Thread: 2004 3.8 #1 cylinder misfire

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  1. #1 2004 3.8 #1 cylinder misfire 
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    Im struggling guys and need your help. I am diagnosing a 2004 3.8 for a young lady. Its got a constant #1 cyl misfire. Its got a new plug, wire, and injector, electic plug in was noid lt tested, (good) and its got 125 psi compression. It has excellent spark running with the #1 wire attached to a spare plug. I changed the plug wires on the coil because its a wasted spark and it still is only #1 misfire.
    I havent checked fuel pressure which I will do monday but........what else could there be? Its got fuel, I verified its got spark, compression??????
    Thanks for ANY suggestions.
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  3. #2 Re: 2004 3.8 #1 cylinder misfire 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    Did you try moving the coils around to see if the misfire follows the coil?

    Another possible cause is the ICM under the coils.

    SMGPFC Member #1
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  4. #3 Re: 2004 3.8 #1 cylinder misfire 
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    Quote Originally Posted by Fivefingerdeathpunch View Post
    Did you try moving the coils around to see if the misfire follows the coil?

    Another possible cause is the ICM under the coils.

    No, I didnt try switching coils. I figured if that side on the coil was bad, when I switched the 2 plug wires, it would follow to that cylinder. And I did pull #1 plug wire and ran the engine with a spare plug snapped in and it has a great spark. As much as I wanted to believe it was a spark issue, it sure seems to be working correctly. How does the ICM control the coil? Can it change the timing or just provide spark?
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  5. #4 Re: 2004 3.8 #1 cylinder misfire 
    Turbo is the way to go. BillBoost37's Avatar
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    I'd redo the compression test. 125psi feels low to me. I would usually see 170-180 across all cylinders in a good engine.

    And I'd always do the test wrong by leaving in all the plugs except the one I was testing based on being lazy. Unhook icm and crank a little.
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  6. #5 Re: 2004 3.8 #1 cylinder misfire 
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    That is how I tested the compression because I was thinking this was a dead cylinder. All plugs were i except #1 and it read 125 psi. But that is enough for combustion. And thats what is throwing me off. Timing cant be off for just 1 cyl. It has gas, spark and compression.
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  7. #6 Re: 2004 3.8 #1 cylinder misfire 
    Solving problems BrandonHall10's Avatar
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    Low hanging fruit for a 3800 misfire is a spark issue. Like stated earlier... Move the coil associated with the misfire. If the misfire moves it's *probably* a coil. If the misfire doesn't move it's *probably* an ICM.

    Part 1 -How to Diagnose Misfire Codes P0300-P0306 (GM 3.8L)

    Part 1 -How to Test Ignition Coil Pack -Misfire Troubleshooting Tests (GM 3.8L)
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  8. #7 Re: 2004 3.8 #1 cylinder misfire 
    Turbo is the way to go. BillBoost37's Avatar
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    Did you test another cylinder for comparison and get the same 125psi?
    I drink..so consider that when reading my posts.

    2010 Audi A6 Dual IC's
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  9. #8 Re: 2004 3.8 #1 cylinder misfire 
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    I didnt check other compression. I figured with 125 that was enough to atleast indicate it was trying. This is a dead cylinder. I will try swapping coils around tonight. I will also report back what I find out for future info.
    Thanks guys!
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  10. #9 Re: 2004 3.8 #1 cylinder misfire 
    Turbo is the way to go. BillBoost37's Avatar
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    The way the pcm reads misfires is based on info from the crank sensor (to know which cylinder) and the knock sensors detecting something being off. Say for example if your compression is low, that could give you a misfire code.

    While you are working on it, if you checked say cylinder 3 compression and it comes up as 180ish, that would point you to maybe a chipped piston or something keeping you from getting good combustion in #1.

