Another Mystery Solved: Wheel of Fortune

by | Jun 2009 | 8 comments

by John Anello
A shop called me in to investigate a no-start condition on a 1996 Dodge Caravan with a 3.3L engine (Figure 1). This shop only had a scan tool in its arsenal of diagnostic equipment. No scope, no graphing meter combined with a component...

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8 Comments

  1. cahurd

    Your article finished my diagnosis. My 2000 Dodge caravan 3.3L engine would occasionally cutout for 1/4 sec under acceleration. The heavier the acceleration the more the cutouts. Also had very occasional nasty starter sounds. I was thinking flywheel at the beginning but wanted to make sure before I took it to a tranny shop. I’m a fairly bright EE so I hooked up my scope to look at the cam & crank signals.Looked like they were OK but my problem was occasional.
    https://ozrc.com/pics/DSC_0049smaller.JPG
    So I was thinking I’d never be able to see an intermittent on the scope. I then programmed a microprocessor to count and record the cam and crank pulses fully expecting to see some missing ones. The result looked a little funny but the pulses were all there even through the engine cutouts. Well something has to be cutting out. So I looked at the coil driver signals..nothing missing there. Then the fuel injector drive. Yes there’s the cutting out.
    https://ozrc.com/pics/DSC_0052smaller.JPG
    But how strange. First a missing pulse and then some strange half voltage during another missing pulse and then back to normal until the next cutout.
    I did a google search for ‘2000 Dodge caravan 3.3l fuel injector waveform’ and up came this article. After reading a little it suddenly struck me why the injector pulse looked so strange. The poor PCM is confused. I better look at the cam & crank signals again.
    https://ozrc.com/pics/DSC_0050smaller.JPG
    Zoomed in you can see the last of 4 crank pulses on the bottom trace and there’s the first of the 3 cam pulses(top trace) starting at virtually the same time. A broken flywheel!
    Now I’m convinced that under acceleration the torque causes a slight shift in the broken flywheel delaying the crank pulses enough to confuse the PCM. So I think I have another example of a broken flywheel that doesn’t sound like it and stays in place except for a little twist. In my case the vehicle runs but has an intermittent problem.
    Now I’m willing to get the tranny pulled to fix what I’m 99% sure is a broken flywheel

  2. cahurd

    Your article finished my diagnosis. My 2000 Dodge caravan 3.3L engine would occasionally cutout for 1/4 sec under acceleration. The heavier the acceleration the more the cutouts. Also had very occasional nasty starter sounds. I was thinking flywheel at the beginning but wanted to make sure before I took it to a tranny shop. I’m a fairly bright EE so I hooked up my scope to look at the cam & crank signals.Looked like they were OK but my problem was occasional.
    https://ozrc.com/pics/DSC_0049smaller.JPG
    So I was thinking I’d never be able to see an intermittent on the scope. I then programmed a microprocessor to count and record the cam and crank pulses fully expecting to see some missing ones. The result looked a little funny but the pulses were all there even through the engine cutouts. Well something has to be cutting out. So I looked at the coil driver signals..nothing missing there. Then the fuel injector drive. Yes there’s the cutting out.
    https://ozrc.com/pics/DSC_0052smaller.JPG
    But how strange. First a missing pulse and then some strange half voltage during another missing pulse and then back to normal until the next cutout.
    I did a google search for ‘2000 Dodge caravan 3.3l fuel injector waveform’ and up came this article. After reading a little it suddenly struck me why the injector pulse looked so strange. The poor PCM is confused. I better look at the cam & crank signals again.
    https://ozrc.com/pics/DSC_0050smaller.JPG
    Zoomed in you can see the last of 4 crank pulses on the bottom trace and there’s the first of the 3 cam pulses(top trace) starting at virtually the same time. A broken flywheel!
    Now I’m convinced that under acceleration the torque causes a slight shift in the broken flywheel delaying the crank pulses enough to confuse the PCM. So I think I have another example of a broken flywheel that doesn’t sound like it and stays in place except for a little twist. In my case the vehicle runs but has an intermittent problem.
    Now I’m willing to get the tranny pulled to fix what I’m 99% sure is a broken flywheel

  3. jesse beiler

    this is so cool . can I get paper edition

  4. jesse beiler

    this is so cool . can I get paper edition

  5. mastertechmagadmin

    Printable PDFs are available for download at the end of every HTML version of the articles found on mastertechmag.com

  6. mastertechmagadmin

    Printable PDFs are available for download at the end of every HTML version of the articles found on mastertechmag.com

Submit a Comment

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Old Habits: Spark Plug Service Now

