Is this hot engine afr ok or do I need to look into something?
03-12-2016, 03:27 PM
#1
Is this hot engine afr ok or do I need to look into something? Car is a 408 turbo car running dual in tank 340s on all of the time. What the car does is when I first start driving it idles at about 14ish afr and if I do a light throttle acceleration, just enough to hear the turbo start whistling, it will drop to around low 12s as soon as I push the accelerator. Cruising afr is around 14ish as well.
Now if I drive it around for about an hour the idle afr goes up to around 16 to 17 and my cruising afr is 15ish and when I do a part throttle acceleration it stays 15ish for a second before it drops into the 13s to 12s. When I get into boost it will drop into the high 11s.
I am just confused as to why it changes and want to be sure I am not going to hurt my new $7000 short block.
Thanks guys
Now if I drive it around for about an hour the idle afr goes up to around 16 to 17 and my cruising afr is 15ish and when I do a part throttle acceleration it stays 15ish for a second before it drops into the 13s to 12s. When I get into boost it will drop into the high 11s.
I am just confused as to why it changes and want to be sure I am not going to hurt my new $7000 short block.
Thanks guys
03-12-2016, 05:31 PM
#3
The tune was done by the same people that built the car, Dynospeed. I know it will change hot vs cold but I didn't think it would lean out so much. I was basically just asking if it seemed normal or if I should take it back to them. I could see it going up folk 14 to 15 but when I'm sitting a light and my afr is 16+ I worry a little.
03-12-2016, 06:24 PM
#7
The reason I'm so paranoid is a few weeks back I took the car out to do some playing and after about 30 minutes my afr got lean line now except then when I would start hearing the turbo whistle it would stutter and the afr would go really lean. I took it to them and my alky control pump wasn't working and they said my second fuel pump want coming in. They fixed all of that but I'm gun shy now because of it.
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03-12-2016, 09:24 PM
#12
I don't think they are related. But it is tough to guess. I would think that hotter fuel would make the engine run richer, and be more prone to knocking/detonation of course. I can't see it causing a lean behavior though. On the other hand, if the pump itself is getting hot, and electrical resistance is increasing between the pump and power source, it can weaken pump output (lower fuel pressure perhaps) so it possible that there is a correlation you can measure. I would try driving on just the one pump and see what happens (simplest diagnostic procedure I can think of)
If you are not into tuning your own vehicle, a great way to richen things up on demand without a laptop AND keep combustion chamber temps down is methanol/water injection. A little box with a dial can get that air fuel ratio down when you need it, from the driver seat, and combats the dangerous high temperatures associated with engine knock. Since the engine is already tuned safely without it, even if it fails there will not be an issue, and it would provide extra insurance.
03-12-2016, 09:30 PM
#13
Why don't you try disabling one of the pumps and driving the car gently, as a diagnostic procedure?
I don't think they are related. But it is tough to guess. I would think that hotter fuel would make the engine run richer, and be more prone to knocking/detonation of course. I can't see it causing a lean behavior though. On the other hand, if the pump itself is getting hot, and electrical resistance is increasing between the pump and power source, it can weaken pump output (lower fuel pressure perhaps) so it possible that there is a correlation you can measure. I would try driving on just the one pump and see what happens (simplest diagnostic procedure I can think of)
I don't think they are related. But it is tough to guess. I would think that hotter fuel would make the engine run richer, and be more prone to knocking/detonation of course. I can't see it causing a lean behavior though. On the other hand, if the pump itself is getting hot, and electrical resistance is increasing between the pump and power source, it can weaken pump output (lower fuel pressure perhaps) so it possible that there is a correlation you can measure. I would try driving on just the one pump and see what happens (simplest diagnostic procedure I can think of)