1980 SC fuel system issues-HELP!

[jay castriotta]

My 1980 SC has started running fair roughly- idles poorly and
backfires when revved too. Prior to this the car would exhibit similar
symptoms intermitently (though always seemed to spontaneously "fix itself"),
but now it seems constant. The car has a 3.2 kit, European exhaust, and
stock K-Jet with the O2 sensor removed. CO had been set to 3.5% when the car
was running properly.

A fuel pressure test showed 55 psi warm control pressure but it took at
least 25 seconds to build that pressure level from the time the car was
started. Attempting to check system pressure by opening the valve on the
gauge actually caused a slight pressure drop and almost stalled the car.
Unfortunately, I can't do fuel delivery volume or amperage draw tests on the
fuel pump at this time because of a problem I encountered with the fuel
filter. I either have the wrong fittings or I have the correct fittings and
the wrong filter. Both fittings that came off the old filter are 14mm
thread (where they go into the filter), but the new filter has 12mm thread
on one end and 14mm thread on the other. The filter I took out had the same
12 and 14 arrangement, but someone had basically forced the fitting in. I
had to cut the filter to get it out. My inclination at this point is very
strongly towards a bad main pump (probably original with ~180,000 miles), but
any suggestions as to other causes for the low pressure reading and/or whats
going on with the filter would be most appreciated.

[emcon5]

Does it still have a frequency valve? If so, is it working? You should be able to feel it buzzing when the motor is running. If it isn't, you may check the power relay under the passenger seat.

Tom

[Nickshu]

Tom may be right. If you disconnect the O2 sensor, you still need the freq. valve...which is pegged at 60% open with the sensor off.

There is a relay which runs the freq. valve under the passenger seat, to the left of the O2 sensor control box. If it does not work, the vehicle will run similar to what you describe....I tried disconnecting it once.

Hope this helps,
Nick.

[jay castriotta]

Curious- where is the frequency valve and where does it live? Any other ways to test it. Thanks for the input!

[Nickshu]

Located behind the fuel distributor. You will hear it buzzing while the engine is idling if you listen in this area (and don't have a Dansk dual-in/dual-out exhaust--I couldnt hear mine if I tried). There is a way you can test its function by jumpering a dwell meter into the line somewhere...but if I recall correctly, you have to have the O2 sensor to do this. It is pegged at 60% open (60% duty cycle) with no input from the O2 sensor. Any compensation for this should be made in mixture adjustment.

Nick.

[emcon5]

It is hard to see, but it is part of a thick fuel hose behind the throttle body, with a electrical plug on top. I tried to get a pic of the one on my car, but it ain't happening, to dark and too much crap in the way. This is a pic of the photo from the Benteley SC manual. To give you an idea of where this is, the little half circle cut off at the top of the pic is the idle adjustment screw. According to the book, the test is to put your finger on it to see if it is vibrating. If it isn't, pull off the electrical connection, and check the resistance of the winding, it is supposed to be 2 to 3 ohms.

If it isn't buzzing, and the resistance is OK, check the power relay under the passenger seat, next to the Jetronic "brain".

Hope this helps,

Tom

[jay castriotta]

I hope you guys are still tied into this Thread- I just wanted to say thanks- replacing the relay for the frequency valve fixed the problem. I really appreciste your help!!!

[john walker's workshop]

one side note, the relay gets it's power from the dome light fuse. the easiest way to see if the frequency valve is working is to unplug the relay and see if the idle falls off. no difference = not working.

[wckrause]

"A fuel pressure test showed 55 psi warm control pressure but it took at
least 25 seconds to build that pressure level from the time the car was
started. Attempting to check system pressure by opening the valve on the
gauge actually caused a slight pressure drop and almost stalled the car. "

Another note:

Taking 25 seconds for control pressure to get to 55 psi is consistant with the cold start operation of the WUR.

You can't check system pressure while the engine is running. You will need to jumper the fuel pump relay so that it runs while the engine isn't running.