Tech Thread Only?

[Kriss Vector]

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[barrym95838]

The four main adjustments possible with a non-independent rear end are toe, camber, caster, and thrust angle.  Not all of them may be applicable to your Jeep, and the lower-price alignments may purposely avoid some of the more difficult adjustments, even if they are applicable.  If it was mine, I would go with the old "Set the toe and let it go, do da, do da ..."

barrym95838
EO/EI144107

[scanner]

barrym95838 wrote

scanner wrote

... I'll wait a week or two, and I'll put another one up.   I would like to see what others have done.

Please don't wait that long, scanner.  I doubt that anyone else could do better, but I also don't want to discourage anyone else from trying.
barrym95838
EO/EI144107

It' been almost a year.   I haven't been posting any case studies because I've been submitting them to training organizations.   This is one that I fixed a couple of weeks ago, and because the platform is so old, there isn't any interest in it.    

This is a 1998 Dodge Pickup with a 3.9L V6.   The complaint is that the engine dies intermittently, mostly after started cold in the morning.   Once the engine was warmed up, the engine would die at random times, but would restart immediately.  

It had been to another shop, and after a few hundred dollars spent on unsuccessful repairs, the customer decided to come to my shop from a recommendation by his uncle.  

The MIL was lit, and here are the codes.



Here's a link to the image

obdii_code.jpg

There is a catalytic converter code, and it was bad, and that's another story.  The cat had no impact on the driveability of the vehicle.  

Since there was a code for the ignition primary circuit, I decided to scope it out with my Vantage Pro, along with the crankshaft position sensor.   The engine shuddered for a second, and I saved the file.

As you can see, it was running fine, it hiccuped, then continued running.



Here's a link to the image

Ignition_Primary_-_CKP.jpg

I zoomed to where the primary dropped out.



Here's a link to the image

Ignition_Primary_-_CKP-Zoom.jpg

What would you do from here?   Is there a part you would change?   Explain your decisions.  What would be your next step?

Michael, don't respond right away, and let everyone play.  

[barrym95838]

Were your scope probes at or near the PCM, or closer to the other end(s)?

barrym95838
EO/EI144107

[scanner]

barrym95838 wrote

Were your scope probes at or near the PCM, or closer to the other end(s)?

The probes were at the ignition coil connector and at the CKP connector.   Had you probed at the PCM, you would have seen the same waveform.

[FiendFX]

Even if you got 1 dead coil on this vehicle, it shouldn't cause the vehicle to stall. I would check the cam and crank signals next.

[scanner]

FiendFX wrote

Even if you got 1 dead coil on this vehicle, it shouldn't cause the vehicle to stall.

I said it was old. :-)   It only has one coil.   It's got a distributor.  

[FiendFX]

Cam and Crank correlation? Is the timing off?

[barrym95838]

I think that if there were mechanical timing issues, the symptom would always be present, not a "glitch" like scanner is showing us.  I'm going to assume that scanner gave us all we need to know in his scope captures ... if that's true, I think I have it, but I'll hold off with my guess until others have had a chance to play.

barrym95838
EO/EI144107

[scanner]

FiendFX wrote

Cam and Crank correlation?

Cam and Crank never dropped out when you felt the ignition dropping out.



Here's the link to the image

Crankshaft_and_Camshaft_Sensor.jpg

Here's the signal at the cursor.  



Here's the link to the image

Crankshaft_and_Camshaft_Sensor-Zoom.jpg

Is the timing off?

I never checked the timing.   Do you routinely check timing on a non-adjustable system?  Was there something in the first waveform that indicated to you that timing was off?    

[D Rochells 150861]

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[FiendFX]

Cam and Crank correlation is good, I'm assuming the previous shop already had changed the distributor, spark plugs and wires. If wire integrity is good, only thing left is computer???

[Centralized Smog]

Coil ground wire short to ground. Maybe to another pcm controlled ground wire.

[scanner]

Centralized Smog wrote

Coil ground wire short to ground. Maybe to another pcm controlled ground wire.

Where do you see the circuit short to ground?   In the primary waveform I zoomed in on, the circuit went to system voltage before the primary started working again.

I'll wait until Michael responds, and I'll reveal the fix.  

[Centralized Smog]

[scanner]

You can also right click on this link and open in another tab.

Dodge_Ignition_Primary.gif

[barrym95838]

Okay, here's my reasoning:

The crank signal looks pretty clean (even during drop-out), and should (in my experience) be necessary and sufficient for a primary ignition ground pulse (which is lacking during drop-out).  It is implied, but not 100% guaranteed from scanner's traces that there are good +12s at PCM pins 2 (F18) and 22 (A14).  It is also implied, but not 100% guaranteed that there are good grounds at PCM pins 4 (K4) and 31/32 (Z12).  

If these conditions are true, I can only conclude that the coil driver at PCM pin 7 (K19) is the source of the glitch.  I would recommend a replacement PCM, after quickly verifying the integrity of the above-mentioned circuits.

barrym95838
EO/EI144107

[D Rochells 150861]

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[barrym95838]

barrym95838 wrote

... after quickly verifying the integrity of the above-mentioned circuits.

... including, but not limited to, the primary coil resistance.

barrym95838
EO/EI144107

P.S.  D, I think that you would quickly get frustrated by my low productivity.

[D Rochells 150861]

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