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Benino · Posted: Fri Mar 07, 2003 4:55 pm Post subject: dwell meter

I want to set my air fuel mixture correctly (or at least kind of close). Does anyone know where you can connect a dwell meter? I searched the forum and couldn't find a clear answer about where and how to connect it. anyone used one before? let me know.

Capt EZ · Posted: Fri Mar 07, 2003 9:07 pm Post subject:

Hey Lizard I think this on is for you
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924RACR · Posted: Fri Mar 07, 2003 10:57 pm Post subject:

What kind of car do you have?
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epsylon · Posted: Sat Mar 08, 2003 1:26 am Post subject:

you'll need to have a '80 or later 924 and the dwell meter connects to the frequency valve.
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Lizard · Posted: Sat Mar 08, 2003 1:26 am Post subject:

sorry Capt EZ, all I know is you use a long hex key and turn something inside the fuel distributor this is on the 924 and 931, on the 944/924S it is all done electronically
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Capt EZ · Posted: Sat Mar 08, 2003 3:21 am Post subject:

that's better than i usually do...I am happy to just keep the smoke in the wire...That is what electricity looks like isn't it?
_________________
Dream as if you'll live forever.
live as if you'll die today. - James Dean

Fly Fast
Live Slow
Margaritaville Airways
1987 924S

Benino · Posted: Sat Mar 08, 2003 4:40 am Post subject:

sorry. I forgot to say I have a 1980 924 NA. So do I have to strip the wires to the frequency vlave?
Once it's connected, do I run the test with the OX sensor connected?

924RACR · Posted: Sat Mar 08, 2003 4:49 am Post subject:

If you wish to use the dwell meter, yes you need to keep the O2 sensor connected. If you pull back the rubber boot, you should have access to the metal part of the connector terminals. Don't strip them, then they'll corrode!

There's notes, probably in the Turbo section of the Tech Section, about adjusting mixture with a dwell meter. It should apply.

FWIW, I used an oscilloscope to try to set mine. Made virtually no progress. I finally ended up just driving it and tweaking it, have it pretty close now. Not that much different than without an O2 sensor, except that without all the electronics in the way I can usually set mixture just by blipping the throttle with the car sitting still, evaluating throttle response.
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Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

924RACR is correct the easiest way it to set the mixture screw in the middle and judge the throttle response.

If you want to try the dwell metter then conect the positive to the black wire on the frequency valve test conector. Its a three pronged conector on the drivers side fender by the firewall. Remove the rubber cap and be carefull not to touch the other two prongs. You may need to make a special test lead for this. Ground the dwell meeter set it at the four cyl setting and adjust the fuel mixture untill the dwell is at 45 degrees. It hasn't worked for me though.
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wdb · Joined: 02 Nov 2002 Posts: 2024

I seen a few air/fuel ratio testors, that use tempeture of exhaust to calibrate air/fuel ratio . does anyone know what temps corespond to 12-14.7 air/fuel ratios, and an inexpensive wayto measure the temps, a thermometer or something that goes to 3000k degrees . the air/fuel ratio is the key to a well running engine, as well as ,milage, and performance . maybe a garden variety thermocouple, from a hot water heater ( cost less then $10.oo),attached to a multimeter would be accurate enough to set the air/fuel ratio . or maybe there is a thermocouple from another area that would be better suited to this . any of you electrical guy's have any thoughts on this , or know how to make an exhaust gas analyser out of an o2 sensor ,for those cars that dont have one .

wdb · Joined: 02 Nov 2002 Posts: 2024

I looked around the web ,from what I read, o2 sensors are not very accurate , so making a exhaust gas analyser from 1 will only give you an idea of the air/fule ratio (average over time), not an exact , to the point measurement . I was interested in a readout that gives a number like 12.5 air/fuel ratio or a temp or voltage that can be converted to an exact a/f ratio . what I found .

http://www.gracieland.org/cars/techtalk/O2_2.html

Benino · Posted: Wed Mar 12, 2003 5:08 pm Post subject:

I don't think I'm in to this temperature stuff. I like the dwell meter idea, (cuz I have a friend who has one that I can use

but I'm kinda worried. Has anyone used a dwell meter successfully? What happened when you tried it Roger?

