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Squirrel Works

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Cylinder #1 missfire
Feb 5^th, 2012 at 7:00pm

The vehicle is a 2003 Chrysler 300 with a 3.5 V6. This has been a long term problem getting gradulally worse. Replaced plugs and did compression test, all normal. This is my first experience with the pico scope so the traces are not textbook.

The file names are self explanatory. Misfire is on cylinder one. Three is included for comparison. The primary appears to not charge the coil correctly. I bought a new coil pack without effect. All resistances are equal between the unhooked coil connectors and ground, 7 mega ohms for the primary and 6.5 kilo ohms on the common lead. I took the connector off the ECM and there is continuity and all are isolated from ground. The connectors are tight and look good. The unloaded voltage trace of #1 and #3 match. I cant get the forum to accept any of my data files. They appear to be too large but are standard psdata files.

Not sure if this is an ECM issue or do other tests need to be done? Thanks for any help.

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Manic Mechanic Senior Member Picogroup Offline Test don’t guess Posts: 188 Clovis California California USA Gender:	Re: Cylinder #1 missfire Reply #1 - Feb 5^th, 2012 at 10:35pm Squirrel Works wrote on Feb 5^th, 2012 at 7:00pm: The file names are self explanatory. Not sure if this is an ECM issue or do other tests need to be done? Thanks for any help. What Files where
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Tom Roberts

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Re: Cylinder #1 missfire
Reply #2 - Feb 6^th, 2012 at 9:19am

Squirrel Works wrote on Feb 5^th, 2012 at 7:00pm:

I cant get the forum to accept any of my data files.

The forums will accept five 15MB files attached to each post. If your files are larger than that, you may be able to reduce the size by saving out one screen, if they are multi screen captures. You can also put them on the drop site.

Another reason your files may not be attaching is if you are previewing your post. When you preview your post, any attachments are removed. This is a security thing. If you want the attachments to stick once you select them, the next step is to select post.

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Tom Roberts
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Squirrel Works Freshman Member Picogroup Offline Posts: 6 Kansas Kansas USA Gender:	Re: Cylinder #1 missfire Reply #3 - Feb 7^th, 2012 at 4:42am Obviously this is confusing me but I have converted these files to .gif files. The unloaded primary file is taken at the connector with the coil not hooked. The problem is in #1 cylinder and the others are normal and included for comparison.
Back to top	_1current_voltogegif.gif (16 KB \| ) _3current_voltagegif.gif (19 KB \| ) secondary_1gif.gif (11 KB \| ) secondary_2gif.gif (12 KB \| ) unloadedprimary_1.gif (11 KB \| ) IP Logged

Tom Roberts Autonerdz Administrator Picogroup Offline Autonerdz Founder Posts: 8,595 Olympia Washington USA Gender:	Re: Cylinder #1 missfire Reply #4 - Feb 7^th, 2012 at 11:15am Robert, I really don't see anything useful there. Please call us. I think we need to have a little session.
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drdiesel1 Super Nerd Picogroup Offline Posts: 1,243 Nevada USA Nevada USA Gender:	Re: Cylinder #1 missfire Reply #5 - Feb 7^th, 2012 at 2:47pm Tom Roberts wrote on Feb 7^th, 2012 at 11:15am: Robert, I really don't see anything useful there. Please call us. I think we need to have a little session.
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Squirrel Works

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Re: Cylinder #1 missfire
Reply #6 - Feb 11^th, 2012 at 6:50pm

Thanks to Tom for all his help on Friday. Hopefully these traces are accurate and have some useful information. My interpertation is that there is not enough curent in the primary of #1. Both setups were identical. Three is a good cylinder. I have checked the coil circuits and the ECM grounds under a 3 amp load with between 100 and 300 mv drop in all. I'm in the process of finding all the engine grounds and cleaning them. I have the ECM off and all pins look good. Will clean where the heatsink contacts the support. I also notice the ECM is a reconditioned unit. Running out of ideas.

