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Cold engine performance issues - AFR ?

Understanding AFR

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Hi everyone

I own a Holden 5L V8, with a Crane 286 cam and other supporting mods.

I'm using a Haltech Platinum Sport GM ECU, with optional wideband 02 sensor

I had a very tune carried out by a professional tuner on a dyno. However to cut a long story short, he looked after me on price, carrying out a fairly basic tune. Got it idling nice, ramped it up, getting the top end right. He was generous enough to invite me to sit alongside him while he set the tune up from scratch. I learned a lot. He then has left it to me to carry out the fine 'driveability' tuning. And it does need some work as it can be a bit cranky under various different driving conditions. I'd like to get the tune right myself rather than leave the car with the tuner (I hate leaving my pride & joy overnight in someone elses workshop, I won't sleep!). Also keen to learn this tuning stuff, gives me a sense of pride doing it myself.

Still very new to all of this tuning. I've completed the Tuning Fundamentals and Understanding AFR courses.

There's a couple of areas I'm struggling to work out, and I suspect it all is AFR related.

I sorted out a cold start issue, where engine would start, but then almost instantly stall. It now starts and idles fine on cold start. However when I bring the revs up a little or worse, try to drive the car with a cold engine, the engine hunts severely until the coolant temp gets up above maybe 30-35deg C. If I lift the engine revs above around 2000RPM it smooths out, but drop below 2000RPM and it starts hunting again. Driving the car cold, the engine feels like the injectors are being cut on/off. Very similar to the old carby days when the engine would suffer from 'vapour lock'.

Assuming it's an AFR issue, and also assumed it's a lean issue being a cold engine symptom. I've experimented a little with the coolant temp correction table. I've richened the corrected AFR in the effected coolant temp range. I thought I may have improved things, but this morning I took it .

So one of the main things I'm trying to understand is what symptoms will an engine usually show when it's running lean or rich ? I'm assuming if it's lean it will hunt, whereas rich it will be more forgiving, but maybe black smoke from the exhaust ?

Can anyone shed any light on rich & lean symptoms ?



It will 'hunt' either way, if playing around with the fuelling isn't working, it may be a problem with the injectors being a little large and/or fuel pressure being a little low for good atomisation of the fuel. If you're running E85, ethanol is known to be a bit harder to atomise and ignite when cold, but I would have expected that to be a bit colder than what you're reporting.

Something that may be making it more difficult for you if using a lambda, is that a rich miss-fire may show as 'lean' because the lambda measures oxygen in the exhaust and a misfire doesn't use the oxygen to burn the fuel, so shows in the exhaust gases.

thanks for reply Gord.

The injectors are overkill for my combo, but have the injector rate set appropriately.

But I don't think it is the injectors as I didn't have this same problem on my previous tune with the same injectors. I rebuilt the engine with higher comp, different cam etc and had it re-tuned to suit. Only had the problem since.

I'm just using the factory fuel pressure regulator (which adjusts with engine load/vacuum). Once again worked well on my previous combo.

I was hoping the symptoms of a rich or lean mixture might be a little obvious.

The other option I was thinking is just to try bumping adding a heap more fuel on the coolant temp correction table for the low coolant temps. Up until now I have just been making small changes, but maybe if I temporarily bump it up by maybe a larger percentage, I should be able to see some sort of distinct change and figure out if I'm going the right way.

Which injectors exactly are you using, and do have the dead times (voltage offset) for the injectors?

It's been so long since I bought/fitted them, so not sure of the specific part number

But I do know they are Lucas/Delphi 42lb injectors

Not sure if that is enough info ?

Lucas 42# Injectors Set of 8 | ZZPerformance

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