Actron Dwell Meter and Idle Hunting

[DrWin]

So, I was looking at this video:
https://www.youtube.com/watch?v=HKT_i82VtIo

I bought an Actron Dwell Meter (not excactly the same model) and tried doing what Chris is doing in the video. It cured my idle hunting by just adjusting the Fuel/Air mixture by a little bit. I connected to the meter at the same spots Chris is doing on the video, but I'm getting a different result:

During Warmup: (Steady, not fluctuating, RPM steady)
66915

After Warmup: (Steady, not fluctuating, RPM varies a little)
66916

I don't get it, why isn't the needle moving when I can hear the RPMs rise and fall?
I understand that the meter isn't monitoring RPMs directly, but I was also under the impression that the output to the diagnostic plug would/should fluctuate?

Bonus question - why are we supposed to look at the 8 cylinder gauge for a 6 cyl car?

Edit:
This is what it looks like when it isnt powered:
66917

[MrChocky]

Bonus question - why are we supposed to look at the 8 cylinder gauge for a 6 cyl car?
66917

Cos it's a sorta cut down V8:

https://en.wikipedia.org/wiki/V6_PRV_engine

"The PRV engine could be seen as a V8 with two missing cylinders, having a 90-degree angle between cylinder banks, rather than the customary 60, but with crankpins being 120 degrees apart. The Maserati V6 of the Citroën SM followed a remarkably similar pattern of development."

Now I know why!

[Michael]

Cos it's a sorta cut down V8:

https://en.wikipedia.org/wiki/V6_PRV_engine

"The PRV engine could be seen as a V8 with two missing cylinders, having a 90-degree angle between cylinder banks, rather than the customary 60, but with crankpins being 120 degrees apart. The Maserati V6 of the Citroën SM followed a remarkably similar pattern of development."

Now I know why!

No not exactly. The manual uses 4cly readings for more accuracy since we are adjusting mixture based off of ignition. You use the 8cyl scale and double it.

That aside, some cars have a simple 2 spade connector with a purple and orange wire instead of the diagnostic port. (use the orange for your signal wire) and ground properly of course. Once in closed loop you should see some movement of needle indicating the o2 sensor is operating. No movement means something is wrong with the o2 signal(bad or dirty sensor, broken wire, Frequency valve, etc.). O2 sensors are cheap and easy to replace and if you don't know when it was done last, replace it anyway. I would recommend getting a Bosch because the price is negligible (around 30-40 bucks) the probe on a good sensor will heat up faster and offer quicker correction vs. a cheap generic o2 sensor. I compared a Dgo sensor and a Bosch sensor from DeLorean Industries side by side and the difference was obvious.

Also make sure your idle circuit is functioning properly. Start by checking the micro switch engagement.

[FABombjoy]

Bonus question - why are we supposed to look at the 8 cylinder gauge for a 6 cyl car?
Because you aren't measuring ignition dwell, rather repurposing a "available in every corner drugstore in 1981" ignition dwell meter to measure the duty cycle on the frequency valve. The oddball settings best match the measurement needs w/ greatest resolution.

Now its easy to buy a multimeter with duty cycle measurement which can also be used, you just have to rescale the manual's from 0-90 degree values to 0-100 percent.

In my brief stint with K-jet turbo, I had an external logging box that did just this, so I could ensure that open-loop modes were triggered properly under boost.

[Bitsyncmaster]

Your mixture is adjusted wrong with it sitting at that low value.

Yes adjusting like that will stop hunting because the lambda is not changing the mixture.

The 4 cylinder was chosen because that lets your read out the dwell values more accurately. It's just displaying the duty cycle on a dwell scale.

You want to adjust your mixture again to get an average 30 to 40 deg. for a 4 cylinder dwell scale.

[Acmetowers]

I've just had to fix this issue with idle hunting and bad emissions. I'd say before you start adjusting the CO check your timing and fuel pressures. My vehicle failed its emissions >9.99% CO HC 674ppm on its annual check. The car was 2 degrees out on timing, system pressure was half a bar too low and control pressure .7 bar too high, after these were sorted I then adjusted the CO (about a full turn) to get the dwell around 35-45 on the 4 cylinder setting. After this C0 was 0.03% and HC 235ppm. Basically make sure your fuel and timing are right before setting the dwell (CO). Also don't buy one of those Chinese red boxed fuel pressure testers they're only suitable as landfill.

