Bill Dearborn

As I have mentioned several times I have an issue with an intermittent reduction in power that limits acceleration and top speed on tracks like VIR and Watkins Glen. Usually the speed reduction is something like dropping from 140 to 130 or 150 to 137.

After this happened at the end of September GM Engineering advised the dealer mechanic to vacuum fill the intercooler to make ensure it had the proper amount of coolant in the system. That was done and I went back to the track on 10/12. The problem showed up again. This time the CEL didn't light like it did the last time. I took the car to the dealer on 11/17/17 and the mechanic checked the intercooler coolant level and found it was still filled properly to GM Engineering requirements. He did find two general misfire codes 0300 that had occurred since the last visit. He will be sending the freeze frame data to them to see if they have any other ideas. I thought I would post the freeze frame info here and see if anybody has any thoughts. Check the attached PDF file. The day was on the cool side and the engine was nowhere near overheating.

Bill

Kaged

Bill,
Looks like all of the misfires are on cylinder 8 at high boost. Have they replaced the spark plug and the coil pack?
I have had issues with spark plugs misfiring under high boost on a STi that wasn't stock. Looking at the plug (Denso Iridium), even with a magnifier, I could not see anything wrong with it. Changed the plug and the problem went away.
Bill

ajrothm

I think I’d change plugs and wires if you haven’t already done that. (I assume you have tho.)

I recently had an intermitten misfire on my 3.5l ecoboost F150 under medium throttle, mid level boost (10-12 psi)... No CEL or codes.

I changed the plugs I had in it (Motorcraft Iridium, gapped at .020”) and all found one that had a carbon track in the porcelain. It literally had a hairline crack in it, not detectable by the eye once I cleaned the carbon deposit off.

Anyway, a fresh set gapped at .020” and it’s back to normal and clean running again. This one sees 18-19 psi on 87 octane and 20-21 psi on 93.

Another example was on my 900rwhp C5Z with relocated coils. I’d pick up intermittent misfires under boost. I’d check the ohms of resistance on the spark plug wires, if any of them were over 400 ohm, it would cause the misfire. It seems LS coils are very sensitive to resistance.

Just FYI.....

Bill Dearborn

Haven't changed anything yet. The car is under warranty and I am letting the dealership mechanic and GM Engineering figure it out for right now. It doesn't impact normal driving and is very intermittent on the track. This is the first time I actually got to see the data. When I picked the car up from the dealership the mechanic had a copy in the car for me. I didn't ask for it but he thought I would want it. Now to see what GM Engineering thinks about the latest history.

Any feedback I can get from other people may help. I have thought misfiring at high rpm could be an indication of a coil going bad. My first experience with that kind of failure was over 50 years ago when my 55 Chevy wouldn't rev over a certain point if it was under a heavy load. It would get up to a certain engine speed and just fall on its face. In the lower gears no problem but in third it would just drop. Now we have a coil for each cylinder and if I am reading the data correctly it looks like high rpm miss under heavy load. If it is one cylinder then it might feel like the power delivery sort of just gets soft. Problem is it doesn't do it all the time and some times it happens when I first go out in the morning and others it waits to the afternoon and affects the car for a while then all of a sudden the engine starts running properly in the middle of a session.

Bill

BEZ06

Hi Bill

I have the GM 100 octane tune. I ran Daytona with it in April, as well as at the NCM HPDE at VIR in June. The car ran great with Boostane Professional added to bring the octane of pump 93 up to 100.

At Daytona I was running 185 mph across the S/F line before braking down for T1 into the infield, and at VIR was doing an easy 157 at the top of the back straight. The car was running strong with pump fuel ant the Boostane!

I ran an HPDE in Oct at Daytona and I think the highest I got was barely 174. I had purchased some additional Boostane, but it was their Premium. According to their data I needed more of it per gallon of 93 than their Professional in order to get it up to 100, and I thought I put in what was needed. But after reviewing PDR videos and seeing the exact same speed coming out of the Bus Stop as at the earlier event but more than 10 mph slower at the end of the run around NASCAR T3 and T4 and down the front stretch, I'm pretty sure I just was not up to the same octane I was at the April event. Ambient temperatures were about the same at both events.

I haven't reviewed any data other Toolbox, and both events show similar coolant and oil temps - just lower top speed into both the brake zone for the Bus Stop as well as across the S/F line of the tri-oval.

I'm pretty sure I was probably getting some knock retard with a little lower octane than I had at the earlier event.

