# Dwell Meter on CIS



## diamono (Apr 26, 2008)

First Post - Hope this question hasn't been asked too many times.
I've borrowed a buddies old Accurate Instruments combination tach/dwell meter to check the mixture on my 88' Cabriolet. I'm trying to follow the directions on http://www.cabby-info.com/cis.htm, but can't get a reading (needle doesn't move). Is there something I may be missing from the instructions? Could I be using the wrong plug (it does have a blue/white wire on it).
I get a good reading in the tach mode when I hook it up, so I may be doing something wrong. The unit has a switch for dwell or tach mode and it has three wires (pos, neg & #1 cyl).
Thanks,
David Wilhite
88' Cabriolet
Middle TN


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## Southcross (Jul 2, 2004)

I don't know anything "specific" about the latter cabbies, if its like the models through '84... if the dwell needle is not moving, and right at about 50%? This usually is an indication of the ECU still being on Open Loop, the engine has to be completely warmed up. The Radiator fan has to run several times, and the oil temp has to be over 80deg Cel. If it still isn't giving a "wagging" signal, then check your connections and the connection to the O2 sensor. O2 sensor may have gone bad too. 
In extreme rich or lean conditions, if the needle isn't wagging and pointing at 20% (rich) or 80% (lean)... your beyond the limits of your ECU to self correct... you need to fix that


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## diamono (Apr 26, 2008)

*Re: (Southcross)*


_Quote, originally posted by *Southcross* »_This usually is an indication of the ECU still being on Open Loop, 

I thought that the CIS systems on Cabriolets up to 90 don't have an ECU.
FWIW, the car is at proper temperature.
Can I put the dwell meter on something else to verify it even works in this mode?


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## Southcross (Jul 2, 2004)

*Re: (dnmwilhite)*


_Quote, originally posted by *dnmwilhite* »_
I thought that the CIS systems on Cabriolets up to 90 don't have an ECU.
FWIW, the car is at proper temperature.
Can I put the dwell meter on something else to verify it even works in this mode?
 if your car doesn't have an ECU, then what are you hooking the dwell meter up to?








Your car would be running in severe limp mode, and the FV not buzzing, if your ECU were not working. 
I'm going to think that if your O2 is known good, then it may be your coolant temp sensor. On the '88 models I do not know if the coolant temp sensor for the ECU is the early On/OFF style, or a variable resistor. It should be located on your coolant outlet on the front of your head, usually has "two prongs". See what happens if you unplug it, one of two things, your engine will freak out or the ECU will suddenly switch to "Closed Loop". If it freaks out then its definitely using a variable resistance coolant temp sensor.


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## tolusina (Oct 19, 2004)

*Re: Dwell Meter on CIS (dnmwilhite)*

Cabby CIS gurus hang out on the Cabby forum, including the author of that write up.
Post here http://forums.vwvortex.com/zeroforum?id=152


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## EuroKid83 (Jan 26, 2005)

*Re: Dwell Meter on CIS (dnmwilhite)*

I use to use a dwell meter to tune my duty cycle but a multimeter is a much better way to set duty cycle. If you let the engine run for at least ten minutes and you still have a reading of 50% duty cycle your O2 sensor is probably bad.


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## kamzcab86 (Feb 14, 2002)

*Re: Dwell Meter on CIS (EuroKid83)*

Don't know if the OP has solved the problem, but I had the same issue (and I'm the one who took the pics for http://cabby-info.com/cis and, well, own the site): the digital dwell meter was stuck on 84° during every reading after the first time the test port was used by a DVOM. Thinking the dwell meter wasn't behaving right, I bought a new meter (duty cycle meter it so happens) and, while it wasn't stuck on one percentage, it produced very peculiar readings. During the D-cell battery tests, the readings adjusted (so did the idle), showing the ECU working, but those readings were way the heck off on both meters. None of it made any sense, but it all was adding up: I long suspected the test port being the problem, so I finally cut the stupid OEM plug off, installed spade terminals and, voila, proper readings! Turns out, the probe wasn't making good-enough contact with the test port.
Moral of the story: If a good meter + good ECU + good frequency valve + good thermoswitch = whacked-out readings, suspect the test port.









_Quote, originally posted by *EuroKid83* »_If you let the engine run for at least ten minutes and you still have a reading of 50% duty cycle your O2 sensor is probably bad.

When the system is in closed-loop, it's supposed to be at 50% ±8%.


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## diamono (Apr 26, 2008)

*Re: Dwell Meter on CIS (dnmwilhite)*

http://docs.google.com/Doc?id=dqvmg42_19fxb5ktcc 
I don't know if the link will work, but if it does it will show the Dwell Meter I am using. I've got a question on which range to use, because 4 CYCL is listed along the tach.
When I set the dwell to 45-40 on the 8 cyl range, it's too lean at startup and it causes ignition in the intake. Right now, I've got it set around 25 and it starts fine. Any experts that can tell me about what range I should be using? Should I take it that a 4 Cyl would be half the reading of an 8 Cyl? I greatly appreciate all the help and info from the forums so far.

