I've had my WOT tune dialed in around 12.8 since the Summer and its been running good. I took the car out today and jumped on it and it was real lean at WOT around 13.4 and pinging. I got out of it but was wondering what would cause the sudden change?? Going on vacation tomorrow so I wont touch it till I get home..If I blow it up before vacation I'll be miserable.

 

Did it engage pe mode?

 

I wasn't datalogging at the time but wouldn't always go into pe? I got an alignment this morning and i have to see if the guy knocked off a vacuum line when i get home

 

Make sure nothing was damaged in the alignment. Sensor could go bad and drop out of pe mode. Any codes? Drive ok when not wot?

Also how much did weather change from last known good run? Cold this time of year it may need more compensation for cold air

 

It was 35 degrees when I did the wide open throttle run this morning and it was pinging at 13.4.The tune was set up in August when I was getting 12.8 .What senser could go bad the o2 sensor? driving at cruise felt fine.

 

Check tps voltage. Verify no maf codes. If it drives normally then should be ok.
Tps reading could cause it to drop out of pe mode but sounds like the issue you have is weather change and no iat compensation.

Cold air could lean it out that much. May just need a better more accurate iat sensor located in air intake and better compensation tables. Else just add another 5-10% to the pe vs rpm table for this cold air. When summer hits lean it back out again to current level.

Big changes in air quality can move an open loop wot tune, when maf is maxed out and no real iat sensor is used

 

I'll ck tps voltage and codes but i think your correct cold air change leaning me out. Stupid question but what is this iat sensor you're talking about? I'm running a closed loop tune.

 

On those maf systems its mat. Manifold air temp. Basically like a water temp sensor but screwed into intake runner or plenum. Its terribly slow reacting and heat soaked most of the time so very inaccurate. Switching to a plastic cage style intake air sensor is much better for cold air compensation. Requires lengthening wires and new bung on intake side piping or try putting in plenum but i like it outside the manifold area. Then retune the tables in 6e.

 

IIRC, on the MAF systems the MAT temperature is only used to enable the EGR. First thing I'd do is to check the fuel pressure under load.

RBob.

 

Good point, i dont recall how mat is used in maf code, but for egr that sounds correct. Need to revisit the code hac to be sure.

Fuel pressure is another concern to have a air fuel mix drop like that. Forgot to mention that, completely skipped my mind.

 

ok guys I don't have any codes and tps is set to .55v at idle and 4.51v at WOT. Fuel pressure is set to 53psi at idle and it was hard to watch taped to windshield at WOT but it looked to go to around 60psi. The temp outside has gone up to 46* and now the AFR at WOT was just between 12.7-12.9 with no pinging..plugs look good...any ideas?

EDIT.... battery just died after that ride, checked battery voltage with TP as well as car gauge.... 10.80v at 750-800rpm idle and 11.10v with car in park and rpms held at 2000 rpms. If my alternator is charger low could it effect the tune? I seem to remember I set up the FP at idle around 56-58 psi now its 53 psi at idle.

 

If battery was low during the pull it very well could have been injector offsets vs battery voltage skewing the tune.

If fuel pressure was stable, then voltage or air quality had most effect imo.

 

Thanks Orr- I haven't really driven the car much since the Summer. I did notice this morning before I took it for the alignment the power windows were really slow. I have had it out in some what cold weather and it was never this lean at wot. The FP gauge never went below 53 psi and even went up a few psi on the wot pull. That time the afr was much better with no pinging but right after I saw the low charge and need to charge it to get it to restart. I guess my best bet is to get a new alternater and see how the tune is with a full charge??

 

Good battery and alternator should help things. See where its at with those changes.

 

I just took my car to the track a couple of weeks ago. I like to manually run my fans in the pits, between passes. I noticed on my last two runs, my car had gotten leaner at WOT…couldn’t figure it out. After looking at my data logs…...my voltage steadily dropped, due to me running the fans for so long.

My first pass showed I was getting 13v to the pump. By the time I made my last pass, I was getting 11.5v and the car was a full point leaner, especially at the beginning of my pass.

So yes, voltage will affect your AFR. If your fuel pump is not getting enough volts, it won’t hold the pressure in the line. Therefore your injectors are spraying a smaller amount of fuel and the car will go lean.

Hope this helps….