Thread: Car running LEAN right after it was running fine for what reason?

Lol, I just looked at my scans when I first noticed this issue. IAT's hit 154°! That was when I was trying to just tune idle. Yeah, I think I'm getting that header wrap. If the speed daddy's rust out, good riddance.

Found another idle scan with 174° So I would mess with idle then immediately scan and drive. I'd look at logs and see it increasingly going lean because of the high IAT's. I'd pull fuel then quit till next day. 2nd day I take it for a scan without doing an idle scan, and boom my car is rich. Rinse and repeat. For two weeks...Dang I'm an idiot. So here's my rookie mistake. I wasn't paying attention to my IAT because I only equated that with the spark table that only pulled a degree or two of timing max. I stupidly overlooked the fact that hot air is less dense which means less O2.

Which means leaner, which means hotter, which means leaner.... I have heard leaner doesn't always mean hotter though. Though maybe I'm wrong about that.

lets delete the evap. pull its vac line and cap it off. see if the trims are more stable.

Originally Posted by Scottydoggs

lets delete the evap. pull its vac line and cap it off. see if the trims are more stable.

That's a good idea. I never saw it mentioned in the guides, but that certainly can help during tuning.

i figure it cant hurt either way. it could be leaking, or doing its thing as the tank level drops. capping it off just removes a possible cause.

"I just loaded my last adjustment and drove for about an hour to get another scan. over the last couple weeks of tuning I've noticed if I make adjustments from scans taken too soon after an adjustment it leans the fueling. I went on grand prix forums this morning and discussed the lean situation and they suggested I unplug my evap and then turn the evap code off. I did so when I loaded this last adjustment. looking at my maf ltft's after this scan was done and they are damn near perfect in every cell recorded. think I have an evap problem?"
~SgtMarshal

Found this in an old thread. I even commented in the thread, lol. Think I'll just delete the evap. Pretty sure I have one or two of the codes disabled already as I've always had a cel for evap I couldn't fix. Between evap and super high IAT's I think we've narrowed down the tuning irregularities.

Also I should be getting the proper values for my sd 60's soon. Finally will have a clean base for a good tune. 😁

Yeah my bad, I use my phone in desktop version and I screwed the formatting up when I copy pasted that quote.

So you think there is an IAT table that effects fueling somewhere? V8 guys have the tables I think. On our car there is only a spark table that only pulls a couple degrees of spark. Would be nice if there wasn't mysterious tables doing things in the background.

I remember when I first did the swap and was talking to a tuner he said he would prefer if I put an IAT in the lower intake.

Well, this is how tuning should be. Was able to dial in my error % within 1-3. And it only took 3 road sessions. Thank you guys so much for the help and inspiration.

Prior to getting htp, my car was so pig rich. On startup it made a horrible noise as the IAC was probably open all the way and sucking in air to keep it running. And it smelled terrible. I much prefer the smell of gas. It was not terrible to cold start, but it took a few seconds. And if i tried to start it while it was still warm, I'd have to throttle it for 30 seconds. Now it starts much quicker and warm starts are instant.

Got my harness extended, just need to get some more tape and wire loom. Then I can tune spark. Really looking forward to that. I switched to an 04 Impala SS spark table. The cruise and part throttle areas are higher than what I had. Car does feel better down low. May be placebo, because I haven't really been able to get on it for weeks. SS WOT timing is very low though. But i have a good base to work with i think.

if you want a higher timing file, the comp g timing hits 18 ish.

evap leak, aka vac leak.

Disconnecting evap certainly helped my tuning logs. Much more consistent. A big thing was also heat creep and my tuning procedure. I would warm up car, drive and tune. Pull over, make adjustments, then repeat. However, as you are sitting with the engine off the heat is saturating the engine. So then I take off and immediately log for another tune. Well, the heat has leaned everything out so now my AFR error % is off again.

I do believe the FWI really helped. With the HAI, Everytime the fans kicked on it would go real lean. Screwed up my logs. Overall it was a combination of things I think. The MAP issue may have been a red herring, or not, but I feel better having a 1 bar because there definitely is other reports of an l36 pcm freaking out when it sees boost. I did not see it going crazy rich on decel today either. Also my lowest IPW I had was 1.7, usually 1.8. Tonight I saw 1.6 for the first time. Not sure what caused that though.

Also, have you guys used Bluecats transmission calculator? I used that a week ago and my car is much smoother shifting. I used to have issues with converter lock in 4th causing knock when I slowly stepped on the gas. Now it locks and unlocks much smoother and shifts like a stock car. I do have a shift kit and increased pressure, but the calculator made everything smooth but still firm. Highly recommend it.

Glad to hear it's running good.