Short Term Fuel Trims
10-04-2010, 09:09 PM
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Short Term Fuel Trims
Hey guys, I recently purchased a dash daq, and have been loving that little device ever since I bought it. There is one thing that has got me wondering: Short Term Fuel Trims.
A little background of my car: 04 Auto w/ 20k miles...AEM intake, GReddy Exhaust, and AP Midpipe. Just replaced the battery.
When I am at a stop light, sometimes the car dips around 500 rpm, and the car shakes violently. I look at some of my readings, and my AFR is reading around 18+, and my fuel trim shoots up to around 20-24...once it hit 25, the car stalls out. I recently cleaned my MAF, and it has helped ALOT...but I am unsure as to what to try next. New Coils? Plugs? Wires?
The car also seems to give a horrible start up. It sits at around 2k RPM, and acts like it wants to stall...after about 15-30 seconds, the car quietly goes back to the normal engine warming up cycle.
So, for those who dont want to read the wall of text: How do I get my short term fuel trims to be more stable? Thanks for your help!
EDIT:
I have also been having troubles in higher RPMs (ie-6k+)...I was having misfires when I was testing the other day. I am assuming coils on this one?
A little background of my car: 04 Auto w/ 20k miles...AEM intake, GReddy Exhaust, and AP Midpipe. Just replaced the battery.
When I am at a stop light, sometimes the car dips around 500 rpm, and the car shakes violently. I look at some of my readings, and my AFR is reading around 18+, and my fuel trim shoots up to around 20-24...once it hit 25, the car stalls out. I recently cleaned my MAF, and it has helped ALOT...but I am unsure as to what to try next. New Coils? Plugs? Wires?
The car also seems to give a horrible start up. It sits at around 2k RPM, and acts like it wants to stall...after about 15-30 seconds, the car quietly goes back to the normal engine warming up cycle.
So, for those who dont want to read the wall of text: How do I get my short term fuel trims to be more stable? Thanks for your help!
EDIT:
I have also been having troubles in higher RPMs (ie-6k+)...I was having misfires when I was testing the other day. I am assuming coils on this one?
Last edited by ejeetology; 10-04-2010 at 09:17 PM.
10-04-2010, 09:16 PM
#2
Hey guys, I recently purchased a dash daq, and have been loving that little device ever since I bought it. There is one thing that has got me wondering: Short Term Fuel Trims.
A little background of my car: 04 Auto w/ 20k miles...AEM intake, GReddy Exhaust, and AP Midpipe. Just replaced the battery.
When I am at a stop light, sometimes the car dips around 500 rpm, and the car shakes violently. I look at some of my readings, and my AFR is reading around 18+, and my fuel trim shoots up to around 20-24...once it hit 25, the car stalls out. I recently cleaned my MAF, and it has helped ALOT...but I am unsure as to what to try next. New Coils? Plugs? Wires?
The car also seems to give a horrible start up. It sits at around 2k RPM, and acts like it wants to stall...after about 15-30 seconds, the car quietly goes back to the normal engine warming up cycle.
So, for those who dont want to read the wall of text: How do I get my short term fuel trims to be more stable? Thanks for your help!
A little background of my car: 04 Auto w/ 20k miles...AEM intake, GReddy Exhaust, and AP Midpipe. Just replaced the battery.
When I am at a stop light, sometimes the car dips around 500 rpm, and the car shakes violently. I look at some of my readings, and my AFR is reading around 18+, and my fuel trim shoots up to around 20-24...once it hit 25, the car stalls out. I recently cleaned my MAF, and it has helped ALOT...but I am unsure as to what to try next. New Coils? Plugs? Wires?
The car also seems to give a horrible start up. It sits at around 2k RPM, and acts like it wants to stall...after about 15-30 seconds, the car quietly goes back to the normal engine warming up cycle.
So, for those who dont want to read the wall of text: How do I get my short term fuel trims to be more stable? Thanks for your help!
10-04-2010, 10:33 PM
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Alrighty,
A little background and then some suggestions. Fuel trims are a closed loop operation where the PCM tries to compensate for problems with fuel delivery. Almost all the values in closed loop are calling for a 14:1 air/fuel ratio. If the PCM is seeing values lower or higher than this it will trim your fuel delivery +/- 24%. You will almost always see some kind of trim because environmental conditions will change air delivery.
Since you are using an AEM intake I would check all your couplers and make sure they are tight and not leaking. I would also ensure that your screens are installed and oriented properly. Any turbulence can cause issues with the MAF as it's very sensitive. After you have checked those items I would also make sure you don't have any vacuum leaks. Coils, plugs or wires do not produce lean conditions in my experience.
If you are having "misfires" in higher RPM's, what are your air/fuel ratios in those ranges?
A little background and then some suggestions. Fuel trims are a closed loop operation where the PCM tries to compensate for problems with fuel delivery. Almost all the values in closed loop are calling for a 14:1 air/fuel ratio. If the PCM is seeing values lower or higher than this it will trim your fuel delivery +/- 24%. You will almost always see some kind of trim because environmental conditions will change air delivery.
Since you are using an AEM intake I would check all your couplers and make sure they are tight and not leaking. I would also ensure that your screens are installed and oriented properly. Any turbulence can cause issues with the MAF as it's very sensitive. After you have checked those items I would also make sure you don't have any vacuum leaks. Coils, plugs or wires do not produce lean conditions in my experience.
If you are having "misfires" in higher RPM's, what are your air/fuel ratios in those ranges?
10-05-2010, 07:12 AM
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thanks for the suggestions (and the education) flash and charles. when the misfires happen, the AFR dips below 11. Also, prior to me posting about this issue, I inspected the screens and the couplers to make sure everything was fine. Sure enough one screen was out of place, so I took apart the whole system, placed it back together, and cleaned the MAF. Those helped out tremendously...I have yet to stall since doing that procedure.
The fuel trims spike (occasionaly) when I am at a stop light, RPM dips, and AFR goes crazy. However, I have not had any stalling issues. I was just wondering if the Fuel Trims had a quick fix without installing a new filter or injectors.
Charles, I totally forgot about that procedure. Thank you guys for bringing that up
The fuel trims spike (occasionaly) when I am at a stop light, RPM dips, and AFR goes crazy. However, I have not had any stalling issues. I was just wondering if the Fuel Trims had a quick fix without installing a new filter or injectors.
Charles, I totally forgot about that procedure. Thank you guys for bringing that up
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