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2005 Cadillac CTS-V Platinum
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Discussion Starter #1 (Edited)
Ok, I rarely drive my V anymore (maybe about 1000 miles a year) and I decided to take it out to detail it yesterday. I took it for a quick cruise around the area and after a few minutes I could hear a light, occasional misfire. When I tried to rev it up it would misfire consecutively and sounded like a machine gun in short bursts. You could feel the power lacking/hesitating during these events.

I recently installed new cutouts as my old ones would not stay sealed when closed.

My V has 82k miles and is cammed, headers, no cutouts, full exhaust (with cutouts). It has been tuned but has always ran pretty rich (as far as I could tell).

If I let the car idle and walk around it doesn't sound like it's misfiring (but it's admittedly hard to tell with the cam lope and full exhaust). It does whether the engine is warm or "cold".

I pulled the codes and one of them was the dreaded P0300 "random misfire". My check engine light is on (not blinking). The other codes seemed related to my O2 sensors/low voltage circuit...which I've always had since having the cats removed.

The spark plugs were installed when the engine was cammed (about 25k miles ago). I am thinking (at the least), that I should change the plugs and the wires.

I'm not afraid to tear the car apart as it's not a daily driver and I've always wanted to dig into it a bit.

Can anybody help me figure this out? I know that misfire is one of the harder problems to correct since there can be so many culprits.

Thanks,
perfect
 

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2005 CTS-V
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Attached is the trouble shooting sequence for the P0300. Additionally, because your car is cammed, valve springs should be considered a maintenance item.
 

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Discussion Starter #3
As always - thanks, darkman!

I'm definitely thinking of pulling the valve covers and having a look around.

If I have the valve covers off - what else should I consider doing? Compression test? Leakdown test? Fuel pressure tests?

Thanks!
 

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Discussion Starter #5
Heavy - fortunately (or unfortunately), I already have the trunion upgrade. When my cam was installed, the shop used double coil valve springs (??) and it pretty much immediately dumped needle bearings once they got the engine running (they realized it during the shake down run and tore it apart before any damage could occur).

The trunion bearing upgrade was done as an immediate precaution against such an event ever occurring again!

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I just realized that it's probably worth mentioning that I did just have my Cadillac serviced for several safety recalls...

One of those recalls was the fuel pump replacement (I'm not sure of the exact details). I did this about a month ago and haven't driven the car since that day (until today). Is there a chance that something from that installation could be causing my issue?

I had the recall done at my local Cadillac shop (which I trust). They also did the front brake lines.
 

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I had the recalls done recently with no problems. I think the largest risk associated with the recall that fits your symptoms would be contamination of the fuel. Specifically, anytime the tank is drained to pull the tank there is some chance fuel returned to the tank could be contaminated.
 

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Discussion Starter #7
I had the recalls done recently with no problems. I think the largest risk associated with the recall that fits your symptoms would be contamination of the fuel. Specifically, anytime the tank is drained to pull the tank there is some chance fuel returned to the tank could be contaminated.
Would fuel contamination cause symptoms similar to a rapid misfire? Should I test the fuel pressure to see if it's within spec (would low or intermittent fuel pressure cause rapid misfire symptoms)?
 

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It is unlikely the level of contamination would be high enough to affect fuel pressure. Water and/or antifreeze (the kind of contaminates found in shop containers) in the fuel can cause misfires. Fuel injected engines, unlike carbureted engines, will still run with bad fuel. Unless the car had a full tank of fuel when you picked it up, I would probably throw in a can of fuel additive and fill it with fresh fuel.
 

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Discussion Starter #9
OK,

I tried digging into this a bit more today. I'm puzzled as to which cylinder is actually causing the problem (or if it's just truly a "general misfire" as P0300 seems to imply). I have an Innova 3160 scanner if that might help me figure out which cylinder to start looking at.

I can't see anything loose, exhaust is not leaking (as far as I can tell), no bad grounds, etc.

Being Father's Day - I took the liberty of ordering a few tools to help me narrow down my tests:

OTC 3054E Noid Light Set (to test if the injectors are receiving pulsed signals from the distributor)
OTC 5613 Vacuum/Pressure Gauge kit (to test vacuum leaks where applicable)
OTC 5609 Cylinder Leakage Tester kit (to ensure that I'm not losing compression to the crankcase, coolant, exhaust, or throttle body/intake)
OTC 5605 Deluxe Compression Tester kit (because why not...?)
Lisle "In-Line" spark testing light
OTC 6859 Spark Tester (like the J 26792 spark tester recommended in Darkman's PDF)
OTC 4480 Fuel Injection Tester kit (to ensure that I'm getting proper fuel pressure after the fuel pump recall service was performed)
And a variety of additional tools to aide in testing all of these different system (spark plug boot pullers, remote starter switch, flexible hose clamp pliers, and an engine stethoscope)
...have a mentioned how awesome my wife is for letting me buy all of this stuff?!?!

Since a lot of these test require pulling the spark plug (leak down test, etc), I'm going to plan on ordering new spark plugs and wires.
Any recommendations for the best n/a (cammed) spark plugs and wires?

