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Intermittent Frequency Valve Operation + Dwell Meter Tuning
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nrwheele  



Joined: 07 Apr 2019
Posts: 15
Location: New York

PostPosted: Tue Jun 01, 2021 6:51 am    Post subject: Intermittent Frequency Valve Operation + Dwell Meter Tuning Reply with quote

I've recently replaced a number of old fuel/ignition system components on my '81 N/A (the list is as follows):

- New fuel injectors + O-Rings
- New AAV
- Refurbished WUR
- New Bosch Fuel Pump & filter
- All new vacuum lines
- O2 sensor
- Spark Plugs, Wires, Distributor Cap and Rotor (confirmed timing was set properly)

While idle seemed fine, it was feeling pretty sluggish while driving (which is not unusual for my car), so I wanted to confirm that the AFR was set properly. Since I have the lambda system, I wanted to set it using a dwell meter, so I followed the process from a number of articles here - let it warm up properly through a few radiator fan cycles, connect the positive lead on the meter to the black wire on the test port, negative terminal to ground, and try to get the dwell reading near 45 degrees.

While doing this process, I could hear the frequency valve buzzing, and when it was, the values on the dwell were pretty close to what I wanted (between 40 and 55 while I was trying to get it to settle around 45). Then, suddenly, I could hear the engine note change, the frequency value stopped buzzing, and the dwell meter was reading 0 constantly. It would stay this way for a bit, then I heard the frequency valve kick back in for a moment or two, and when it did, the dwell jumped back to roughly where it was previously (between 40-55), then the frequency valve would cut out again, and the reading would peg at 0.

I tested the frequency valve according to the shop manual, and the resistance was in spec (between 2 and 3 ohms); I also just smoked tested the vacuum system and everything seemed to be sealed up properly.

My main question is, what controls the frequency valve in the system? Is it normal for it to work intermittently, or are you supposed to hear the buzzing constantly when it's running?

Since I've owned the car, I've felt power surges while driving - the car would idle fine, but feel slow to accelerate. After driving a while under load, the car would bounce back and forth between having power and being sluggish; when it finally settled on the power end, the car felt nice and responsive at all speeds, good acceleration, etc. I have a feeling that it is related to the problem I'm hunting down now, but I'm not sure how.

I'm at my wits end here trying to figure out what's going on, so any advice on the frequency valve/lambda system/dwell meter tuning would be greatly appreciated!
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW

PostPosted: Tue Jun 01, 2021 2:44 pm    Post subject: Reply with quote

Valve is run by the lambda computer taking input from the O2 sensor and throttle switch.

I'd start by checking the throttle switch for function and adjustment. I'd also check the big connector to the computer for corrosion and fitment.
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nrwheele  



Joined: 07 Apr 2019
Posts: 15
Location: New York

PostPosted: Tue Jun 01, 2021 11:30 pm    Post subject: Reply with quote

Appreciate the advice! I'll start checking those two things out. Just to clarify (and please forgive my ignorance on lambda/K Jetronic, this is all fairly new to me), but when you refer to a "lambda computer", are you referring to the EIS unit? Or is there some other computer that I am totally unaware of? I didn't think the models as early as mine had anything else, but it wouldn't surprise me if they did. I'm just trying to wrap my head around how this lambda system works.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2315
Location: MI

PostPosted: Wed Jun 02, 2021 1:17 am    Post subject: Reply with quote

Sounds to me like you are loosing power or ground intermittently to your lambda system..

Their should never be a time that the frequency valve goes to 0 as long as the fuel pump power circuit is running..

The switches on the TB make the frequency change a bit, but will never make it go to zero..

Frequency valve operation is critical to a good running car..

The lambda computer is under the dash to the right of the steering column I believe..
Power is on the fuel pump circuit and not sure where it grounds..

I would be checking it’s power to see if it stays on while the FV is cutting out, and checking it’s ground..

