# dwell meter cis



## konakle (Feb 8, 2010)

I have a 1984 rabbit gti. When checking the dwell for air fuel ratio with the lambda test port i am gettieng a reading of 9.9 to 10. I believe this is running rich. Turning the allen screw on the feul dist. doesnt change it a bit. Even with the o2 sensor unplugged. What would make this car run so rich? I've checked timing, new plugs, air filter, fuel filter, fuel pump, dist. cap and wires, injector seals. The car only has 112,000 miles and is clean as a whistle.


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## murphysf (Jun 15, 2009)

*Dwell Meter Connected and Configured Correctly?*

Interesting Post, I also have a 1984 GTI and just failed smog two days ago. I came to the forum to ask a question about the lambda dwell readings. 

But first, about your problem. Does your dwell meter have a cylinder setting? Are you on 4cyl, if there is not a 4cyl setting you could put it on 8 cyl and just double the reading that you are getting. 

With the car warmed up and at idle the dwell should be between 40-50, 30-40 or lower is rich and 50-60 or higher is lean. 

The lambda signal should fluctuate or oscillate between two values, for example on my car it oscillates between 40-46 degrees. 

I noticed that with the O2 sensor disconnected the system is open loop and defaults to a steady 40 degrees. 

If you are truly getting 10 degrees I would suspect a faulty fuel injection control module. 


As I said earlier, confirm that your dwell meter is configured and functions correctly. 

Have you measured the voltage coming out of the o2 sensor?


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## konakle (Feb 8, 2010)

I have not taken any voltage readings off the o2 sensor yet. I used a dwell meter from a guy i work with. He had an old analog dwell meter that he has had for years and it gave me a reading of 10. I thought well its an old meter, so i bought a new one with 4 cyl setting,[digital] and it gave me the same exact reading.


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## murphysf (Jun 15, 2009)

*frequncy valve?*

can you hear the frequency valve buzzing? its located just next to the fuel dist


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## konakle (Feb 8, 2010)

Yes i can. The buzzing comes and goes. I was told this is due to the o2 sensor relaying info to it.


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## ny_fam (Apr 3, 2004)

Could be your O2 sensor is bad, also when you make a change to the mixture you really need to rev the engine past 3k rpms a few times then let it settle. Also before you test you have the let the fan cycle two times so that you know its warmed up enough.


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## konakle (Feb 8, 2010)

I checked voltage at the o2 sensor and it bounces between .007v and .014v. The car is warm when checking it. fan has run a couple times. If the o2 sensor was bad, when i unplug it shouldn't it lean itself out. I also checked the cold start valve today. I took it out and put it in a bucket, started the car and nothing came out. it was already warm so nothing should come out. I know thats not stuck open now.


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## Glegor (Mar 31, 2008)

konakle said:


> I checked voltage at the o2 sensor and it bounces between .007v and .014v. The car is warm when checking it. fan has run a couple times. If the o2 sensor was bad, when i unplug it shouldn't it lean itself out. I also checked the cold start valve today. I took it out and put it in a bucket, started the car and nothing came out. it was already warm so nothing should come out. I know thats not stuck open now.


o2 sensor should have almost a full volt coming out of it..


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## konakle (Feb 8, 2010)

Glegor. Your post made me think. I had the volt meter on ac. On dc the o2 sensor reads .819v. I did some searching again today and found a fuel injector, by testing it with starter fluid, to have a leak. Even though i changed the o rings, something is leaking. Did more research and found the injector holder has a gasket also. Only one cylinder almost stalls the motor out when being sprayed. I'll try new fuel injector holders and gaskets and see what happens. Thanks. I'll get this car running like new!


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## konakle (Feb 8, 2010)

So i had some time today and tried the dwell meter again. This time i checked and the motor was slightly warm. Started it and it read 24.6 and about 20 seconds later it went down to ten again. If i'm right this means it was lean upon start up then got rich. I would think this would be the other way around.


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## ABA Scirocco (May 30, 2001)

konakle said:


> Yes i can. The buzzing comes and goes. I was told this is due to the o2 sensor relaying info to it.


You were told incorrectly, the O2 sensor does NOT relay anything to the frequency valve, both the O2 sensor and the frequency valve communicate ONLY with the ECU. The ECU receives a 0-1V signal from the O2 sensor and it sends a 70 Hz pulse width modulated signal to the frequency valve. It's this 70 Hz signal from the ECU that causes the buzzing, it is (or should be) constant, if the buzzing of yours comes and goes, that's the first thing you need to fix. Don't even bother trying to adjust the mixture until you've got the frequency valve buzzing continuously. BTW, the most likely cause for a flaky frequency valve is an intermittent fault in the ground circuit for the ECU. 