[DrWin]

I've just had to fix this issue with idle hunting and bad emissions. I'd say before you start adjusting the CO check your timing and fuel pressures. My vehicle failed its emissions >9.99% CO HC 674ppm on its annual check. The car was 2 degrees out on timing, system pressure was half a bar too low and control pressure .7 bar too high, after these were sorted I then adjusted the CO (about a full turn) to get the dwell around 35-45 on the 4 cylinder setting. After this C0 was 0.03% and HC 235ppm. Basically make sure your fuel and timing are right before setting the dwell (CO). Also don't buy one of those Chinese red boxed fuel pressure testers they're only suitable as landfill.

Thanks, that's good to know. Care to recommend a suitable (quality) fuel pressure tester?

[DrWin]

No not exactly. The manual uses 4cly readings for more accuracy since we are adjusting mixture based off of ignition. You use the 8cyl scale and double it.

That aside, some cars have a simple 2 spade connector with a purple and orange wire instead of the diagnostic port. (use the orange for your signal wire) and ground properly of course. Once in closed loop you should see some movement of needle indicating the o2 sensor is operating. No movement means something is wrong with the o2 signal(bad or dirty sensor, broken wire, Frequency valve, etc.). O2 sensors are cheap and easy to replace and if you don't know when it was done last, replace it anyway. I would recommend getting a Bosch because the price is negligible (around 30-40 bucks) the probe on a good sensor will heat up faster and offer quicker correction vs. a cheap generic o2 sensor. I compared a Dgo sensor and a Bosch sensor from DeLorean Industries side by side and the difference was obvious.

Also make sure your idle circuit is functioning properly. Start by checking the micro switch engagement.

Yeah, I have the 2 spade connector setup, and took care to connect/ground properly. I think I'll try to change out the O2 sensor like you suggested. I suspect that hasn't been done in quite a while. I have a generic one sitting on the shelf, but I'd rather try the Bosch one, now that you recommend it, if I can find one.

[DrWin]

Your mixture is adjusted wrong with it sitting at that low value.

Yes adjusting like that will stop hunting because the lambda is not changing the mixture.

The 4 cylinder was chosen because that lets your read out the dwell values more accurately. It's just displaying the duty cycle on a dwell scale.

You want to adjust your mixture again to get an average 30 to 40 deg. for a 4 cylinder dwell scale.

Right, I see that. So I'm gonna try to get the needle moving again by replacing the O2 sensor, and the trying to get the mixture set to hit between 30 - 40 deg. on the 4 cylinder dwell scale (15-20 on the 8 cyl.).

[Acmetowers]

Regarding what kit to use, I made one based around a 6 bar calibrated gauge with bits from the Chinese kit and some banjo fittings from some old fuel lines. But to make your own all you need is a good gauge, a couple of meters of fuel line, m8 and m10 banjo to barb connections, a "t" barb connection and a fuel shut off valve. Costs the same as the red boxed kit but will be calibrated.

Sent from my SM-N950F using Tapatalk

[Ron]

Doc, I don't know where the "15°" is coming from unless it is because a lot of people like to run it rich, but the manual says "35-45° (reading pulsates)" swinging, so it should swing across 40°, which is 20° on eight cylinder scale.
The specs also calls for the engine to be fully warm, pipes hot, etc., not right after coming out of "closed loop", as in the video. (After a drive, to also clean the plugs etc, is good.)
The RPM is supposed to be temporarily set to 950 during the procedure.
And, being picky, the meter's ground should be connected to the ground reference connection at the right rear air horn (Blue).
I agree with Acmetowers, as the manual says that all base settings should be checked before setting the CO. (See D:04:01-05)

Since your reading looks close cold ("50-60, steady") and showing ~4° when warm (low/lean), it may be so far off that you haven't been turning it enough to matter, as Bitsy mentioned (common mistake). So, you might try the following (before/while you wait on your goodies):
First, keep track of where the screw is now ( just in case ;-).
Remember turning CW=Right=Richer and turning CCW=Left=Lean. (Needle works opposite!)
Turn the screw sloooowly to the right in increments to get it down to swinging across 20°.
Once you get it close, a little goes a long ways (very touchy to get exact).
Don't forget to plug the hole and wait a few seconds before taking a reading.

