SaturnFans.com
what's new (beta) - classifieds - forums - photos


Go Back   SaturnFans.com Forums > Models > Saturn S-Series > S-Series Tech
Register FAQ Members List Groups Calendar Chat Room Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
Old 12-24-2013, 05:30 PM   #1
dakota1820
Advanced Member
dakota1820 will become famous soon enough
 
Join Date: Sep 2011
Location: Saint clair mo
Posts: 645

2000 SL1
Default short term fuel trim

I changed my oil and installed a fixed orfice pcv valve. Fired it up and I notice after a few minutes running it stumbled slightly. Did it the last time I started it and
et it idle. Felt like the idles coming down like normal and then for a split second it falls off. Like one singal missfire, I hook up the scanner and am watching live data and notice the following.
Ign adv 21.0
second air atmos
stft % -25.8
Ltft % -7.8
Vehicle speed 0
fuel sys 1 clsd
fuel sys 2 n/a
O2s11 (v) 0.735

That was all the info I got a picture of. The temp was around 145
why is the stft so far negative?

REWARD EXCELLENCE!

Add to dakota1820's Reputation
Rate the quality of this post and help dakota1820 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
dakota1820 is offline   Reply With Quote
SaturnFans.com Sponsored Links
Old 12-24-2013, 05:53 PM   #2
fdryer
Super Member
fdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond repute
 
fdryer's Avatar
 
Join Date: Jan 2006
Location: NYC
Posts: 43,527
 

2003 L-Series 3.0L Sedan
Default Re: short term fuel trim

When any engine is first started (cold) the normal start up air/fuel ratio is to run as rich as possible while raising idle above normal to ensure the engine doesn't stall. Unless you are familiar with most internal combustion engines, all car/truck/diesel engines need a rich fuel mixture simply because it works no other way. If you are not familiar with how engines run and now add a live display of sensors, you're doubling the complications of trying to understand how an engine runs and what sensors are displaying numbers. To add more complications, monitor the display after a full engine warm up and observe sensors change values. The easiest sensor to follow is the coolant temperature as it reflects outside temps before start up and increases as coolant warms up.

Fuel trims are dynamic - values change from cold start up to fully warmed up. A negative number means the pcm is trying to lean out fuel mixtures since the O2 sensor detects a rich fuel mixture (cold engine). As the engine warms up, high idle rpm drops, the rich fuel mixture is leaned out and will show fuel trims near zero. Ignore a few percentage points positive or negative. Since the O2 sensor is detecting a/f mixtures, the pcm is continually richening and leaning fuel mixtures many times a second. You're only seeing a fraction of a second of display time, not an analog view. Monitor live display over the course of a cold engine start up, while driving, and parked just before engine shut down to see values change. Fuel trims will vary less than a few percentage points with a fully warmed up engine.

...
VCX NANO

REWARD EXCELLENCE!

Add to fdryer's Reputation
Rate the quality of this post and help fdryer reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
fdryer is online now   Reply With Quote
Old 12-24-2013, 05:57 PM   #3
dakota1820
Advanced Member
dakota1820 will become famous soon enough
 
Join Date: Sep 2011
Location: Saint clair mo
Posts: 645

2000 SL1
Default Re: short term fuel trim

I did replace the manifold o2 sensor. Last week. Ive never had below -14 stft before. Then change was kinda surprising.

REWARD EXCELLENCE!

Add to dakota1820's Reputation
Rate the quality of this post and help dakota1820 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
dakota1820 is offline   Reply With Quote
Old 12-24-2013, 06:50 PM   #4
fdryer
Super Member
fdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond repute
 
fdryer's Avatar
 
Join Date: Jan 2006
Location: NYC
Posts: 43,527
 

2003 L-Series 3.0L Sedan
Default Re: short term fuel trim

Correlating how EFI works, reading and interpreting live displays and when these readings are taken relative to whether the engine is first started up or after a hot race lap around a track is a lot of information to juggle. The first thing to do is to see what's displayed on a normal engine - this becomes the baseline of reference for comparing future info when problems arise. Without a reference to go by, guessing what's wrong or wondering why a reading is displayed without a baseline can be confusing to anyone.