I'll be running Daytona again the weekend after Turkey Day and I have some more Boostane Professional on order to bring the octane up to where it was in April. Or, I dunno, but I may just have to fill up with $10 per gallon 100 octane at the track!!

I know you think you may have some misfiring going on - not just knock - and I don't believe you have the 100 octane tune, but I'm thinking a little higher octane might help out.

Additionally, my brother-in-law's C7 Z06 had some bad misfiring and he had a "Service eLSD" message. It thought that message was totally off the wall in relation to his engine problem, but after reviewing a bunch of threads on the forum to find some info for him, a LOT of forum members have gotten that message and the actual problem was unrelated to the rear end - that message has actually been from misfiring due to injector, spark plug wires, and other ignition stuff, etc. My b-in-law had a couple injectors replaced and hasn't had the problem since.

So....I'm thinking bring you octane up a little, but if you're getting misfires, or the any of the codes indicate misfiring, I guess you may have injector or ignition problems. Or if it's cylinder #8 it may be from those rear cylinders getting hot - that's the reason that for the 2017 model year they raised up the intercooler bricks in the rear to get better cooling to the #7 and 8 cylinders.

Good luck, and keep us informed about what you find out!!

Bob

ajrothm

If they haven't even changed the plugs yet, absolutely do that first.

There is a bunch of intermittent condition issues a "bad" plug can cause. You pull the plug and it can look completely normal, and be broken down inside...

I can't tell you how many times on my turbo bike and C5Z that I changed plugs and corrected weird/intermittent issues, most of the time only occurred under load.


Here is the Ecoboost plug with the hairline crack in it. Truck ran fine until it would get into boost, then it would "studder"... Not even a full misfire....Like it was getting half of the spark. It was arcing through the crack in the plug to the stick on coil.


Look between the two black brackets [ ]... cracked all the way down.

Mike Jesse

Bill,

Had a similar experience with my 17 Stingray.
It to was only under heavy load in the higher gears.
I did the simple stuff first and discovered 2 plug wires not fully connected at the sparkplug.
After removing and reinstalling all 8, things are normal.
I went ahead and after pushing the wire onto the sparkplug used my cotter pin tool to lift up the boot and "burp" the air that is trapped.

Never know.

lordofwar

my buddy has a intermittent misfire,found 1 plug wire not seated all the way.pushed it in to the correct seat and problem went away.

Bill Dearborn

So far the dealer mechanic hasn't found any sort of ignition issue. I plan on talking to him next week to see if he thinks it is a possibility. I want to work with GM on this since I am not the only one having the problem. The car is under warranty and I am not doing anymore track events until the March/April time frame. When I was at VIR in June with the NCM there were at least 3 other cars with the same symptoms.

Several people have mentioned spark plugs and wires along with the ignition coil as possible problems. I have started thinking it could be a coil that is starting to break down and can't handle high rpm, high engine load spark duties.

Another person pointed out the fuel rail pressure sensors weren't showing equal voltage readings which could point to a fuel system issue. Cylinder 8 seems to have most of the misfires and fuel rail #2 pressure sensor is the one reading the low voltage. However, both fuel rails seem to have close to the same fuel pressure in psi so I don't think the voltage level is as important.

Bill

Bill Dearborn

At one of the VIR events in June (maybe the NCM event) I was talking to somebody at the gas pump and didn't realize I put about 10 gallons of the 100 octane fuel into the tank until the guy I was talking to asked, "Are you sure you want the expensive stuff?" Then filled the tanks the rest of the way with 93. Not sure what octane I had since the passenger side tank was filled with 100 and the driver's side with a mix of 100/93. Despite the mistake I still had the same type of power reduction.

One person has contacted me and mentioned I should try and get the car on a chassis dyno and see if we can duplicate the misfire under more controlled test situations.

Bill

NSC5

Since the misfire is only on one cylinder and under higher load/RPM conditions there is a high likelihood that it is the plug or the coil pack. This is the operational environment (road course, high throttle, high RPM) that requires the ignition system to be in top condition and if there is a problem it will show up first under these conditions.

Before high energy/output ignition systems were available most providers of gasoline powered marine engines expressly forbid the use of resistor plugs and wires (which are used to reduce radio interference). The reason is these resistor plugs and wires were sufficient to often prevent clean firing of the plugs under high RPM full load operation; normally not an issue for cars but an important point for the same engine in marine service which would normally run for very long periods of time under these near full load conditions.

