1UZ engine running REALLY lean after 'heat soak' while idling?

[stradlater]

SO I've tuned the 1uz up pretty well, at idle it's 14.7, at light cruise it's 14.5-14.7 and then boost it's getting around 13's...

But, lets say that I'm idling somewhere for a bit while we make some changes, and it gets hot.

Then, when I go to take off, it's OFF THE CHARTS lean, so much so sometimes that it actually doesn't even make any power/stalls.


I'm trying to figure out why this is. When this happened last, the coolant temperature wasn't exactly LOW, but it wasn't over 100 either, more like around 90.

Only two things I can think of is that something is getting hot and leaking either fuel or air, but the fuel pressure doesn't seem to drop.

So then, the other thought is that it's really hot air and metal, which is making the fuel evaporate in the inlet manifold. This one is a long shot, but it's about all I can come up with.

What are peoples thoughts on this one?

[CrUZida]

Have you tuned the 'tip in throttle' section?
Or 'throttle pump'

Depending on what the ecu calls it.

FYI, IMO "around 13's" is scary lean for a 1UZ on boost...

[stradlater]

Nah, I haven't worked onthe throttle pump bit, I don't even yet konw what that means.

How would it help this scenario?

I figured 13's was ok, but if you think it should be richer, I might push it down to 12's.

[Duk]

Do you have an inlet air temperature correction map?
Is it, for some strange reason pulling fuel out with an increase in IAT?

Failing a computer tuning issue, it could be something weird like dropping voltage from a dud alternator getting to hot.

[stradlater]

I've watched the voltage, and it stays constant, as does the fuel pressure.

My thought of the inlet air temp correction was there too, however I've got that function turned off at the moment...

Is there such a thing as fuel evaporating?

[Duk]

Is there such a thing as fuel evaporating?

Yeah, but it can only evaporate into the air stream that is going into the engine. So it 'shouldn't' make a difference.

Look at the cold and hot injector open times when idling, to see how much they change.

Do the cruise AFR's change with temperature?

Coolant temperature correction map???

[stradlater]

I have actually put fuel BACK IN at 100 degrees on the coolant correction map. Previously it was 0%

How do I check the injector open times at cold vs hot??

The cruise AFR's only change with temperature after it's been sitting, when it kind cools down again (a tiny bit after rolling for a bit) then it's alright again.

but, I'm talking, going 14.7 to 20 on cruise...

[Duk]

How do I check the injector open times at cold vs hot??

Does you software show an actual injector duration/duty cycle that is being used? See if this changes with temperature increase.
What system are you using?

The cruise AFR's only change with temperature after it's been sitting, when it kind cools down again (a tiny bit after rolling for a bit) then it's alright again.

but, I'm talking, going 14.7 to 20 on cruise...

20:1 cruise AFR's I'm surprised it can behave well enough to drive

[thechuckster]

you need to look at your acceleration tuning (ak TPS or throttle enrichment etc.). It's the change in MAP (from the throttle opening up) that's sending you to an area of your map that you've tuned for steady state running not load.

The TPS enrichment should be driven by the rate of change of the TPS.

IAT correction will also be a factor if you;re heat-soaking the plenum and intercooler. If the engine is at normal temps then CLT correction should be nil.

[CrUZida]

As the IAT gets hotter, put some fuel in and pull some timing out.

Throttle enrichment was the term I was looking for (thanks Chuck).

[Jonny Rochester]

I am guessing you have coolant temp and air temp gauges on your engine. I expect you can use the laptop or hand controler and see what the temperatures are. The next thing is to calibrate this. Use another independent thermometer. Make sure that when it's 15degrees in the morning, both sensors read 15degrees before you start it. If the readings don't make sense, you have to calibrate it. Take a series of resistance reading from your sensors and type the data into your ECU. This is most important.

Tune the fuel map once the motor is warmed up, with zero corrections. Look at the 3D graph of your map and get rid of holes and spikes.

Next, look at your temp compensation. Then tune the temp compensation the next morning when you start it.

[TheDarkRaver]

My vote is on throttle enrichment, which will more than likely be the root of your problem (I was having the same problem and also after turning the car off and letting it sit for 10 mins then starting it back up, for the first 10 or 20seconds it would run REALLY lean)..

If you do a google search about throttle enrichment it will all become clear why it is important.. All to do with the atomisation of the fuel etc.

[stradlater]

Yeah, I think you are right on the Throttle Enrichment thing.

I've no idea how it works yet, and the numbers look scary complicated, but I'll figure it out and whack it in. That will hopefully fix my problem.

Thanks for your input guys.

[TheDarkRaver]

What type of ECU are you running?

In the user manual it usually gives you some idea of how to set it up and the base settings.