Negative LTFTs at idle.

[Tokay444]

Hey guys. I'm bone stock, 2007, 91000kms with a dashhawk to monitor. -12 LTFT at idle.
Any ideas where I should start?

[4G63]

Boost/vacuum leak. Make a tester let me find the link.

Edit: Boost leaks are usually positive fuel trims or >8%. Vacuum leaks are usually negative <-8%. Someone please correct me if I'm wrong I may have it backwards. Regardless follow the link make a tester. Take off ur intake filter fasten the tester over the intake silicone run conpressed air through and listen for leaks. Find leak and stop leaks.

That or your MAF is calibrated wrong. I'd check the leak first they are annoying as hell and most often the problem

Should cost u like 12$ to make one

http://forum.mazda6club.com/mazdaspe...oost-leak.html

Edit edit: because it's at idle I'm def gonna point to a vacuum leak

[R.MS3]

A smoke test at your local shop would point to any vaccum leaks easily.

[Tokay444]

Ok thank you. I'll have to get on the tester.
Any negative side effects that go with a vacuum leak?

[R.MS3]

It can give you several problems from misfire, to rough idle, on and on.

I would do a boost leak and a vaccum leak test to make sure everything is good.

[Tokay444]

Ok thanks guys.

[easy]

i believe trims go "+" when its a vacuum leak because its pulling in unmetered air and goes "-" when there's a boost leak because its loosing metered air. Someone correct me if im wrong.

[R.MS3]

When i had a boost leak, the trims were way UP so i think the first guy is correct. I had a leak on the TIP connection to the turbo.

[rfinkle2]

A cool link related to the discussion.

http://www.stealth316.com/misc/obdii_fuel_trim.pdf

[Tokay444]

Thanks finkle. Now how do I test for a leaking injector?

[silvapain]

Originally Posted by AdrenalineRush Boost/vacuum leak. Make a tester let me find the link. Edit: Boost leaks are usually positive fuel trims or >8%. Vacuum leaks are usually negative <-8%. Someone please correct me if I'm wrong I may have it backwards. Regardless follow the link make a tester. Take off ur intake filter fasten the tester over the intake silicone run conpressed air through and listen for leaks. Find leak and stop leaks. That or your MAF is calibrated wrong. I'd check the leak first they are annoying as hell and most often the problem Should cost u like 12$ to make one HOW TO FIND A BOOST LEAK - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum Edit edit: because it's at idle I'm def gonna point to a vacuum leak

Other way around. Boost leaks will show up as large negative trims under boost, and vacuum leaks will show up as large positive trims under idle or coasting.

Sounds to me like it's just the MAF curve needs to be tuned.

[Tokay444]

The car is stock. I have no tuning method as of yet. The trims come into check when getting on it, and go zero at wot.

[SilverDemon]

Dirty Air Filter.....

[Tokay444]

I had it out before the winter and it looked clean. I will have another look. I'll even let it idle without the filter to see if that brings them back into spec. Thank you.

[Tomas]

Originally Posted by SilverDemon Dirty Air Filter.....

This

[silvapain]

I wouldn't worry too much about it, even if you're stock. OEM's don't tune the curve to the MAF in every car that comes off the line, so there's going to be some error. As long as you're not noticing any power loss issues, no DTC's, and not loss in fuel economy, then you're fine.

[SilverDemon]

could also be a dirty MAF sensor....O2 sensor going out.....but start with the cheap problems first

[m4tic]

Originally Posted by Tokay444 Thanks finkle. Now how do I test for a leaking injector?

run the engine for a few seconds to build fuel pressure (or hold the gas to the floor to just turn over the engine)

with key on engine off, monitor fuel pressure, it should hold the psi when you shut the engine down... and slowly leak down pressure 400+ psi

if anything in the fuel system is leaking, pressure would drop right away

[Tokay444]

I've noticed quite often that it holds dipsi for quite some time. Thank you. That helps.

[cbspeed3]

i notice that my trims go negative at idle when the temp gets above 80 degrees here in new orleans.when the temp gets around 55-60 degrees my trims are pretty much at 0. and when it gets really cold my trims go positive at idle.

