No Frequency Valve Buzz. Im Stumped

[ncp546]

Hey everyone.

I am currently working on my dads early 81. PO had taken the mixture plug out so i know the dwell is going to be off. I am now in the mits of dwelling it back to where it should be. However, my lambda is stopping me i believe. My Frequency valve is no longer buzzing. Come to think of it not sure if it ever has since we have owned it. With the FV not buzzing my dwell is not reading anything at all. That being said when i jump the RPM relay it buzzes and my dwell will read (car off) i have tried a different Lambda ECU, 2 RPM Relays, 2 Lambda Relays, cleaning the ground at the FV, tapping the FV and have now changed the o2 sensor to a brand new one. Am i missing something? Is the mixture so far off that it will not buzz? With the car running one pin on the FV connector is not reading 12V. Car will run very poorly, i have tried getting the mix the best i can by ear just to even have the car move past 15MPH. Any thoughts or info would be very appreciative. Thank you in advanced!

[Bitsyncmaster]

I just though of another reason you may be having problems reading dwell when the engine is running. The lambda ECU runs two ground wires up to the bulkhead connectors and then the engine harness connects those two grounds to a ring terminal that bolts to the engine head. Make sure that ring terminal is bolted to the head.

I think there is a quick connect on the engine harness before going to that ring terminal.

[David T]

If the dwell is off far enough you may not hear the frequency valve buzz. There is a procedure where you turn the mixture screw to just get the injectors to spray. Then you can make your fine adjustment using the dwell meter but of course, the frequency valve MUST buzz and you also do have to plug up the hole over the mixture screw. Try unplugging and plugging the plug on the frequency valve. One some cars I fixed they had bad/dirty connections and that gets the frequency valve to buzz.

[cis6409]

The 2 wires in the frequency valve connector are red/brown which comes from the fuel ecu and red/purple from the 5 pin lambda relay.
Check the bulk head connector. Bottom row (white one) and see if one of the male pins was pushed in too far and not making contact or dirty/loose.

Another check is With a multimeter check both grounds for the frequency Valve at the fuel ecu behind drivers seat , you ll have to remove the black long connector and check pins 5&16. They both need to have continuity to battery ground.

Shane

[ncp546]

Thanks for the inquires guys. Someone must have answered my prayers because I went back to start testing more options and the FV is now buzzing. I am getting a dwell reading but it’s not moving so I believe I am in open loop? 60CB8569-F082-4445-B2AF-4A6B14D32758.jpg

[David T]

The motor has to warm up to get in to "closed loop" and the O2 sensor has to be working which means the mixture has to be at least close. Go to D:04:15. There are different conditions you can test the Lambda system.

[ncp546]

Visiting this thread again. FV stopped. Again. I have no 12V to the plug at the FV. I have 12V to the lambda relay. I’m not too amazing with a multimeter but I believe I have connectivity at pins 5/16 behind the drivers seat lambda computer. If I unplug the o2 sensor not a thing changes. If I push the full throttle plate not a thing. However if I still jump the brown and yellow/red striped wires at the rpm relay it will buzz.

[Elvis]

Hi, someone gave you wrong information, the FV always has to buzz when the engine is running.

When the mixture is too far off it will eventually restart with a starting PWM and try to get back into the control loop.

your problem might simply be the RPM relay - broken solder connection of the relay. known problem that they need
some TLC every 20 years or so :-)
It's a simple repair.

[ncp546]

Hi, someone gave you wrong information, the FV always has to buzz when the engine is running.

When the mixture is too far off it will eventually restart with a starting PWM and try to get back into the control loop.

your problem might simply be the RPM relay - broken solder connection of the relay. known problem that they need
some TLC every 20 years or so :-)
It's a simple repair.

Awesome place to look! Dave M also pointed me into the direction of the rpm relay. Turns out inside the white connector that plugs into the rpm relay the yellow/red stripe wires had their terminal not touching the rpm relay. It was hard to find, but after replacing the terminal the car is back up and running!