Help with AFR in tune

[[email protected]]

Would someone mind taking a look at these two logs? I'm having a problem with erratic AFR's. All was going well with tuning and this has started the past couple days. Afr's on the same day and even the same drive change up to full points. I can hop in and drive and my afr error histogram shows within 1-2 percent, then on the next drive ten minutes later the histogram shows off as high as 15 percent. I am unable to see what is causing it. My wideband is an aem 4110. I'm thinking that it may be going bad. When I start it, the wideband does the warmup then reads roughly 14.5 for a few seconds, then it starts going slowly down to around 11 then immediately back to 14 or 15. Truck is 2500HD 6.0 2WD 4l80e Elgin 1839 220/224 .575 112LSA Deka 80's. Any help would be greatly appreciated.

[ryan_axberg]

that is what the wideband does when it warms up. It goes down to the bottom then it starts reading actual afr.

[kingtal0n]

first guess is massive iat swings. Try disabling the iat sensor temporarily to see if the massive fuel swings go away. Theres no way to tune a gen3 afaik for iat compensation out of power enrichment.

I also notice the lack of gradual a/f slope. The enrichment should happen gradually, say 14.7-15.2 air fuels are fine until 50kpa. From 50kpa to around 80kpa usually more like 13.2's. Sloping down to 12.8-13.2 from 80-95kpa and finally 99kpa-105kpa usually 12.0 to 12.5's. For most stock engines with mild compression and smallish camshafts, sort of general idea.

[SultanHassanMasTuning]

check your fuel pressure

[[email protected]]

Fuel pressure is around 46-50 at idle. It is around 50-52 just cruising around. It goes up to 56-57 at higher kpa. If I unplug the regulator vacuum line, pressure goes to 60. Iat adder is disabled in the tune. My flow rate for my injectors is set straight across at 92. Since fuel pressure is changing, should I change that to reflect the fuel pressure or do you all think my pump is suspect?

[kingtal0n]

you can't change or disable the iat adder in many gen3 computers. If you are just going to ignore the simple diagnostic advice people give you why bother posting in the first place? Why don't you take a screen shot of the place that you are assuming is disabling the iat adder as a function of fuel and iat and let someone confirm that it does not work the way you are assuming it does.

[[email protected]]

If you are just going to ignore the simple diagnostic advice people give you why bother posting in the first place?

I appreciate everyone that has helped out. I have done everything everyone has suggested. Checked fuel pressure and looked at the tune. Iat adder under the fuel tab table is zeroed out so I was assuming it would not add fuel. I also removed and tested the wideband and it checked out fine.

[kingtal0n]

I appreciate everyone that has helped out. I have done everything everyone has suggested. Checked fuel pressure and looked at the tune. Iat adder under the fuel tab table is zeroed out so I was assuming it would not add fuel. I also removed and tested the wideband and it checked out fine.

And I am trying to tell you there may be no such thing. post a screen shot do you know how to do that? Press print screen, then open paint, the PASTE. Then CROP the picture so it just shows the desired info. Then show us what you see

Or post the tune file and i will open it and look ifyou have the right tab.

[kingtal0n]

In my car/swap if the temp changes by 10*F the a/f ratio changes around 0.3 or 0.4:1. So I can be sitting on 80*F and 14.8:1 air fuel, but then it heat soaks to 98*F and I see 15.8 or 16:1. In your log I see the similar trend but worse because your temps seem to sky rocket much higher. You can disable the temp sensor by simply flattening the IAT temp calibration cell.

[[email protected]]

Thank you. I have been super busy with work and finally think i have it figured our. I do believe it is the iat causing the swings. I did find an injector connector that was loose and was causing intermittent issues . That is fixed now and am still adjusting the ve table. Ever since the ambient temperate has warmed up, after the truck gets warm, it has a hard time starting and staying running. I have attached a log. Any thoughts?? Thanks in advance!

[kingtal0n]

Its running lean as hell. The cts 217*F and IAT 100*F is not helping.

