Tuning power FC for driveability, having a little trouble around the idle area.

[240z4u]

Hey folks, I thought this would be a good topic since fuel prices have risen and I don't feel the need to burn a gallon of gas at idle! lol

I just swapped my TPS out to a SOHC KA unit mounted on a 57mm land rover throttle body. At the same time I lowered the idle back down to 750rpm from 1k. The car idles fine closed throttle, but I have a flat spot right off idle where the car starts to surge and can die if I let the clutch out.

I don't actually think this is due to the new TPS setup, I am able to get the idle switch to close and see 4vdc+ at WOT. I think its a tuning problem I uncovered when I dropped the idle. I notice though, that when I gently press the throttle that the tps voltage isn't moving at all until the throttle has moved far enough. I am wondering if I managed to damage the TPS by trying to turn it too far (stupid me wasn't paying attention).

Throttle input is about what you would use trying to creep through a parking lot in 1st or 2nd. I get the surging in all the gears at very low RPMs. Is this a tuning problem ya think? Or something related to my TPS? Like I said, I can get voltages set within range. The monster TB isn't helping driveability at all I am sure.

Also, how do you guys go about tuning very light throttle with your Power FC? Just go for a long cruise and datalog?

Thanks! - Evan

[Broadfield]

Your throttle body size won't really matter. I run a 70mm on mine with a Power FC D-Jetro and mine is OEM smooth throughout the power band no matter the temp outside. It's all in the tuning!!!!! I actually had mine tuned by Charles at Adrenalin in St. Louis and all I can say is I have never been more impressed with a tuner. He literally spent 3 hours alone on just getting idle, partial throttle and off-throttle recovery dead on.

[240z4u]

Well, throttle body DOES matter if its not tuned for it I guess was my point. Glad to hear there is a good tuner in St. Louis. Dare I ask how much you spent total on the tune? Feel free to email me if you don't want to put it out there.

Thanks for your experience!

Evan

[Darius]

Dumb question, but did you go through the idle learn process for 20+ minutes?

What AFRs are you tuning for in those cells?

[240z4u]

Dumb question, but did you go through the idle learn process for 20+ minutes?

What AFRs are you tuning for in those cells?

Darius, I did do the idle learn procedure but have not done it since I changed the throttle body and intake manifold. I didn't think it would help since the problem seems to be right off idle. I can do a relearn tonight.

I generally shoot for mid 14s at idle. I have had a pretty good idle at 14.5 in the past.

Evan

[Darius]

Since you changed the TB and TPS I would definitely redo the idle learn. Some TBs might let more or less air past at full-closed. Also, it would be difficult to get the TPS set exactly the same as the last idle learn you did.

Redoing the idle learn will allow the PFC to figure out the idle control valve settings it needs.

14.5 is a good idle number. I'm going to try to get it to idle at 15 if the EGTs stay down and it doesn't stall.

[240z4u]

Since you changed the TB and TPS I would definitely redo the idle learn. Some TBs might let more or less air past at full-closed. Also, it would be difficult to get the TPS set exactly the same as the last idle learn you did.

Redoing the idle learn will allow the PFC to figure out the idle control valve settings it needs.

14.5 is a good idle number. I'm going to try to get it to idle at 15 if the EGTs stay down and it doesn't stall.

Okay good tip, thanks alot. Ill go ahead and redo the learn .

I did have idle in the low 15s at one point, but on occasion the exhaust would get kind of poppy sounding. My car was three colors at the time, so that really finished off the image nicely! lol.

Evan

Darius, does the Power FC come with O2 feedback enabled? I can't read the language they used for on/off.

[Darius]

Yes and you'll want to have it ON until you have a good tune and confidence in your maps.

If you turn it OFF and you haven't tuned it at all, the engine will run like crap.

The O2 feedback also must be turned OFF while you are datalogging.

[240z4u]

Yes and you'll want to have it ON until you have a good tune and confidence in your maps.

If you turn it OFF and you haven't tuned it at all, the engine will run like crap.

The O2 feedback also must be turned OFF while you are datalogging.

