Bill Dearborn

What is the normal operating parameter for the fuel pressure sensor voltage? Should there have been a code thrown? Related to your observation the dealer mechanic says the fuel level sensor readings are all over the place which he thinks indicates the fuel is sloshing around in the tanks. He thinks that is causing the fuel to be aerated and when it gets pumped up to the DI pump the aeration results in a lean fuel mixture being injected the cylinders. The GM engineers disagree with that but don't have a rationale for why the fuel level sensors have such readings.

Bill

badhabit_wb

I'm not sure about the parameters but I wouldn't have thought there would have been that much difference. It could be load related and your mechanic may be correct the fuel could become aerated. If the fuel was sloshing away from the pump I guess that should happen. Did this happen on the straight or coming out of a curve. Either could cause fuel to slosh. Does it happen with a full tank of fuel or after you've run a couple of sessions and the fuel is low? If you could narrow down all the variables that you are aware of it will probably help the tech narrow it down. I'm not a mechanic so you can take my observations with a grain of salt but it sounds like you have a decent mechanic working on it. The more you can isolate the problem the more likely you will be able to fix it.

Bill Dearborn

The history files show the fuel tank was 89% full on one occasion. That means the left side tank was full and the right side was probably about 75% full. It is far above the fuel pump inlet. The mechanic is thinking the sloshing is getting air mixed into the gas in the tank not at the pump. That would mean very small air bubbles in the gas like you would see if you put water into a blender and turned the blender on.

I am pretty sure the misfires occur as I accelerate up the straight. From what can be seen in the pdf I attached previously the misfires occur at just over 5K rpm at 100% engine load with the speeds in the low 100s which means the car is pulling hard in third gear. There may be something else happening at a lower level as it seems the car is loggy even in 4th gear above 5K but there is no misfire data recorded. They also seem to be in cylinder #8 which along with #7 in the LT4 are the two cylinders that run hot. By hot I mean higher combustion temperatures than the other 6 cylinders.

Bill

badhabit_wb

It seems like, if I remember correctly, that the larger supercharger bricks and cover were added to address those cylinders running lean. It may be a design issue rather than air in the fuel. I figured from the printout that you had to be on the straight but I was just making sure you weren't in the esses which could definitely cause fuel to slosh back and forth. I wonder if the fuel is boiling in the lines? It probably shouldn't be but that would probably have similar results to air ingestion and may be more likely as we push the engine harder. I had the same problem with a 70 big block car I ran and we finally put in a larger fuel pump and a bypass line to circulate fuel back to the tank. Problem solved. These engines have a lot more fuel pressure and it's probably less likely to be that I just thought I'd throw it out there.

360Lemans

Quote:

Originally Posted by badhabit_wb

It seems like, if I remember correctly, that the larger supercharger bricks and cover were added to address those cylinders running lean. It may be a design issue rather than air in the fuel.

YEP, badhabit you get it!! SOOOO many have chased this issue and I just don't understand why Bill you ignore this known problem?? I know you don't have an A8. With my 2016 A8 Z07 at VIR second and third lap starts with seat by the pants power loss, then check engine light or misfire codes and even random codes. 4th lap complete limp mode, some times no engine light at all just full limp mode . I have had the Z in two different GM dealers and the best TECH can't figure it out. Badhabit is right on the money GM knows, why do you think larger bricks did not fix the problem for forum members that know how to track their 2017 models?? Can you say ZR1 and new Camaro with 11 coolers

Poor-sha

I don't think this is Bill's issue and it wasn't my issue. First, Bill's car (and mine) never had issues like this when new when the ambient temps were much higher. It seems like after these cars have a lot of track time on them it starts becoming an issue. I posted this in the other thread but in both of my cases the issue was a bad catalytic converter. I don't know if that was my issue the third time as I just sold the car.

Maybe it is the cats breaking down. Perhaps the coils or plugs aren't up to lots of hours at high RPM use and start to fail. Perhaps there is oil build-up that is affecting the back cylinders. I don't know but I'm glad Bill is ******* this issue as I suspect more and more folks will start having it if they track their car a lot. I was just ahead of the curve a bit on that.

badhabit_wb

I think it's great he's trying to chase it down. His converter temps seemed high but I'm not sure what they should be at that load and rpm. Do they have heat shields on them? Poor-sha did yours have heat shields? That could cause the converters to overheat. I guess if the converters could be removed and a converter delete pipe used in it's place that would remove one variable.

Bill Dearborn

The problem is intermittent. Sometimes it starts affecting performance and it will last for a day. The first time I experienced it was last year at the Glen. Starting with the third session of the day I was getting very poor top speeds on the back and front straights. I had a lot of tire vibration that day so thought that all of the vibration could have caused timing to be pulled. The car performed very closely to what my 97 C5 performed and I ran another 5 20 minute sessions with the car performing like that. It never went into limp home mode and never through a code. You can't say the car is in limp home mode if it is capable of pulling 137 mph at the end of the back straight when it should be pulling 150+.

