Mostly looking for some feedback from anyone experienced with P050D and P0300 codes, but also have a few specific questions at the bottom. I've read through everything I could find about these on this forum and elsewhere, but most of the threads don't end with any conclusive diagnosis / fix.

My 2017 Z06 recently threw a P050D code about 2 weeks ago so I took it to a local dealer. Dealer said they also saw P0300 -- however I never saw this on by OBD2 before taking it to the dealer, not in actual or pending faults -- it does show as pending in my OBD2 now when it happens. See diagnosis under item A in the image below:



Note the B item of the pic is the dealership declining to add the new radiator to prevent overheating, stating I didn't have proof of overheating occurring, even though I had taken it to them in 2018 because it went into limp mode, and had the ECU flashed to update the MAF tables, which they also refused to do under warranty. According to their own statement on this sheet "documented complaints of overheating prior to the special coverage" is necessary, and that's exactly what I have -- a complaint lodged with them in 2018 about my car overheating and going into limp mode.

I declined the fuel injector repair for a couple of reasons:
1) if I'm going to have $4500 worth of work done on it and it's already out of warranty (injectors don't qualify for the 6/60K power train warranty) I may just take it to a performance shop instead and get a bunch of power added.
2) I'm not sure the diagnosis is correct, for reasons I'll get into below:

First, I find it very odd that all 8 fuel injectors (or even 5 of 8) would fail at once. The tech read misfires on 5 of the cylinders. The pressure drop was on ALL 8 cylinders.
Second, I've seen so many different causes for this, from everything to a SINGLE bad spark plug to a coolant leak. My understanding is a coolant leak is not likely to cause misfires on multiple cylinders.
To me, the proposed solution doesn't quite line up with all of the data so far, and I want to be sure I'm getting the true issue fixed before dropping $4500.

So, I got the car back and changed out 4 of the spark plugs (driver side) and wires yesterday. I just happened to have purchased these a few months ago for future use and because there was a rebate. These are STOCK AC/Delco plugs, exactly the same as the ones I took out. None of the spark plugs l removed looked bad, no exceptional carbon buildup as far as I could tell.



However, I think the misfires may be worse than before. I'm not entirely sure, however, because I only get the misfires when I'm at 75%+ throttle (or maybe in certain gears / RPMs... not sure), but I have to be on the throttle. Unfortunately I didn't try that on the way back from the dealership or before changing the plugs out, so I'm not sure if this it actually got worse. I'll pull all of the plugs again on that side and check them just to make sure I didn't crack one or something, but I've changed plugs before and I have the tools, so I don't think I did anything wrong here. Note that I also hadn't seen the P0300 before but the dealer did... maybe they tested it at higher throttles than I did before I took it in.

The plugs say they are gapped correctly from the factory so I didn't re-gap them or even check the gaps, but I did compare them and they all looked the same to me.

A little more specifics:
- There is no white smoke coming out on start, and no smell of anti-freeze
- My intercooler coolant looks like it might be low (about 1/2 to 1" of space at the top of the tank -- my understanding is there should be NO air in there). I read somewhere that this may be the cause, not that it's leaking through the gasket, but that it can cause a heat issue that results in P050D / P0300. Not sure of the veracity of that.
- I replaced my battery after getting it back from the dealer. It was the original battery going on 5 years so it was time (got an Optima Yellow Top).

Questions:
1) I've seen history reports, but my OBD2 won't show me these (I think this is called Mode 06). Not knowing which cylinders are misfiring makes this pretty difficult to diagnose. Does anyone have a recommendation for HOW to get a history report without going back to the (quite unsatisfactory) dealership? I know I can get a subscription here https://www.acdelco.com/techline-con...rmation-system for 3 days for like $20, but I'm not sure what hardware is required beyond a laptop.
2) Doesn't low pressure on ALL injectors sound like something more systemic, like low fuel pressure to begin with, or maybe something else (low voltage, carbon buildup)?

I'm considering taking it to a different dealer to see what they suggest. If there's anyone in the Dallas / Fort Worth area with a recommendation for a dealer / corvette shop, I'm all ears.

Thanks ahead of time for any pointers.

 

I didn't read anything about low fuel pressure. Your service tech did an injector drop test which is a common method of checking the balance between the fuel injectors. This is balance in terms of the amount of fuel delivered in a particular time. A difference of 10 psi would indicate a significant imbalance. At a minimum, the injectors with the lower drop should be replaced.

Edit: Your intercooler needs to be bled. The trapped air won't cause a misfire, but it will cause the timing to be retarded due to a high IAT.
Edit2: It's a hail mary, but a bottle of Techron might help the injectors.

 

Ah, yes, thanks. I missed the detail that it was a pressure "drop" which would indicate it's a difference in the pressure before and after. I was thinking it was just a indication that it was lower than expected on all injectors. Still, I'm curious as to what could cause all the injectors to malfunction in that way since according to the tech it was all 8 injectors dropping ~60 psi. I don't mean it's implausible, just that it seems like it should help indicate the root cause. I'll do some more searching with that in mind.

