924Board.org

[TBrown]

After breaking the threads off the o2 sensor and taking my exhaust off again, I just got all put back together and running. Idle and timing are spot on. Im trying to use a dwell meter to adjust my air fuel mixture. Im turning the 3mm allen one eighths turn at a time and weighting 10 seconds for the engine to adjust. Ive turned it cw and ccw till the engine stumbles and set it right in the middle but the meter stays at 55 degrees. I dont want my mixture to be to lean and get detonation. Does anyone have any experience using the dwell meter method. Ive gone through all the posts using the search feature and I cant find anyone who has had this problem.

I know how much yall like pictures so heres the broke threads in the exhaust and o2 sensor.




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Tangerine Dream- 1980 924 Turbo
Silver Surprise- 1979 924 Turbo
1977 International Scout ii
1982 Yamaha Sr185
1978 Kawasaki KZ650
1974 Honda CB360
1973 Honda CB750

[Jaf]

Erm, I've never heard of a method of using a dwell meter to set the fuel mixture. I thought the meter was only ever used to show how long the points are open? How did you connect the meter?
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1978 924na

[Benino]

I'm not completely sure of this because I've never had the wiring for the idle switch connected on my car... but it could be that the computer sets the frequency valve at some set frequency when the idle switch is clicked, which would explain why you always see 55 no matter how u have your 3mm adjuster set. I know the full throttle switch does this to ensure that the mixture is sufficiently rich at full throttle. you might want to unplug the idle switch wiring at the throttle body before trying to set the air fuel mixture with the dwell meter.

Again, just a guess on my part.
I have successfully used a dwell meter to set my mixture in the past and I don't have the idle switch wiring connected.
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1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA

[TBrown]

Jaf heres the links to all of the posts ive found on using the dwell meter method.

http://www.924board.org/viewtopic.php?t=3754&highlight=fuel+adjustment+dwell+meter+metre
http://www.924board.org/viewtopic.php?t=8184&highlight=air+fuel+mixture+dwell
http://www.924board.org/viewtopic.php?t=6270&highlight=air+fuel+mixture+dwell
http://www.924board.org/viewtopic.php?t=13311&highlight=air+fuel+mixture+dwellhttp://www.924board.org/viewtopic.php?t=13311&highlight=air+fuel+mixture+dwell

There are many more but those are the ones ive bookmarked. Do a search for air fuel mixture and dwell meter.

Ok Benino ill give that a try ill tell you if it works. I hope it does. I think I got it pretty close with the stumble to stumble and then in the middle method. I actually richined a little more just to be on the safe side.
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Tangerine Dream- 1980 924 Turbo
Silver Surprise- 1979 924 Turbo
1977 International Scout ii
1982 Yamaha Sr185
1978 Kawasaki KZ650
1974 Honda CB360
1973 Honda CB750

[ideola]

[Jaf]

[TBrown]

Haha yeah I'm happy with it I've got about 700 into it total without insurance and plates that's later this week

Now all I have to do is fix he oil leak from my distributor housing, it's leaking right onto my exhaust manifold
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Tangerine Dream- 1980 924 Turbo
Silver Surprise- 1979 924 Turbo
1977 International Scout ii
1982 Yamaha Sr185
1978 Kawasaki KZ650
1974 Honda CB360
1973 Honda CB750

[Benino]

Just a couple more comments on the air fuel mixture adjustment.

Under normal warmed up operation, as long as you aren't way off with the air fuel ratio adjustment screw, on cars with the o2 sensor, your air fuel ratio will be correct. The frequency valve will adjust the mixture based on input from the o2 sensor.

However... When the engine is cold or when the full throttle switch is engaged, I believe the o2 sensor is ignored and the frequency valve goes into a set duty cycle to ensure a constant air fuel mixture. Under either of those conditions, the air fuel mixture very much depends on how the 3mm adjustment screw is set.
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1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA

[alexvex]

Good to see you're still working on it and not giving up!
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--Alex--
1992 Porsche 968 (VW 2.5L I5 Turbo swap in the works)
1995 Audi 90 Quattro Sport (4.2L V8 Swap)
2010 Touareg TDI
Past Pcars: 80 931, 87 924S, 87 951

[Slam]

Benino has it. Engine temp makes a big difference for the simple reason the O2 sensor won't talk to the control unit when it's cold. There's also a temp sensor that you need to check to make sure it's talking to the control unit when it should. Are you shooting for 45 on the dwell meter?

Interesting that this came up now, because I just learned about this method from a friend of mine and tweaked the mixture on Chrenan's old car. Boy did THAT wake it up!
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'84 944 - kid blew motor
'83 944 - resting comfortably. For 12 years
'87 944 - sideswiped by trucker
'80 924 - gone
'78 924 - gone
'77 924 - rusting comfortably