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Mystery Leak? Lean condition

Even the dyno tunes I have seen that DO 3800s dont spend a ton of time worrying about MAF curves. They just concern themselves with WOT tuning.
 


I forgot to mention that I had the car scanned after rebuilding by chevy to see if I needed a case learn, and the tech showed me the fuel trims and both long and short fuel trims were right at 0 percent at idle and when reved. The only real mods I've done since then is L26 upper swap, smoothing out tb lip, headers, catback, and CS144 alternator swap. None of those should affect the trims right??
 
thats not a normal condition, zero at idle and revved. its gonna move.

case learn has more to do with the timing of the crank cam and icm, nothing to do with fuel trims.
 
Did the tech reset the Fuel Trims by anychance? That will cause them to read 0.0% for a while till they relearn.
 
Scottydoggs said:
thats not a normal condition, zero at idle and revved. its gonna move.

case learn has more to do with the timing of the crank cam and icm, nothing to do with fuel trims.
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That's what I thought.... not sure why he was checking them anyhow. and sorry, I meant short term moved and long term stayed at 0. Lol
 


Iceman6669 said:
Did the tech reset the Fuel Trims by anychance? That will cause them to read 0.0% for a while till they relearn.
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I honestly don't know. I don't think he did. He said he just hooked up the tool and read data. Didn't charge me or anything. Forgot to mention it because at the time, I knew nothing about fuel trims, so I didn't even know what he was talking about. Do you think it's worth getting someone to vacuum test and smoke test? How much does that usually cost anyhow?
 
IDK what a smoke test will run you, but you might be better off finding a tuner locally to see if they cant adjust the tune to see if thats the problem.
 
wstefan20 said:
That's what I thought.... not sure why he was checking them anyhow. and sorry, I meant short term moved and long term stayed at 0. Lol
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thats still not right, stft will dance all over when driving around, 0 at idle is wanted, and wot it will read 0. unless things are really messed up somehow.

ltft will move too, being your not tuned normally its gonna be neg #'s all the time cause they set the tune up rich. could be -15 at idle then -10 / -8 ish driving and or wot. going to a pos # is not wanted at all.
 
Hm... ok. I think if it's cheap enough I'll get a buddy of mine to vacuum test just in case. It would really suck if I tuned compensating for a vacuum leak and found it later... I'll post what the results are.
 


wstefan20 said:
Hm... ok. I think if it's cheap enough I'll get a buddy of mine to vacuum test just in case. It would really suck if I tuned compensating for a vacuum leak and found it later... I'll post what the results are.
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I couldnt agree more.... Only reason I lean towards it NOT being a vac leak is that vac leaks usually spike the LTFTs to 16.4(or -16.4 I cant remember)
 
haha thanks guys! Yeah. It could still be a leak, or a combination of the two. It's close to 16% and the fact it drops near 0 when you give it gas makes me suspicious.
 
Well, as an update, I started tinkering around with things and came up with some interesting stuff. Turns out the catch can wasn't leaking, but it was restricting flow to the map sensor so the readings were off, thereby throwing off the fuel trims.

Haven't tried relocating the map sensor yet (being lazy putting off soldering wires). On top of that, somehow I lost my mind and forgot to connect the pcv breather hose to the throttle body adapter, so I've basically been sucking unmetered air through the pcv intake passage, throwing off the maf readings and masking as a vacuum leak (also why the propane test didn't find a leak).

So now after resetting the pcm, my stft are between +-5% (good) but my ltft are bouncing between -12-+8% trending slightly negative. I'm fairly new with fuel trims, but I'm fairly certain from what I have gathered that the ltft shouldn't be moving around this much.

I plan on driving for a few days as it is and seeing if things level out. The car does drive a LOT better though.

Concerning part is that it idles at 700-750rpm. Not sure if that's low. The coolant temp is 87-89C which is several degrees colder than where it stayed before. I'm running stock 5/8" radiator, green coolant, literally everything on the coolant system is new, stock 195F thermostat, ported lim coolant side passage, blocked lim to uim heater ports. Main thing I changed was porting the coolant side passage. Basically, is this normal?
 


With a stock tune they will bounce around. A little negative is good, you’d rather be running a little rich than a little lean.
 
I've heard that from a few people so I think everything's ok. I'm still going to run a few tests and possibly even get a smoke test done just cause. I'm running a bit cold in my opinion, so I think I'm going to end up replacing my thermostat and ect sensor while I'm there just in case.
 
Well, I'm finally starting to get serious before I go and tune my car so I don't tune in a vacuum leak or something stupid like that. Still waiting on the acdelco ECT sensor to come in, but just got the acdelco IAT sensor. Unfortunately just as predicted, no change.

So, in the spirit of diy, I started building my own smoke machine for detecting vacuum leaks. I decided to go the less brutal method and use nichrome wire and tiki wicks to burn mineral oil run off the battery. I went a little more expensive and used an actual mini regulator in place of a propane regulator (I think it was $15 vs $10?). I can't take credit for the idea, found some youtube videos and adapted my own. If it works, I'll post a how-to later.

20180115_191549.jpg
 
Well, think I might have found part of the issue finally.... built a diy smoke machine for finding vacuum leaks, and within about thirty seconds, I found the issue.... a leak where my throttle body bolts to my adapter.... in short, turns out my throttle body is warped! This is officially the last part of my original engine other than the water pump pulley, a/c compressor, power steering pump, flywheel, and metal parts of the mounting brackets that came with my car. Every other piece and sensor has been replaced... lucky me... other issue it seems is the rear o2 sensor. I have code P0420 because my high flow cat stops conversion after a certain engine load (can't keep up), and a few people have told me this can also mess up fuel trims, so I'm hopefully getting it tuned tomorrow with the help of a few members here!
 
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