I’ve just been trying out Northampton Motorsports new rolling road, with some worrying results.
It seems my ECU is dumping huge amounts of fuel into the engine after you go over 4500 RPM’s.
They sugest I need a new ECU that can be properly tuned to the car.
They have recomended an “Opeck” system at the cost of £900.
Does anyone have any sugestions on how I can get this problem solved?
Is your car unmodified (i.e. not turbo or supercharged)? If so, it’s completely normal, harmless and I wouldn’t worry about it at all.
The MX-5 ECU uses a simple narrowband lambda sensor, which only tells the ECU if it’s above or below air/fuel ratio of 14.7:1. Above 4,000 rpm at any more than moderate acceleration, it’ll ignore the lambda sensor and use its stored fuel map unmodified (so-called “open loop” operation). The stock fuel map is pretty rich, and that’s probably what’s shown on your diagram.
I’m curious about the figures on your diagram - the lean low rpm figure of 0.9V looks normal, but the 0.75V figure isn’t what I’d expect from the stock sensor (more like 0.1 to 0.2 V). Was the figure from the rolling road’s own sensor?
If you do decide to investigate going down the route of a replacement ECU, there is a bit of power to be gained and a bit of fuel economy too, but it doesn’t come cheap, as you see. There are alternative ECUs available for less than you were quoted though. Try searching for “Megasquirt” or “Adaptronic” for instance.
It has an induction kit, 4-2-1 manifold, cat-bypass, larini exhaust and a lightweight flywheel.
It was from the rolling road sensor
I guy at Northampton Motorsport did say that if the ratio didn’t change, I could have got quite a good power increase.
He was concerned about the amount of fuel going through the exhaust as he said it could damaged the engine. Something about wearing out the piston rings.
Yep mine does that as well if you cruise down the motorway at over 85 the LC1 shows about 12-13, rather than the usual 14.5-16 below 4k rpm.
Does this mean that the car will be more economical if cruising below 4K RPM? Or is the open/closed loop switch dependent on throttle position also?
I would say yes and the switch doesn’t seem to be dependent on throttle position.
Thanks everyone for your advice, I think I will just leave it as it is for now.
Just to add a bit more info - by monitoring the stock lambda sensor output, I discovered that the open loop/closed loop switchover does partly depend on throttle position.
Below 4,000 rpm, the ECU almost always runs closed loop control, but sustained full throttle can provoke it into going open loop.
Above 4,000 rpm it’s easy to provoke it into going open loop with just moderate acceleration, though it’s possible to keep the car running in closed loop if you’re gentle with the loud pedal.
Does that explain why motorway cruising at 4500 - 5000 rpm is not as catastrophic on mpg as I thought it should be? [:)]
The “R” stands for “revolutions”, it is already plural and needs no “s” after “RPM”.
I get an actual nervous twitch when I see or hear this.
…and don’t get me started on Jeremy Clarkson and his “torques”.
Torque is measured in Nm or ft-lbs.
Clarkson’s deliberate misuse is his joky way of saying blokes love to quote performance figures, even if they don’t understand what they mean. It’s also a little bit self-deprecating (“I can quote the statistics, but I don’t pretend to be an engineer”).