...
VCX NANO

REWARD EXCELLENCE!

Add to fdryer's Reputation
Rate the quality of this post and help fdryer reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
fdryer is online now   Reply With Quote
Old 12-24-2013, 08:08 PM   #5
dakota1820
Advanced Member
dakota1820 will become famous soon enough
 
Join Date: Sep 2011
Location: Saint clair mo
Posts: 645

2000 SL1
Default Re: short term fuel trim

Well my honda isnt a fair comparison it is newer and is more complex. What is typical stft for a saturn? I understand what it is. Negative 25 seemed excessive from anything ive ever seen.

REWARD EXCELLENCE!

Add to dakota1820's Reputation
Rate the quality of this post and help dakota1820 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
dakota1820 is offline   Reply With Quote
Old 12-24-2013, 08:42 PM   #6
fdryer
Super Member
fdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond repute
 
fdryer's Avatar
 
Join Date: Jan 2006
Location: NYC
Posts: 43,527
 

2003 L-Series 3.0L Sedan
Default Re: short term fuel trim

Frankly, I don't know. Having a V6 L300, my stft (after a full warm up) shows -1.5% and -0.78% (two, 3-cylinder banks). I've never monitored stft at cold engine start up. Remember, what you see depends on when the engine was monitored; cold engine, fully warmed up, over heated, etc.. Having a 'big picture' helps otherwise tunnel vision occurs easily.

Google short term fuel trim for an overall idea. Just remember they may leave out the part about cold engines when engines are expected to run rich. A normally running engine should have stft near zero (fully warmed engine).

After wading thru as much information that can overwhelm most not willing to learn anything about EFI systems, some of the reasons for high negative numbers (higher than -10%); faulty coolant sensor/t-stat/map/leaking injector(s)/faulty fuel pressure regulator.

...
VCX NANO

REWARD EXCELLENCE!

Add to fdryer's Reputation
Rate the quality of this post and help fdryer reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
fdryer is online now   Reply With Quote
Old 12-24-2013, 09:36 PM   #7
1sksc2
Member
1sksc2 has a spectacular aura about1sksc2 has a spectacular aura about
 
Join Date: Sep 2011
Location: yuma
Posts: 387

1996 SL2
Default Re: short term fuel trim

My sl2 when warm stft is around -17 and my ltft is at -.78 to .78
You don't have to worry about short term it's the long term you need to be worried about. The reason for your short term being so low is because your in neutral and the iac is open more creating a huge vacuum leak. Once you put it in drive your idle will go down and the short term will be better. But will never be perfect. And after that your long term should go from negative to positive. If it doesn't then have a small vacuum else where.

REWARD EXCELLENCE!

Add to 1sksc2's Reputation
Rate the quality of this post and help 1sksc2 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
1sksc2 is offline   Reply With Quote
Old 12-24-2013, 11:05 PM   #8
fdryer
Super Member
fdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond reputefdryer has a reputation beyond repute
 
fdryer's Avatar
 
Join Date: Jan 2006
Location: NYC
Posts: 43,527
 

2003 L-Series 3.0L Sedan
Default Re: short term fuel trim

^ I don't know where your information is from but you're misinformed. Stft is the pcm trying to lean or richen fuel mixtures compared to parameters, to return mixtures back to stoichiometric ideal, 14.7:1 or zero. Whether there's a high, medium or low vacuum, a/f ratios are measured from O2 sensor readings and compared to what should be used. Rich mixtures are seen as negative percentages - the pcm attempting to lean fuel while lean mixtures are seen as positive percentages - the pcm attempting to richen mixtures.

Coolant temperature, map, tps, intake air temperature, rpm and O2 sensor output are used to determine short term and long term fuel trims. Its much more complicated than iacv position.

...
VCX NANO

REWARD EXCELLENCE!

