Need help -25 ltft.

Status
Not open for further replies.
Joined
Oct 14, 2015
Messages
357
Location
Washington
Platform is 2012 cruze 1.4 manual. I have a hot dynotune on it and its been perfect for about 6 months until now. My idle is super rich and has a rich missfire if i hold rpms below 1500. Driving is perfectly normal. The ltft like to hang around -3 to +3 while driving normal or under hard pulls. Just idle is giving me a issue. Injectors are stock 26lbs. I have 60 lbs injectors i plan on swapping in to eliminate a leaky injector. "Yes the 60's have been dyno tuned too" i originally i swapped back to stock injectors for mpg while commuting. The stock are just about static on pulls past 5k rpm. So heres what i tried. Cleaned maf, went back to stock intake "best maf placement", new front o2 sensor, no exhaust leaks, no boost/vacuum leaks, plugs good, coil good. Im mechanically inclined i just have basic tools atm. My guess is do my injector swap then look at maf for issues. Thoughts?
 
If I read your post correctly you answered your own question, leaking injector.The ECM is pulling fuel.
A repair ASAP and an oil change is in order as it probably heavily diluted with fuel running like this.
 
So you have 2 different calibrations......One for the 60# Injectors & One for the 26# Injectors?

My first thought would be injectors.....Followed by, Sucking raw fuel from the EVAP, Or you have a ton of fuel in the crankcase.

While it's possible for a MAF to over-calculate.....It's very rare in my experiences.


Tuners love to turn-off/disable DTC's ......It's not unheard of to have to return the vehicle to stock & let the PCM do some diagnostic work for you!
 
Just replaced my evap purge solenoid. It was $20 so i didnt think it would hurt. No change with that.
Originally Posted by clinebarger
So you have 2 different calibrations......One for the 60# Injectors & One for the 26# Injectors?

My first thought would be injectors.....Followed by, Sucking raw fuel from the EVAP, Or you have a ton of fuel in the crankcase.

While it's possible for a MAF to over-calculate.....It's very rare in my experiences.


Tuners love to turn-off/disable DTC's ......It's not unheard of to have to return the vehicle to stock & let the PCM do some diagnostic work for you!
 
The thing is it will do it on and off. Its done it the past 3 days. It used to be like twice a week at a random stoplight. Now its done it everytime i idle once warm.
Originally Posted by Trav
If I read your post correctly you answered your own question, leaking injector.The ECM is pulling fuel.
A repair ASAP and an oil change is in order as it probably heavily diluted with fuel running like this.
 
You said you had a leaky injector, did you confirm this or is this just a guess? You FT numbers at normal driving rpm and taking fuel away at low injector ms at warm idle is a good indicator of a dripping injector. Cold the engine is in open loop and needs the richer mixture, that is the reason you don't notice it as much.
Leaking/dripping injectors tend to worsen with use.

As at warm idle the injectors are running at 3 ms or less so it does not take much of a drip for the ecm to pull fuel from all injecors attempting to bring it into stoichiometric.
Like Clinebarger asked, you have a tune for the 60lb correct? 60lb is not a plug and play replacement for 26lb. At warm idle these will likely run at 1 ms or less.

You need to check the system not just one part of it. This is just one possibility.
 
Yes i have a tune for the 60's. Im only assuming at this point. Ive noticed worse mpg, more vibrations, less power, slight bit more turbo lag. First i thought it was a purge event. But not if its having to subtract fuel? Just today it did it again. It would slowly creep up from -3 "where is normally sits at idle" to -27. The problem is gone once i start driving. Then say i stop again and now it wont do it and acts perfect. My plan was to switch back to the 60's and see what happens. If it doesnt get better i could say it wasnt a injector problem right?im still learning im sorta book smart but lack hands on.

Originally Posted by Trav
You said you had a leaky injector, did you confirm this or is this just a guess? You FT numbers at normal driving rpm and taking fuel away at low injector ms at warm idle is a good indicator of a dripping injector. Cold the engine is in open loop and needs the richer mixture, that is the reason you don't notice it as much.
Leaking/dripping injectors tend to worsen with use.

As at warm idle the injectors are running at 3 ms or less so it does not take much of a drip for the ecm to pull fuel from all injecors attempting to bring it into stoichiometric.
Like Clinebarger asked, you have a tune for the 60lb correct? 60lb is not a plug and play replacement for 26lb. At warm idle these will likely run at 1 ms or less.

You need to check the system not just one part of it. This is just one possibility.
 
Correct, if you run the 60's with the tune for them and the issue persist chances are it is not the injectors (unless of course in the unlikely event one of them is dripping).
 
Yeah... switching injectors back and forth without changing the tune? That's not how it works.

Part of your "tune" is identifying to the ECM the flow characteristics of the injectors. This is the foundation for all fueling calculations by the controller.

Example: A 3 ms pulse from a 60 lb/hr injector is .0232 cc. A 3 ms pulse from a 48 lb/hr injector is .0150 cc. From an operational standpoint, the engine will need the same fuel at the same engine speed and load regardless of which injector is in place. However, running the 48 lb/hr injector will require a significantly higher duty cycle to achieve the fueling when compared to the 60 lb/hr. Yes, the ECM has some capability to adjust for this. That's your fuel trims. However, it does not have *that much* capability. It needs to be told some foundational information first, like the injector data, to accurately adjust the fueling.

It goes beyond pulsed flow data as well. Static flow data and voltage offsets (how the injector performance varies at different system voltages) are part of the equation as well. Just tossing in injectors without any follow up in the ECM is a total crapshoot as to how it is going to perform.

Also, swapping injectors isn't going to net you better fuel economy. Again, that's not how it works. An engine needs as much fuel as an engine needs. The ECM's job is to determine what the current operating demands are (inputs), then adjust system operation to meet those demands (output). Changing injectors doesn't change the demand for fuel, which is what determines fuel economy, it just forces the ECM to change it's operation to compensate.
 
Just a update to everyone, i swapped tune/injectors back to 60 and the issue is alot better. I did turn the key on with the 26 injectors out and one of them got damp so i assume its a tiny leak. I thought swapping would fix it. but just wanted some more advice and it worked. Thanks everyone who commented.
 
Status
Not open for further replies.
Back
Top