_Modified by dnmwilhite at 5:54 AM 5-15-2008_


_Modified by dnmwilhite at 7:21 AM 5-15-2008_


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## Southcross (Jul 2, 2004)

should be using the 4-cylinder scale... anything registered above 50% is lean, below 50% is considered Rich. Your "Wag" should be between 40-50%


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## diamono (Apr 26, 2008)

*Re: (Southcross)*

So do I use half of the 8 CYL scale? Notice that there is a Dwell scale for 8 CYL and 6 CYL, but the Tach scale has 4 CYCL on it. There is not a 4 CYL scale listed.


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## Southcross (Jul 2, 2004)

*Re: (dnmwilhite)*


_Quote, originally posted by *dnmwilhite* »_So do I use half of the 8 CYL scale? Notice that there is a Dwell scale for 8 CYL and 6 CYL, but the Tach scale has 4 CYCL on it. There is not a 4 CYL scale listed.
hrmm not sure.... I'd have to go find my Dwell Meter, I think thats correct


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## tolusina (Oct 19, 2004)

*FV-QR*

Use twice the 8 cyl dwell scale reading to get the 4 cyl scale equivalent.


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## EuroKid83 (Jan 26, 2005)

*Re: Dwell Meter on CIS (kamzcab86)*


_Quote, originally posted by *kamzcab86* »_When the system is in closed-loop, it's supposed to be at 50% ±8%.

It should fluctuate between 45% and 55% duty cycle in closed loop, not 50%±8%.


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## tolusina (Oct 19, 2004)

*Re: Dwell Meter on CIS (EuroKid83)*


_Quote, originally posted by *EuroKid83* »_
It should fluctuate between 45% and 55% duty cycle in closed loop, not 50%±8%.

The range will vary somewhat according to the condition of the oxygen sensor. 50% ± 5% isn't far off from 50% ± 8%.
50% ± 8% is the spec listed in Bentley.


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## EuroKid83 (Jan 26, 2005)

*Re: Dwell Meter on CIS (tolusina)*


_Quote, originally posted by *tolusina* »_
The range will vary somewhat according to the condition of the oxygen sensor. 50% ± 5% isn't far off from 50% ± 8%.
50% ± 8% is the spec listed in Bentley.


I agree, I was just pointing out the fact that the duty cycle should vary between a specified range not stay at a fixed value. On a side note, if your using a digital multimeter to set your duty cycle be sure to set it to read the negative trigger slope. http://****************.com/smile/emthup.gif


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## tolusina (Oct 19, 2004)

*Re: Dwell Meter on CIS (EuroKid83)*


_Quote, originally posted by *EuroKid83* »_
I agree, I was just pointing out the fact that the duty cycle should vary between a specified range not stay at a fixed value. On a side note, if your using a digital multimeter to set your duty cycle be sure to set it to read the negative trigger slope. http://****************.com/smile/emthup.gif 

Um, the op had questions about what he read on http://www.cabby-info.com/cis.htm

Among the many answers on that page is the notation under the chart that states, _"Negative slope %; if readings are positive, subtract from 100"_

Spend a little time looking that page over. Yes, there are omissions, but they are few.


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## kamzcab86 (Feb 14, 2002)

*Re: Dwell Meter on CIS (EuroKid83)*


_Quote, originally posted by *EuroKid83* »_It should fluctuate between 45% and 55% duty cycle in closed loop, not 50%±8%.


_Quote, originally posted by *EuroKid83* »_
I agree, I was just pointing out the fact that the duty cycle should vary between a specified range not stay at a fixed value. 








That's what the little ± symbol means: 50% is the baseline ("ideal" in Bosch's eyes) reading _plus-or-minus_ (i.e., fluctuating range of) 8%; that translates into a reading _range_ of 42-58%. As Ron said, that "50% ±8%" is listed in the Bentley Service Manual; I didn't just pull it out of thin air. 