I wanted feedback left on, I was under the thought that it only worked around the idle/low load area?

I had no idea I had to turn it off to datalog! EEK

[Darius]

I'm a little foggy on that as well. It wouldn't make sense for the ECU to try to stay at a stoichiometric AFR above 2000-2500 rpms so it must switch to the base map above a certain rpm/load point.

Yes O2 feedback must be turned off when you log though or it will jack up your readings. Also, when you log make sure you aren't engine braking ever. If you do, the engine goes lean (22-25 AFR) and any cell the tracer passes thru will get some false lean readings mixed in a raise the AFR averages. Cells with low number counts will be affected more, obviously.

[240z4u]

Alright that makes much more sense then. I think your correct, as it does sound similar. I usually map and have someone hit the stop button before I decellerate.

Thanks - Evan

[gawdzilla]

you don't have to turn it off to datalog... but turning it off gives you the most true readings without the ecu trying to do small lean/rich corrections due to o2 feedback.

how are your A/Fs looking when it's feeling boggy? is it tipping in lean or going too rich? when you blip the throttle gently how do the A/Fs behave?

basically you want the small blips and very light driving to stay pretty close to 14:1, maybe 13s if you want. if the A/Fs look good i'd start playing with the timing. bump the timing 5 degrees + and - to see if the motor feels less boggy. you can't really hurt anything playing with the timing drastically with very low load like your parking lot cruising...

my car had horrible low throttle cruising just as you described. blipping would be super unresponsive and the car wouldn't drive normal at all coming off of stoplights and such. had a friend drive the car and made sure AFs were ok first. then i started moving the timing around a lot while he was doing starts/stops coming off idle, etc. in a parking lot while i sat in the pass seat. in general my timing was way too retarded so i advanced it (+10 deg in some spots) to cure the low throttle transitional driving.

just spend some time playing with it and experimenting knowing you can't really hurt anything. ask your friend to keep repeating the flat spots and see if he can feel them getting worse or better as you do some adjusting.

oh and i wouldn't really bother logging. just get someone to drive as you look at the cells you're in while the problem is occurring. adjust in real time and get feedback from your buddy driving.

[240z4u]

Sounds good, I will do that. I have not had my laptop in the car so I have no idea if its trying to go rich or lean on tip-in. It does lurch pretty bad once it picks back up though.

Evan

[240z4u]

Alright, I done did the idle relearn. I also dumped stock maps back in with injector and maf corrections. It idles just as smoothly as I could ever hope for. I had the stereo on and thought the motor died because it was real smooth.

Tip in problem disappeared... UNTIL I headed out to tune the top end. I had my Fiance' run the laptop and shut off closed loop (simplified tuning x100!) I have fuel dialed in after 10 pulls or so.

I get back into town, and its got that tip in crap again. I am pretty sure the problem is actually with my TPS. I think I tweaked it when I installed it and the lower end of the TPS signal is not linear. Watching the signal confirms that as well. Ill have to take it apart and see if I damaged it. I really need to find a better mounting method. It fits the rover throttle body perfectly, but sits clocked about 90 degrees to the stock holes.

Anyway, thats the update for now.

Thanks guys, the closed loop tip is a phenomenal one!

Evan

[USMCgetsome]

fab up small slotted brackets. If its at 90' your throttle position sensor should respond to it as half open. I had the same issue when I tried a vg30dett tps. Idle was great. Depress pedal. Choked motor. LOL. Failure!

[240z4u]

fab up small slotted brackets. If its at 90' your throttle position sensor should respond to it as half open. I had the same issue when I tried a vg30dett tps. Idle was great. Depress pedal. Choked motor. LOL. Failure!

It is on a bracket, just not quite as stout as I would like it to be.

Interesting bit of info your sharing here! Were you ever able to get satisfactory tip-in performance? Seems like the resistance is actually too high in this TPS, which is why I assumed I had broken it. I think the VG tps is pretty much exactly the same as the one I have.

Evan

[Taterbug]

I second the good tuning Adrenaline does out of St Louis. Charles tuned my Rb25det and now no drivavbility problems at all. Highly recomend and will use them for future upgrades