Strange fuelling issue - Throttle Pot?
Discussion
I fitted my AEM wideband today to hopefully help figure out why the car is being so heavy on fuel and also to spread the cost of the Megasquirt install that I am hopefully ordering next month, and interestingly the car seems to be running ok but with just a few anomalies that I wanted some opinions on.
-Under full throttle it sits fairly steady around 12:1 (Ok I think)
-Cruising at 60 to 70 mph it stays roughly at 14.5 but even with the throttle steady bounces between 13.8 and 15.0 every half a second or so
-Ticking over it sits steady at 14.9 four out of five times but then it will sit at 12.0 the next time I pull over. If i drive off and stop again it will go back to idling at 14.9
Judging by the fact that the ECU seems to be wanting to constantly adjust the fuelling even when cruising with a steady throttle seems to suggest to me that the TPS might be acting up, which I will check out tomorrow, but does anyone else have any ideas why it might be doing this.
Its not really a massive issue as I am ditching the 14CUX soon anyways but it would be nice to get to the bottom of the heavy fuel consumption before making the change.
Any ideas?
-Under full throttle it sits fairly steady around 12:1 (Ok I think)
-Cruising at 60 to 70 mph it stays roughly at 14.5 but even with the throttle steady bounces between 13.8 and 15.0 every half a second or so
-Ticking over it sits steady at 14.9 four out of five times but then it will sit at 12.0 the next time I pull over. If i drive off and stop again it will go back to idling at 14.9
Judging by the fact that the ECU seems to be wanting to constantly adjust the fuelling even when cruising with a steady throttle seems to suggest to me that the TPS might be acting up, which I will check out tomorrow, but does anyone else have any ideas why it might be doing this.
Its not really a massive issue as I am ditching the 14CUX soon anyways but it would be nice to get to the bottom of the heavy fuel consumption before making the change.
Any ideas?
Sounds perfectly normal to me.
- Full throttle is a bit rich, its it not forced inducted I would expect more like low 13s but it won't do any harm.
- On cruise it'll be using the lambda sensor feedback to get to a predefined target, probably around 14.7 to 15. Its the constant looping of checking the feedback and making adjustments you're seeing as it should be.
- Probably nothing to worry about, it could be the 5th time you stop the air coming is a bit hotter (sitting in traffic) and hence thinner so with the same fueling appears rich.
The TPS is easy to check with the megasquirt and to put your mind at rest you can datalog the throttle on a run and check it doesn't jump around unexpectedly.
- Full throttle is a bit rich, its it not forced inducted I would expect more like low 13s but it won't do any harm.
- On cruise it'll be using the lambda sensor feedback to get to a predefined target, probably around 14.7 to 15. Its the constant looping of checking the feedback and making adjustments you're seeing as it should be.
- Probably nothing to worry about, it could be the 5th time you stop the air coming is a bit hotter (sitting in traffic) and hence thinner so with the same fueling appears rich.
The TPS is easy to check with the megasquirt and to put your mind at rest you can datalog the throttle on a run and check it doesn't jump around unexpectedly.
Running rich is back with a vengeance 
As you know a couple of days ago it seemed to be running fine, today the whole way to work the AFR didn't go above 13:1, and was cruising at 12.5 at any speed.
Another strange thing i noticed it that even whilst going down hill and totally off the throttle it was still around 12.5, whereas i believe the injectors should be shutting off on overrun, and before it was going lean off the scale as i would expect?
Going to email ExtraEFI know and get the bits ordered up but I am still suspecting throttle pot maybe :/
As you know a couple of days ago it seemed to be running fine, today the whole way to work the AFR didn't go above 13:1, and was cruising at 12.5 at any speed.
Another strange thing i noticed it that even whilst going down hill and totally off the throttle it was still around 12.5, whereas i believe the injectors should be shutting off on overrun, and before it was going lean off the scale as i would expect?
Going to email ExtraEFI know and get the bits ordered up but I am still suspecting throttle pot maybe :/
It wont be TP, this has no affect on the overall mixture other than full throttle enrichment. I really would not get to hung up about this, it sounds like fairly standard 14CUX behaviour, This plot I took shows the same. The yellow is the AF ratio, and purple the TP, you can see it clamping at 14.7 most of the time, but with extreme swings as the TP sharply changes.
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