Old Habits: Spark Plug Service Now

A whole lot of evolution has occurred since most of us first started replacing plugs, so it’s time we re-examined our procedures and incorporate the latest subtleties

read more
Keeping Gasoline Fresh

Keeping Gasoline Fresh

The life span of the gasoline you buy at your local station can range from several months to a couple years from the day it was refined depending on how it was stored.

read more

8 Comments

  1. cahurd

    Your article finished my diagnosis. My 2000 Dodge caravan 3.3L engine would occasionally cutout for 1/4 sec under acceleration. The heavier the acceleration the more the cutouts. Also had very occasional nasty starter sounds. I was thinking flywheel at the beginning but wanted to make sure before I took it to a tranny shop. I’m a fairly bright EE so I hooked up my scope to look at the cam & crank signals.Looked like they were OK but my problem was occasional.
    https://ozrc.com/pics/DSC_0049smaller.JPG
    So I was thinking I’d never be able to see an intermittent on the scope. I then programmed a microprocessor to count and record the cam and crank pulses fully expecting to see some missing ones. The result looked a little funny but the pulses were all there even through the engine cutouts. Well something has to be cutting out. So I looked at the coil driver signals..nothing missing there. Then the fuel injector drive. Yes there’s the cutting out.
    https://ozrc.com/pics/DSC_0052smaller.JPG
    But how strange. First a missing pulse and then some strange half voltage during another missing pulse and then back to normal until the next cutout.
    I did a google search for ‘2000 Dodge caravan 3.3l fuel injector waveform’ and up came this article. After reading a little it suddenly struck me why the injector pulse looked so strange. The poor PCM is confused. I better look at the cam & crank signals again.
    https://ozrc.com/pics/DSC_0050smaller.JPG
    Zoomed in you can see the last of 4 crank pulses on the bottom trace and there’s the first of the 3 cam pulses(top trace) starting at virtually the same time. A broken flywheel!
    Now I’m convinced that under acceleration the torque causes a slight shift in the broken flywheel delaying the crank pulses enough to confuse the PCM. So I think I have another example of a broken flywheel that doesn’t sound like it and stays in place except for a little twist. In my case the vehicle runs but has an intermittent problem.
    Now I’m willing to get the tranny pulled to fix what I’m 99% sure is a broken flywheel

  2. cahurd

    Your article finished my diagnosis. My 2000 Dodge caravan 3.3L engine would occasionally cutout for 1/4 sec under acceleration. The heavier the acceleration the more the cutouts. Also had very occasional nasty starter sounds. I was thinking flywheel at the beginning but wanted to make sure before I took it to a tranny shop. I’m a fairly bright EE so I hooked up my scope to look at the cam & crank signals.Looked like they were OK but my problem was occasional.
    https://ozrc.com/pics/DSC_0049smaller.JPG
    So I was thinking I’d never be able to see an intermittent on the scope. I then programmed a microprocessor to count and record the cam and crank pulses fully expecting to see some missing ones. The result looked a little funny but the pulses were all there even through the engine cutouts. Well something has to be cutting out. So I looked at the coil driver signals..nothing missing there. Then the fuel injector drive. Yes there’s the cutting out.
    https://ozrc.com/pics/DSC_0052smaller.JPG
    But how strange. First a missing pulse and then some strange half voltage during another missing pulse and then back to normal until the next cutout.
    I did a google search for ‘2000 Dodge caravan 3.3l fuel injector waveform’ and up came this article. After reading a little it suddenly struck me why the injector pulse looked so strange. The poor PCM is confused. I better look at the cam & crank signals again.
    https://ozrc.com/pics/DSC_0050smaller.JPG
    Zoomed in you can see the last of 4 crank pulses on the bottom trace and there’s the first of the 3 cam pulses(top trace) starting at virtually the same time. A broken flywheel!
    Now I’m convinced that under acceleration the torque causes a slight shift in the broken flywheel delaying the crank pulses enough to confuse the PCM. So I think I have another example of a broken flywheel that doesn’t sound like it and stays in place except for a little twist. In my case the vehicle runs but has an intermittent problem.
    Now I’m willing to get the tranny pulled to fix what I’m 99% sure is a broken flywheel

  3. jesse beiler

    this is so cool . can I get paper edition

  4. jesse beiler

    this is so cool . can I get paper edition

  5. mastertechmagadmin

    Printable PDFs are available for download at the end of every HTML version of the articles found on mastertechmag.com

  6. mastertechmagadmin

    Printable PDFs are available for download at the end of every HTML version of the articles found on mastertechmag.com

Submit a Comment