_Modified by kamzcab86 at 8:24 PM 6-2-2008_


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## fowvaydriver (Jan 11, 2005)

*Re: Dwell Meter on CIS (diamono)*

just an fyi... your lambda valve relay could be spent. do you hear the lambda valve buzzing?
-jess

_Quote, originally posted by *diamono* »_First Post - Hope this question hasn't been asked too many times.
I've borrowed a buddies old Accurate Instruments combination tach/dwell meter to check the mixture on my 88' Cabriolet. I'm trying to follow the directions on http://www.cabby-info.com/cis.htm, but can't get a reading (needle doesn't move). Is there something I may be missing from the instructions? Could I be using the wrong plug (it does have a blue/white wire on it).
I get a good reading in the tach mode when I hook it up, so I may be doing something wrong. The unit has a switch for dwell or tach mode and it has three wires (pos, neg & #1 cyl).
Thanks,
David Wilhite
88' Cabriolet
Middle TN


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## EuroKid83 (Jan 26, 2005)

*Re: Dwell Meter on CIS (kamzcab86)*


_Quote, originally posted by *kamzcab86* »_







That's what the little ± symbol means: 50% is the baseline ("ideal" in Bosch's eyes) reading _plus-or-minus_ (i.e., fluctuating range of) 8%; that translates into a reading _range_ of 42-58%. As Ron said, that "50% ±8%" is listed in the Bentley Service Manual; I didn't just pull it out of thin air.

TITE.


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## diamono (Apr 26, 2008)

*Re: Dwell Meter on CIS (fowvaydriver)*


_Quote, originally posted by *fowvaydriver* »_just an fyi... your lambda valve relay could be spent. do you hear the lambda valve buzzing?
-jess


The lambda valve buzzes at it should and I can adjust the mixture to the point of it not working if I choose to. Lot's of info here, but my primary question was just on the use of the old analog dwell meter.
For now the engine is starting easily and running smooth at all times. Thanks to all for the help.


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## EuroKid83 (Jan 26, 2005)

*Re: Dwell Meter on CIS (kamzcab86)*


_Quote, originally posted by *kamzcab86* »_







That's what the little ± symbol means: 50% is the baseline ("ideal" in Bosch's eyes) reading _plus-or-minus_ (i.e., fluctuating range of) 8%; that translates into a reading _range_ of 42-58%. As Ron said, that "50% ±8%" is listed in the Bentley Service Manual; I didn't just pull it out of thin air. 
_Modified by kamzcab86 at 8:24 PM 6-2-2008_

OK ± doesn't automatically mean "fluctuating range of" it just means plus or minus. Most people who don't have a basic knowledge of K-Lambda are not gona pick up on that so take some pamprin and go back to bed.


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## kamzcab86 (Feb 14, 2002)

*Re: Dwell Meter on CIS (EuroKid83)*


_Quote, originally posted by *EuroKid83* »_
OK ± doesn't automatically mean "fluctuating range of" it just means plus or minus. Most people who don't have a basic knowledge of K-Lambda are not gona pick up on that so take some pamprin and go back to bed.

LOL! Wait, seriously... You come back *10* days later to say that?!







WTF??!















Since you took the time to post that brilliant reply, allow me to take a moment to straighten things out, ummmmmmkay?
You disagreed with the closed-loop range I posted by saying:

_Quote, originally posted by *EuroKid83* »_It should fluctuate between 45% and 55% duty cycle in closed loop, not 50%±8%.

It would seem, by ^that reply, that you understand the ± to mean "range". But, it's only a 3% difference, which _tolusina_ pointed out, even using the ± to explain, to which you replied:

_Quote, originally posted by *EuroKid83* »_
I agree, I was just pointing out the fact that the duty cycle should vary between a specified range not stay at a fixed value. 

Ooooookay, then; you do understand, or you don't? You're contradicting yourself, which is why I felt the need to clarify as to what the ± means. So, you're arguing with me, yet you agree with Ron (sort of), both of us saying virtually the same damn thing.







Aaaaah, I get it; it's a sexist thing, right? Girls aren't supposed to know jack sh*t when it comes to cars, math and science, right?
The Bentley Manual chart doesn't say "50% with a fluctuating range of around 8%" nor does it say "a reading range of 42% up to 58%"; the genius author(s) thought it wise to use shorthand to simply say "50% ±8%", something anyone with a high school diploma is "gona pick up on". But, pardon me, rather than using the mathematical meaning of _plus or minus_ in that one reply of mine to explain what that symbol means (because your replies sounded like you didn't know), maybe I should've used the scientific meaning of _give or take_, which "indicates an inclusive *range* of values that a reading might have" (Wikipedia, bold emphasis added by me). Is that better? Does that make more sense?
Sheesh... all this over a stupid symbol...















Untwist your panties, put down your Wii and go back to school.


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## tolusina (Oct 19, 2004)

*Re: Dwell Meter on CIS (EuroKid83)*


_Quote, originally posted by *EuroKid83* »_
OK ± doesn't automatically mean "fluctuating range of" it just means plus or minus. Most people who don't have a basic knowledge of K-Lambda are not gona pick up on that so take some pamprin and go back to bed.


± is a grade school arithmetic symbol, it means "Plus or Minus", any eight year old should know that. 
Maybe you can check back in for a refresher.


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