If you chart the performance of the frequency valve over time, the changing duty cycles would look like this.









There are four modes of operation for the CIS ECU, they fall into two categories, closed-loop and open-loop. There is only one closed-loop mode in it, the ecu accepts the input signal from the O2 sensor and adjusts the pulse width it sends to the frequency valve accordingly, reducing the pulse width corresponds to leaning out the mixture. In open-loop mode, the ECU ignores the signal from the O2 sensor and drives the frequency valve with a constant pulse width. There are three closed-loop modes, warm-up mode used when the engine is first started up, this gives time for the O2 sensor to come up to operating temperature, the oxy-themo switch controls whether or not the ecu runs in warm-up mode. The second open-loop mode is full throttle enrichment mode (WOT mode), it's controlled by the throttle switch (not all models have this). And finally, there's limp-home mode, if the ecu isn't in one of the other closed-loop modes AND it's not receiving a proper signal from the O2 sensor, it switches to limp-home mode and drives the frequency valve at a constant 50% duty cycle. It's important to note that during any of the open-loop modes, the ECU is operating strictly on pre-programmed values and it has no idea at all what the mixture is actually for this reason it's important to get the base mixture setting right or the pre-programmed values may result in a mixture that's WAY out.


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## konakle (Feb 8, 2010)

Thanks for that info. I checked the grounds coming through the fire wall and cleaned them. These are the ones coming from the ecu. The frequency valve buzzes for the first 15 seconds of start up then you cant really hear it. Also when checking the dwell, as i have stated before it reads ten and if i close the full throttle enrichment switch it goes to 14.4. Am i not understanding this right. I thought if the numbers went up it was leaning the mixture. Closing this switch also triggers the fv to buzz again. Unpluging the o2 makes it go to 14.4 too.
How can you test the frequency valve? I know, I have looked but all tests explained that i have seen are vague.


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## konakle (Feb 8, 2010)

I also checked voltage at the frequency valve. It wasnt buzzing so i unplugged it. across the two terminals i had 10 volts. Hit the full throttle enritchment and i get 12.6


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## ABA Scirocco (May 30, 2001)

Depending on ambient noise etc, you may or may not always be able to hear the frequency valve buzz but nevertheless it should be operating all the time, if you can't hear it, you should be able to feel vibrate when touch it. I don't if it's the same on all VW's but on my Scirocco, the ecu grounds to the engine at the cold start valve, the last time I had symtoms remotely similar to yours, it was that connection that was faulty. You can check the resistance of the frequency valve coil, I don't have the specs in front of me now but I'll get them to you later. Other than that, I know of no direct test for the frequency valve, all of the other tests are indirect i.e. observing how the engine behaves when you manipulate the duty cycle. 

What are you using to measure the duty cycle? I ask because numbers like 10 and 14.4 are not what used to seeing, typically if everything's set up right you can expect to see around 50% when running normally and something like 67% with the throttle switch closed.


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## ABA Scirocco (May 30, 2001)

konakle said:


> I also checked voltage at the frequency valve. It wasnt buzzing so i unplugged it. across the two terminals i had 10 volts. Hit the full throttle enritchment and i get 12.6


About those two terminal, one gets power directly from the fuel system relay, when measured against a good ground it should be at or near battery voltage whenever the fuel pump is running, that's what powers the frequency valve. The other wire (iirc,it has a brown strip) goes to the ECU and get grounded at 70 Hz at whatever duty cycle the ECU determines is appropriate because this wire isn't a consistent solid ground, the voltage reading between the two terminals doesn't really tell too much. 

BTW, how well does the engine run with the frequency valve disconnected? It should run like crap and smooth out when you reconnect it.


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## konakle (Feb 8, 2010)

I did check the red w/black stripe to ground and had 12 v. When i cant hear the fv operating and unplug it there is no difference. Unplug it plug it back in still no difference. it buzzes when i first start the car and the motor sounds good then the buzzing dies out and it idles a litttle rougher. Not bad though. Im using a multimeter with a 4 cyl dwell setting on it. And the brown and blue wire test port.


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## ABA Scirocco (May 30, 2001)

Is this car new to you? Because it sounds like maybe a previous owner was having problems with the frequency valve and adjusted the mixtured screw to the point where it would run reasonably well with the frequency valve disconnected, I've done this myself as a temporary "fix" so that I could drive the car until I had time to fix it properly. 

