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So I got this code a few times, but only upon startup, and only on random cold starts so it wouldn't pop up ever time. At the time my car was factory stock so I sent it in to the dealer and they changed all 8 injectors and after that its never come back.
no to my knowledge the MAF has ever been cleaned. Factory air cleaner and bridge. No other engine mods on this car.
I've been thinking like you that maybe the PCV has oiled the MAF. That would explain the slight tendency to go lean. Easy to check and easy to overlook too! Thanks for the suggestion!
Bill, call me before you mess with the MAF they are delicate. Maybe pull the TB and see if there is oil in the intake.
no to my knowledge the MAF has ever been cleaned. Factory air cleaner and bridge. No other engine mods on this car.
I've been thinking like you that maybe the PCV has oiled the MAF. That would explain the slight tendency to go lean. Easy to check and easy to overlook too! Thanks for the suggestion!
Bill, call me before you mess with the MAF they are delicate. Maybe pull the TB and see if there is oil in the intake.
will do. The p0300 began showing up even before 10k-13k miles ( I would delete it and go back out) and it could have been oiled at that point but less chance than at 54k miles. I have the car on the lift now and will change pads and bleed the brakes tomorrow. I will look in the throttle body then.
Hi Guys !!...if the car is still under warranty and this issue was brought to GM's attention they should still honor the warranty until the car is fixed !!...these misfires really need to be addressed with a scan tools freeze frame data and see what some of the data PIDS are showing...k24556, if you have a Vantage Pro look under "component testing"...look under "sensors" and it will show you how to check injectors and secondary ignition...I have a Vantage Pro also but use it for everything but for the scope which is mediocre at best...the 4 inputs I look at for misfires are Cam/Crank, fuel and ignition...now with the pressure transducer I'll use that too...I doubt the dealership even uses a scope never mind "in cylinder pressure analysis" !!… the plug wires are pretty well insulated so I use a COP signal probe and put it right over the coil packs...you should try the pressure transducer...let me know if you have any issues with it !!...good videos below !!
Since the first documented occurrence was at about 13k miles GM has been very good about honoring the full warranty. The 5yr-100,000m power train warranty is good until February 2020. The problem is that since the dealership cannot test the car at the speed where the code is triggered it is up to me to return to the track and spend $1000 in fees and parts to verify that the firing the parts canon at it did not fix the issue. And of course each time the parts canon is fired, Chevy customer assistance closes my case and declares the problem fixed. So when I verify that the problem is not fixed I start the process all over again.
Unfortunately, my Vantage PRO is V 11.4, so it doesn't cover the C7 direct injection. however, I have a FSM, and though it is quite laborious to use, It will have enough direction to get us started.
Regarding the pressure transducer, I'll start a thread in the C5 test&tune section with a pic of what I rigged up. I just finished a proof of principle test to see if it would respond to pressure. works, but more work is needed.
That is one long video on misfires. I've seen the SD videos on the Vantage Pro. They are pretty easy to use, but I find the buttons counter-intuitive. Why you have to confirm every step with a yes button seems really old school. Setting triggers is a pain too on the V-P scope. Oh well learn and yearn. I think the meter graphing function has enough sensitivity for most the tests. For a car 2011 or older, the V-P has some great functionality.
the scan tool Autoenginuity has sensor outputs for high and ground signal outputs, and from what I'm reading in the FSM, the PCM tests the signal circuit often and should throw a code. So far, no CMP or CKP codes on Bill's car. Early on we pulled up a test point for the CKP, but the sampling rate bogged down our data stream. If it is the CKP, then it might be the reluctor wheel moving WRT the crank. I haven't looked at the engine exploded view to see how it is attached to the crank. What I do know is only Stretch Armstrong could get at the CKP sensor w/o removing the right cat and starter. The CMP isn't much better, I think the water pump may need to be removed to get at it. IfI back-probed either one, I would probably go to the PCM first. If I found a signal problem, then would then go to the harness. Especially for the CKP.
I didn't know the C7 has GDI but those engines do have issues with carbon buildup on the back of the valves...the carbon acts as a sponge and what you'll have is a lean misfire...don't know if the OP had looked into this or if that was addressed ??...the cleaning of these valves should be a part of normal maintenance on these engines !!
I had thought of the same thing.....build up on the back side of the valves but the issue began before 13k miles and always on the same 2 cylinders 4 and 7. Certainly they could have seen some build up early but unlikely. When the valve springs were replaced, the tech said the valves looked ok. The question is how do you clean it without removing the heads?
You can buy some cleaners from your friendly parts store or take the car to a shop that has specialized equipment to do this...it is normally just the intake valves.
