negative LTFT's at idle

[littlevictories]

So this puppy has been getting like 13mpg around town.
Bank 1 LTFT at hot idle, closed loop -4.8
Bank 2 -6.4


Dead stock 2002 flex fuel 5.3 with a dead stock lt1swap "tune"


Hope to throw an LM2 on there in the next week or so

[BR3W CITY]

Neg LTFT means going rich, so things like a vac leak are easy targets. If you don't have a full exhaust or have an exhaust leak the ecm may be overcompensating with fuel.

I'm not sure if FF injectors need different scaling in the tune or not.

-4-6 really isn't that bad considering the can go 20+ with a big leak

[littlevictories]

yeah I was thinking vacuum leak. any usual suspects i should look for?

here's whats weird though. at light cruise the trims are dead nuts between 1 and 2, sometimes a 3

[littlevictories]

ps, full exhaust


motor does have like 160k on it, valve seals maybe?

[BR3W CITY]

Leak at the EVAP solenoid, crack in the plastic manifold that only comes open under certain vacuum conditions, exhaust leak near the 02.

Valve seals aren't my first thought since I've seen these dang this in the 250's and not passing smoke. Are you getting blowby/accumulation, or smoking?

[littlevictories]

I had a pretty good amount of oil in the intake when I popped it off to replace the knock sensors, so I set up a catch can to minimize that.

Your comment about a crack has me thinking of a big skuff on the plastic cap at the back of the intake, the one directly opposing the TB. Looks like the guys at the yard drug it up the firewall when pulling it out.

Gonna have to get after it with some carb cleaner I guess…that does work on these e-lectrofied motors right?

[mattcrp1]

Don't forget the vac regulator on the fuel rail for a leak. -4&-6 aren't to bad but brw3 is right that is slight over fueling. Also maybe a bad injector spray pattern or slight drip. Also how long is it idling and what are the stft at idle?

[littlevictories]

good ideas. I've been told the FF injectors like to go bad when they sit. Like un-cleanable kinda bad.

I guess I should try the cheapest fixes first. Plugs look pretty good. Check for vac leaks and throw the LM2 on there when I get a sec.

Dang thing JUST developed a tiny fuel leak. I put the hard line bulkhead in the worst possible spot…right next to the header collector. Gonna move it back down the frame a ways and use some heat wrap on the soft lines.

[mattcrp1]

Post a pic of your fuel system. I just ran mine in nylon, just curious how every one is doing there fule system. I wonder if this is a normal type reading for a flex fuel system.

[ls1nova71]

The tune is different for flex fuel injectors, did you tell him this when you sent in your PCM to be programmed? Also, did you replace the intake gaskets after removing the intake? Lower mile engines you can usually get away with reusing them, but with 160k on the clock, I'd replace them.

[68c10airstream]

If your pcv valve is still being used, it can pull in fuel vapors from the crankcase and easily cause long term fuel trims like what you are seeing. Is the oil change getting due?? When i was doing drivability repairs up north i would usually finalize my repairs with a oil change to clean things up. I have more experience with mopars than gm, but =/- 5% ltft #s are ok. Much beyond that will usually lead to fault codes. Back in the 80's during feedback carb repairs i would pull the pcv out of the valve cover and let it breath fresh air and by tailpipe emmissions it was putting in as much fuel as the idle circuit did in the carb, black tailpipe, short trips in winter, etc. Changing oil and filter made a huge difference, but didn't remove all the vapors. Long story to illustrate my point but good info that usually isn't mentioned. Good luck.

[littlevictories]

Originally Posted by mattcrp1

Post a pic of your fuel system. I just ran mine in nylon, just curious how every one is doing there fule system. I wonder if this is a normal type reading for a flex fuel system.

I have tried posting pics a million times, but this BBS seems to not play well with my flickr account.

https://www.flickr.com/photos/lammer...th/13235453384

there's a link to my account, it's public and you should be able to scroll through and see my junk pile.

I'm pretty much mirroring the stock return type system, but with -6 line to and from the tank. I used the fragola fittings and e85 hose from performance dynamics.

[littlevictories]

Originally Posted by ls1nova71

The tune is different for flex fuel injectors, did you tell him this when you sent in your PCM to be programmed? Also, did you replace the intake gaskets after removing the intake? Lower mile engines you can usually get away with reusing them, but with 160k on the clock, I'd replace them.

