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@slobbergoat mikec7Z has a great understanding on these cars and knew exactly what my problem was. Check PM

23/C8Z

kiss system. use race gas additive to a couple tanks and see if problem goes away. something tells me the fuel you're using is the issue.

slobbergoat

Quick update - have had the garage check the manifold pressure (fine), intercooler bricks (fine), purge the intercooler tank, check O2 sensors and Cats (within reason according to ODB reader).

Will be attempting to siphon the tank to see if somebody's jammed sugar into it, then removing driver's side fuel and running passenger side out of gas.

Is now with the local GM Holden dealer who has an Gen5 compatible GM ECU diagnostic tool so maybe we'll be able to learn more this way.

Mikec7z

I read your post too fast, sorry about that.

Mikec7z

was it cold outside when the misfires happened? What altitude are you above sea level? Do you have an x pipe or catless downpipe added to the car? Do you have an aftermarket intake added to the car? Do you have a pulley swapped on the car?

I think i asked you all of these in PM already. Did not get answers. Odds of the mechanic solving what your problem is, are slim to none.

slobbergoat

To clear up - was just going to siphon the driver's side and allow the tanks themselves to clean themselves by running the car. Dropping the passenger tank would be an enormous effort I agree and not solve anything either - by 'removing the drivers side fuel' I just meant actually siphoning it some of out, not removing the tanks completely.

The misfires occured at a fairly normal temperature over here (about 25 degrees celcius) - we're about 50m above sea level so not a high altitude.

No modifications have been made to the engine itself yet - everything's original.

Sorry if I didn't answer you over PM just yet - had all of this done last week and only got the details back this morning.

Mikec7z

no problems, just hate to see people waste money and time.

So, you are at low altitude, seems like you say you are 150 ft above sea level or less. This is a key to the puzzle that people ignore, and it does matter.

Do you have an air filter like a BMS on the car or an x pipe without cats? Those 2 alone will cause the condition you are running into at your altitude.

How fast are you going when it happens? Will it do it at WOT at 70mph? or do you have to get up over 100mph?

Mikec7z

it could be the fuel for sure, they are right. The car can siphon all the fuel out on its own just while it is idling, its always kicking the fuel from the passenger tank over to the drivers tank, i think you know this already however.

slobbergoat

I'm still running the factory air filter the car came with - it's a bit dusty @25,000 miles but otherwise doesn't have any holes or anything that I could see giving it too much air flow.

I've had it happen twice when cruising at 100km / 60mph - these were temporary CELs that went away and did not flash. During a pull up to about 100mph I had it come on and actually flash for several seconds - this was after reconnecting the battery before the drive and just after the engine oil had come up to temperature.

slobbergoat

I will give this a go before getting the supercharger off to look at the injectors or anything - since I usually refuel before half a tank it could be that some crap fuel is getting periodically drawn into the pump.

I've never really given much credit to fuel injector cleaner or most octane boosters as they seem to be in the snakeoil realm - is there any point to trying these or will just a fresh tank of high octane be best?

Mikec7z

how old is the battery?

slobbergoat

Original for the 2016 so I'd say running on 3-4 years now depending on the production date. It has skipped my mind actually to get it tested - I'll have to add that to the list.

Mikec7z

replace the battery. Put in new fuel. I bet you will be good to go.

Mikec7z

batteries don't last more than 3 years in hot climates, sounds like you are in a hot place, so your battery is done. That's all. If you have not done the fuel yet, get the battery first, you'll need a new one soon anyway even if it not bad right this moment, and its not worth the headache of trying to solve this without making sure the battery is good.

Problem still persists after battery, then do the fuel. If the fuel does not solve it... then come back and we here will all work on it further.

Next thing I would do after that is get a program that can monitor your LOW SIDE fuel pressure. If it is dropping below 60psi, there is your problem.

If pressure is okay, then next thing is look for a clog.

I would swap your fuel filter. Who knows, where you are, maybe a tiny piece of sand is blocking one of the tiny injector holes, so that cylinder is running lean because the sand cant fit though the holes on the DI injector tip.

If fuel pressure is okay, and fuel filter replaced, and problem continues then the next thing to do is pull the injectors, and see if you can clean them out at least. As others mentioned, those being replaced may solve your problem. Since they are expensive as hell, What you can do is swap what cylinder the suspect injectors are on... and then if the problem follows the injectors, after they have been cleaned... then you know you need new injectors as you have isolated the variable that it can only be them causing your issue.

If the issue does not follow the injectors, then I am out of ideas for now.

That above list would be my plan of attack. You aren't wasting money doing those things, they all need to be done soon anyway.

slobbergoat

Thanks for the list - I'll see what happens tomorrow with draining the tank and the new battery.

Looking at my ODB reader there's a bunch of fuel pressure options for live diagnosis that I can look into. Should the fuel pressure be statically hovering around 60psi or will it drop with throttle? I haven't hooked it back up to the car yet so I'll need to see if the reading is for the low side rather than at the rail (or both).

Also - do you think the multiple cylinders misfiring on the same bank (though 1 and 3 far less than 5 and 7) likely unrelated to one another? The passenger side also experiences a few misfires, so I think it could just resistances across wiring / fuel pressure showing themselves?

Mikec7z

At WOT, low side fuel pressure should be 71psi. It is allowed to fall to 65psi or so, but if it starts to fall below that... then you've found your problem. (in-tank pump is going bad, or you have an extra air flowing device and you aren't telling me the truth (catless, intakes, pulleys, filter, etc)

I think your misfires are from heat or lack of fuel. When the blower coolant tank has a large pocket of air at its top, then the blower pump shuts off, and the blower air gets very hot for 3 min stretches. Then the car does all sorts of strange things.

It would really help me to know WHERE you are located exactly so i can be brainstorming climate, etc.

slobbergoat

Thanks - i'll take a look tomorrow and see what the pressure readings are.

I checked the intercooler tank after it being purged and the air bubble is still quite large - seems like I should do it myself but I assumed the garage would be able to take care of at least that much. Is the intercooler setup a properly sealed system or does it gradually lose coolant over time?

I'm in the North Island of New Zealand - https://www.google.com/maps/place/Hamilton specifically. Weather tends to be highly humid and about 25-30 celcius during summer, which isn't particularly hot but I imagine the humidity makes a large difference.

At this point I think I will take the car back from the garage and do the remaining work myself as they haven't really done anything that I can't do myself.

Mikec7z

car has to be on a steep tilt, nose up. And it takes time. Watch the vids of how we all do it with the clear hose from the home depot or lowes.

The tank being low is your problem. Bill D can help out a lot in this department too, he has threads about this also.

slobbergoat

Cheers - I'll see at getting the car back after the siphoning tomorrow and start doing the work myself instead.

If it comes to doing the fuel injectors, is it necessary to replace all O-rings as per the GM service manual or is that unnecessary? I don't mind doing things by the book, but I'd rather not overdo it either.

Mikec7z

shouldnt take long to run the car out of gas just driving it around. The last thing i would do is pay someone to help me do that I think you will be able to solve this on your own. My first email to you, i think i mentioned, if you are in a hot place, and your blower fluid is low, then that is the problem. I dont remember tho, i deleted the email because i am out of inbox room