I have short and long term fuel trim along with Maf and Map sensor data leading up to when the misfires increment from 112 to 190 and then to 275. This would have been when the P0300 code was triggered the second time. I do not have the O2 sensor data for that period. Can I determine lean misfire condition without O2 data?
If you don't have O2 sensor data PIDS you can look at your fuel trims...a injector misfire would show itself with higher long terms...a lot of excess oxygen in the cylinders...an ignition misfire fuel trims will be somewhat lower...good video below !!
Here is a 2 page summary of data from VIR on Nov 8. The misfires only occur on Cylinders 4 and 7. The first trigger of the P0300 code was the previous day (11-7) and occurred at 112 misfires and 116mph. But in this log you can see the misfires increase to 190 then to 275 at which point the car went into limp mode and told me I was a scum bag if I did not get off the track. The sampling time here is about 7 seconds because I was logging lots of sensors (except the ones I really wanted O2) so the data is a little skewed. At the point of increase from 112 to 190 and to 275 I am at full throttle at a little less than 140 and the car has shifted to 6th where I immediately go to full brake.
Can you tell me what you see from the data?
thanks
bill
edit: I am adding data from the GDS2 freeze frame when the P0300 was first triggered on 11-7.
Camshaft Position sensor--4004 rpm, Crank Position sensor--not part of Freeze Frame, Current Gear--not part of Freeze Frame, Vehicle Speed--116mph, MAF Sensor--31.06 g/s ( 4.108 lb/m), MAP Sensor--2.47 PSI, Engine Speed--4000rpm,
STFT Bank1--0%, LTFT Bank 1-- -5%, Cyl 7 History Misfire--112, STFT Bank 2--0%, LTFT Bank 2--- -6%, Cylinder 4 History Misfire--112. Brake Pedal Position Sensor--78% Accelerator Pedal Position Sensor--0%
Last edited by Car54; 12-17-2019 at 01:04 PM.
Reason: add freeze frame data
Has the Crankshaft Position Sensor (CKP) been replaced ???...the CKP is where the ECM gets the misfire info from..it would be nice to scope the signal wire ( my CKP signal waveform below) to see if the signal drops out when the misfire occurs...I would try that !!...a scope would really be best to see what's going on at speed !!
The Crank Position Sensor has not been replaced. Scoping the signal wire when the misfire occurs sounds like I would need to run a wire from the CKP to the scope inside the car and either have someone hold the scope or try to secure it in the car while i am on the track on the back straight at VIR at 140mph. I am not questioning the need to do it just the practical feasibility of getting it done. It is not impossible, just difficult. I will work on it however.
The sensor is not that all expensive so I would not worry about scoping it but I would suggest using an OEM sensor...aftermarkets are just no good !!...oh, and BTW you wouldn't need to have someone actually looking at the scope in the car...you would just put it on a long time base, go drive, and just go back and look at the info that has been saved !!
You are right. $20 for the CKP is not much. You would think however that while TAC has fired the parts canon at really expensive parts, they would have chosen a really inexpensive part that controls when the ECM thinks there is a misfire. Sometimes the logic of some of the things GM does just escape me.
When GM replaced my ECM, the tech also had to do a crank position sensor relearn. It appeared after that repair, the misfires had moved from 4 & 7 to 3 and 6. That measurement was by my OBDLink at highway speeds. After I got to the track, the misfires that trigger the P0300 are only cylinders 4 & 7.
Bill, we should be able to back probe at the PCM for the CKP and the CMP sensors with the Vantage Pro, and see if anything is off. We have the FSM, so we can find the respective signal wires and the values. There are lots of YouTubes on this, but none for a C7 Corvette, so we would be plowing fresh fields doing it. I think both South Main Auto and ScannerDanner have some good vids IIRC.
There is a dense forest of metal between the CKP and your hand. TO change it requires removal of the RT exhaust (Corvettes ALWAYS require a torch on the EXH nuts) and the starter. It makes a whole lot more sense to backprobe at the PCM and test the living crap out of it before just R&R.
When the misfires were shifting between 4,7 and 3,6 I thought maybe the reluctor ring might be moving slightly on the crank. I looked at the FSM and while it shows the CK reluctor at the back of the crank, and no mention of removing or replacing. So, I'm guessing it is an interference-fit on the crank with some sort of aligning key. The LT1 is a 58 tooth (two teeth missing) so each tooth is 6 degrees apart, and there is a 2-tooth WV gap (West Virginia, that is). The gap is used to reference the firing order.
I think back probing to look at CKP/CMP variance on a lab scope and blaze down the track is a bit of a fool's errand. But we did blaze down CMP data logging, so I'm up for a science fair project.
Regarding BC928's post, if you live nearby and want to share in our chaos, and we share yours, let us know. I know you are getting frustrated, and in the end, you may have a similar root cause to Bill's car.
12-09-2019, 05:14 PM
