase after it initially starts. 1 = slowest and 10 = fastest. If it takes too long to get to idle then increase the number. If you're getting yellow flames during Fuel Ramp then decrease it. The correct value depends on how strong your pump is and your fuel system restriction.

You may have to play with these parameters to suit your application. Use your HDT and pay attention to what the engine is doing during each phase of the start.

Joe

ravill 11-28-2017 08:57 AM

I have stopped using a fuel solenoid with my propane start jets. I've seen them gum up and can have the symptoms you describe.

An easy way to check is to disconnect the fuel line at the turbine and try a start to see if fuel comes out. If you are worried about running your bearing dry, pour some kero down the engine then blow it out and then do a start.

Good luck!

Larrythelathe 12-01-2017 12:12 PM

Does anyone have the standard factory settings?

Also why can I on!y post five times

Mugu 12-01-2017 10:50 PM

you must check that the optical sensor does not enter the light

joeflyer 12-02-2017 05:29 AM


Originally Posted by Mugu (Post 12387780)
you must check that the optical sensor does not enter the light

Wren uses a Hall (magnetic) sensor, not optical.

joeflyer 12-02-2017 05:32 AM


Originally Posted by Larrythelathe (Post 12387692)
Does anyone have the standard factory settings?

Read post #14. If you can't get it to start by adjusting those parameters, then you need a new fuel pump.

Mugu 12-02-2017 05:55 AM


Originally Posted by joeflyer (Post 12387824)
Wren uses a Hall (magnetic) sensor, not optical.

old wren 54 with orbit ecu have optic rpm

joeflyer 12-02-2017 08:08 AM


Originally Posted by Mugu (Post 12387834)
old wren 54 with orbit ecu have optic rpm

I wasn't aware of that. However, the vast majority of Wrens have Gaspar's ECU with a magnetic sensor. We don't know what the OP has. My parameter discussion above applies to the Gaspar ECU. Most likely his problem is the fuel pump (been there, done that).

Larrythelathe 12-02-2017 04:59 PM

Sensor
 
Mine has the optical sensors but they have been made redundant and no longer connected. RPM is fine. I can get it started I just cringe as its a blow hot flame out the back.

jefff 12-02-2017 10:00 PM

I have settings for Fadec and Xicoy ECUs that I run on my Homebuilt Wren 54s. You can run them in the manual or auto mode. What ECU are you running? Auto start or manual mode? If your flame is coming out at start up it sounds like you are feeding in to much propane. Does your Wren have two glow plugs?

Larrythelathe 12-02-2017 10:02 PM

Gas
 
I would agree but if I try less gas it does not light. I will look at what ecu I have. I have just the one plug

Mugu 12-02-2017 10:07 PM


Originally Posted by Larrythelathe (Post 12387967)
I would agree but if I try less gas it does not light. I will look at what ecu I have. I have just the one plug

try to instal the glow with no the brass oring, to go more inside and have to start with low gas


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