It needs tuning. Increase fuel in the VE map for idle regions. I never use a maf so I would disable that.
Increase fuel for afterstart enrichment at high temps. there are several tables for this. One is CTS one is IAT, then there are blends, check if blending is on or off in the tune file. I would turn it off to make things simpler. Also you may want to keep the engine from touching 220*F coolant maybe get a 180Tstat to help hold 190~. I know after shut down it can creep but that is where the CTS afterstart enrichment comes into play.

[[email protected]]

Its running lean as hell. The cts 217*F and IAT 100*F is not helping.

It needs tuning. Increase fuel in the VE map for idle regions. I never use a maf so I would disable that.
Increase fuel for afterstart enrichment at high temps. there are several tables for this. One is CTS one is IAT, then there are blends, check if blending is on or off in the tune file. I would turn it off to make things simpler. Also you may want to keep the engine from touching 220*F coolant maybe get a 180Tstat to help hold 190~. I know after shut down it can creep but that is where the CTS afterstart enrichment comes into play.

Maf is unpugged and all dtc's are set accordingly. Do I need to zero out the maf table? The iats are high because of heatsoak. Once I drive they go down to around 75-85. Once it "catches" after a hotstart afrs are pretty close. I'll increase the fuel for afterstart temps and turn off the blending this evening and see what that does. Thank you for the help!

[kingtal0n]

If you start the engine heat-soaked, its no problem because there are tables that add fuel for startup heat soaked. You can compensate for that.

the problem is, once your engine has been running for a while, the enrichment is all gone. So if you heat soak again while driving there is no enrichment coming, it will just run lean.

there are a couple ways to deal with this:
1. relocated IAT sensor so it doesn't heat soak easily
2. slightly enrich the regions where the engine tends to heat soak (in the ve table) say around idle
3. install a variable resistor between the IAT sensor and ECU so you can manually adjust the temperature (remove the heat soak manually)

1 is the best solution
2 isn't necessary if you do #1 properly, let it run slightly lean 15.5's 16.0 idle cruise is fine

3 the reason I don't love this one is because sometimes you forget the knob is turned, maybe. I do. So I used a very low resistance (800ohms total) so I wouldn't forget it was turned (I have the extra timing and fuel on cold side of 80*F iat)

[[email protected]]

The iat is located behind the throttle body in the intake. I did this to prepare for the time when i eventually go FI. Where would you suggest I move it to? I did add fuel to the IAT multiplier under cranking fuel under higher temps but it did not seem to help. I have attached two more logs. One is normal driving. The other is after two minutes sitting after the first log. It took two or three tries starting before it ran. Thanks again for the help.

[5FDP]

Since you haven't posted a tune yet we can't see what you've done with it yet.

You say the MAF is unplugged but is the MAF fail high set to zero with the 3 dtc's set to MIL on first error? Not having that done could cause it to not want to fire up first try.

[[email protected]]

Here is the current tune. Thank you.

[[email protected]]

Anybody know what to do for the hot start issue?

[5FDP]

The VE looks way off. There should be zero reason for the high values in the low area's of the map. The fueling has to be completely off with how it's setup right now.

Where is your wideband installed? Do you have cats still??

And to me, if your fuel pressing is doing a 10psi dance depending on load, having the IFR at 92lb/hr wouldn't be accurate all the time.

[[email protected]]

Wideband is installed about a foot past the manifold on the driver's side. Cats are still installed. The areas that are high are when I let off the throttle and map bottoms out I believe but not sure. Should I scale the ifr or do you believe I have a fuel pressure issue?

[5FDP]

If the wideband is before the cat, it's fine. The 2500's were goofy with the cat locations in some of those years.

If you look at a stock VE, the table doesn't have that spike in numbers from 15-40kpa and 1500-2800rpm so yours shouldn't do that either.

Where did you get your injector data from? I looked through the change log and I only see the flow rate has been changed.

If you didn't change the min injector pulse, offset vs volts settings and the short pulse adder for the deka injectors that is going to part of your fueling problem.