Lean Misfires at 2700-2800 rpm

[keithmac]

Went on a long run today, so had a good few miles to see how the fault progresses. Cruising at around 2500 to 3000 rpm with light throttle put the AFR to 16:1 constantly (no closed loop operation), the car is under no load so Mitsu may have mapped the ecu this way to increase fuel economy?. It just seems like there`s a big hole in the fuel map that`s been mentioned many times before and the car is on the verge of missfire from the factory, give it 15 year old injectors/ fuel pump and fpr and it`s just been pushed over the top?.

[TurboBob]

what were your trims doing during this time?

[keithmac]

I didn`t have the logger with me, just the Wideband and display. If I get chance with the stock setup I`ll have a go at logging the fault. Slight TPS position change brought more fuel in (I know the TPS is fully functional), must bump the ecu to the next cell in the fuel map?.

[keithmac]

Just having a look on Jeffs site for some pointers on tuning my Emanage with regards closed loop operation and I came across this, the Spyder VR4 fuel map;



As you can see on the map, low load and low throttle inputs command an AFR target of 16:1+, what we`re seeing on the widebands. I`ve gapped my plugs under book value, maybe that along with the lean condition which is mapped in at the factory is causing my miss?.

If you could map it just right, to bump the fuel into the 15`s where the ecu is not in closed loop operation you could effectively map out the lean spot without the ecu trying to correct your alterations?.

Putting my 450 injectors in tomorrow with the hotwire mod, then I`m off for a datalogging session to see what`s up.

[DoctorDex]

Interesting theory.

If it is correct, you'd think that the missing problem would become more pronounced with increasing injector size (for those of us who don't have a greddy ultimate ems or AEM) or with increasing fuel pressure because the ECU would be seeing less load.

EDIT: Does anybody with a EMS ultimate system or AEM have this problem?

I'm anxious to see your results.

[keithmac]

Hopefully I`ll have something to report tomorrow or Monday, using that table you can pick out the trend to where the ECU goes into closed loop operation, which is where you don`t want to make any real alterations as that`ll knock the trims out.

I think I`m going to try doing a 360 to 440 or 430 change in the Emanage, this`ll give me a slightly rich condition and then I`ll see how the ecu trims it out and what happens elsewhere as a result.

For the OBD1 cars, maybe raising fuel pressure slightly will bump the AFR`s up across the board, leave the trims to cut fuel where necessary - but full load may end up being too rich..

[DoctorDex]

[quote=keithmac]I think I`m going to try doing a 360 to 440 or 430 change in the Emanage, this`ll give me a slightly rich condition and then I`ll see how the ecu trims it out and what happens elsewhere as a result.
QUOTE]

Are you using an emanage ultimate system with injector level control? If so, then you'd think the injector level control would prevent the misfiring problem (if it is caused by the ECU seeing too little load ), as the stock ECU should be at the correct point on the fuel map during cruise.

[TurboBob]

With the OBD-1 cars, you should be able to tune it to the rich side so that the trims are bottomed, and in that area of the map the O2 trim is running about 60 - 80 or so. That way, when it goes into open loop for the 16:1 area, it will be a little richer than it wanted when it sets the O2 trim at 100.

Bob

[keithmac]

Mine happened before the car ever saw the Emanage (blue), I`ve had a result but it`s taken an Emanage to sort it for me..

I`ve richened it up into the 15`s where the lean miss occurred and it`s completely cured it, cars a joy to drive!.

Then I fitted 450`s and kept eveything else the same (apart from emanage injector size change) car ran 11.5:1 AFR on boost, then I hotwired the fuel pump - no other differences at all and the same run yielded 10:1 afr`s, can`t believe the difference the hotwire made! (this didn`t affect low load areas though..).

So to sum my problems up, for some reason the car dislikes 16:1 or leaner AFR`s on part throttle (even though it`s part of the stock map), increasing fuel in the missfire region to produce approx 15.5 AFR completely cure the missfire, best the car has ever driven!. The fuel trims do not seem to affect the part of the map where the miss occurs, so closed loop/ instant fuel trim can compansate for added fuel in other parts of the map and you still have richened up the 16+1 area.

The only problem if you do not have a fuel controller would be WOT, you could alter base fuel pressure to richen it up, close loop will take care of the lower end but you`ll be too rich at WOT.

Hope some of this helps you out?.

[keithmac]

Bob beat me to it..