924 turbo · Posted: Wed Mar 12, 2003 8:50 pm Post subject:

I've followed the instructions for setting the mixture with a dwell meter, and have at least been successful in setting the mixture to dance around 45 degrees on the dwell meter. I'm not sure I believe that it's the right setting, though. If I had an exhaust gas analyzer, I'd test it, set the mixture correctly, and then check the mixture to see where it was on the dwell meter. It seems to run too rich when set at 45 degrees, at least in my case.
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Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

Mine would dance around 45 also. I just recently got a book on CIS systems. It does cover the dwell meeter procedure, and normal is 40-60 degrees. The Engine Control Unit sends ten pulses a second what you are mesuring with the dwell meeter is the duty cycle of those pluses. I do not fully understand the system I have read the book through one time. I plan to work on the frequency valve so I will start putting the book to practical use. Right now I belive its an electrical problem on the 81's the frequency valve is also used for throttle enrichment. I still think that the mixture can be set be ear if you are familiar with the car. Here is the best way I have found.

Turn the mixture screw clockwise untill the engine sputters and dies and mark that spot. Then turn countercloockwise untill engine sputters and almost dies then mark that spot. Somewhere in the middle + or - about 1/3 of a turn You will find a spot where the Idle is at its hightest point, and the engine runs smooth. At that point give the accelerator a tap and check the throttle response. The throttle response should be quick, if the engine lags then the mixture is probably lean turn the mixture screw clockwise to richen it. If the exhaust smells like gas turn the mixture screw counterclockwise to lean it out. Then clean your plugs take the car for a drive and remove the plugs. If they are a tan color you are good. If they are black then your running rich, if they are white or ash colored you are running lean. Once you get good throttle response and the plugs are tan. Go ahead and mesure the O2 sensor voltage (2-4 millivolts) and the frequency valve (45 degrees) I think those readings will be fine.
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1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
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Smoothie · Posted: Sat Apr 24, 2004 8:18 am Post subject:

I've been having some fun (not) with NJ motor vehicle inspection. Last time, 2 years ago it just barely passed the NOx (nitrous oxides emissions) by 10 with a reading of 1368. The max permissible was 1378. This year I go and get a 1346 on NOx, but the permissible limit is now 1323, so it fails for emissions. Ok I can take a joke and not too big a deal, I figure it's a bit on the lean side, so I'll richen it up a bit to drop the NOx, go back for a second inspection (luckily first in line, so no wait). It fails again and the NOx has actually gone -up- to 1374 while CO% has gone -down- from 0.92 to 0.84. (CO% should go up if it's turned up richer (and I turned clockwise which is correct to richen)) Alright then, I figure just maybe I got confused and finished up with a leaner setting when I thought I'd gone richer, so I give it a good 70 degree clockwise turn - no doubt that's richer, and go for another inspection (timed just right again and first in line). It fails again with an even higher NOx reading of 1461 and CO% has dropped further to 0.59!
Sooo I figure I must be in a tug-o-war with the lambda system and give the dwell meter trick a try. Pop the cap off that 3-wire connector at the top-left of the engine compartment, dwell meters' green wire to black wire of 3-wire connector, dwell meters' black wire to ground, 4 cyl setting, switch to "dwell" and voila! a reading, but of only about 10 - so, the tug-o-war suspicion's confirmed - as I turned it up richer the lambda system compensated and apparently overcompensated to lean it out. Then watching the dwell meter, I turn the mixture counterclockwise to lean and the dwell meter starts reading higher, good, keep going, it keeps going, but only to about 40 on the dwell meters' scale. It wouldn't go any higher than that and turning the mixture screw further toward lean then started to bring the dwell meters' needle back down. Weird stuff - the reading should have kept going higher. Also tried that trick where you disconnect the wire to the o2 sensor and ground the end opposite from the sensor - this should simulate a reading of max lean to the lambda system and cause it to compensate by going max rich with the frequency valve and a reading of 90 on the dwell meter, but it showed zero.
Anyway - enough aggravation for one day. I'll try setting the mixture by using the dwell meter, leaving the lambda system hooked up and go for one more inspection try in a week or so. If still NFG, I may resort to disconnecting the lambda, going without it and setting the mixture a bit rich with a CO meter. One other possibility is unplugging that other connector that's on the same side, just a foot or so lower down, that retards ignition timing some - I'm thinking that might bring NOx down, hopefully enough to pass.
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