How Often Do You Adjust Your Dwell?

[kings1527]

I've looked for answers on this and didn't find any so I thought this would be most applicable to a new thread.

Just out of curiosity, I hooked up my dwell meter to see how things were and I was reading a steady 10. My car's been running and idling great. No issues there whatsoever. The last time I adjusted the dwell was back in late January and I was surprised to see it change so much.

Is it normal to have the dwell fall off and have to readjust it somewhat frequently? I was under the impression that once it's set, it should stay unless you do major work to the fuel system.

Thanks!

[Patrick C]

I can't get the needle on my dwell meter to move at all. I think it was at a steady 40. I adjusted the mixture screw, o2 sensor is hooked up, etc and the needle never moves. The car runs fine, so I left it alone.

[kings1527]

I definitely have the right connection, ground, and a good functioning dwell meter and the needle moves with my adjustments. But I was surprised that I had to make such a big adjustment to get it between 35-45 (O2 sensor still hooked up) after not doing any kind of work on the fuel system in a long time. Like I said, it was at 10 when I started.

Hmmmmm....

[Bitsyncmaster]

It should never need adjustment again. That's why they put a plug in it. I think I've checked mine a few times and it does not seem to need any changes.

[Michael]

I have had my car for over 4 years, and put around 17k miles on it....never checked or touched it.

[kings1527]

Interesting, thanks guys. That's what I thought. Now that I think about it, my dwell was adjusted by Danny at DMC CA when I went to take to it get smogged and I'm wondering if they leaned it out to help things along with the test. And after that test, it idled immaculately at 750 without the RPM gauge fluctuating at all. Now that I put it right back in the spec range, it still idles great but maybe about 95% of the awesomeness as before. I guess I could adjust it back down to 10 if I really wanted.

[Bitsyncmaster]

It should not matter much if the dwell reading changes a little over time. The Lambda system is keeping the mixture set to 14.7 AFR with the engine warmed up. You're looking for setting the dwell to the mid range so the Lambda can compensate the most for altitude, temp and gas changes.

But that mixture setting range will affect your open loop mixture (engine warming up). So some people may set it on one end of the range to try to reduce idle hunting.

[David T]

It doesn't hurt to check the duty cycle on the Lambda system but it can change over time. If it does, the object is not to readjust the mixture screw but to find and fix what caused the mixture to change. Could be a problem in the ignition system or the fuel system. Depending on how long it has been it could be dirty/worn spark plugs, contaminated O2 sensor, bad pattern on a fuel injector, a vacuum leak, etc. You DO NOT fix any of this by twiddling the mixture screw.
David Teitelbaum

[kings1527]

It doesn't hurt to check the duty cycle on the Lambda system but it can change over time. If it does, the object is not to readjust the mixture screw but to find and fix what caused the mixture to change. Could be a problem in the ignition system or the fuel system. Depending on how long it has been it could be dirty/worn spark plugs, contaminated O2 sensor, bad pattern on a fuel injector, a vacuum leak, etc. You DO NOT fix any of this by twiddling the mixture screw.
David Teitelbaum

Thanks David. I always appreciate your input. All of those things are new except for the fuel injectors which I cleaned last year. But I'll keep them in mind. I'll reset the dwell to the proper setting and recheck it later to see if it moved again.

[kings1527]

It should not matter much if the dwell reading changes a little over time. The Lambda system is keeping the mixture set to 14.7 AFR with the engine warmed up. You're looking for setting the dwell to the mid range so the Lambda can compensate the most for altitude, temp and gas changes.

But that mixture setting range will affect your open loop mixture (engine warming up). So some people may set it on one end of the range to try to reduce idle hunting.

I see. Thanks for that, Dave. I was getting zero idle hunt at 10 on the dwell and now I'm getting a very tiny bit at a spec setting, so that might be very well what the story was.