At a total loss...

gmcman

Member
Dec 12, 2011
4,656
I believe the platinum is a bit stronger for direct injected engines. Either one will work, I've switched to the platinum and works great.
 

zkepler00

Member
Apr 8, 2019
8
Florida
I want to say I've been having the exact same struggles as you have recently. My trailblazer has been out of commission for over 5 weeks due to cylinder 4 not running. I've checked and replaced darn near everything with still no luck. The cylinder has spark, fuel, and compression. I can take the coil pack off and get a plug to spark properly out of the engine. I took the fuel rail off and had that fire so I could watch the injectors fire. I also took the valve cover off to make sure everything was moving and doing what it should. I started this whole ordeal by swapping coil packs. Then, I replaced the injectors, injector harness, and intake manifold gaskets. Then the spark plugs with 2 different kinds. I have swapped out the cam angle sensor and crank position sensor, no luck with them. I replaced the coil plug for a better connection to the coil pack. I even got a new computer and it still didn't help. I know my engine is all good, I'm under the impression that something is wrong electrical. I have had no luck and the po304 struggles still persist. No one I have talked to has been able to help me, I am at a complete loss.
 

Johnnyjh84

Original poster
Member
Dec 2, 2020
26
Michigan
This is a valid point. Was it a screenshot during fluctuation? Can it hold 600 RPM when warm, +- 5-ish RPM?


What is your alternator output voltage at idle? Use a DMM, not the dash gauge.

I would want to make sure the valves are seating. Using a vacuum gauge, you can connect to the evap port on the TB, or the port on the intake resonator, I would use the TB.

If the needle is steady, meaning a very slow, gentle swing, almost imperceivable, when the TB is controlling the idle is good. If the needle bounces back and forth rapidly, even a little bit, that would indicate an intake valve not fully seating.

Take an index card, or envelope, hold against the exhaust flow of the tailpipe, the exhaust should keep it pushed away. If it slaps back to the tailpipe, then you might have an exhaust valve fully seating.

I would still try another known good coil one more time, only since you have done other things since then.

Make absolutely sure the coil connection is good, use some electronics cleaner but MAKE SURE the connector is DRY before re-connecting.

My go-to in a situation like this will always be a can of BG44K, not any other treatment, but 44K specifically. Then I would re-evaluate after a tankful. It's pricey, but no snake oil.

Still not ruling out another plug/coil if all else fails. After that, then more in-depth digging will be needed.
Newest pisc hopefully these help. Ton as of misses on 3
 

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gmcman

Member
Dec 12, 2011
4,656
I would pull the #3 plug and inspect. If it's extremely fuel fouled it may need to be replaced. Not as much of an issue with iridium plugs but they are still susceptible. Does the #3 coil have the spring inside the boot?
 

budwich

Member
Jun 16, 2013
2,027
kanata
trims seemed to have improved since the original posted data. These posted data show an rpm that is not idle... I am assuming it is a freeze frame capture associated with the coding of the misfire.
Something "interesting" maybe is that the "current count" has no registered counts for the "troubled" cylinder... what's with that... ie what is the attachment about?
 

gmcman

Member
Dec 12, 2011
4,656
If I have a misfire, I generally don't see a previous history using my OBD adapter through the Torque app from subsequent drive cycles, only current.
 

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