When I got the car home the dealer mechanic couldn't find anything wrong with it. Then I went to VIR for another event and had no issues at all. This year I started getting sessions at VIR where the performance was lower than expected. A lot of times riders have no idea anything is happening unless I tell them. The most obvious occurrence was at the Glen this year. I was there for a 3 day event and on the afternoon of the last day the performance dropped off. During the last session I took a friend for a ride. The first three laps the car ran fine and then it started falling off and I mentioned that it wasn't putting down all the power it could. Then on the 7th lap we were going uphill through the Esses with a wide open throttle and I suddenly felt the car surge as full power came back and the car ran fine the rest of the session which added up to another 7 laps.

This isn't an over heat situation like the A8s have. The coolant and oil temps are no where near overheating levels. If it was an overheating situation it wouldn't go away when the engine was at its hottest operating temp.

There are only a few cars that seem to have the same issue. When I was the NCM VIR event this year there were 3 other owners reporting similar results. We ran out of time or the GM engineers that were there would have been able to put a monitor on the car to see what was happening.

The one thing I do know this year is it happens more often and it sometimes just disappears in the middle of a session.

So what kind of things would cause misfire symptoms that come and go. Over heating more than likely wouldn't, a failing coil might, an interruption in intercooler cooling might, a cracked spark plug might as well as a spark plug wire that is starting to break down. On the fuel side maybe the system runs lean every now and then.

Having seen the emails the GM Engineer has shared and talking to the mechanic at the dealership the engineers believe the issue is in the intercooler circuit. The first thing the mechanic did when he got the car in his bay was take the cap off the intercooler to make sure it was filled to the point he filled it before I went to the track. It was still filled to that level.

Bill

Mad Dog 24

Bill its disappointing the issue cannot be found. We have identical cars although I have the 100 octane GM tune as of this year. I've never felt such a power loss this passed season. Although a few yeas ago sometimes on 93 octane it would act a bit sluggishness but very minor. One would think that if my car has no issues then maybe it could have to do with mapping. I will need to pay attention next year more. I bet this is a non issue for drivers that don't push their car 9 to 10\10ths consistently.

Having the car come alive while going up the esses at WGI at WOT would make my heart skip a beat!

badhabit_wb

I had the front clip off my car last weekend installing the secondary radiator. I looked at my intercooler tank and there was a small bubble that looked like what I'd seen as normal. I'm wondering now if I should have gotten that last bubble out. It could be that the tank is too small and there's not enough cooling capacity there unless everything is optimal. If you have a problem there it would explain the off and on nature of your problem better than most of the other things that have been mentioned.

Poor-sha

No aftermarket heat shield on my car.

badhabit_wb

I guess the intercooler circuit is looking more and more likely...I hope it's that simple honestly. Granitelli makes tank that holds a gallon and three quarters more fluid that might add enough extra capacity to at least solve that part of the equation.

Bill Dearborn

You need a small bubble at the top of the reservoir for expansion. When GM had the mechanic vacuum fill the system before I went to the track the bubble at the top went down to the point the side of the tank started radiusing toward the top. Afterward the vacuum fill the bubble was about half as deep. However, the bubble in the plumbing at the top of the system was eliminated. If you take the cap off the intercooler plumbing near the alternator you should not see any air in the horizontal section of the T. The coolant needs to come up in the vertical part of the T although it doesn't have to come all the way to the cap. From the internal emails I have seen there are some GM engineers pushing for the release of an improved tool that makes proper filling of the charge cooler easier.

When I took the car back to the dealer on Friday the first thing the mechanic did was remove the cap and check to make sure the charge cooler coolant level was still at the level he filled it to.

Bill

360Lemans

First of all you are in a different class than most. I have been on the track with you and observed your driving on several different VIR events. Your driving skills are sooo good. you don't overdrive like most of us. (I drive like I stole it. You drive like a seasoned Lemans driver) I can almost bet you your temps are lower than most and with better lap times.

I had the same experience you stated above, never had issues like this when new (1st year) and the ambient temps were much higher toward the end of season. Then starting second season in May, BAM first track day at VIR limp mode and it went down hill from that point. I through the same codes as Bill, the first Tech bled the intercooler cooling system with no luck.

In my opinion most of us had no issues when new but after the intercooler starts loosing just 10% efficiency by daily driving IE bugs dirt and track use, the intercooler cant keep up to task. This can elude to all kinds of problems with supercharged engines like Cats, plugs on and on.

I hope Bills problem is as simple as wires or plugs.

360Lemans

Bill whatever the fix is please keep us up to date. I read your post above and its the same intermitting problem I have, I also felt the car surge as full power came back and the car ran fine.

BTW my A8 has never overheated, engine oil and coolant temps are high but not extreme. I will be installing LG additional intercoolers hopefully in the next couple of months, I'm pretty sure that will be the fix.