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Old 01-19-2022, 11:17 PM   #1
Sat-sl2
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Default #4 cylinder misfire, at a loss. URGENT

I have a 2000 Saturn SL2 with 170,000 miles. A couple days ago it starting running like crap, and eventually produced a check engine light. I got the code read and it produced a po304 clyinder #4 misfire.

New parts:
Spark plugs
Wires
4/1 ignition coil

#4 cylinder misfire still remains and if I switch the #1 and #4 wires on the new ignition coil the misfire goes to cylinder #1 producing a po301 code leading me to believe it's the ignition control module.

Grabbed 3 used junkyard icm thinking one of that had to be good.

Changed them a out and the misfire is still persistent. Just to eliminate it I got a new crank position sensor and the misfire also remains.

What am I missing? Could it be the ecm or something else? I don't want to stick money into the car as it is not worth that much and don't want to waste my time on it as I need to be doing college homework and scholarships. I would hate to junk it for something simple.
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Old 01-20-2022, 01:01 AM   #2
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Default Re: #4 cylinder misfire, at a loss. URGENT

Swap the 1-4 coil with the 2-3 coil. A new coil can not be considered to be "known good" anymore. Everything is returnable now, so that "new" coil may have been damaged by a previous buyer.

I don't think it is likely either the ICM or PCM is the problem, since the same circuitry fires the 1-4 coil (in the same manner) for #1 and #4. The only things "different" for #1 and #4 are the spark plugs, plug wires, and coil outputs.
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Old 01-20-2022, 02:42 PM   #3
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Default Re: #4 cylinder misfire, at a loss. URGENT

I swapped the coils and it still reads a po304 code after clearing it... I called a local shop and they can't take it
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Old 01-20-2022, 04:49 PM   #4
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Default Re: #4 cylinder misfire, at a loss. URGENT

With the coils still swapped, try swapping the #1 and #4 wires at the coil again. Let's verify this problem still stays with the coil tower that is supposed to be for #4
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Old 01-20-2022, 07:08 PM   #5
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Default Re: #4 cylinder misfire, at a loss. URGENT

The new coil was on the 2/3 side and plug wires for 1/4 we're switched at the terminal with code cleared. It throws a po301 like before. Both coils are good.
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Old 01-20-2022, 09:35 PM   #6
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Default Re: #4 cylinder misfire, at a loss. URGENT

Just checking to be sure... you are swapping plug wires at the coil, correct?

Have you done this wire swap several times now, with no other changes, to be sure the problem reliably stays with the #4 coil tower? If so, it has to be a bad coil, or a very strange issue that has me stumped. As I said before, everything except the coil secondary winding (high-voltage power to the two towers) is exactly the same whether 1 or 4 is firing
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Old 01-21-2022, 12:02 AM   #7
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Default Re: #4 cylinder misfire, at a loss. URGENT

Try an even different ignition control module.

Check the wire connectors for cleanliness and corrosion, and check that the lugs on the engine block where the module bolts down. Make sure the back of the module has a good clean surface to make connection to the block.

And as a previous poster says, I'd exchange that new coil for a replacement, just in case. Just because the new one came in a box, doesn't mean it was new. I, personally, have had more than one case where the product in the box was someone else's return to the store. And the store just put it back on the shelf.

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Old 01-21-2022, 01:54 AM   #8
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Default Re: #4 cylinder misfire, at a loss. URGENT

I've scuffed up the icm mounting surfaces multiple times so that shouldn't be an issue. I will try to get another coil and see what happens tomorrow.
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Old 01-21-2022, 10:35 PM   #9
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Default Re: #4 cylinder misfire, at a loss. URGENT

Check the lugs on the control module that plug into the bottom of the ignition coil. There could be a bad connection when the coil sets down onto it.

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Old 01-24-2022, 03:28 PM   #10
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Default Re: #4 cylinder misfire, at a loss. URGENT

Sooo turns out it's a dead cylinder, only gets 30 psi on #4. Idk why the misfire switches but the car is not worth a new motor. She'll be ran around town for a bit and then junked eventually.
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Old 01-24-2022, 04:27 PM   #11
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Default Re: #4 cylinder misfire, at a loss. URGENT

I failed on this one! I nearly always suggest a compression-check as the first basic test, for any engine issue.

Worse yet, I got focused on the miss seeming to follow the coil tower. It wasn't. When the 1-4 coil towers were swapped, the cylinder numbers were "reassigned" by the PCM, since the #4 spark output of the coil determines the base for the cylinder ID. It was always #4 that was misfiring, but it got reported as #1 once the wires were swapped.
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Old 01-24-2022, 05:38 PM   #12
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Default Re: #4 cylinder misfire, at a loss. URGENT

I failed as well, I had a tester but never got it out because I got focused on the misfire changing cylinders. Oh well.
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