Add to fdryer's Reputation
Rate the quality of this post and help fdryer reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
fdryer is online now   Reply With Quote
Old 12-24-2013, 11:38 PM   #9
satlite440
Senior Member
satlite440 has much to be proud ofsatlite440 has much to be proud ofsatlite440 has much to be proud ofsatlite440 has much to be proud ofsatlite440 has much to be proud ofsatlite440 has much to be proud ofsatlite440 has much to be proud ofsatlite440 has much to be proud of
 
Join Date: Jul 2011
Location: kent wa
Posts: 1,053

2001 SL2
Default Re: short term fuel trim

acording to everything gm has taught me in the last 20 yrs short term trim is basicly a buffered moment by moment reading of what the pcm is doing as far as fuel/air mix a neg reading is the pcm taking away fuel by decreasing the injecter pwm to a lower duty cycle to reduce fuel...NOTE all gm o2 sensors are stupid (untill you get into the lambda wide band o2's) they do not know the difference between a leaking/suck open injector or a gross air leak or heavy oil fouling in the chamber.. all it mesures is the o2 content...the more incomplete the burn or heavy hydrocarbins makes the o2 level go down hence the pcm takes fuel away as a sratagy to reduce the chance of melting the piston if it were to be a stuck open injector...the lon term trim is the over all # you need to watch as if the pcm is always reduceing or neg #'s you have a vac leak or some other issue that is the root cause.. most offten it is a weak or lazy post cat o2.. it is the post cat o2 that the ecm uses to determin long term trim adjustments as it is getting a true(if the sensor is good)reading of the cat's oxegen reserve and how efficent...older cars 90 up to 95-96 or obd2 are only active in closed loop starting in obd2 the closed/open loop thing was mostly done away with as we went to a system that was always ready due to heated o2's..i have alawys advised replaceing o2 in pairs on a bank pre and post cat as if you have an issue with a precat o2 being lazy the post cat one has been posioned for lack of a better word and may be lazy due to garbage in/garbage out..not to mention if you have burnt coolant or alot of oil the post cat o2 don't like that alot...hth

...
shure you can trust the government,just ask us indians all about it...

heavy line the final protective fire line of the dealership

REWARD EXCELLENCE!

Add to satlite440's Reputation
Rate the quality of this post and help satlite440 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
satlite440 is offline   Reply With Quote
Old 12-24-2013, 11:57 PM   #10
OldNuc
Super Member
OldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond repute
 
Join Date: Apr 2008
Location: Far Southwestern Iowa
Posts: 66,693
 

1998 SC2
Default Re: short term fuel trim

The Saturn does not use the post cat O2 sensor for anything but CAT efficiency monitoring. Absolutely no mixture control in any way.

STFT is used to periodically update the idle and cruise trim tables and then zeroed. The LTFT is the current table value. This is all cleverly accomplished with nothing more or less than input from the front O2 sensor only once the car reaches --operating temperature-- table updating commences. Operating temperature is in the 150 to 160F range and is not defined in the FSM as a specific set point. This implies that there is a bit more to what constitutes operating temperature. The values for the other 3 trim tables are derived from the cruise table

REWARD EXCELLENCE!

Add to OldNuc's Reputation
Rate the quality of this post and help OldNuc reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
OldNuc is offline   Reply With Quote
Old 12-25-2013, 12:08 AM   #11
1sksc2
Member
1sksc2 has a spectacular aura about1sksc2 has a spectacular aura about
 
Join Date: Sep 2011
Location: yuma
Posts: 387

1996 SL2
Default Re: short term fuel trim

oldnuc if i remember right when i was having my bad fuel mileage it was you who was trying to teach me not to really worry about the short term and worry more about the long term. and thats what i did. i have the message in my inbox somewhere. lol no biggie though. i just dont like to go into so much detail when explaining things.

REWARD EXCELLENCE!

