Infiniti G20 Nissan Primera Forum banner

negative long term fuel trims

1.2K views 10 replies 4 participants last post by  Robj80  
#1 ·
I recently grabbed a scanner in order to see why I kept getting p0172 which is system rich. My LTFT is -3 at idle but during partial throttle it's -21.3! My STFT bounce from negative 10 to positive 10. That is the wide spectrum for the most part it stays +/- 5. It seems to be better when I'm in third gear. I usually see around -16 when in third but fourth and fifth I'm higher.

Can anyone help me figure this out? I'm not throwing p0172 right now but I'm afraid the LTFT will continue to rise and eventually I will trip the code. What can cause a normal LTFT at idle but rich while partial throttle is applied?

Sorry I don't have any freeze frame data available since I haven't tripped the code since I got the scanner! Figures I finally buy a scanner and now no light on!
 
#4 ·
Well this problem wasn't here when I first had the car tuned? Actually it didn't show up until a year later? So what could have changed?

What would your suggestion if the emanage sucks? Standalone?

I don't think the emanage can be that bad considering I've been using it for 120k miles with 259cc injectors and my only problem is a system rich code that may or may not be related to the emanage tune!
 
#10 ·
It doesnt even hold a candle to other piggybacks, so duh that was a stupid comment

I have a theory but this may be crazy?!? Well when the car was tuned the EGR was untouched. Meaning all the vac lines were still hooked up but there was no EGR tube. And where the EGR tube is suppose to be was NOT plugged. Wouldn't that cause the valve to suck in fresh air while it was activated? In other words during partial throttle? Now if I went and plugged the vac lines between the bpt and EGR which would stop the EGR from functioning what affect would this have on my fuel trim?
You talked about no tube between it and the exhaust? If so then yes it would have been sucking in engine bay air when activated. So you disconnected it and its good now?
 
#7 ·
I guess I have a boost leak but i'm having no drivability problems, no coast down stall, no backfiring, no black smoke, no sooty bumper, no fouled plugs, and I'm getting about 28mpg! The car is a dream right now!

anyone know at which point the comput trips the DTC? I want to know how close I am to throwing a code?

I have a theory but this may be crazy?!? Well when the car was tuned the EGR was untouched. Meaning all the vac lines were still hooked up but there was no EGR tube. And where the EGR tube is suppose to be was NOT plugged. Wouldn't that cause the valve to suck in fresh air while it was activated? In other words during partial throttle? Now if I went and plugged the vac lines between the bpt and EGR which would stop the EGR from functioning what affect would this have on my fuel trim?
 
#8 ·
hummm....u might wanna go back to the vac leak! cuz a vac leak will show up with testing, but u want find it easily just by look'n...water and soap...
 
#9 ·
My car idles at 21 in hg and it's rock solid! This would lead me to believe there isn't a vacuum leak. I need to clean my engine bay anyway so I guess I could kill two birds with one stone!

My light hasn't been on in a week and all of my monitors are ready except for EGR. I'm going to try and pass emissions today! I'm only a little late, it was due in february......07!
 
#11 ·
Yes there was no tube between the EGR and the exhaust. But all the vac lines were hooked up. This would mean that the EGR is sucking in fresh air when activated (i think). Well I was haveing a stalling problem and wierd shutting off problem so I was inpsecting vac line and noticed the egr. I figured it was sucking in fresh air so I searched the forum and couldn't find a block off plate for the low ports. I then read that all you have to do is remove the vac line and cap the BPT and EGR. This will stop the EGR from sucking in air. So that's what I did! I didn't notice any difference in performance? I didn't have a scan tool back then so I have no idea of this affected my fuel trims? I'm going to rip out all that crap and install a block off plate soon though. Now that I know I can pass emissions with out it.

BTW Grimsta you always seem to disagree with my part choices?!? I posted up about the Bosch O2's and you stated how they weren't the best choice and now my emanage sucks! You seem to be quite knowledgable about many things and seem to be an asset to the community but in the defense of the parts I'm using I don't know of a single other sr20 powered car that has racked up over 123k turbo miles on the stock sr20de using the stock 259cc injectors. Those bosch O2's and that greddy e-manage must be half way decent to accomplish this! Sure I have had a system rich code but we still don't know if the e-manage is the problem. Plus if it is it's easily tuned out!

Just to let everyone know I haven't had the code in over a week and I passed CT emissions. Only things I've changed are my MAP sensor and my air filter, which was very very dirty! Maybe that's all I needed and my negative trims are due to my tune! I'm sure they will show negatives because the computer is trying to get back to 14.7 and we all know a turbo car is not running 14.7 air/fuel! I can't tell yet if my LTFT are climbing, lowering or have leveled off. I have to keep an eye on it for a few more days.