digital dwell angle meter??

[mark '87 930]

I've replaced my O2 sensor as I had fried it when i took it off my old exhaust... but recently (as it has been functioning well for over a month) the car feels like it is bogging down again under boost. I disconnect the O2 sensor and it is fine!

The O2 sensor is working though as I tested it with a VM. The manual says to check the computer though, and it says to do it with a "digital dwell angle meter" What is that? You are supposed to connect it between the diagnostic port and ground (sounds like voltage to me) and measure it in percentage.

Can anyone explain that maybe let me know what this tool is or if I can use a Digital meter and convert to percentage somehow?

[Early_S_Man]

Mark,

Digital Dwell Angle readings can be measured with simple automotive meters like the Actron CP7676, or more expensive meters like the Fluke 189 [current model] or older Fluke 88 that can still be found on eBay-- even though discontinued for a few years. Even an oscilloscope could be used and the duty cycle could be calculated by hand ... such as with an old Tektronix 465 that can be had for a song on eBay. Or you could use a Tektronix 7854 lab scope and do the calculation with the built-in waveform calculator!

Dwell angle is just an obtuse way of expressing duty cycle ... it originated back when all engines had points in their distributors, and GM decided to get fancy and design distributors with points adjustment capability while the engine was running!

If your service manual gives a dwell angle reading ... it should also give a duty cycle, but it can be calculated, too, indirectly to give a reading that would be equivalent if you have a meter that only gives duty cycle.

[mark '87 930]

I have a fluke 77 series II which doesn't seem to have any type of frequency metering...

I actually had it hooked up to my O2 sensor as I was driving (I just replaced the batteries) and the readings are vastly different from the first time I put it on...

I'm seeing as high as 0.8V when I accelerate... would that not mean that my O2 sensor is bad? I thought it was supposed to be between 0.05 and 0.1V max?

[Early_S_Man]

Mark,

No, an oxygen sensor typically fluctuates between 0.1 Volts and 0.9 Volts when operating normally.

Fluke recently put owners and service manuals of selected discontinued models online -- free download. Here is the URL for the search page:

http://us.fluke.com/usen/support/manuals/default.htm

I found the following charts in the 88 manual:





I suggest downloading the 88 manual, because it has procedures for many automotive measurements we use and discuss here!

[mark '87 930]

I'd need a digital meter that can do that though.. I'll have to pick one up.

[Porsche_monkey]

Mark: I have a dwell meter somewhere, if you want to figure out how to use it. email me if you want me to look for it.

[mark '87 930]

Paul,

I meet with Mike this morning.. great guy... I'm just going through things I need to sort out and this is one of them.. I am reading the Bosch fuel injection book.. and the O2 sensor test adn computer are apparently working according to the results of the test. Someone mentioned a relay somewhere for the mixture control ECU..... I need to locate it and verify that. It seems to bog under load with the O2 sensor connected. It only bogs when the boost starts to kick in. It's intermittent though.. seems to be when the engine is cold.

[pope]

Sorry for the thread resurrection but if I were to get one of the meters that have a duty cycle function from here would I be able to use the tables in this thread to calculate the dwell angle?

This off the user manual:
- Duty cycle: pulse width: 100microsecs - 100ms, Frequency range: 5Hz-150kHz, sensitivity: <0.5V RMS, Overload protection: 250V DC or AC RMS

[304065]

Uhh, you don't need a table, just do the following equation

Dwell angle divided by (360 divided by number of cylinders)= Duty cycle.