help me tune out these misfire plz

[tattooedsgt]

So a little back ground, i have a LS1 completely stock other than long tube headers. My LS1 PCM bricked, so i bought a 99 silverado PCM that was tuned for a 5.3 and Im in the process of setting the LS1 perimeters from my old STOCK tune. So doing some idle tuning and the motor seems to be running fine, no rough idle, and idle in drive is OK. My question is why with stock perimeters i have misfires, I never logged any misfires when i had my old PCM. So just wondering how to fix this issue?? Ive attached my tune and scan file. Now the only difference that i didnt change the silverado tune to match VE table of the LS1 but the timing is matches the LS1 stock tune. Also during the scan file i did a LTFT relearn.

[mbray01]

Your best bet would be to write entire your old file into the new ecm. This way everything is the same. You can copy over differences, but would require a little touchup, but would be close. Me personally if you have the old file, write entire it into the pcm

[tattooedsgt]

I logged misfire perimeters and found that I have misfires on #1 and #6 cyl. so i removed the plug, looked good BTW, adjusted the gap to .050. checked wire on those cyl and even swapped the 1 and 3 and 4 and 6 wires to see if the misfire would migrate to the other cyl, nope. Ive attached the scan files just with misfire channels. weird thing is that the motor idles fine, theres no stumbling or hesitation. Could the injectors or the coils be faulty on those cyclinders??

[alsediri85]

Spark plug, wiring, coil, low cylinder pressure, low flow from injecter( eng running too lean). All of them could cause misfire. I would swap coil first and then check the cylinder pressure using a compressor tester.

[tattooedsgt]

Since it was running OK at idle i decided to take her out to just see if i would get any misfires while driving and i got 0 misfires, 0 knock. It seems like i only get misfires when the engine temp is approaching 190+. Attached is my scan file. Car ran pretty decent for just a stock tune. No hesitation, stumbling or anything. Should i be worried about those random misfires at idle??

[Oleblu]

If you don't believe there is actually a misfire then adjust the misfire counter tables in the engine diag section. Of coarse compare them first before you go changing stuff that might not need changing.

[5FDP]

.050 is still a really large gap. GM switched to .040 after like 2000-2001 likely because they too knew the gap was far too large to begin with.

[tattooedsgt]

.050 is still a really large gap. GM switched to .040 after like 2000-2001 likely because they too knew the gap was far too large to begin with.

Na, .050 is fine. I went with stock NGK TR55 plugs, had no issues with them what so ever.

But i plan on taking a long drive with my car and do some logging. I was surprised how well it ran with that first initial tune. it seems better with this new 5.3 PCM than it did with the LS1 PCM.

Any pointers based on first log file above? I am running LTFT and STFT enabled so it seems like the trim are kinda all over the place but it runs OK.

[dermotw]

-Did you run a crank relearn?

Different people have different ideas about it, but GM say in the manuals that it must be run if you change ECU or "any rotating part of the engine"..

Since you got an ECU from a different engine variant, I would think it would make a difference. The ECU stores data about the engine rotational behaviour and thats how it decides on a "misfire". According to GM, the data is unique to every engine/crank/flywheel combination, even in identical cars/engines.

A write entire of the PCM with you old file would copy the old learnt parameters across imho, but writing the cal won't.

[Earwax]

As Dermotw mentioned,a crank relearn must be done when a ECM,crank or cam sensors, reluctor wheel, cam sprocket,etc is changed. It also is to be done when reprogramming the ECM.Regardless if it set a code for crank relearn or not.

[tattooedsgt]

Im a little hesitant of doing the crank relearn...are they any links to reference just make sure i dont mess anything up. Last thing i need is to brick another PCM or damage the motor. the whole reason i bricked the first PCM is because i did write entire for SD tuning.

[tattooedsgt]

I tried doing the the crank relearn based on the info in the VCM scanner.

CASE Learn: To use the CASE learn function please follow these steps:
Ensure the engine is at normal operating temperature (ECT > ~65C).
Put the vehicle into park (auto) or neutral (manual).
Turn off all accessories and A/C.
Turn the vehicle off.
Apply the parking brake.
Press the brake pedal. Keep the brake pedal depressed during the entire procedure. REQUIRED for successful test completion
Start the vehicle and let it idle.
Press Begin.
Gradually rev the vehicle to fuel cutoff (around 4000-5000 RPM's) over a period of about 4 seconds. When fuel cuts out, immediately release the throttle.
Allow the engine to come back to an idle.
Turn the ignition off for at least 15 seconds. This step is required for the VCM to store the newly learned configuration.