Yessir, I did have the conversation with Brendan (lt1swap) about flex fuel tunes. Basically, without the fuel composition sensor, the truck just assumes regular gas (e10 here). I have read the duty cycle on the FF injectors (when used for regular gas) is no where near as efficient as the regular gas injectors. I kind of wish I had taken the time to rustle up a regular harness and injectors. Hindsight 20/20…

Yep new gaskets in there. The old ones were smooshed flat.

[99RegalGS]

Try unplugging your MAF and see what they do. When I got my truck going my LTFT's were in the negative teens. After checking everything and even buying a new MAF it ended up being the tune, as my intake plumbing changed the way the MAF read...

[First c10]

Originally Posted by 99RegalGS

Try unplugging your MAF and see what they do. When I got my truck going my LTFT's were in the negative teens. After checking everything and even buying a new MAF it ended up being the tune, as my intake plumbing changed the way the MAF read...

99,
I have a problem with my stft and ltft 's running lean stft 29.7 I unplugged my MAF and they went to +\-.8 and the idle smoothed right out. What did you have to do to your tune? Any idea what I should to do?
Thanks
Scott

[littlevictories]

finally got the LM2 to work. I guess it has a floating ground type circuit and did not like the stock dash lighter ground. ran a wire to the firewall and it's good. probably get some honest AFR's in the next couple days.

99regal, First c-10,

How are you guys running your MAFs as far as location, type, intake?

[First c10]

I am running a spectra cold air intake for the truck I got the motor from. I bought a new MAF sensor also.
You can kind of see it in the picture.

[littlevictories]

damn looks nice.

i did a similar thing, ebay CAI for a 2002 silverado

put the LM2 on it today. dead nuts 14.6 when it goes closed loop.

gonna swap the ho2's side to side and see what that does.

after that i'm gonna try swapping injectors side to side. got 2 plugs on the richest bank that look a little darker than the others.

awhile back Brew said ya oughta factor in HPtuners into your swap budget. I second this and would like to add a wideband sensor to the list.

damn handy lil tool.

[First c10]

Well I maybe trying all that myself. Funny thing with these computers is you need to reset the computers often. I have been playing with mine. I think I have a bad MAF. Since it was a new one I didn't think it was it but I had a problem as everything was lean so I cleaned MAF and it started working. Then it went back to the old way so I am going to just get a new MAF and try it.

[BR3W CITY]

Originally Posted by littlevictories

damn looks nice.

i did a similar thing, ebay CAI for a 2002 silverado

put the LM2 on it today. dead nuts 14.6 when it goes closed loop.

gonna swap the ho2's side to side and see what that does.

after that i'm gonna try swapping injectors side to side. got 2 plugs on the richest bank that look a little darker than the others.

awhile back Brew said ya oughta factor in HPtuners into your swap budget. I second this and would like to add a wideband sensor to the list.

damn handy lil tool.

They sold a version of the HPT kit with a wideband a while ago, they probably still do. Its REALLY nice if you can afford it, but its definitely a cost thats hard to swallow.

[littlevictories]

Originally Posted by First c10

Well I maybe trying all that myself. Funny thing with these computers is you need to reset the computers often. I have been playing with mine. I think I have a bad MAF. Since it was a new one I didn't think it was it but I had a problem as everything was lean so I cleaned MAF and it started working. Then it went back to the old way so I am going to just get a new MAF and try it.

did you de-screen it? i read that is a big no-no

[BR3W CITY]

The lc9 uses the drop in style maf, not the screened unit that fits the whole pipe.

[littlevictories]

oh gotcha. duh

[99RegalGS]

I have a home made intake that goes to the driver's side with the MAF directly behind the filter.

To correct my negative fuel trims I did closed loop logging and scaled the MAF table as needed.

Originally Posted by First c10

99,
I have a problem with my stft and ltft 's running lean stft 29.7 I unplugged my MAF and they went to +\-.8 and the idle smoothed right out. What did you have to do to your tune? Any idea what I should to do?
Thanks
Scott

That's quite a large fuel trim. I would double check and make sure you don't have a vacuum leak or air leak between your MAF and throttle body. I would highly doubt your new MAF is faulty and the scaling for the MAF to be way off with a intake designed for these truck engines.

[littlevictories]

alright, sold some of last year's mtb racing stuff and spent the $200 for new injectors

talked to a teacher in the auto tech program at my school, says the flex fuel injectors are notorious for leaking at high miles. according to him the low duty cycle, coupled with low pressure for flex fuel systems means when they are used for regular gas they get dirty all up inside their guts.

he did say a couple tanks of e85 would help, but i dont have the fuel composition sensor or hp tuners to switch it to the e85 fuel map