Add to 1sksc2's Reputation
Rate the quality of this post and help 1sksc2 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
1sksc2 is offline   Reply With Quote
Old 12-25-2013, 10:20 PM   #12
dakota1820
Advanced Member
dakota1820 will become famous soon enough
 
Join Date: Sep 2011
Location: Saint clair mo
Posts: 645

2000 SL1
Default Re: short term fuel trim

Hey everyone and merry Christmas. I noticed my fuel trims today after driving home car was at 201 degrees. We just pulled in the garage. The stft was .08 ltft was -20 why is the long term so negative?

REWARD EXCELLENCE!

Add to dakota1820's Reputation
Rate the quality of this post and help dakota1820 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
dakota1820 is offline   Reply With Quote
Old 12-25-2013, 10:34 PM   #13
OldNuc
Super Member
OldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond repute
 
Join Date: Apr 2008
Location: Far Southwestern Iowa
Posts: 66,693
 

1998 SC2
Default Re: short term fuel trim

Because you are running rich for some reason. As this is most likely a cruise trim table value I would suspect an exhaust leak between the head and cat as the first choice and 2nd would be a restricted preCAT if installed or CAT but #2 is not a high probability.

This is how you find that size of exhaust leak.
Exhaust leak check.
--Locate a low pressure high volume air source, reversible vacuum cleaner, large fan, leaf blower or what ever you can find.
--Loosely couple to cold exhaust at the tail pipe, or direct fan at tail pipe.
--Spray every inch of the exhaust between the head and CAT inlet with a mixture of 2 or 3 drops of dish soap and water in a spray bottle.
--Pay close attention to the lower flange, lower support clamp, and flex connector.
--The flex connector is under the protective braid so it requires quite a bit of solution to show any leaks.

REWARD EXCELLENCE!

Add to OldNuc's Reputation
Rate the quality of this post and help OldNuc reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
OldNuc is offline   Reply With Quote
Old 12-25-2013, 10:42 PM   #14
dakota1820
Advanced Member
dakota1820 will become famous soon enough
 
Join Date: Sep 2011
Location: Saint clair mo
Posts: 645

2000 SL1
Default Re: short term fuel trim

Wouldn't the exhaust leak have a sound? I don't hear an leaks. Can't I put a rag in the tailpipe and if I do have a leak won't that magnify the sound?
I didn't get readings like this till I replaced the upstream o2 sensor either. It isn't a universal o2 though . Its a direct fit.

REWARD EXCELLENCE!

Add to dakota1820's Reputation
Rate the quality of this post and help dakota1820 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
dakota1820 is offline   Reply With Quote
Old 12-26-2013, 12:20 AM   #15
OldNuc
Super Member
OldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond reputeOldNuc has a reputation beyond repute
 
Join Date: Apr 2008
Location: Far Southwestern Iowa
Posts: 66,693
 

1998 SC2
Default Re: short term fuel trim

You have to pressurize a cold system and use soapy water. You will neither hear ors see this small of a leak.

REWARD EXCELLENCE!

Add to OldNuc's Reputation
Rate the quality of this post and help OldNuc reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
OldNuc is offline   Reply With Quote
Old 12-26-2013, 12:29 AM   #16
dakota1820
Advanced Member
dakota1820 will become famous soon enough
 
Join Date: Sep 2011
Location: Saint clair mo
Posts: 645

2000 SL1
Default Re: short term fuel trim

Actually come to think of it I put a fixed orfice PVC valve a few days ago ever since then it's been really weird.....

REWARD EXCELLENCE!

Add to dakota1820's Reputation
Rate the quality of this post and help dakota1820 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
dakota1820 is offline   Reply With Quote
Old 12-26-2013, 01:08 AM   #17
SL19302
Master Member
SL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to all
 
SL19302's Avatar
 
Join Date: Jan 2011
Location: Drums, PA
Posts: 3,350

2000 SW2
2002 SL1
Default Re: short term fuel trim

This is just my opinion, but I personally dont like this whole fixed orfice PCV valve system, I think it causes excess pressure to build up in the crankcase and cause issues with seals and potentially cause oil leaks, People who are using a Fixed orfice PCV valve to correct oil consumption are throwing money down the drain, The problem is the rings on the engine, If you did a rebuild with drain back holes and new rings and installed the original PCV valve back into the engine it wouldnt use any oil as designed, The reason the fixed orfice valve cuts down on the amount of oil going into the intake system is because the rings are worn and your engine has excessive blowby, Thats why the oil is being forced out the PCV system into the intake, Its a band aide masking an underlying problem just like stop leak.