I followed the instructions to the T and currently on my tune i have the rev limiter set to 6200 RPM. Anyway i went to up to 5K and held it there for 4 sec and the fuel never cut out. I tried again and went to 6K for 3-4 seconds and fuel never cut out. I felt kinda hesitant to push the motor any higher than that. So next i went into to the editor and lowered my rev limiter to 5K. Tried the same instructions again and just held the motor bounce off the rev limiter and still the fuel never cut off. Anybody got any ideas on that??? Are there different procedures im not aware of???

After i tried the crank relearn i wasnt sure if it took or not so i went for a drive. I still have some misfire issues when the motor is at higher temps and this time the misfire was alot bigger and had moved cylinders from the previous logs. But after i got on the road the car ran decent. Did a high RPM pull and i had no misfires or knocks. Seems like my misfire issues is only at higher coolant temps like 190-200. I also had this weird knock at like 5 MPH too that shows only on the chart but not on the graph. And BTW im not getting any misfire codes or crank relearn codes what do ever.

Attached my more recent log, please check it out and let me know what you think, Id like to get this all figured out before i tune any further.

[5FDP]

I would still lower the gap. Even this TSB from Ac Delco says too.

https://www.acdelcotechconnect.com/p..._03D-J-171.pdf

Then work on those very high fuel trims.

[IARLLC]

I believe that the e-brake and parking brake signals are needed in order for the system to enter crank learn mode. As this is a swap....maybe those two are not wired up?

I have seen a few cars misfire until the crank learn was done. Not every car by any means....but a few.

[dermotw]

As IARLLC says, you need the inputs wired to ECU, also it can be a bit 'funny' about how long you wait after you press start etc. But it worked for me, after a couple of attempts. You don't need to play around with rev limiters etc, and you don't need to hold it at rpm, just let it climb up until it suddenly cuts out & spins down when the ECU 'sees' it reach its test limit. If it doesn't cut by say 5500, go back & try again! It is the slowing down, after it cuts fuel, that is important, THAT is when it measures & stores the data...

BTW you will only see the misfire code after a while, if its not too bad. It will take some amount of time to trigger a DTC, could be many hours of driving...

EDIT: I don't see any misfires in the last log?

[tattooedsgt]

Yeah the brake is tried into the PCM via relay on my painless harness(attached PDF) but the parking brake is not. So im not sure if the relearn will work or not. I supposed i will try again and maybe call Painless and ask if they know if its possible to do the crank relearn with the wiring as it is.

As far as the misfires in the log, the misfires only last for a few seconds in the very beginning of the log file. When that misfire happened i didnt even notice the motor misfire or stubble at all. Anybody have any ideas on why the scanner would pick up a knock on the chart/channels but not the graphs??

[tattooedsgt]

So i was able to do the crank relearn even with this being a swapped motor. So i ran through the procedure and rev'd the motor up to 4k and held it there. I was waiting for the VCM scanner to say hey its learned or something. Or waiting for the fuel to cut out. Then after initially hitting the relearn button, getting the promt to start reving i clicked OK, motor was a 4K RPM and hit the relearn button again and instantly the fuel cutout and then let the RPM's come back down, shut the motor off for a minute, sweet it worked. But to just verify it worked and i had no misfires, I scanned the car at idle and let it get to op temp...NO misfires logged. Good shit. thanks to all that helped me hopefully this thread will help others too.

[AutoWiz]

Hey so when the misfire codes come back, I just want you to consider a few things. First and foremost there is a code that stores in history when the cmp/ckp relearn needs to be done. There is no way that cmp/ckp coorelation can affect or impact individual cylinders like just 1 and 6. Also it is important that we understand exactly what the pcm defines as a misfire and how they get detected. You see the controller looks at engine speed in between individual ignition events. This can not be something impacted by a tune because the engine slowed down from one ignition event to the next but then picked back up speed in the same revolution of the engine. Misfires are a mechanical failure. If we want to argue a p0300 random misfire from a excessively rich motor choking on itself that might be an arguable thing. But a p0301 or p0306 is a problem with cylinders 1 and 6. Now aside from coil, injector, spark plug, and wireset and wiring, The LS engine family seems to be known for it's valvetrain issues. Sometimes they break a valve spring and sometimes the spring inside a lifter collapses. The latter is more common and will usually bring you to an isolated misfire on that cylinder.