In any event, you've got to get the frequency valve working properly before you can adjust the mixture. There are only 3 things that can cause the frequency valve to malfunction, a faulty ecu, a faulty frequency valve or faulty wiring into or out of the ecu. It's been my experience that the ecu and frequency valve are very reliable, the same can't be said of the wiring. So, it still sounds like it could be a faulty ecu ground to me, check the grounds at the wiring harness at the ecu. DO NOT use a volt meter or ohm meter to check them, use something that draws a fair bit of current like a light bulb, on the ecu wiring harness, it's pins #2 and 10 that are the grounds, if the light bulb glow more dimly when connected to the wiring ground than it does when connected directly to the negative terminal of the battery, that's an indication that the ground circuit is weak.


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## konakle (Feb 8, 2010)

Yup the car is new to me. Its in pretty mint shape. Just want to get it running perfect if i can. I'll check those at the ecu. And thanks for your help on this. I appreciate it!


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## ABA Scirocco (May 30, 2001)

Good luck! Let us know how you make out.


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## konakle (Feb 8, 2010)

Update! 
So i got the new fuel injector holders, rabric washers and injector seals in the car. Wouldnt you know three of them I could twist out by hand. One of them I could wiggle around before trying to take it out. Started the car and revved it. It stumbled like crazy. So I leaned the mixture out a bit and the frequency valve started buzzing again. Revved it up and got know hesitation at all. Took it out for a ride and it drives awesome. I still think some more air fuel mixture tuning will help but that @#[email protected]@ dwell meter still reads ten. 
About the frequency valve. I turned the screw counter clockwise until i heard it start to buzz and went an 1/8 turn more. That where it sits now. At idle it buzzes again. I just dont want to go to crazy going counter clockwise with that screw. I dont want to lean out the motor.


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## ABA Scirocco (May 30, 2001)

If the ecu, O2 sensor and frequency valve are all working properly and the ecu is operating in the normal closed loop mode, turning the mixture screw doesn't actually adjust the mixture because the ecu will counteract any changes that you make at least until you exceed the ecu's ability to compensate. You might now be wondering why bother with the screw at all? It's important to get it adjusted properly so that the mixture is correct when the ecu it operating in one of the open loop modes. 

You might find it an interesting and instructive exercise to hook a digital voltmeter up to the O2 sensor and a dwell meter to the frequency valve and then see how they respond as you turn the mixture screw.


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## konakle (Feb 8, 2010)

I'm up for that. What would i be looking for readings on the frequency valve? I'll see if i can find info in the mean time.


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## ABA Scirocco (May 30, 2001)

If everything's working right, you want to see the duty cycle on the frequency valve up around 50% at idle with a warm engine (that's 45° on a 4 cyl dwell meter)


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## konakle (Feb 8, 2010)

My duty cycle still reads 9.9 still and when testing the o2 sensor while plugged in and running it bounces from .111 to .819. If i unplug the o2 sensor as i just did a couple minutes ago the motor dles smoother. I'm using the test port with the blue and brown wire. When i first start the car its around 20.9 for 20 or 30 seconds and drops to 9.9.


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## ABA Scirocco (May 30, 2001)

It's normal for the O2 sensor reading to bounce around when the sensor is up to temperature, it should average around 0.5-0.6V but, I'm at a loss to explain the dwell readings you're getting.


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## konakle (Feb 8, 2010)

I've used an analog and brand new digital. I might try to test it at the ecu. pin 17


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## ABA Scirocco (May 30, 2001)

Just a thought, I've used both an analog dwell meter and a digital meter with a duty cycle function, in both cases, the meter gets connect between the ground side of the frequency valve and battery ground (that's what the test connector is) and because the frequency valve is switched on the ground side, the digital meter which reads the percentage of time the connection is above ground potential, it would give me an inverted reading i.e. a actual duty cycle in the frequency valve of 60% would read as 40%, 70% reads as 30% etc. Any chance that's what's happening with you? If so, 20.9% for cold starting would be about right, what reading do you get when you close the full throttle enrichment switch?


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## konakle (Feb 8, 2010)

So I grabbed a beer and stared at the motor again. I have another parts gti so i grabbed the computer out of. Plugged it in and my meter read 30.9. I dropped my beer! No not really, that would be bad. But i got 30.9. Adlusted the mixture screw to 45 and it hovers around 43 to 47 now. Plugged the old ecu back in and i got ten. Plugged the spare in and i get 45. I guess it was the ecu.


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## ABA Scirocco (May 30, 2001)

konakle said:


> Plugged the old ecu back in and i got ten. Plugged the spare in and i get 45. I guess it was the ecu.


 
That's a pretty conclusive test imo. 