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_1currentandvoltoage.psdata (4093 KB | )

_3currentandvoltage.psdata (4167 KB | )

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Tom Roberts

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Re: Cylinder #1 missfire
Reply #7 - Feb 12^th, 2012 at 9:51am

Squirrel Works wrote on Feb 11^th, 2012 at 6:50pm:

Hopefully these traces are accurate and have some useful information.

Much better. Wink

In your 3 file I can see coil current on D and secondary on A. C appears to be coil primary using an attenuator but not the probe so the scaling is wrong. Not sure what B is. Looks like coil positive, again with an unscaled attenuator.

If this is all correct.....

In your 1 file....It appears as though the PCM is turning the coil on for only 50 microseconds.

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PRESTON LSD Guide Picogroup Offline "Fix like a champion today" Posts: 4,959 Jensen Beach Florida USA Gender:	Re: Cylinder #1 missfire Reply #8 - Feb 12^th, 2012 at 10:39am I was on the same thought process as you were Tom, but hesitated to say anything until more information came out since the scaling seemed weird and I was unsure about what channel was hooked to what and where. I wonder what would do something like this? Oh, and where is the coil amperage reading being measure from?
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Squirrel Works

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Re: Cylinder #1 missfire
Reply #9 - Feb 12^th, 2012 at 11:12am

A channel is the secondary. B channel is a lead common to all the coils. C is primary voltage and D is current. I take it that if the 20X attenuator is on, one doesnt adjust the scale? The current and secondary probe scales are adjustable? The common lead also has a capicator connected which I checked out to the best of my ability. It's not shorted and looks good, ie not burned. This common also goes to a device called the "short runner valve". Makes no difference if this is unhooked.

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Squirrel Works

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Re: Cylinder #1 missfire
Reply #10 - Feb 12^th, 2012 at 3:45pm

I light of the above I reacquired the traces in the correct manner. The KV on the secondary is not as high and after I was done I realized the clip had come off but I did not redo it. Incidently, I assume all the leads that have grounds have to be grounded each time. I have cleaned all grounds and checked all wires and connectors and the problem persists.

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_1currentandvoltoagerevised.psdata (3849 KB | )

_3currentandvoltagerevised.psdata (3927 KB | )

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Tom Roberts

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Re: Cylinder #1 missfire
Reply #11 - Feb 12^th, 2012 at 4:04pm

Squirrel Works wrote on Feb 12^th, 2012 at 11:12am:

I take it that if the 20X attenuator is on, one doesnt adjust the scale?

You put the attenuators on the scope but just didn't tell the scope they were there so all the voltage is 1/20 of real voltage.

If you need help with this call or post in the PicoScope Help board in the Picogroup section.

Nice job with the screen time and samples adjustment you are a quick study. Wink

If you hooked everything up right and the scope is grounded to B-, as it should be, then your #1 primary drive is invalid. The PCM driver is highly suspect since there is not a shorted coil causing this, nor a bad PCM ground. If a shorted coil was causing the driver to shut down, the current would have spiked. It didn't, and your sample rate is good so you would have captured it. If the PCM ground was bad, the other coil current would not be normal and it is.

You may want to probe that #1 primary at the PCM and place the current probe around the same wire near the PCM just to confirm you don't have a bad connection between coil and PCM.

OK, just saw your second set of files.

Now you have scaling correct.

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Squirrel Works

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Re: Cylinder #1 missfire
Reply #12 - Mar 3^rd, 2012 at 4:26pm

Final followup to the above problem. Chrysler has the computer game locked up. I looked for a used ECM which of course has no warranty and still has to be "flashed" by the dealer. Decided to go with a re-manufactured dealer unit. I couldn't install it because the car won't start without first being flashed. The first computer was defective, took ten days to chew through that. Got the car back last week and it runs great. The picoscope gave me the confidence to spend the $600.00 needed for the fix. Next project is figuring out why my wife's car has a sluggish starter.

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