Last year I got a P0300 code in my LQ4-swapped S10. It would have some problems misfiring when I revved it high while sitting, but seemed fine in normal driving. It appears this code is just the start of diagnosing, and in many cases it will be accompanied by other codes that will help let you know what is going wrong. However, I don't have any other related codes (except a knock sensor low voltage code, that I don't think would be an issue). The truck gets fed 91-93 octane, and the engine is stock. Codes were cleared at the beginning of the year, and it hasn't come back, but then I also haven't free revved it yet, either.
From reading, it seems like it could be plugs, wires, coils, injectors, crank position sensor, cam position sensor, etc.. I would rather not throw parts at it. One thing I read was that you can check individual cylinder misfire counts to help narrow down the problem. I cannot find a way to read this in either OBDFusion or in HPTuners. There are other codes that could tell me if a bank is misfiring, but no counts as far as I can tell, and nothing with individual cylinders. Is this a limitation of the ECM I have (stock 2001 6.0 LQ4 ECM)? If not, anyone able to point me in the direction to see these numbers?
If you haven't set a misfire code, don't worry about it. Move on down the road until it sets something again, or not.
NOHOME
MegaDork
5/21/24 6:08 p.m.
Interested in where this goes. From where I am sitting, a cylinder "misfire" is only the ecm deciding that a coil did not fire. I can see how this might be detected.
How would the ecm know if there were a non-ideal cylinder firing event in a given cylinder caused by any other situation? ie if I had a dead plug or wire, how would the ecm detect the "misfire" if the coil were doing its job?
ShawnG
MegaDork
5/21/24 6:19 p.m.
I just dealt with a P0300 code plus o2 voltage codes on my 2019 Silverado.
Scanner showed misfires on 1,3,5,7.
I believe found the misfire data in the emissions section on my Innova 3040RS
Replaced B1S1 and problem solved.
Some OSes won't set codes for specific cylinders, you have to go into data to see a misfire history.
i have never tried it with HP Scan (or whatever the software is called) but it should be there. You may have to write a table to be able to see it. And yes I have the terminology wrong, it's been about five years since I've played with the software.
LS wiring has no direct method the ECU can use to tell if a coil fires - that is possible if the ignition module is internal to the ECU, or if like some Toyota models the coil or ignition module has a separate pin for a spark confirmation signal. I suspect the LS ECU used its high resolution crank trigger to measure crank acceleration instead.
MadScientistMatt said:
LS wiring has no direct method the ECU can use to tell if a coil fires - that is possible if the ignition module is internal to the ECU, or if like some Toyota models the coil or ignition module has a separate pin for a spark confirmation signal. I suspect the LS ECU used its high resolution crank trigger to measure crank acceleration instead.
That's pretty much how everyone does it. If the crank doesn't accelerate when cyl 1 fires, it sees that as a misfire. P0301, in that case.
I'll have to look at the software again, but I had dug around looking for it, and didn't see anything. Could have missed it, though.
Wonder if being a 24X crank trigger means it does not have the resolution it needs to get that data.
Oh, it has the resolution. OBD-II demands it. It has to set a code for a misfire but they don't require that the code be cylinder specific, just that it can flash the MIL if there is a catalyst damaging misfire.
IIRC the 24X does fancy things with tooth width that allows exact cylinder pair identification practically as soon as the engine starts turning. It knows where the crank is at all times.
Another thought path you can take here if you are physically observing misfire behavior but nothing is electrically or electronically incorrect would be fuel delivery. If it's happening high rpm/ high load I'd wonder about a clogged injector or fuel filter.
In reply to RacetruckRon :
High RPM/low load is usually a false misfire, because the crank pattern needs to be learned.
Alternatively, there's the issue with getting the injector connectors mixed up on the passenger bank.