As for the coolant, yes, I expected it would need to be bled, just wasn't sure if that could be related to misfires. What I read in relation to it prior was that it could allow hotter air into the chamber, but not sure how that in itself would cause a misfire, so maybe that's not what it was implying.

Thanks for the reply, it was helpful!

 

During an injector balance test, all eight injectors are expected to drop the EXACT SAME AMOUNT! A drop of 0 psi is not possible.

 

Find yourself a "diagnostic" shop and don't go to a dealership or your friendly Joes auto repair down the street...I'm sure there are quite a few in your area !!...a diagnostic shop will be using a scope and scan tool...they will be able to find the misfire...any higher end scan tool will show current and history misfires...mode 6 is unfamiliar territory for most techs...I find valuable information there !!

 

I've already contacted one shop that specializes in vettes before I posted this, I just haven't heard back yet, probably because it's the holidays.

However, I'm still interested in learning as much as I can on the way. I know of at least one OBD scanner that costs about $120 that will show me mode 6, which I understand should allow me to see misfire counts myself, but I was hoping to also find someone with some experience using the AC Delco Tech2Win subscription. It looks like an MDI2 kit is what's required for that: https://www.acdelco.com/content/dam/...rface-tool.pdf but they won't sell it online and I haven't tried calling to inquire yet. I've seen a bunch of what looks Chinese knockoffs for around $300, but I'm dubious of those.

 

I removed the driver side spark plugs I put in and they all look fine. The gaps match the original plugs.

However, I tested the new wires and they're all 3.8 K ohms and the old wires are all 2 K ohms. All seem fine (no loss of connectivity when wiggling them around or anything). I went back to a GM parts site and the wires are GM # 12716289. Checking my parts box, it looks like I got GM # 19301299. They look identical. Maybe the extra resistance is enough to retard the spark and cause more misfires with my injectors already malfunctioning. I'll just replace with the original cables for now.

I ordered these from RockAuto.com and all I can figure is that they had the wrong ones showing up under " 2017 CHEVROLET CORVETTE 6.2L V8 Supercharged" because my order invoice shows them under that category, but they are not showing under that category:



But they do not show up under that category now:



Learned my lesson there -- always double verify the part numbers I'm ordering.

 

If you have too much air in the intercooler you can get misfires in Cylinders 7 and 8. With air in the intercooler, those two cylinders don't receive as much intake cooling as the other 6 cylinders. Combined with the fact the two rear cylinders have higher combustion temperatures than the other 6 you will see some misfiring on those two cylinders. However, it won't be a noticeable misfire while driving it will be a noticeable reduction in power at high RPMs. Engine temperatures (coolant/oil) will more than likely not be anywhere close to overheating when you see this.

As for the warranty extension for overheating you don't qualify for that if you haven't had an On Track Overheating situation. That is clearly spelled out in the TSB that announced the extension. It isn't just having a code indicating the car overheated you need to show it was on track. When you had the 2018 overheating claim did you show them anything indicating this happened while on track? Videos from the PDR help a lot to prove the incident happened on the track as the video data stream includes the vehicle health information including max coolant/oil temperatures per lap) and various performance parameters such as max Gs pulled, cornering speeds, max speeds, lap times, etc, etc.

Bill

 

Thanks, Bill. It wasn't clear to me from my letter that being driven on a track was a requirement, just that it had overheated and entered reduced power mode. On a re-read I think you're probably right, though as it says "Diagnosis or repair for conditions other than the condition described above is not covered under this special coverage program." and the "condition describe above" is "vehicle may overheat and enter a reduced power mode when driven on a track at sustained high speeds in high ambient temperatures". I'll try to dig up my documentation, but I'll do it with another dealer next time. Unfortunately I didn't have my PDR running at the time.

 

It seems to be fixed now.

I replaced the spark plug wires with the originals AND did a Sea Foam treatment (both in the fuel tank and spraying into the throttle body while holding the car at 2000 RPMs) and the misfires are gone. I could not repeat them at WOT after this when it was easy to do so before the Sea Foam.

So, it seems the dealer's notes were correct, in that it was the injectors malfunctioning, though the service manager mentioned a coolant leak as the possible cause over the phone. It seems I neglected to mention that was part of the diagnosis in the original post (though I mentioned later that a coolant leak seemed less likely with multiple injectors having trouble). That was the thing that didn't add up for me initially. Add to that, I had no record of P0300 on the OBDII scan before going to the dealer -- though I was clearly getting them afterwards.

With Sea Foam making a huge difference, it makes sense that multiple injectors had carbon fouling, though, since they're all getting the same gas.

To wrap this up and answer some of my own questions:
1) I used the following Sea Foam products:

This goes in your gas tank.

. This is sprayed directly into the throttle body while holding the engine at 2000 RPM.

2) If you want to see detailed diagnostic info you can get a 3 day subscription to ACDelco Techline Connect for, I think, $20. However, you'll need an MDI2 tool to do anything and those aren't sold online. You'll have to call GM directly. The number is available at https://gmtoolsandequipment.com. I don't know the cost, because I didn't get one. There are sub-$300 tools out there that claim to be MDI2's, but I suspect they're Chinese knockoffs (which may work perfectly well, you just never know).