Probably you have a bad plug however it could be a weak coil pack AND if the coil pack is replaced then the plug should be also because certain plug faults can lead to coil pack damage. A plug with an eroded gap or an internal break in the conductor will cause the coil to build up a higher than normal voltage level before the plug fires while a break in the insulator with a carbon track fault to ground will cause a higher current discharge than normal; neither are good for the coil pack.

Bill Dearborn

Another good point. It might be worth asking the mechanic talk to the GM engineer about replacing #8 plug, wire and coil.

Bill

geterdone

Any good aftermarket coil replacement options. On almost every car I have owned two things I always make sure I have is the best ignition options and Tune.

Bill Dearborn

I want the car stock. I want no chance GM won't cover it if a major engine failure happens on track. I had a valve drop on my C6Z while running down the front straight at the Glen and GM replaced the engine under warranty. They did check to make sure the engine wasn't tuned.

At speeds of 100 to 150+ mph the infinitesimal performance gain from a tune isn't worth the cost of replacing a $20K engine.

Bill

DinkyDonut

I realize the car is under warranty, and it's easier to let the dealership take care of it, however, I'd still propose a simple test:

Move coil, wire, and spark plug to neighboring cylinder number 6. Run the car again. See if the misfire has moved to the new cylinder -- the code would be something like P0306, if I'm not mistaken. If the fault has moved, move each of the three items back, and see when and where the misfire moves with.

BEZ06

My C6 ZR1 had a similar problem. It was primarily a street car, but when my C6 Z06 LS7 blew I took the ZR1 to the NCM event a Sebring at few years ago.

The car ran great until above about 5000 rpm, then it accelerated a lot more slowly and top speed was way down. After the event I took it to the dealer and we did a test drive - the tech was in the passenger seat with a Tech2 hooked up to the OBDII port. He saw what happened above 5000 rpm and told me that it was getting a bunch of knock and misfiring.

I left the car there and the next day they called and said they thought replacing the $20 knock sensor would solve the problem. I went over that afternoon and test drove the car again but it still did the power loss thing above 5000 rpm.

After 3 or 4 days of the dealer and the Tech Center working on it they finally decided it was a Catalytic Converter problem. They replaced the Cats and I never have had the problem again. I don't know what data gave them the info that the Cats were a problem.

I see in your printout that the "Calculated Catalyst Temperature" is more than 100° different between the banks - I don't know whether that's significant or not, or indicates a Cat or O2 sensor problem that could be sending info to the PCM that it needs to pull power.

As you've mentioned in other posts, Chebie's experience with the C6 ZR1 and Cat problems is probably why they have the C7 Z06 running rather rich.

Bob

Poor-sha

I mentioned this before but I had similar symptoms with my 2015. Both times the fix was to replace the catalytic converter. One time or had actually cracked and was shooting for gas at the knock sensor and melted the wiring.

NSC5

Poor combustion events, i..e. "misfire" will increase the cat temperature because there are more unburned hydrocarbons hitting the cat and burning there. This result differs from the in cylinder enrichment strategy designed to reduce cat temperature which increases the fuel to air ratio resulting in a cooler but still complete burn in the combustion chamber while the misfire results in unburned fuel reaching the cat causing the temperature to spike.

This issue is the primary reason OBD II requires a flashing CEL when a sustained misfire is detected because the level of raw fuel reaching the cat can result in rapid damage and potential vehicle fire. In Bill's situation the firing of cylinder is 8 marginal and is randomly misfiring enough under certain situations to store a code but not sufficiently sustained to trigger a flashing CEL. Very infrequent misfires are ignored as glitches since they can be due to a sensor glitch, the next level up is significant but not sustained misfire which is what Bill experienced, and the top level is sustained misfiring which then triggers the flashing CEL. The flashing CEL means change engine operating conditions immediately (i.e. reduce load); if the flashing then ceases it is safe to drive in for service but if the flashing continues then the vehicle should be parked and transported to a service facility.

Lasco001

Bille

We also had some Z06 with these errors.
Mostly it was the plug, twice the spark plug and once the sensor boost.

The Z06 is very prone to high temperatures and bad gasoline
Water at the engine should not exceed 105 °
Intake Temp should not exceed 75 °

The next time,
Your mechanic must completely log the data when you go to the race track.
The GM system is perfect for the diagnosis on the racetrack.
When we're on the racetrack with customers, my diagnostician always has it with them.
The problems can be seen and solved very quickly

Cölestin

davepl

I think it makes perfect sense to let GM try to sort it out under warranty, but: a high boost misfire on a single cylinder on a supercharged engine is an ignition leak of -some- kind. Replacing the plug and wire should be done just as a diagnostic step to rule it out if nothing else.