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After advice on where to begin looking.
Only happens on very cold mornings when I driving at 50kph in 4th gear down my street. I get a couple of split second hesitations/misfire which show on the AFR gauge as rich spikes. Jumps from 14.5 down to 10. something and quickly jumps back to 14.5. Theres a couple of seconds between each hesitation but no rhythm or rhyme to them. Completely random.
By the time I reach the end of the street (1.5kms) and turn onto the next long 50kph road the hesitation is gone and never returns. It doesn't happen if I drive in third (higher revs).

I initially thought spark plug misfire as I'm still running the stock SE coils with plugs gapped to a bees dick. I've read the trade off is potential spark blow out on cold cruise, but I also read a misfire will show as a lean spike, not a rich spike so I don't think it's this.

Only happen this time of the year when the weather locally gets really cold in the mornings.

I forget, are you on a standalone ECU? I think you are ... Can you log it to see whats happening? Look for how much fuel is being injected (pulsewidths) and compare that to when the engine is a hair warmer. Also, check what compensations are doing at low temps, maybe it's not tuned well at those extremes and it's dumping extra fuel.

Misfire will show as lean as all the O2 is getting to the wide band, or at least some of it is not getting burned in the (non-)burning mixture.

I'd be looking at ice (in Newcastle?!?) on the IAT (or CLT) causing a rich mixture, but that would be in all gears presumably. It is possible that there is icing in your inlet tract, on an obstruction of bend? Are using a stock MAF, that has a grid that could conceivably ice up?

Is your ECU doing anything according to the gear the car is in, which might lead to a misfire-inducing condition in 4th?

I have suffered carb icing in my old Datto 1600 when the corrugated tube taking hot air from the exhaust manifold to the air cleaner disappeared, it would start missing around Lake George but I couldn't find anything wrong (and I had a piloting background where carb icing and carb heat was a real thing), but eventually found that was the cause - big lump of ice sitting on top of the venturi! We don't have venturis but maybe other bits could ice up in certain conditions.

HTH, please keep us updated - you have aroused my curiousity!



(On preview - what Lachy said about compensations, especially if they are by gear)

ManiacLachy wrote:I forget, are you on a standalone ECU? I think you are ... Can you log it to see whats happening? Look for how much fuel is being injected (pulsewidths) and compare that to when the engine is a hair warmer. Also, check what compensations are doing at low temps, maybe it's not tuned well at those extremes and it's dumping extra fuel.

Yes standalone ecu. I will borrow a laptop and get a log, see if there's anything obvious. It feels exactly like a single quick short misfire. but runs fine between events.

greenMachine wrote:I'd be looking at ice (in Newcastle?!?) on the IAT (or CLT) causing a rich mixture, but that would be in all gears presumably. It is possible that there is icing in your inlet tract, on an obstruction of bend? Are using a stock MAF, that has a grid that could conceivably ice up?

Is your ECU doing anything according to the gear the car is in, which might lead to a misfire-inducing condition in 4th?

HTH, please keep us updated - you have aroused my curiousity!

Doubt it would be ice. Sorry I should have clarified when I said "really cold" is actually like 7-10 degree mornings here. Not like the cold you get down there in the Canberra region but certainly much colder here than it was a couple of weeks ago. Car is garaged so doubly doubt ice.
No gear specific setup in the tune so not that, but now you've said that, it does make me wonder if its an engine protection kicking in momentarily. Though, If it was say low oil or fuel pressure engine protection doing an ignition cut, that would also read lean too right? (And I'd assume the CEL would illuminate).

Ok I need to get my hands on a laptop. Likely ECU related rather than mechanical/electrical.

Roadrunner wrote:Doubt it would be ice. Sorry I should have clarified when I said "really cold" is actually like 7-10 degree mornings here. Not like the cold you get down there in the Canberra region but certainly much colder here than it was a couple of weeks ago. Car is garaged so doubly doubt ice.

[Thread drift/on]

Keeping it warm and cosy is nice for all sorts of reasons, but icing is not one of the main ones.

Icing is temperature and humidity dependent. Where a venturi is involved, say for a carburettor or for vacuum-driven instruments (as on my old C172), the pressure drop/increased velocity through the venture results in a temperature drop, so air temp a few degrees above freezing results in it dropping below zero, the venturi cold soaks (mostly aluminium), and the ice forms on the leading edges and builds up from there. Same for aircraft wings, which have de-icers for that reason. Our manuals told us to turn on deicing at about 10* above freezing (something like that anyway). So if you are 3-5* above zero air temp, a carb will cold soak eventually to below zero. I doubt there is much risk up there though. And you don't have a venturi anyway.

That is what was happening with my old Datto, cruising at steady throttle in temperatures just above freezing. It could be well below zero when I started it and drove out of the carport in Goulburn, but it was 30 or 40kms later the problem stopped the engine, though you could feel it being choked up progressively for some distance before that. The two solutions were to stop cruising at 75-80mph and vary the throttle to disrupt the stable airflow which breaks up the ice accretion, and to reconnect the heat pipe to the air cleaner - problem gone, never to recur.

[Thread drift/off]

Geeze, I need to get a life ...

CEL isn't a trust worthy indicator once you have a standalone ECU, so don't go by that.

What plugs are you running? If you haven't already, it might be time to upgrade them. Stock coils should be fine if they're in good condition. What happens if you leave the car to warm up for 10 minutes, then drive down the road?

But first, get a log. Also take a look at the warm-up enrichments and the like. Find out what they're doing at 10* vs what they're at the temperature when everything is fine.

Ok finally managed to get a log. Of course it never happens when the laptop is plugged in But did eventually manage to capture only 1 minor stumble. How do I go about uploading the log file here?
Reviewing the live log in Eugene, it appears MAP Prediction and Acceleration Enrichment flags activate moments before the rich spike and stumble, then turns off and it all returns to normal.
I've exported and loaded into Megalogviewer and selected channels that show this.
You can see the AFR is steady 13.9 then drop down to 11.1 and then pick back up to 13.9 again.
I also noticed the TPS signal in MLV looks crazy spikey? It only varies from 7.5% to 9.5% though so maybe that's just megalog viewers scale being too aggressive?
I'll be honest, I've not use MLV before so hopefully this gives some insight?

So after some more playing it's definitely acceleration enrichment enabling. I can force it to happen by quickly jabbing the throttle slightly. Must be set too sensitive at cold temps as it doesn't do it anywhere else. I think it's only problematic in the mornings when leaving home as my street is quite bumpy and I'm unknowingly bouncing my foot slightly on the throttle on the bigger bumps. Would explain the jittery throttle trace.
I don't know what I'm doing tuning wise and the car runs smoothly everywhere else so don't want to mess with an otherwise excellent tune unless someone has a simple to follow guide on how to adjust this on an Adaptronic Modular/Eugene without blowing things up
Otherwise I'll just drive around it. It doesn't happen every time. Just have to wedge my foot in so it can't bounce on the throttle till the end of the street.

I don't know much about Adaptronic I'm affraid, so I couldn't give you specifics. You could take a look at the menus and see if there's a temp/AE adjustment and tweak it. But I completely understand why you might be a little hesitant to mess with the tune.

If you can drive around it while it warms up, and it only happens on cold days when you can't help but be jerky with the throttle ... then I wouldn't stress too much about it.