Jam ecu afr

[A L 3 X]

Right, I've got a jam ecu on my Glanza, and I've noticed it doesn't seem to give a steady afr, basically if I floor it and climb through the revs it will initially drop to approx 10.5, and dependant on gear will climb to around 11.5 nearer the redline....obviously this isn't lean but is it safe to be fluctuating?

 

[ChrisD]

It depends on the boost you got near the limit.

My stock ecu is like that...10.5 on high boost, 11 on low

 

[A L 3 X]

I'm running 1 bar through it mate? I think boost does drop to like 0.95 higher revs though

Is that normal then?

 

[weeJohn]

Pretty much, the parameters in them keep the engine running pretty safe, they are only using the stock O2 sensor for feedback so the have to keep it safe.

 

[Jay]

They tend to throw a lot of fuel in to maintain safety. Those figures sounds about right, 11.5 would be a safe area.

Jay

 

[A L 3 X]

Ah thats cool then, I just wasnt sure if they were meant to fluctuate.

I have noticed though that sometimes if on part throttle it drops quite rich, yet full throttle its fine as above, its like cos its not drawing in as much air it richens it up...weird though?

 

[AdamB]

If your on part throttle and say 0.5 bar boost, it will still run quite rich as turbo motors are mapped using the map sensor as a load reference rather than rpm based

 

[Rev]

Definitely agree when on boost but to clarify further when does closed loop ( o2 sensor) finish and open loop start at part throttle?

In practice I find a change occurs at 0psi but I read TPS low mode is 10-20% while WOT is 78%-80% throttle ( open loop ) on stock ecu.
I guess I am wondering eg. if you are not on boost and driving up a hill on part throttle then floor it you are still only using the o2 sensor ( closed loop ) from 10% - 78% Throtttle ?

 

[A L 3 X]

Definitely agree when on boost but to clarify further when does closed loop ( o2 sensor) finish and open loop start at part throttle?

In practice I find a change occurs at 0psi but I read TPS low mode is 10-20% while WOT is 78%-80% throttle ( open loop ) on stock ecu.
I guess I am wondering eg. if you are not on boost and driving up a hill on part throttle then floor it you are still only using the o2 sensor ( closed loop ) from 10% - 78% Throtttle ?

Thats far too technical for me lol, what does closed and open loop mean?

What Adam said sounds correct, although its more like if its full boost on part throttle, it feels a bit flat and drops quite rich, until you floor it then after a second it leans off and picks up.

I was told it could maybe be the fact the TPS only works as on or off on the manual, so it could be detecting the throttle as open, and seeing 1 bar boost, but obviously as the butterfly is part closed there isn't in fact as much as as thought so the mixture is richer? If i nail it through the gears on WOT its fine.

 

[Rev]

CLOSED LOOP > Basically closed loop is when the ECU corrects the air/fuel ratio based on the oxygen or air/fuel ratio sensor, the system is said to be in closed loop.
Closed Loop usually at warm idle , cruise and moderate acceleration.

Open loop has a bit more explanation.
OPEN LOOP > Briefly Open Loop Mode uses ecu fuel map without o2 sensor - in cold start, deceleration and high load conditions

The ECU will be in open loop mode when:
• starting the engine. ( NOTE Toyota water sensor control commences at 500 RPM )
• the engine is cold.
• hard acceleration. ( includes being on boost )
• during fuel cut-off.
• wide open throttle
• older cars used Throtttle position sensor for open loop ( TPS% as posted above )
• If car leans beyond o2 sensor range it can go to open loop mode.
• Excessive High temp is detected.

 

[A L 3 X]

Ah I see so could i be reaching the point it goes to open loop and therefore is dropping a bit too rich?

 

[AdamB]

Its too hard to tell unless you know the switchover point from open loop to closed loop.

 

[A L 3 X]

it certainly sounds like it, either that or the fact the tps only senses on or off, as this is the only time it seems to drop slightly overly rich, all other times its fine.

 

[AdamB]

The switchover from open loop to closed loop is determined by engine temperature, when X temperature is reached it will switch to reading sensor values rather than the fuel map. The TPS certainly doesn't help things, but it will be mapped on the safe side.

 

[Rev]

Good point , the ecu also adds fuel by going to open loop to cool the engine down at high temperature idle and some times at high temp high revs but with a turbo car at high revs I thought you should already be in open loop mode once the car hits postiive boost?
A high rev example for my auto would be crusing in OD at 3000 rpm, off boost , part throttle and closed loop the car may switch to open loop if engine temp was too high.

 

[AdamB]

There would be no need to keep switching between open and closed loop simply because a compensation fuel map can be used which will take into account variations in air temp, air density etc. This is normally a +-10% of the values in the original fuel map.

 

[Rev]

I find the ecu compensation at normal idle leans the injector cycle with high air temp at idle rather than richening it as revs are usually dropping it needs less fuel to maintain afr.

 

[AdamB]

That would make sense as less air is entering the engine as detected by the map sensor.
The temperature can be a bit confusing as air temp increases there is less oxygen in the air to combust so less fuel can be used, yet since air temp is increased fuel might be added to cool the intake charge.

 

[Rev]

Thats certainly worth considering especially with rough idle.
Regarding the JAM ecu in this post I thought it would already be in open loop at 1 bar so its not an open loop closed loop question. Maybe as said it is just adding too much fuel for saftey due to the high boost?

 

[A L 3 X]

thats the thing at full throttle full boost its fine, its at half throttle full boost, hence my thinking that the tps is sensing throttle as open, boost as 1 bar and therefor thinking there is more air than there is due to the butterfly restricting some air?