You seeing it go to zero from the black test wire indicates that it is the signal to the frequency valve stopping, and not a problem with the FV itself..
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nrwheele  



Joined: 07 Apr 2019
Posts: 15
Location: New York

PostPosted: Thu Jun 10, 2021 11:55 am    Post subject: Reply with quote

Thanks for all the advice! This is why this forum is invaluable.

I'd just like to clarify one point on this topic - the dwell meter I am using is a digital one, and when the meter is on the 4 cylinder setting, without the leads being attached to anything, the value is registering as 90 (typically a little closer to 88.5, but roughly around there). This value of ~90 also holds when the leads are connected to the test port but the car is off, i.e. when the lambda computer is not providing a signal. From what I understand from my reading, anything below the golden number of 45 means the engine is running rich, anything higher and it's running lean.

I'm not sure if that is how dwell meters typically operate (this is my first time using one), but the values I'm getting seem a bit backwards to me. If my understanding is correct, I think that means that when my frequency valve cuts out, my engine is running super rich when it is reading 0.00, and the lambda computer may actually be functioning correctly and reading the condition as rich.

My guess (and I may be completely wrong here) is either A) the lambda computer has an issue (grounding, something else weird), or B) Something is causing my car to have a temporary rich condition. Maybe the AFR is just that far out? I'm really not sure where to begin looking for something that causes a temporary rich condition if that is really the case.
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Thu Jun 10, 2021 9:14 pm    Post subject: Reply with quote

Neh..
Your reading the output of the lambda based on what it decided to do because of whatever the O2 sensor reads, not reading the O2 sensor..

When the lambda is operating and its reading the O2 as rich, the number will go down, reducing fuel flow from the fuel distributor..
If it’s set too lean the lambda will compensate by raising the duty cycle to increase fuel flow..

It should never read zero while it’s operating.. It doesn’t go low enough to go to absolutely zero..

It is a bit weird that your gauge defaults to 90..
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924-76  



Joined: 05 Jun 2006
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Location: Ontario, Canada

PostPosted: Thu Jun 10, 2021 11:34 pm    Post subject: Reply with quote

Have you try unplugging the O2 sensor?
When you unplug the O2, the Lambada system goes to safe mode and run on 50% cycle (or something like this), providing a rich mixture (somewhere around 9 or 10 AFR) as safety for the engine.
This would take away some component while you are troubleshooting.

I have an 80 924 turbo and I'm running without the O2. All I had to do is reset the idle mixture and problem solved. My O2 kept going on and off, so the car was running fine for 20-30 min and then going rich for a bit and so on. I changed the O2, but the problem persisted, so I pulled it off and been running fine since.
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nrwheele  



Joined: 07 Apr 2019
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Location: New York

PostPosted: Fri Jun 11, 2021 1:50 am    Post subject: Reply with quote

Thanks for the detailed explanation Fasteddie313, the lambda system is starting to make a lot more sense to me.

It makes sense that the dwell should never read 0; since mine is apparently backwards, then on a normal dwell meter, it would be pegged at 90 I'm guessing? I'm still not certain what would cause the lambda computer to output that. If I understand your explanation, that would mean my mixture is severely leaning out then if the number is rising to 90? Should the lambda computer ever even get to that point?

Per your post 924-76, I'll try unplugging the O2 sensor just to remove it from the equation temporarily and see what happens then. I assume there is some kind of quick disconnect for the O2 sensor other than disconnecting it AT the O2 sensor? I've seen mentions of the wire that can be disconnected along the driver's side fender (the one that leads to the EIS unit), but I wasn't sure if that wire was the O2 sensor connection or something else entirely.
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Fri Jun 11, 2021 2:50 am    Post subject: Reply with quote

Is your frequency valve even running while you see your meter pegged either at zero or 90?

Feel the frequency valve.. it vibrates a lot..

If it is ever not running, their is something wrong..

