HAILERS

If someone has a wideband on their car, and has a few minutes to spare, will you do something for me. There is a phenomena that is puzzeling me. If I'm driving at a steady speed, say 60mph, I'll see something like a afr of 14.3 to 14.6. Now while driving at this steady pace, if I come to a slight downhill section in the road, and barely let off the throttle in order to maintain my 60mph, the afr will change to 13.2 to 13.6. Hey! That ain't right. Its getting richer when I let off the throttle. Shoulda got leaner, like a afr of 15 or 16 something. Happens each and everytime I'm at a steady speed (15mph and up, you pick the speed)and just barely let off the throttle. I mean just millimeters.
I've duplicated this on both my n/a and turbo cars. So, if you have a real wideband 02, could you sometime when going to work, the store whatever, drive at a steady speed, then just barely let off the throttle while observing your afr,and let me know what happens.
By the way, I disconnected my tps on the n/a car and drove to work today. I let off the throttle as described above, and noticed the afr went from the mid 14's to I THINK, the 17's or 16's. What I would have expected from the beginning with the tps connected.
If its not clear what I want from the above, just say so and I'll try again. REally need someone with a wideband to do this, not a narrowband, please.

j9fd3s

iTrader: (3)

i notice my 3 rotor with haltech does the same thing, on a slight down hill, not enough to coast and not enough to keep a steady throttle it runs richer. i also notice that it cant be a big hill where the map sensor value will change. ie you're cruising along at a steady speed and
vacuum (say -12psi) and you get to the hill the vacuum stays the same (-12) but your foot comes off the gas a little bit. the haltech like the stock ecu seem to only use the tps for idle and the accelerator pump (the stock ecu runs the acv too) i can unplug the tps and it makes no difference. so my theory is that the load inputs to the ecu dont change even though the conditions do

mike

HAILERS

j9fd3s
Thanks for the reply and its good to see it has happen to someone else. Slight difference here. I drove home in the last hour with the tps disconnected, and it does not do it. In fact it'll hold the afr figure of say 14.5 afr as I barely let off the throttle, for quite a while, before turning to a afr of 14-16 afr. Under the same conditions, but with the tps connected, it would have gone to a richer figure of say 13.4, and if I REALLY let off the throttle, would show 25.5 afr, due to tps causing fuel cut on the injectors.
Still good to see someone else seeing similar. I might try disconnecting the vac from the pressure sensor tomorrow to see what happens.
One reason for this obsession, is the new Texas emissions and the use of a treadmill at 15 and 25mph. What if the tester is doing the 15mph test, and to maintain the 15mph and not overshoot, feathers the pedal????? Heck. Its going to go from the afr of 14 to the richer 13's! High HC'S maybe.

Scott 89t2

I think I notice the same thing on mine. (stock 02...) it goes a bit richer when you let off a bit

hugues

That is really strange that fuel enrichement situation.

HAILERS,
have you also monitored the output from the air flow meter. If I am not mistaken, the ECU needs to compute the air used by engine in terms of weight then look at engine speed and throttle position to determine how much fuel needs to be supplied. So if the AFM output is not constant, then we are missing a variable here.

I would think the outside air pressure and temperature stay the same during the experiment, so only the AFM output needs to be monitored.

I think it also necessary to keep track of the RPM as you let off the throttle. Do you keep the rpm constant as you feather off the throttle.

Just wondering,
Hugues -

Samps

I'm curious if the afr balances out after a few seconds? Maybe the ECU and fuel system cannot react quite as fast as your foot. When you let off the gas quickly the air supply is instantly restricted but the fuel supply remains the same (richer condition) until the TPS, AFM, and ECU can determine the right amount of fuel. Which might cause a few seconds of delay. I'm just guessing; sounded logical to me.

hugues

Without knowing the values of the AFM output voltage during the experiment, I would agree with what SAMPS is saying. The engine has less air coming in although the fuel supply kinda stays the same because of some lag (until it is eventually reduced), so the AF ratio is richer that what you would expect.

Now, why don't you get the same behavior when the TPS is disconnected. I would tend to think the ECU is looking at a different fuel map and/or is bypassing some sensor input, giving a more logical behavior but a behavior probably not expected by the pple that designed the ECU maps with a connected TPS in mind (note that the designers may have overlooked some situations like this one where less fuel would have been better, maybe for simplicity ... still, a car with TPS on will probably run better than a car without TPS in most situations even at part throttle).

Hugues -

Scott 89t2

hmm.. the reason mine does it is because it goes from closed loop to open loop when I let off alittle bit. so it's goes from the back and forth loop of 14.7 to rich. I think it stays there.

Wankel7

How did you find those numbers? Was that with a wideband and your looking for confirmation?

I should have mine in my car with in 1-2 weeks

James

j9fd3s

iTrader: (3)

hailers, if the smog guy is smart he will very slowly roll on the throttle and off, you dont want the acceleration enrighment, or the decel fuel cut-->bac valve, both of those will throw the readings way off.

mike

HAILERS

Thanks for the replies. I've been real busy car this morning changing primary injectors(not related to any problem) Car acts the same after the replacement. On the way to work today I'll monitor the afr some more. I've put the tps back on.