[Bitsyncmaster]

I think they say 950 RPM to reduce the hunting a little which some of that hunting is caused by the O2 sensor running to cold. But the RPM does not really affect the dwell readings.

[Ron]

+1 ...I would think the 02 sensor temp being up to its temp may be more important than the hunting (signal).

[deloreandmcxii]

Love this thread. I’ve been trying to learn more about our lovely fuel system lately and this popped up! Thanks for all your insight!

What should the frequency valve be doing in a car which has eliminated the o2 sensor but is otherwise fairly stock (aside from an old custom exhaust)?

Is the fuel mixture adjustment procedure the same?

[Bitsyncmaster]

Love this thread. I’ve been trying to learn more about our lovely fuel system lately and this popped up! Thanks for all your insight!

What should the frequency valve be doing in a car which has eliminated the o2 sensor but is otherwise fairly stock (aside from an old custom exhaust)?

Is the fuel mixture adjustment procedure the same?

Disconnecting the O2 sensor wire would result in the FV running at 50% duty cycle (45 deg. dwell). Yes you still adjust the mixture with the adjustment "screw" but you would need a wideband tail pipe meter to set the mixture to a known value. I would guess you do the same if you unplug the FV or not power the lambda system.

[Elvis]

why don't you buy a simple 20-30$ oszilloscope instead of that dwell sh.. ?

we're in 2021 not 19821 anymore



we have smartphones now and don't use phone booths anymore...

[Ron]

why don't you buy a simple 20-30$ oszilloscope instead of that dwell sh.. ?

we're in 2021 not 19821 anymore



we have smartphones now and don't use phone booths anymore...Because then Michael would be posting pics of you taking a leak while splitting hairs...

[Bitsyncmaster]

why don't you buy a simple 20-30$ oszilloscope instead of that dwell sh.. ?

we're in 2021 not 19821 anymore



we have smartphones now and don't use phone booths anymore...

Those face book adds for a 100 Mhz Oscope must be a joke. My 200 Mhz scope was $400.

[FABombjoy]

I have an ancient history, pen sized Oszifox scope from 1998 and its good enough to set CO.

Lots of hobby scopes for cheap, for example
https://www.amazon.com/Quimat-Pocket-Size-Oscilloscope-Protective-Assembled/dp/B0728GCBLD/

$33 delivered and displays duty cycle for you.

[Bitsyncmaster]

I have an ancient history, pen sized Oszifox scope from 1998 and its good enough to set CO.

Lots of hobby scopes for cheap, for example
https://www.amazon.com/Quimat-Pocket-Size-Oscilloscope-Protective-Assembled/dp/B0728GCBLD/

$33 delivered and displays duty cycle for you.

Cool. That should work for dwell checking. 200 Khz bandwidth is good enough for that.

[Acmetowers]

One issue with a digital display is the visual swing, it's a lot easier to see with an analog gauge. I've tried a fluke 123 scope to measure the signal but it was easier with a 1980s dwell meter.

Sent from my SM-N950F using Tapatalk

[Michael]

Because then Michael would be posting pics of you taking a leak while splitting hairs...

My photo cache of DeLorean owners relieving themselves would make Chris Burns envious.

[Citizen]

why don't you buy a simple 20-30$ oszilloscope instead of that dwell sh.. ? we're in 2021 not 19821 anymore we have smartphones now and don't use phone booths anymore...


One issue with a digital display is the visual swing, it's a lot easier to see with an analog gauge. I've tried a fluke 123 scope to measure the signal but it was easier with a 1980s dwell meter.

I better get with the program! I inherited this from my father, been using it for years now, mostly for older cars that don’t have a tach. Still use it, seems to work great so have never seen the need to buy a new one.

66931

Can you guess the vintage?

...

[deloreandmcxii]

Disconnecting the O2 sensor wire would result in the FV running at 50% duty cycle (45 deg. dwell). Yes you still adjust the mixture with the adjustment "screw" but you would need a wideband tail pipe meter to set the mixture to a known value. I would guess you do the same if you unplug the FV or not power the lambda system.

Am I understanding correctly that you could either have the FV running (at constant 50%) or disable it and enrich the fuel mix to compensate - and achieve the same performance?

[Delorean Industries]

Am I understanding correctly that you could either have the FV running (at constant 50%) or disable it and enrich the fuel mix to compensate - and achieve the same performance?

