RE: [DML] RE: Strange acceleration problem
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RE: [DML] RE: Strange acceleration problem

Dave,  Here is my answer. 
The demand for fuel is higher when the engine is cold. 
The warm up regulator when cold has about a 1.5 bar of pressure (22PSI ) on
top of the control plunger in the fuel distributor. This allows the plunger
to rise higher allowing more fuel to flow to the injectors in the cold stage
of the engine. In other words it's running richer and needs more gas. 
Then as the car warms up and the resistor in the WUR heats up it allows the
bi-metal arm to start the change from a WUR to a CPR or control pressure
regulator ( CPR ) ( 3.8 bar 55 PSI ) it puts more pressure on the FD control
plunger by not allowing it to rise as high and feed as much fuel to the
About the same time all this is going on the 02 sensor is also leaning out
the fuel by allowing it to return to the tank. Hence: Less fuel is needed in
just a fuel minuets. 
With-in a few minuets after all this is done and the car is popping back
thru the air flow meter like a small back fire, then your running to lean
and normally the WUR is running to high on fuel pressure via the control
plunger if everything else is in order.
If your running ok after heat up then the demand for fuel isn't there as of
yet. But, If the filter isn't changed soon, then it will start leaning out
even after it gets warmed and start popping back thru the air flow meter.
When I'm dealing with the 911 Porsche people about this rich and lean
situation, a new fuel filter is the first thing I sell them or have them put
on. The reason is out of sight, out of mined on the filter and they forget
about it. Then we can analyze after that. The reason they have the problem
is because they redline the RPM's most of the time before they shift or it's
a 930 turbo. 
John Hervey


-----Original Message-----
From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On Behalf Of
Sent: Saturday, October 22, 2005 1:39 PM
To: dmcnews@xxxxxxxxxxxxxxx
Subject: [DML] RE: Strange acceleration problem

Can someone explain to me how a bad fuel filter can cause hesitation and  
back firing only when the engine is cold? 

D² & 6530

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