Since my scanner isn't telling me exactly which cylinder is having the issue - does anybody have any advice as to where I should start?

In combination with Darkman's PDF, I will perform the following tests (probably in this order, unless told otherwise):

Check for inconsistent spark first (using the spark plug tester or inline spark light).
Check the resistance of the individual spark plug wires.
Use the noid light to ensure that the injector is actually getting a pulse.
Perform the "Fuel Injector Coil Test" (Darkman, could you provide me this document so I know what parameters to measure against?)
Check the fuel pressure is within specification (I could do this at any time).
Inspect/replace the spark plugs (and wires).
During the spark plug inspection/replacement I am wanting to check the compression and leak-down (really just for self-satisfaction to confirm that everything is running OK in the engine internals)
Pull the valve covers and inspect the valve springs and other drivetrain components).

Am I missing anything? Am I over-thinking this?
 

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Discussion Starter #11
Thanks, Darkman!

Do you think my testing methods are sound? P0300 seems like a real pain to try and narrow down without lots of testing of a variety of options.
 

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A GMTechII scanner could tell which cylinder or cylinders are misfiring.

Your approach is fine.

I would consider looking at the valve springs first depending on their mileage - at 10,000 miles after market springs should be visually inspected. If there are high-rpm misfires, which could be valve float, the a random sample of the valve springs should be tested for spring rate. Although the likelihood that the issue in the case involves the valve springs is low, valve spring issues can cause more damage.
 

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Discussion Starter #13

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Discussion Starter #14
Alright, some of my tools I ordered came in today :worship:

The first thing that I decided to test was my fuel pressure. On the front (of the engine) of the driver side fuel rail, there is a black plastic cap that I unscrewed that revealed a shraeder valve for testing the fuel.

I used my new fuel pressure tester and (after purging the line), turned the key to the "ON" position (engine NOT running, but fuel pump and dash powered up). I could hear the fuel pump wail to life for a few seconds and my fuel pressure gauge read "53.5~54PSI".

It would bleed down to 51~52PSI after a few minutes of the key being removed.

When I started the car the fuel pressure gauge would read 56PSI.
*Note - the car was completely "cold" at this point

As a frame of reference - what should I expect for fuel pressure in a 2005 LS6 CTS-V?

I did not get a chance to rev the engine or go driving to observe the real-world fuel pressure (my 15mo was asleep and momma get's super pissed when I wake him up with the Caddy). I will do that tomorrow if anyone thinks it's worth checking the fuel pressure at operating conditions.
 

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Discussion Starter #16
Thanks! I have a new filter that I'm going to throw on tomorrow, but I'm not expecting any different results.
 

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Discussion Starter #18
Friday midnight update...

I pulled all of the spark plugs and inspected them.

The good news: the boots pulled off super easy (seriously!)
The even better news: all of the plugs look fine and all of the wires measured their correct resistance (AC DELCO "0746" series - measured between 746-760ohms between the 8 wires).
The bad news...still no culprit for the misfire and it's definitely still there..."popopop" under heavy acceleration typically between 3-4k (also happens when rolling out from a stop).

I still plan on doing compression and leak-down tests so I just put the original spark plugs back in (with the original wires). I'll change them out for new plugs/wires when I button her all back up.

Note* I still need to perform a proper spark test to ensure that the spark plug is getting it's power.

For real though - pulling the boots was probably the easiest part of the job for me. These plugs and wires are only about 25k miles old. The wires had a "cool sox" that wrapped around the wire/boot with a spring at the end (on the spark plug). All it took was a slight tug and they popped right off (maybe too easily, I dunno..)

One thing that really helped on the passenger side spark plugs was removing the spark plug coil rail (?) that sits on top of the valve cover. Removing this gave me much better access to the plugs. I didn't have the pull the battery/tray/dipstick like others have tried.

On the driver side, I disconnected the wire loom that run along side the shock tower.

Tomorrow's task is to wire the "remote starter switch" to the starter so that I can turn over the engine for some additional testing. All signs point to crawling under the car for that task.

Any advice will be appreciated. Have a great weekend!
 

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Note* I still need to perform a proper spark test to ensure that the spark plug is getting it's power.
An easy way to check each plug to see if it is firing is to plug an uninstalled plug into each plug wire one at time and see if it fires when the engine is turned over and/or running. The plug has to be grounded against the engine during the test. This is best done in low light conditions so that can see the spark, and do not hold the plug or wire during the test.

I think you would have noticed a difference in one of the spark plug tips if you had a cylinder that was never getting fire. I also think you are looking for an intermittent misfire (occurs only part of the time under certain load conditions) as opposed to a dead miss (one cylinder never fires). It is easier to find an intermittent misfire if you know at which cylinder it is located because you can check components, such as ignition coils or fuel injectors by swapping them from cylinder to cylinder to see if the misfire follows the component. The individual fuel injectors can also be tested with a multi meter-see attached.
 

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Spray the exhaust headers with water from a spray bottle while it's running to find the cool/non-firing cylinders. It sounds to me lke you've got some broken valve springs or sticking valves.
 
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