    Is this an NA or SC engine?
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  11. #10 Re: 2004 3.8 #1 cylinder misfire 
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    I swapped the coil out with a good one and it stayed right there in #1 cyl. I am going to do a fuel press test tonight although it has the new injector. I am starting to think it might be the ICM board although....This is a wasted spark system correct? If when I swapped #1 and #4 plug wires on the towers, and it was the tower/side for #1 coil that was bad, shouldnt it have moved to #4 cyl?
    I will try doing a compression test again. If it is at 125psi and the rest are at 180 psi, would that be enough of a difference to missfire that hard. Last night, under 1000rpm it barely stayed running.
    Thanks
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  12. #11 Re: 2004 3.8 #1 cylinder misfire 
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    It is not a SC engine. If like billboost said, if a low compression reading tells the crank and knock sensor somethings not right, or if it was a bad coil, wouldnt that also leave #4 misfiring also?
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  13. #12 Re: 2004 3.8 #1 cylinder misfire 
    Killa Bee Scottydoggs's Avatar
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    id get a junk yard icm, or buy a used one on line. most go for like 20 or so used, new they are over 100.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  14. #13 Re: 2004 3.8 #1 cylinder misfire 
    Turbo is the way to go. BillBoost37's Avatar
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    If moving the #1 and #4 wires didn't change it, then it's not the coil or ICM. If the tower for one of the posts on the coil were cracked, the issue would move when you swap the wires. The ICM fires that coil for #1 and #4, the only reason it wouldn't fire on one of the two would be if you need to do a crank relearn. BrandonHall10's Regal recently had a similar issue and when he was done shotgunning parts on, he did a case aka crank relearn and magic occurred. It'll happen from time to time and I can't tell you the hours etc I spent trying so many things to learn that one.

    If compression is low in #1, yes 50psi is plenty for the sensor to realize it's a lame duck cylinder. And.. it'll give you a misfire code.

    I've worked on far too many of these engines and try to help others based on the experience. The way I would diagnose this is check that code is there for sure. Then swap plug wires, after that check the plug, next up is compression test and then crank learn. If you notice, my plan is in order of saving money and the usual order to find out what is going on.

    Heck I once bought a Regal from four hours away. Body was great and engine wasn't running right. I couldn't quite place the sound it was making along with a misfire, knock retard etc. Got it on trailer and got it home. Scanner said cylinder 4 was the issue. I put a compression gauge on to find 0psi. The piston was completely missing from the cylinder with the rod/pin flopping around. Later I located the piston in the oil pan in about a million pieces lol.
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  15. #14 Re: 2004 3.8 #1 cylinder misfire 
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    Wow, I sure hope that isnt the problem here. LOL. The wires and plugs are new. And I ran it w #1 plug wire and a different plug grounded and it was lighting up like it should. I am going to do a compression test again tonight comparing #1 and a different cyl. Are you talking 50psi difference between cylinders would indicate a bad cyl or 50 psi in that cyl would indicate bad? T code comes up wight away after clearing and I can read how many misfires and it has to be everytime its at TDC.
    I think Im at the crank relearn stage then. Can you explain that process?
    Thanks guys!
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  16. #15 Re: 2004 3.8 #1 cylinder misfire 
    Turbo is the way to go. BillBoost37's Avatar
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    I'm saying that if #1 is 50psi lower than all the rest, it will cause a misfire code to be thrown.

    The crank learn requires a scan tool that is capable, HP Tuners or an Aeroforce gauge. There are likely other tools that will do it as well. Dealer can perform it too.
    I drink..so consider that when reading my posts.

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  17. #16 Re: 2004 3.8 #1 cylinder misfire 
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    Today I pulled #1 plug and one other. #1 compression was just as good as the other cyl so I think compression is no longer a question. Fuel rail press is 50psi. So I am stumped. Sooooo, new plugs. wires, Ive eliminated compression, fuel press, new injector, coil, ICM.
    So, I am thinking it has to be a crank relearn like you suggest. My scan tool wont do that, so I think Im just going to have to have her take it into a dealer for that.
    Atleast it has kept her daughter home during these lockdown day of the virus, so parent are happy.
    Thank you all for your help and best wishes in these virus days.
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  18. #17 Re: 2004 3.8 #1 cylinder misfire 
    Turbo is the way to go. BillBoost37's Avatar
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    It is sure an odd one when nothing else fixes it as these are typically very easy and reliable motors. And then you come across that one oddball that needs the crank relearn.
    I drink..so consider that when reading my posts.

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