Help me understand what happens in PE

[BlackGS]

I'm starting to wonder if I have another issue here. I ran a new scan today. There were no changes to the tune, but I ran a 12.5 AFR in WOT which brought 3* of KR. Trims were positive again. The IPW's seemed about the same range as previous runs that produced 11.5 AFR. Any thoughts on this new scan?

[krunchss]

Noob here trying to learn....Throwing an idea into the mix...Sometimes a left field analysis will trigger an answer from a more experienced member :P

Eddie posted above...

"The O2 sensor is pretty much ignored in PE. The PCM uses ECT, IAT, TPS, MAP, RPM, and MAF to calculate fuel in PE."

The one that stands out most here to me is IAT. IAT has potentially to change drastically and if you're comparing a WOT run from after a few mins of driving to one where the car stood still for a while, maybe is this the culprit? A Heatsoaked IAT? Dunno...

When I was trying to tune VE / MAF at idle, I let teh car idle for extended periods of time while it learned the trims before recording a scan. Each iteration got me closer to 0 from the negative side until I was down to about 0 to -3...Then just watching the scanner while idling BANG, LTFT jumped to -10 and stayed there. I suspect heatsoaked IAT caused this and invoked some other fuel trim table as a protection against a high IAT reading...Again, dunno. But I did see it.

Krunch

[Perforator]

The only thing at WOT that the IAT could possibly affect is timing.

[Perforator]

Maybe your wideband is on the fritz? I don't know that's really strange.

[krunchss]

The only thing at WOT that the IAT could possibly affect is timing.

OK, fair enough, but what would happen in a situation like I just mentioned? Heat soaked IAT cause a large - jump in the fuel trims, throwing off the previousley "Tuned" LTFTs....Now what happens from this point when you go WOT? Will he still lock in a LTFT of 0 when he enters WOT? NOW what will happen for the rest of the scan?

I'm not claiming I know what's going on...just thinking out loud here.

Krunch

[BlackGS]

Maybe your wideband is on the fritz? I don't know that's really strange.

I am pretty sure the wideband is correct. The reason I think this is because the KR is there. When I ran 11.5 AFR, there was no KR, but at 12.5 there is 3 degrees. I have noticed in the past that as soon as I get to 12+ AFR, I start to get KR constantly.

I added 5% to the MAF table from 8000hz up and did a quick run. The AFR went back down to 11.5 and no KR, but IPW's still look about the same!

Krunch may have something with the IAT, but I'll have to look at those values across the many scans. The quick run I did today had IAT's in the 50+ range because I had the car sitting for a couple minutes before taking off. The scan I posted this morning had IAT's in the 30's. That's just two scans though. I have about 50 I'll have to look through.

[JFDugal]

I added 5% to the MAF table from 8000hz up and did a quick run. The AFR went back down to 11.5 and no KR

Looks like that's the right direction to take. Keep an eye on the AFR's over the next couple PE runs and see if the change is consistant.

Also, do you have a fuel pressure gauge? Monitoring your fuel pressure while in PE may provide some useful info.

[krunchss]

Good luck with it...Again, my main purpose was to get people looking at it from maybe a different angle maybe. Sometimes we find answers in the strangest places...If you're running out of options...what's the harm in looking at something else? Nothing to loose.

Krunch

[Perforator]

OK, fair enough, but what would happen in a situation like I just mentioned? Heat soaked IAT cause a large - jump in the fuel trims, throwing off the previousley "Tuned" LTFTs....

Why would a heat soaked IAT affect the LTFT's?

[Perforator]

I added 5% to the MAF table from 8000hz up and did a quick run. The AFR went back down to 11.5 and no KR, but IPW's still look about the same!

I had a problem about a year ago where the engine would just shut off under heavy acceleration. Couldn't for the life of me figure it out. I ended up starting from scratch again. I took my stock bin, copied my tranny settings, ifr and maf table over, pe stuff. Flashed that and the problem went away. That's why I mentioned starting from scratch. I know with the powrtuner, I could never change my ifr table more than once without screwing something up. Whenever I needed to change it, I changed the stock file and copied my settings over. Maybe something in your current tune got FUBAR'd.

[krunchss]

I dunno...you tell me...I seen it happen on my car IRL.

Sitting on a parking lot...scanning, but not logging, watching the STFT and LTFT waitng for them to learn a little before I logged for data....scanner looked like this as IAT increased to over 50 or 60 degrees C...

-3
-2
-3
-3
-2
-2
-3
-10
-10
-10
-10
-10
-10 Etc....

After several iterations of my tuning for trims, LTFTs were coming down...I thought I had them finally in a sweet spot and watched them explode right in front on my eyes...I have no explanation, just noticed that the IAT was heat soaked at the time.

