HydroStream6

iTrader: (16)

Well I've been trying to get the drive-ability tuned on this thing for a little while now, but I'm having a really odd problem. The car is open loop speed density, no LTFT, with STFTs open loop enabled. I've made countless logs lately without changing a thing in the tune, and I'm getting wildly varying STFTs.

For example, I went for a drive last night after the car had been heatsoaked, and all of my STFTs were in the 30-50% range for the entire 10 minute drive. They came down very slightly as I went on but these values are still huge!

Then this morning on a cold start, my STFTs were all in the -4 to +6% range, which I would consider much more acceptable, but still, something weird is going on here.

And these aren't the only two logs to show this, I have a bunch of logs with wildly varying fueling.

It seems heat related to me, but I can't see any correlation between fuel and IAT or ECT. I'm to the point now where I think it's something more mechanical, like hot injectors, or hot fuel itself.

I ohmed out the injectors in the past when hot and their resistance did go up while hot, but they were all within 1 ohm of each other. I wanna say they were up in the 16 ohm range when hot.

Or perhaps with my return fuel system now, I'm heating up the fuel itself where it's changing something dramatically? Or perhaps I could be aerating the fuel with the return and this could what's causing this?

I'm running out of ideas and time. I go back to school full time in two weeks. Any thoughts? It's a weird one for sure.

Thanks,
Adam

Ericmck2000

Sounds like a issue my truck was having on a hot day...

I run a procharged silverado, one day, the weather was oh.... 110-115 outside, the truck was running generally shitty... I got on the interstate, floored it, and at the peak of 2nd, it just started cutting out and driving like my old carbed 350 in the middle of the winter, I hooked up my datalogger and my stfts were all 50-60% and IATs were around 150-160, Anyways, i let it cool down and it ran fine, when its nice and chilly out, it runs like a champion, when its a hot day, and my intercooler gets heatsoaked and my IATs go up above 130, it doesnt like to run.....

Ericmck2000

If you figure out how to fix it, lemme know. I think it has to do with the tuning..

pber13

I'm not 100% sure how a custom tune differs from a factory PCM in this respect, but a stock vehicle's STFT will usually change very rapidly, and the LTFT stabilizes it. 30-50% is waaay high though. maybe you should try looking at the fuel tables for the speed density?

HydroStream6

iTrader: (16)

The weird thing is there doesn't seem to be any correlation between the stfts and the ect or iat. This is why its hard for me to believe its tuning issue and leaning towards mechanical.

NoGo

iTrader: (2)

I would guess tune.

Take a look in your open loop EQ table and make sure your aren't trying to command the car too far off of where your narrow band O2 sensors are accurage (ie 14.7)

Also, do the STFT slowly drift up or is it a step change?

HydroStream6

iTrader: (16)

EQ table is all 1s.

When I logged on the way home from work (after the car sat 8 hrs), STFTs were say between 5 and 10. On the way TO work that morning (car sat all evening and overnight) , they were much less, say 0-5. After I got home from work, the car sat for about an hour, then I went out and did some more logging. This is what I'm referring to as the car being "heatsoaked". As soon as I started her up, STFTs were in the 50s. They eventually came down a bit but still very high, 20-30%.

I have logs I can post of everything if that helps.

HydroStream6

iTrader: (16)

Could one bad O2 cause something like this? One is brand new but the other is 4 years old. They both function though.

Also, the passenger side O2 is mounted such that it sees exhaust from both sides of the engine. There's no way I can avoid this because of the turbo kit's design. The drivers side feeds into the rear of the passenger side log manifold which goes into the turbo.

The drivers side O2 is mounted traditionally.

AVB

iTrader: (9)

Probably something you've already checked but...

Fuel pressure good when hot?

Johnv

I would say thats most of your problem right there.

Dont think you will have much luck running closed loop with a single turbo setup if you can't sample both banks independently with narrow band o2s.

Just tune it in SD open loop and be done.

HydroStream6

iTrader: (16)

It did the same exact thing when I had it running straight OL with no fuel trims as well. Except instead of the STFTs going up like crazy, the AFR just went up like crazy until I shut the engine off.

Here's two logs from my drive home. From work to the bank while the engine was cold. Then from the bank to home. I was in the bank five minutes. I've attached the current tune as well. Check out the fueling. Pretty close for the first log, then WAYY lean on the second. I'm stumped.

I'm tempted to go back to the maf and see if the problem goes away. Will the 3 bar map instead of the stock 1 bar map give me any problems if I flash back to a maf tune?

HydroStream6

iTrader: (16)

I noticed my map sensor gets pretty hot as well. Anyone ever heard of that causing a problem?