Engine backfire - WUR
09-09-2004, 02:20 PM
#1
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Engine backfire - WUR
I have a 1983 911SC 3.0 Euro car. I am having a problem with the car backfiring through the airbox upon rapid acceleration of the engine when it is cold. I recently installed a pop off valve in the air box and the backfire problem seems to have appeared as I can only remember it doing so very infrequently in the past. Maybe it was not as noticeable before as the valve pops open readily now. I have checked for air leaks on the pop off valve and can find none. The car starts fine warm or cold, idles ok, and once warmed up runs great.
In attempting to diagnose the problem I installed a test gauge and recorded the following information.
System pressure – 69#
Control pressure
Engine cold and running – 35# at 80 deg. F (80 deg. F is about as cold as it gets here in the early mornings)
Engine warm and vacuum connected – 56#
Engine warm and vacuum disconnected – 47#
The Warm Up Regulator is Bosch # 0438140089
I have been unable to get any information for my car or a pressure graph for the WUR. The information for the US cars is different as my car more closely matches a 1979 model than an 83’. My car only has a catalytic converter and smog pump. It does not have lambda control or any devices other than the WUR, Aux Air Regulator, Aux Air Valve, Deceleration valve, and Cold start injector and temp. sensor.
Do you have access to pressure/ temp. graph for the WUR?
Do you know if I have the correct WUR for my application?
My WUR has a small screw and jamb nut on the top. Is this to enable it to be adjusted? Did it come that way or was the WUR modified? If it needs to be adjusted with this screw how do you do it?
Do you know where I can get a shop manual for my car? I already have a Bently manual, a Haynes manual, and a Bosch FI manual by Probst. Problem is they do not address some of the unique differences of the Euro cars. An owners manual would be nice to have also.
I know these are a lot of questions. I would like any help you can provide. The nearest Porsche repair facility is a three hour drive from here and they mainly want to mess with race cars. If you cannot help me perhaps you can tell me where to find help.
Thanks
In attempting to diagnose the problem I installed a test gauge and recorded the following information.
System pressure – 69#
Control pressure
Engine cold and running – 35# at 80 deg. F (80 deg. F is about as cold as it gets here in the early mornings)
Engine warm and vacuum connected – 56#
Engine warm and vacuum disconnected – 47#
The Warm Up Regulator is Bosch # 0438140089
I have been unable to get any information for my car or a pressure graph for the WUR. The information for the US cars is different as my car more closely matches a 1979 model than an 83’. My car only has a catalytic converter and smog pump. It does not have lambda control or any devices other than the WUR, Aux Air Regulator, Aux Air Valve, Deceleration valve, and Cold start injector and temp. sensor.
Do you have access to pressure/ temp. graph for the WUR?
Do you know if I have the correct WUR for my application?
My WUR has a small screw and jamb nut on the top. Is this to enable it to be adjusted? Did it come that way or was the WUR modified? If it needs to be adjusted with this screw how do you do it?
Do you know where I can get a shop manual for my car? I already have a Bently manual, a Haynes manual, and a Bosch FI manual by Probst. Problem is they do not address some of the unique differences of the Euro cars. An owners manual would be nice to have also.
I know these are a lot of questions. I would like any help you can provide. The nearest Porsche repair facility is a three hour drive from here and they mainly want to mess with race cars. If you cannot help me perhaps you can tell me where to find help.
Thanks
10-09-2005, 03:28 PM
#5
An engine backfire usually results from a lean mixture. As IXL088 has posted,
your warm control pressure (56#) maybe a little high causing a lean condition.
Your can disconnect the WUR connector for a short time allowing the control
pressure to drop, & then re-correct, to see if the richer mixture resolves the
backfire.
You also need to check that the system pressure doesn't drop under
heavy loads.
your warm control pressure (56#) maybe a little high causing a lean condition.
Your can disconnect the WUR connector for a short time allowing the control
pressure to drop, & then re-correct, to see if the richer mixture resolves the
backfire.
You also need to check that the system pressure doesn't drop under
heavy loads.