I still suspect your power and ground to the lambda computer itself..
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nrwheele  



Joined: 07 Apr 2019
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PostPosted: Fri Jun 11, 2021 3:54 am    Post subject: Reply with quote

When the dwell meter pegs at 0 (or 90, depending on how you look at it), the frequency valve is NOT running. When the engine is running (somewhat) well, the dwell reading is fluctuating around 43-47 and I can clearly hear the frequency valve buzzing. When the the engine bogs down (and all of this is at idle, btw, not even under load), that is when the dwell meter hits 0/90 and the frequency valve does not seem to be running. How long it cuts out for varies, but when it resumes, the dwell readings bounce back to a somewhat normal range, and the engine seems to be running smoothly.

I'll definitely check the power sources if I can find their locations. My other though is, is there anything else that feeds into the lambda computer? My thought being a temperature valve or something along those lines that's dying and giving incorrect data?
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Fasteddie313  



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PostPosted: Fri Jun 11, 2021 4:54 am    Post subject: Reply with quote

Switches on the throttle body afr for the lambda system also..

NOTHING that the lambda system sees or does would ever have it completely stop operating the frequency valve..

Frequency valve always runs at some duty cycle no matter what the lambda is up to..

If it is completely stopping, something is wrong completely stopping the lambda system somehow..
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nrwheele  



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PostPosted: Fri Jun 11, 2021 5:15 am    Post subject: Reply with quote

What is confusing me the most is, if the lambda computer was losing power, I would expect my meter to be reading 90, like it does when it is disconnected or the car is not running. With it jumping to the opposite extreme, I'm guessing SOMETHING is stopping the frequency valve from operating, and the computer is reading it as such. The frequency value is in spec for its resistance, but maybe it has a bad electrical connection or something along those lines?
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Fasteddie313  



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PostPosted: Fri Jun 11, 2021 5:40 am    Post subject: Reply with quote

Maybe your meter is reading a slight resistance there making it read 0..

What does it read with your car completely turned off?
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ted von Kampen  



Joined: 14 Oct 2016
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PostPosted: Fri Jun 18, 2021 7:19 am    Post subject: Frequency valve and ECU and O2 sensor Reply with quote

I recently got my Lamda system running on my 81. Took awhile to get going as the O2 sensor was disconnected. I had been using the O2 sensor wire to check mixture. It should read 0.5 VDC at 14.7 to 1 mix ratio. However I was chasing acceleration and mixture. In the course of getting the Lamda back on line, I discovered the O2 sensor went open circuit and no longer worked. I got a new one and when installing I found my old sensor was loose and not screwed in the pipe tightly. Mine is working and the frequency valve runs all the time and I can use the dwell meter to read out. My advice is check the O2 sensor for tightness and consistent output. Just put a voltmeter from the sensor wire to ground and run for awhile. If the sensor goes open circuit intermittently it might be the source of your problem.
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nrwheele  



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PostPosted: Sat Jun 19, 2021 8:57 am    Post subject: Reply with quote

I recently replaced my O2 sensor on the car, but I haven't tried reading the output of the sensor directly, so that will probably be my next test.

I was actually able to have some success in the tuning department. I'm not sure what was different from previous attempts, but the frequency valve was buzzing nicely for a good 15 minute period, and I was actually able to tune it with the dwell meter. I even gathered up the courage to take the car around the block a few times. While the frequency valve was running, the car felt fantastic, setting the AFR properly made a huge difference. A couple times when I was driving, I could tell the valve stopped working because my power was suddenly gone, and when I pulled in at my home, and checked under the hood, the valve was silent.

I appreciate the advice Ted, especially from someone who just fixed theirs on the same model year. I'm obviously not a lambda expert here, but per Fasteddie's excellent explanation, the frequency valve should never stop even if the O2 connection is poor (even if disconnected entirely, it should run at the preset duty cycle if I remember correctly). My current thought is that either the lambda unit is faulty or there is a wiring problem somewhere (my guess is the latter, due to its intermittent nature).

I'll certainly check my O2 though (thanks again on the advice), I want to get every part of this lambda system sorted so I can actually enjoy this car before winter

If you have any other tips on getting the lambda system up and running, I'd love to hear them!
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