...
2015 Subaru Forester Limited "Prinny"
2000 SW2 Still Running Strong- 160K Traded In
2002 SL1 Still has Its Training Wheels on at 88K Traded In


CHECK YOUR OIL!

REWARD EXCELLENCE!

Add to SL19302's Reputation
Rate the quality of this post and help SL19302 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
SL19302 is offline   Reply With Quote
Old 12-26-2013, 01:24 AM   #18
dakota1820
Advanced Member
dakota1820 will become famous soon enough
 
Join Date: Sep 2011
Location: Saint clair mo
Posts: 645

2000 SL1
Default Re: short term fuel trim

I was told it would help smooth the idle . My saturn doesn't burn oil so I was using for that puroose only.
what symptims would I have if the fuel regulator was going bad?

REWARD EXCELLENCE!

Add to dakota1820's Reputation
Rate the quality of this post and help dakota1820 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
dakota1820 is offline   Reply With Quote
Old 12-26-2013, 01:37 AM   #19
SL19302
Master Member
SL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to allSL19302 is a name known to all
 
SL19302's Avatar
 
Join Date: Jan 2011
Location: Drums, PA
Posts: 3,350

2000 SW2
2002 SL1
Default Re: short term fuel trim

Is this the 95 or 02?

...
2015 Subaru Forester Limited "Prinny"
2000 SW2 Still Running Strong- 160K Traded In
2002 SL1 Still has Its Training Wheels on at 88K Traded In


CHECK YOUR OIL!

REWARD EXCELLENCE!

Add to SL19302's Reputation
Rate the quality of this post and help SL19302 reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
SL19302 is offline   Reply With Quote
Old 12-26-2013, 01:48 AM   #20
anmasher
Senior Member
anmasher has a spectacular aura aboutanmasher has a spectacular aura aboutanmasher has a spectacular aura about
 
anmasher's Avatar
 
Join Date: Oct 2012
Location: Martinsville, IN
Posts: 1,557
 

1995 SC2
1996 SL2
Default Re: short term fuel trim

Quote:
Originally Posted by SL19302 View Post
The reason the fixed orfice valve cuts down on the amount of oil going into the intake system is because the rings are worn and your engine has excessive blowby
No... Oil control rings are different from compression rings and the two are not related. If you recall ehunter's engine, he had over 200psi compression and 100% of his oil consumption (1qt/300mi) was coming from gummed up oil control rings. Sometimes the cylinders and rings do show significant wear, but truly worn compression rings in these engines is extremely rare.

REWARD EXCELLENCE!

Add to anmasher's Reputation
Rate the quality of this post and help anmasher reputation points. Click the reputation button near the bottom left corner of this message box. Thank you!
anmasher is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Short Term Fuel trim -20 to -35 until ~160degF, normal? ssewall S-Series Tech 35 10-24-2011 10:06 PM
Reset LTFT (Long Term Fuel Trim) td1238 S-Series Tech 6 07-07-2011 09:49 PM
Long Term Fuel Trim 1996SL11.9L S-Series Tech 31 03-09-2010 04:34 PM
long term fuel trim at idle---95 SC2 derf S-Series Tech 24 02-04-2010 08:56 AM
Neat way to get car for short term - SC2 piney S-Series General 1 01-17-2002 04:31 PM


All times are GMT -4. The time now is 03:36 PM.

Advanced Forum Search | Advanced Photo Search


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
SaturnFans.com. The Saturn Enthusiasts Site.