Suddenly goes very lean on startup, no changes made to tune!

[cpelton]

I installed a turbo about 2 weeks ago on my 03 4.8L truck and got the tune pretty close. Suddenly (past 2 days) the truck goes very lean about 30 seconds to a minute after startup (every startup after it has sat for a bit) at first I thought my wideband was just off because it takes a bit to warm up and be accurate but I noticed as it read lean i could feel the truck bog down idling out of my driveway. After a couple good rev's everything goes back to normal. WTF? Havent touched the tune for over a week why now?

[cpelton]

could it be a dirty MAF?

[WS6FirebirdTA00]

post you tune, a log and if you are running MAF (which I assume you are with post 2).

[cpelton]

ill take a log this morning thanks.

[12secSS]

Also, where is your wideband mounted (pre or post turbo) and do you have cats? Do you still have emissions equipment?

[dhpro]

I installed a turbo about 2 weeks ago on my 03 4.8L truck and got the tune pretty close. Suddenly (past 2 days) the truck goes very lean about 30 seconds to a minute after startup (every startup after it has sat for a bit) at first I thought my wideband was just off because it takes a bit to warm up and be accurate but I noticed as it read lean i could feel the truck bog down idling out of my driveway. After a couple good rev's everything goes back to normal. WTF? Havent touched the tune for over a week why now?

I had/have the same prob...cold start idle...I'm a newby, but my tuner showed me a table where u can add or subtract fuel at strart-up...otherwise u can leave it and the PCM will learn it over time. Its been 2wks and mine's almost normal. R/

[cpelton]

My Wideband is behind the turbo, rear mount. I still have cats. I'm running in closed loop with the MAF, running 6psi. Here is a log of a startup this afternoon you can definately see it goes very lean after a few seconds. I have also attached my current tune. What I dont understand is why would it only start doing this in the past couple days? I havent touched the tune in over a week and it has started fine every time.

[cpelton]

I added injectors 2 weeks ago as well, they are Delphi 43.82lb/hr @ 58 psi but it's been running fine with them.

[cpelton]

anyone? same problem with going very very lean at startup. I got the WOT fueling right where I want it now but I dont get why it goes so lean after a minute or so when i first start it up?

[WS6FirebirdTA00]

read/search, SD does that from a heat soaked IAT.

[cpelton]

this is happens the worst when the truck is cold and has been sitting overnight though.

[cpelton]

this is frustrating.. I found this: http://www.hptuners.com/forum/attach...6&d=1167919898 on another thread, so I changed my tables to match. Well this morning I figured that fixed it... nope still going lean.

[The Alchemist]

Did anyone ever figure this out? I searched lean cold start up and found this thread. It's not a maf issue, I'm speed density right now with the maf unplugged, it's not heat soaked IAT sensor and it was reading 60 degrees and the thermometer in the garage read the same. It was very lean until the motor got up to 150-160 degrees and it started to come back down. I have the long term fuel trims turned off because I'm tuning via wideband O2 AFR error. It honestly goes to around 18:1 at startup, but the weird thing is the commaned AFR was 12.6 :1.

Any help is appreciated.

[WS6FirebirdTA00]

you need to adjust the OLFA, it can't be 1.00 in OL at colder ECTs

[Russ K]

Your open loop table is all 1.00. So you will have no cold start enrichment.

Russ Kemp

[The Alchemist]

Ok, so I need to change that table. Let me go back and take a look at previous versions and see where that got changed. Would a stock table be ok? What also has me stumped is that according to the log, the computer was calling for an AFR of 12.x:1 at startup, but it stayed super lean.

I'm just confused at why it went the opposite way with fueling on startup.

[The Alchemist]

Something just isn't adding up. The computer was calling for a richer startup, and it was running leaner. As the motor comes up to temperature, both the commanded and actually AFR move closer to stoich. What the heck is going on?

[Russ K]

Try this tune, I set up your open loop table.

Russ Kemp

[The Alchemist]

Thanks for the help Russ...

Just posting an update. I tried a couple things suggested and the car doesn't go super lean at startup anymore, but it is still 2-3 points leaner than the commanded AFR at cold startup. I noticed today that with the car sitting there at idle, it stayed between 40-45 kpa at 850-900 rpm as the motor warmed up. The injector pulse width on both banks stayed the same, but the AFR read by the wideband richened up as the engine temperature increased. The only thing I can think of is as the engine warms up and the wideband O2 warms up, the reading at the wideband also richens up.

[Russ K]

Always turn on the wideband for ~30 sec before starting the engine.

Russ Kemp