There are some that don't claim to be MDI2 but claim to work with Techline connect. I didn't try these. You can see from the comments that people have had various levels of success and even the successful ones seemed to have put a lot of effort into getting it working.

There are some cheaper alternatives that will allow you to see mode 6 data (specifically, cylinder misfire counts) like .

3) Double-check your part numbers when ordering (i.e. don't just trust that the web site you're using is showing you the right part -- I figured Rock Auto wouldn't be wrong, but it seems it was in my case). I do not know for sure that the higher resistance in the plug wires I got were increasing misfires because I also did a Sea Foam treatment before re-testing, but maybe it was contributing.

4) I'll do the intercooler bleed following the instructions here once the parts come in.

5) I've been gassing up (only 93 octane) at a single Kroger, almost without exception, for the life of the vehicle. This makes me question the quality of the gas there. I will probably swap to some other fuel with cleaning additives after this, but I will definitely be doing a Sea Foam or Techron treatment now and then, too.

Thanks to everyone who offered suggestions, especially Laserdude2215 for clearing up what the injector balance test meant -- in retrospect I should have looked up exactly what that was from the start -- and also for suggesting Techron hail mary, which seems to have worked, even though I decided to go with Sea Foam instead after watching Project Farm tests on YouTube and because Sea Foam had the upper engine treatment (not sure if Techron does).

 

MDI2 Kit from GM Tools and Equipment
Just for future reference. It's $790.70 online.

 

Also, for future reference... the reason I didn't see the price is when you browse the site and search for MDI all of the first two devices say "Call for pricing".



If you click on the EL-52100 GM MDI2 KIT link you "This item is not currently available online".



Then I noticed at the bottom of the search results page is another MDI2 kit with a different part number EL-52100-AM, vs. EL-52100.



I only saw the EL-52100 links. I'm guessing these are either discontinued or non-North America versions of the same thing.

 

p050d is usually a bad injector. GM replaces them all as a set so that the characteristics match. You can get a set of lt4 injectors for around $500 and it will resolve your issue more than likely.

 

While you are correct, P050D is the sign of a injector going bad, GM does not replace them as a set. They replace the offending injector only. I have had the work done twice now, I requested all of the injectors be covered and GM refused and only paid the dealer to replace any injector that failed.

On the LT1 the injector swap isnt bad at all, I swapped my LT1 injectors over to the LT4 injectors, HPFP, LT4 fuel rails and the lowside LT4 fuel line. The LT4 engine will be a little tougher since the supercharger has to come off in order to change out the injectors.

 

Interesting, I only say that as my friend that works at a dealership replaces all 8 on vehicles with this code. Never singles. He must be doing something to keep cars from coming back.

 

Believe me I wish they would replace all of them, I would rather have a matched set in regards to the miles on them.

 

Thanks. I'm confident it was carbon fouling on the injectors now. I got only P050D initially but after getting it back from the dealer who reset the codes, I was only getting P0300, which means multiple injectors misfiring. Sea Foam (both the gasoline additive and the throttle body "top engine" treatment) have fixed the problem. That said, I am planning on just replacing all of the injectors myself in the near future.

 

Just to clarify, P0300 is not a injector misfire. It is a random cylinder misfire. Once the misfire targets are reached the ECM will pop a P0301, P0302, P0303 for the correlating cylinder the misfire was determined to be on. The C7Z is prone to cold fouling the plugs, especially if the car is just started for a minute and then turned off. I had brand new plugs in my 19 C7Z, shop had the car for 2 weeks for clear bra and ceramic coating. they did a bunch of 1 minute start ups moving the car around the shop and cold fouled the plugs. I ended up taking the car on a drive and once up to temp hammered on it for a bit to get the cylinder temps up and it cleared the plugs up and the car ran perfect.

 

Yes, I think that's correct. According to various other sources I read, my understanding was that in cases where multiple cylinders are misfiring the ECM may never give the more specific codes. I don't know if that's a correct understanding but I thought it might be intentional to indicate there could be another issue such as low fuel pressure. Unfortunately the GM tech didn't say what the misfire counts were, only that it occurred on 5 of the cylinders, and I couldn't see the counts with my OBDII reader. It may be that the more specific misfire codes always fire and my car never reached the thresholds required (it's in the 100's iirc).

I don't think my issue was the spark plugs since I've pulled and swapped my plugs and they didn't look fouled at all compared to reference images.

However, I always thought it was somewhat suspicious that I would have 5 injectors start misfiring at the same time (within 10 miles of driving) if the issue were due to carbon buildup. In that case I'd expect to get a P0300 and over time get more and more misfires on different cylinders, but I got the P050D and P0300 on a single day, didn't drive it again until I took it to the dealership, and the dealership said it was misfiring on 5 cylinders. This all happened with 10 miles of driving. It really makes me wonder if it was just a fuel problem all along, like a tank of bad fuel or dirty fuel.

At any rate, I've had only one misfire since trying Sea Foam which was before I'd even burnt the full tank of gas with the Sea Foam in it. I then switched to a 93 octane Gulf fuel with additives and I've had no issues. I'm not entirely satisfied the power is completely back to what it was, but it's pretty darn close.