For clarification, when I'm easing off on the pedal, its like next to nothing when I ease up. Compare it to steping on an egg and trying not to break it, except in the reverse. Make sense.

More clarification: I know that when you let off the pedal, that the tps will cause the injectors to cut off. I'm nowhere near that, as far as letting off the pedal .

I've thought about the afm a bit. Its like I'm letting off the throttle plates a miniscule amount, and maybe the flapper does not move at all, therefore creating a richer reading???????? Your right. I need to monitor the afm position when doing this.

P.S I'm convinced now that all series four have this trait. One thing I noticed this morning though. I went up a grade or hill and maintained 15mph. The afr tracked 14.5 all the way and I could ease off the pedal just a tash and still had the 14 plus afr.

CAn't emphasize enough, the easing of the throttle I speak of is almost imperceptable. Its not a lifting off the throttle and the tps cutting fuel etc.

And I'm using the wideband from Tech Edge.

HAILERS

I'll never get ready for work if I don't get off this computer.

I just realized something. On my turboii car when I noticed this *problem*, I noticed the following. I have two leds inside the car. They go to the green check connector for tps adjustment etc. Whenever you are accelerating, you will see the led that goes to the switching solenoid(see wiring diagram) will come on, indicating the switching solenoid is *on*. Well whenever I ease off the throttle, and notice that the afr has gone rich, at the same instant, the led for the switching solenoid goes out. The reverse is if I apply a touch of pressure on the throttle, the led comes on and the afr goes to the 14's afr again.

I don't think the switching solenoid and switching valve in the acv have a thing to do with the *trait*, since on my turboii I have removed the acv. Therefore no mixing of fresh air or taking away fresh air from the 02 sensor in any way.

The ECU is doing something when it sees/does not see a ground to that LED for the switching solenoid. Darn, gotta go work. I'll think about the above answers. Thanks.

Scott 89t2

I'll watch my AFC AFM readings on the way home and I can watch throttle % to let you now how much I'm letting off. I'm talking about a little too. like a few % off.

BlackRx7

sounds correct, would explain for the massive backfires our cars get on deceleration

hugues

Yes,
I believe the AFM is not reacting to your feathering the throttle pedal. So, the engine has less air but the AFM output barely changes. Maybe, you AFM is not sitting perfectly horizontal and that affects the movement of the flapper. Dunno.

I don't think it makes sense to look at what happens when the TPS is disconnected since who knows what the ECU decision making is in that case. Anybody's guess, I suppose.

BTW, HAILERS,
do you know if the ECU for S4 actually has different fuel maps for different throttle positions (beside closed and WOT). Does the ECU actually look at the TPS for the actual position of the plates or does it only care about the fact that it's closed, wide open, or part (that is, neither closed nor wide open). I tend to believe that the ECU has only 3 fuel maps (closed, wide open, and part). If you have any info that says otherwise, please share.

Thanks,
Hugues -

j9fd3s

iTrader: (3)

www.16paws.com
the tps controls the idle and lowspeed operation (up to like 2k rpms), it also runs the acv, and maybe an accelerator pump function too.
the afm and the map sensor measure the same thing.
if you look in the right book you can see that the ecu maps are divided into "zones", like idle, low speed, high speed low load etc. we also know that the ecu looks at at least 3 different maps (in different places on the board) before it does anything

mike

HAILERS

I've decided that I'll never really be able to figure this out, and that it is common to all series four RX's anyway. If I disconnect the tps, it does not act the same, the afr remains in the 14's whether I barely let off on the throttle or not. Its really not a clue, since the ECU is probably defaulting to some other fuel map inside when the tps is disconnected.

I went to the series five fsm, page F1-77, and it indicates under fuel injection amount: *medium load*.....*warm engine*......{RICH AND LEAN}. Kinda implies that the mixture under medium load can vary from rich to lean. Whats screwy about that is when I've barely lifted off, and the afr has gone from 14's to 13's, and then I reapply that little bit I lifted off, the afr goes to the 14's. Sorta *** backwards.

To think all these years, on a long road trip I'd feather the throttle when going down a steep hill, thinking that I was using less gas! Not so. Using a touch more. Screwy.

And to a question I saw earlier about whether the mixture returned to the 14S after a period of time of the throttle being eased off.....no, never returned. And a note here. When easing off the throttle, I was trying to maintain the same rpms. Not letting the car fall below whatever the given speed was that I lifted off at.
I'm satisfied there's nothing peculiar about my cars. Just made that way. I need to put a lock on my hood and throw the key away, and just drive the darn thing. Go back to sailing.

Scott 89t2

haha ... the same thing happens when I press the gas... off the gas it's full lean. give it a little bit and it goes full rich. give it a bit more and it drops to 14's.

HAILERS

I just worry too much about emissions. Did the wifes 86 this morning and the figures speak for themselves. I like the word PASS.