I find this kind of interesting, these ecus are very reliable, they don't fail often but when they do, they usually fail completely, yours is the first "partial" failure that I'm aware of. Anyways, congratulations. It looks like you're ready to carry on tuning.


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## konakle (Feb 8, 2010)

Thanks. Just took it for a ride around the lake and it runs awesome. No hesitation. No stumble. Idle drops to 900 and stays. The exhaust isnt as loud also. I'll run it for a bit and see how it goes. Maybe some more fine tuning but i'm happy now. I want to THANK YOU for your help on this. You took alot of time to help. Dont know who you are but you seem to know your stuff. Thanks again! Maybe next year i'll get my autotech magnacharger on it!


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## ABA Scirocco (May 30, 2001)

You're welcome. I've been messing around with these cars for close to 20 years, I've picked up a fair bit along the way and I'm always happy to share what I know.


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## konakle (Feb 8, 2010)

Ok. So car has been running good. Still a little rough idle. Been doing some more research and the coolant temp sensor appears to play a big role. I checked mine and got no resistance. So its bad. I ordered another one and i'm waiting for it to come in. In the mean time i know that when the motor is warm the temp sensor should read around 150 ohms resistance. So i put a 150 ohm resister into the temp sensor connections. My idle smoothed right out. My dwell though reads 69.7 and stays. It was at 45 before putting the resistor in. Did doing this tell the ecu to run in a certain mode?


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## ABA Scirocco (May 30, 2001)

The only temperature sensors are for the water temperature gauge and the oil temperature gauge but these sensors NOT involved with your type of CIS system in any way. There are however two thermo-switches, they're simple that turn on or off at a specific set point. One controls the cold start valve, it's referred to in the manuals simply as the thermo-switch, the other one is called the oxy-thermo switch, I talked about that in my first post this thread.


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## konakle (Feb 8, 2010)

I did refer to that post many times. when i ordered the part it was under coolant temp sensor and my book calls it that to. The wire diagram in the back of the book calls it the oxy sensor temp switch. I know the thermo time switch controls the cold start injector and understand how that works. This switch is on the outlet side of the coolant from the motor. When its around 32 deg. it should read around 4800 6800 ohms and when warm at 212 deg. it should be around 150 ohms. The one in the car gives no reading at all. Warm or cold. So i put a 150 ohm resister between the two connectors to simulate a warm engine. This is when i got the 69 deg dwell which sounds like the computer went into cold running enrichment, or warm up mode. I believe 72 deg dwell plus or minus 2 deg is cold running enrichment.


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## konakle (Feb 8, 2010)

Ok scratch that last post. I think i figured out the switch and sensor. I had them mixed up. I'm learning! If i have it right the temp sensor gives you the ohm reading for your dash gauge and the oxy thermo is open or closed dependent on temp which tells the ecu to run in cold enrichment or not.


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## ABA Scirocco (May 30, 2001)

konakle said:


> Ok scratch that last post. I think i figured out the switch and sensor. I had them mixed up. I'm learning! If i have it right the temp sensor gives you the ohm reading for your dash gauge and the oxy thermo is open or closed dependent on temp which tells the ecu to run in cold enrichment or not.


Correct:thumbup:


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## konakle (Feb 8, 2010)

So I just pulled off the intake manifold off. New gasket should be in tomorrow. That should solve questioning that gasket.


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## GDR (Sep 25, 2000)

konakle said:


> Ok scratch that last post. I think i figured out the switch and sensor. I had them mixed up. I'm learning! If i have it right the temp sensor gives you the ohm reading for your dash gauge and the oxy thermo is open or closed dependent on temp which tells the ecu to run in cold enrichment or not.


Correct


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## ABA Scirocco (May 30, 2001)

konakle said:


> So I just pulled off the intake manifold off. New gasket should be in tomorrow. That should solve questioning that gasket.


I don't think I mentioned this earlier and I should have; the very first step in trouble shooting any type of CIS system is to *check for vacuum leaks and eliminate any that are found*. Getting a proper mixture over the whole rev range but, especially at idle, relies to a great extent on ALL of the air entering engine being metered by the air sensor plate, when there are vacuum leaks, it's not and if you try to make adjustments when there's still a vacuum leak, it's nothing but an exercise in frustration. Along the same lines, if there's an exhaust leak prior to or close to the O2 sensor, that can cause the O2 sensor to give a false lean reading to the ecu with similarly frustrating results.


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## sprocket007 (Oct 14, 2002)

Good thread, I have been having some poor running and the freq valve does not seem to buzz continiously, I have some things to check!
Thanks!


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