[Tokay444]

Yeah, all winter they seemed to be in the ball park, -3 to -5. Now that it's warmer, they are falling. Going to check the air filter right now.

[cpolly69]

just wanted to reiterate what was said here about trims and this issue:
vac leaks get you positive trims - because the ecu sees unmetered air and thinks it needs to supply more fuel in order to compensate for more air
an over abundance of fuel (or one perceived by the ecu) gets you negative trims -
as already said issue is most likely with simple air flow difference from the filter, a dirty maf, or even possibly an o2 sensor starting to be out of tolerance - in an extreme case it's even possible there is an issue with the fuel system, but as this is a stock car, that's pretty unlikely

[Tokay444]

The di pressure actually rises for a bit after shut down, and it registered 64 psi before start up this morning. And that was sitting all night. The LTFTs didn't move when I removed the filter, but the air was crisp this morning and it was idling around -7 to -8. But I've seen as low as -15 on warmer days...
Going to do a maf cleaning next.

[cpolly69]

it's normal for a bit of pressure to stay in the area from the high pressure cdfp to the injectors after you turn the car off - that's where the sensor that you are reading is actually located - in the fuel rail over on the left side -
you should see 400-500 at idle (ecu decides what it will be based on load, so if you do something like turn on the ac it will go up) and about 1700 at wot

[Tokay444]

Yes thank you. I just wanted to point out my di pressure was holding, because finkles link stated my problem could be a leaky injector and bmorrisj pointed out a good method to check.

[rfinkle2]

CRC makes a Maf cleaner if you want to give that a shot.

I've used it well over 50 times with absolutely nothing but positive effects on a few different cars.

You can pick it up @ your local auto parts store.

[Tokay444]

Thanks again finkle. I'll pick some up tomorrow.

[Tokay444]

So, I got some maf cleaner today after seeing -16% LTFTs at idle.
Took intercooler of and intake up the the tip.
Cleaned all the piping and tightened down all the hose clamps and bpv.
Maf was filth on the front side. Clean it up nice and reinstalled it.
Went for a cruise, and at first idling was zero for both STFT and LTFTs. I know this is the leading stage.
After about 30 minutes of driving at differential speeds, things started to register. I saw -10% LTFTs at idle once, but for the most part it was -9. Under light load and cruising LTFTs were -7. Medium load they were around -5 to +1 and obviously at wot they were both zero. I guess my next question is, is this now something to be worried about? Should I still look into a vac/boost leak test? Will my LTFTs just fall back down to -16 in the next few days?

[manelscout4life]

what do your stft now look like?

did you reset the ecu after cleaning the maf?

[Tokay444]

I did. I had the battery leads twisted together from the start of tear down. My STFT bounce around a lot while modulating the throttle, but settle out around -5 at idle and between 3 and -3 at cruise. But I've seen it go from -9 to +16 before settling out.

[MaverickX3]

I'm in the same ball park right now. Its been getting warmer in Edmonton so my LTFT have been about -13 to -11. I'm thinking I too will clean the maf again (did it sometime last year, used the CRC stuff). At idle and engine braking it jumps up to -11/-12.

I'm running the stage 0 v106 map to get the bugs fixed out before the goodies go back on. MPG was pretty nasty this last tank

[MaverickX3]

What should I expect for DI pressure before start up (KOEO) when the car has sat outside for the night? I measured 61 this morning. It was at 400 once I turned her off and the pressure gradually went down.

[Tokay444]

When I turn mine off, my DI rail pressure climbs for about ten solid minutes before it starts to fall. It hit over 1500psi before it started to fall the one time I watched it.
In the morning I'm right around 55psi.

[cpolly69]

it will eventually go down to almost nothing after sitting a decent amount of time -
i know this for sure b/c taking your cdfp off after the car sitting for a few days is the best...

[MaverickX3]

Or you don't and open up the pressure line and gasoline sprays in your engine bay. That was awesome :O

For the record I was lazy lol