Replace Frequency Valve?

jeffephrata · 07-13-2014, 05:52 PM

I am working on my new to me 82 911 SC Targa (mint green...I call it the PGM (pee green machine). I replaced the front valance with the original one since this picture was taken.

I'm kind of old, can't see very well and this is my first 911. I like it but it is frustrating not being able to see much inside the engine compartment. The car only has about 63,000 miles on it and is in great condition...it had been stored for a long time when I purchased it last month.

Oddly enough, it starts right up and runs fine...but I don't think the frequency valve is working.

Every once in a while, I will hear it when I turn the key on, but mostly it does not buzz or vibrate at all. I have installed a new O2 sensor on the Cat and also put in a new relay, but nothing changed. I can't get at the valve to test continuity.

I also noticed that the connector for the O2 sensor wire located in the engine compartment was badly cracked, almost broken in 1/2...thinking that this connector might just provide continuity, I glued it back together (!). I'll buy a new one...

1. Can the frequency valve be removed if the rubber air cap is removed first to provide access to it?

2. Should I just replace the frequency valve or are there other culprits which should be checked out first? I did replace its relay (under the passenger seat) with a new one and none of the fuses are blown. I also checked the O2 test plug for power and ground and it is ok.

3. In addition to replacing the relay, I started out this project by installing new spark plugs, distributor rotor and cap and insulated plug wires, new vacuum lines and some of the oil breather hoses. I also adjusted the valves and timing.

The Capacitor box hums when it is turned on. I assume this is normal.

I need some advice! Thanks, Jeff

Bob Kontak · Bob Kontak's Garage

Hey Jeff,

That's my son's name.

Love the color.

Where are you located? I think we can get you straightened out.

Get one of those $30 flashlight headbands from Home Depot or Lowes for starters. I am 57. I can't see squat without the headband and stout reading glasses.

The O2 connector is part of the original harness. However, there is a guy here that makes a nice replacement unit and it's just what you need.

There is a very small chance your freq valve is toast.

I will send you my phone number via the private messaging if you want to chat. Can't say I will fix the problem but I have wrestled with this stuff enough to know a little.

All the best.

don gilbert · don gilbert's Garage

Get a dwell meter and check it at the test plug. Lots of threads on checking it, never ever have i come across a bad f. valve. Can you feel the relay under the seat click when you turn the key on?

don gilbert · don gilbert's Garage

The f'valve not only keeps the mix at stoich, it also enriches the fuel mix when you go past the 35degree switch on the throttle body. At high rpm's, you are lean (not good) if your control press is to high, you are very lean. Some are hard to hear, some are loud,,but put your hand on it and you can feel it buzz. Its just a elec fuel injector bleeding press. from the head. Dwell meter is the best bet though, must have an operating 02 sensor.

john walker's workshop · 07-13-2014, 07:40 PM

did you check the interior light fuse? the relay gets power from it. a test light at the relay plug should show 12V at 87 and 87A. one to the computer and one to the FV.

don gilbert · don gilbert's Garage

Getting old and forgetting things...worst culprits are the grounds under the seat for the control unit. Remove seat, sand and prep. contact area of the ground wires, there are several , apply d. grease

T77911S · 07-14-2014, 02:25 AM

Quote:

Originally Posted by john walker's workshop

did you check the interior light fuse? the relay gets power from it. a test light at the relay plug should show 12V at 87 and 87A. one to the computer and one to the FV.

could also be just a bad connection of the fuse if it sometimes works.

i would think if it was not working it would not run or run very badly.

jeffephrata · 07-14-2014, 03:23 AM

I will try all of the above, thank you. I do have a dwell meter, but not an O2 sensor. I think I might be able to borrow one locally. Thanks again, j.

don gilbert · don gilbert's Garage

You can get a bosch one wire at O'rilys for 20 bucks that will work fine, unless you want to pay 120.00 for one with the factory connector. You can cut the old conn. off and just crimp.

blpetry · blpetry's Garage

Just went through this... As others have said, your car will run like total crap unless your FV is operating. Also, I don't believe you will ever hear it operating unless the engine is running, and its difficult to hear over all the other stuff going on.

I don't think you need to even check it, but you can by removing the airbox cover and air filter, turning the key on, and reaching in and *briefly* pushing up gently (one finger is all that's needed) on the metering plate back in there. When you do this you should hear two noises, but they are distinguishable from one another. The first is the squeal of the injectors squirting fuel into the cylinders and the second will be the distinct and buzz of the frequency valve. Of course, the CD unit will be humming, but that starts when the key is turned to the on position (and if you're over 50, you may not even be able to hear it at all

.

You are squirting raw fuel into the cylinders while doing this, so keep it to a minimum, and consider waiting for awhile to start after doing it.

HTH
Brian Petry
Springboro, OH

boyt911sc · boyt911sc's Garage

Jeff,

The FV relay gets power from fuse #18 and this is the electrical circuit for the dome interior light, glove compartment, FV, etc. The FV relay is energized by the power coming from the FP terminal (30 @ FP relay socket).

Test run the FP (manual operation) by jumpering terminals 87a & 30 (FP relay socket) with ignition switch @ ON/RUN position (not start). Once the FP is running and there is power from S18, the FV should start to vibrate. Use your left hand to reach behind and below the throttle body. There will be a distinct vibration you could easily detect once you touch the FV.

BTW, unless you have a super sensitive hearing, the vibration (sound) of the FV is hardly audible. Keep us posted.

Tony

hbkramer · 07-14-2014, 10:35 AM

Jeff,
might you be hearing (or not)

the fuel pump buzz.
kramer

Bob Kontak · Bob Kontak's Garage

Just spoke with Jeff on phone. Nice guy.

I offered to call because I just thought if he can't see as well as the rest of us, a little help over the phone is not a bad thing.

I am taking the liberty to speak for Jeff. He fiddled with fuse, component connections and the car is running smooth. He is keen to do the dwell meter test. He can hear the cycling of the engine at idle when in closed loop. Looks good for him.

He is interested in the name of the fellow that made the batch of 02 connectors.

Here's the link - louie85

O2 Sensor connector

jeffephrata · 07-14-2014, 12:18 PM

I hope I am not repeating myself, but this might just appear twice. I used to work at a software company and now I am even more computer illiterate than ever! Anyway, thanks to all of you and especially Bob for the good advice. I checked and adjusted the mixture so that at 950 RPM the dwell cycles from about 42.5 to 46, maybe not that much, but in that range, so I am going to leave it as is until the temperature and humidity improve in Pennsylvania. The FV must be working to get that cycle effect. However, I still hear a rather loud buzzing (which I thought was the FV and is not) from the rear of the car. Not all of the time either. Chipmonks?