Krunch

[Perforator]

Could have been a lot of things. Evap, cat protection, egr, bad spark, bad injector, o2 sensor, exhaust leak, who knows. You can't just cherry pick iat's and say that's why it happene.d

[starks]

was it alot colder when it went lean? my scans changed considerably from 0* to 30* F. just a thought...obviously cold air is more dense, so you've got more air comming in vs the other day.

[BlackGS]

Here are some numbers I gathered up for you all to chew on. These were all WOT runs using the same MAF values. Some of the runs were using a 2.8" pulley, and the others used a 3.1" pulley. The commanded AFR for all the runs was 10.8-10.9.

Pulley IAT AFR KR IPW Timing kpa
3.1 21* 11.8 2.5 14.7 15-17* 182
3.1 25* 11.5 2.5 14.5 17-18* 175
3.1 27* 11.5 0 14.5 17-18* 174
3.1 30* 11.3 2.8 14.5 17-18* 177
3.1 32* 11.4 1.4 14.5 17-18* 184
3.1 43* 11.6 0 12.8 17-18* 161
3.1 45* 11.3 1.4 14 17-18* 175
2.8 52* 11.5 1.8 14.5 16-17* 189
2.8 52* 11.6 0 12.3 17-18* 160
3.1 54* 11.1 0.5 13.8 17-18* 178
2.8 54* 11.1 0 13.3 17-18* 167
3.1 55* 11.4 0 13.3 17-18* 172
2.8 57* 11.8 2.6 14.5 16-18* 189
2.8 59* 11.5 1.4 14.5 17-18* 186
2.8 61* 11 1 14.5 17-18* 185
2.8 62* 10.8 0 14.5 17-18* 184
3.1 68* 11 0.8 13.5 17-18* 170
3.1 68* 11.2 0 13 17-18* 167
3.1 70* 11.1 0.5 12.5 17-18* 164
2.8 70* 11.2 0.5 14.1 17-18* 185
2.8 72* 11.6 0 14.2 20* 180 (ECT 110*)

Here is also a quick visual on the data. I'm not really seeing any trends from temps other than KR is little more likely at colder temps.

[Eddie-98GTP]

Just to throw this out...

I believe there is an IAT fuel modifier. There would almost have to be. Warmer air will require different amounts of fuel than cooler air. If you really want to be sure, get a resistor and jump the IAT sensor, that way there will be no change at all. A 2200 ohm resistor will show about 90*.

[Perforator]

Just to throw this out...

I believe there is an IAT fuel modifier. There would almost have to be. Warmer air will require different amounts of fuel than cooler air. If you really want to be sure, get a resistor and jump the IAT sensor, that way there will be no change at all. A 2200 ohm resistor will show about 90*.

It's probably not a fuel modifier but a calculation. I'm sure they firgure intake air temperature into the injector pulse width calculations. You know BlackGS, you have different pulley sizes, different commanded a/f ratios, you have to simplify things. Command one fuel ratio, use one pulley size. Get that working right and then move on from there. I changed my a/f ratio from 11.4 to 11.2 in PE and I only got to 60 something tp% but the a/f ratio definelty changed lower like I wanted. Not saying that's the answer because every car is different and every calibration is different but you have too many variables.

[BlackGS]

You know BlackGS, you have different pulley sizes, different commanded a/f ratios, you have to simplify things...

The commanded was the same for all those runs listed. The pulley was changed because of colder temps, which keeps the maximum kpa more consistent. If I run a 2.8 pulley in colder temps, I will get 195kpa, which is too much. Therefore, I think the pulley change keeps things more consistent over all.

[Perforator]

I know what you mean about the pulley and I guess it is a good idea to look at the IAT's. I still think you should zero the rpm time table so you run a flat a/f ratio. It makes it easier to adjust the MAF table that way but to each his own.

[bilemke]

I know what you mean about the pulley and I guess it is a good idea to look at the IAT's. I still think you should zero the rpm time table so you run a flat a/f ratio. It makes it easier to adjust the MAF table that way but to each his own.

The zeroing of the rpm/time table is a good point. But, the logic of comparing it to the MAF isnt, in my opinion. You will not see the same MAF at the same RPM all the time. Thus, by zeroing the RPM/Time table, you loose the the ability to change the fueling for a given MAF value at different engine speeds. While I imagine it should change much for for RPM, I can see changing the fueling slight still.

[Perforator]

The zeroing of the rpm/time table is a good point. But, the logic of comparing it to the MAF isnt, in my opinion.

The point of zeroing the rpm time table is to run a consistent a/f ratio. It's much harder to hit a moving target. All I'm saying is use one a/f ratio. Get your MAF table tuned in PE to match it. Then when you change it with base pe, it should change in your scans also. I don't know, I don't have the problem BlackGS is having. When I lower my commanded my actual lowers too, it was just a suggestion. When there are too many variables it's usually best to try and remove as many as possible to trouble shoot.