To step in on this with knowledge on your car after servicing recently. Your car does not have an oxygen sensor in the custom exhaust or a working frequency valve circuit. You can still make a base CO adjustment with a wideband oxygen sensor but not with the method involving dwell on the lambda circuit.

[deloreandmcxii]

To step in on this with knowledge on your car after servicing recently. Your car does not have an oxygen sensor in the custom exhaust or a working frequency valve circuit. You can still make a base CO adjustment with a wideband oxygen sensor but not with the method involving dwell on the lambda circuit.

Thanks Josh! Yeah, I was just trying to understand how things work. So given my FV isn’t running, the fuel mix must be tuned richer to compensate - right? And because without a O2 sensor anyway, the fuel mixture would be a constant either way (Fv running at 50% vs Richer mix and no FV)

Am I understanding?

[Delorean Industries]

The fuel mixture is working off it's base curve without any type of dump from the valve. Essentially it just isn't looking for anything as it is mechanical and doesn't know any better aside from the warm up curve from the CPR. You can safely set this with a wideband and be good to go. The Lambda system isn't critical to the car. Your mpg will see negative results from this. Recommendation would be to set to 14.7 +/- .3 and be good to go. This was checked when we installed our braided fuel injection line kit procedure. Your adjustment was off due to the number of vacuum leaks on the intake system, pipe of agony leak, manifold issue at w pipe etc. Once all of those were corrected it was in the 14's.

[Dhennick99]

Are the mixture values the same with an automatic, or should the dwell be adjusted either more rich or lean?

[Ron]

Yep - The spec is for stock, auto or manual.

[Azar]

So, I was looking at this video:
https://www.youtube.com/watch?v=HKT_i82VtIo

I bought an Actron Dwell Meter (not excactly the same model) and tried doing what Chris is doing in the video. It cured my idle hunting by just adjusting the Fuel/Air mixture by a little bit. I connected to the meter at the same spots Chris is doing on the video, but I'm getting a different result:

During Warmup: (Steady, not fluctuating, RPM steady)
66915

After Warmup: (Steady, not fluctuating, RPM varies a little)
66916

I don't get it, why isn't the needle moving when I can hear the RPMs rise and fall?
I understand that the meter isn't monitoring RPMs directly, but I was also under the impression that the output to the diagnostic plug would/should fluctuate?

Bonus question - why are we supposed to look at the 8 cylinder gauge for a 6 cyl car?

Edit:
This is what it looks like when it isnt powered:
66917

Hello, did you fix the problem? My Dwell is dead steady at 27-28 on 8cyl scale...

[Bitsyncmaster]

Hello, did you fix the problem? My Dwell is dead steady at 27-28 on 8cyl scale...

If it steady with those numbers, your wide open throttle switch may be on all the time. Try disconnecting one wire from the WOT. That signal is also shared with the thermal throttle enrichment "sw". That could also be stuck on all the time.

Dose your FV buzz?

[David T]

If it steady with those numbers, your wide open throttle switch may be on all the time. Try disconnecting one wire from the WOT. That signal is also shared with the thermal throttle enrichment "sw". That could also be stuck on all the time.

Dose your FV buzz?

It can also be because the O2 sensor is either not connected or is no good.

[Bitsyncmaster]

It can also be because the O2 sensor is either not connected or is no good.

Then it would indicate 22 to 23 deg. Of course the accuracy of the dwell meter may be in question.

[mark w]

its been said in this thread that the scale the manual uses for Dwell checking is the 4 cyl scale, and when viewed on a meter like the popular Actron, one must double the value displayed on the 8cyl scale to get 4 cyl values.

this results in a on meter reading of 22.5 8cyl scale for a value of 45 on a 4 cyl scale- when the 02 sensor is unplugged.

But, the manual, shows that one should set to 6 cyl scale ! (and this is in only one place that I can find, on page D:04:01 )

71637

[Bitsyncmaster]

its been said in this thread that the scale the manual uses for Dwell checking is the 4 cyl scale, and when viewed on a meter like the popular Actron, one must double the value displayed on the 8cyl scale to get 4 cyl values.

this results in a on meter reading of 22.5 8cyl scale for a value of 45 on a 4 cyl scale- when the 02 sensor is unplugged.

But, the manual, shows that one should set to 6 cyl scale ! (and this is in only one place that I can find, on page D:04:01 )

71637

If you set to 6 cyl that 45 deg number would never show up.