Reading fuel trims and more

[turbosporttsi]

how do you properly read LTFTs and STFTs? i took a reading today at idle and this is the info i got from the scanner. (im getting fault codes of P1188, P1189, P0173....all fuel trim/adaptation codes)

RPM ~800
ENG LOAD- about 7%
spark advance- 5
hfm volts- 2.03 to 2.31
O2 volts- .82 to .93

LT sensor 1- -8.6
LT sensor 2- -0.8

ST sensor Bank 1 sensor 1- -0.8
ST sensor Bank 1 sensor 2- 99.2
ST sensor Bank 2 sensor 1- -4.7
ST sensor Bank 2 sensor 2- 99.2

STFT bank 1- .80 to 2.3
STFT bank 2- -2.3 to -3.9


how does this look? do i need to take WOT readings or data log while cruising?

[dinans3m3]

The LT sensors are what function? If they are recording the LTFTs in bank 1 and bank 2 the one -8.6 is pretty high at idle. Does it fluctuate increasing or in decreasing values? Otherwise it looks good for idle. Mine was also good at idle but when i drove it around a few more miles i saw the LTFTs increase beyond 11% which was obviously throwing me fuel trim codes after 40-50 miles. This was due to a vac leak. At idle everything was in proper form.
IS the HFM readout in volume or voltage? I have never seen a scantool that reads out voltage :dunno except maybe a real sophisticated one..

[turbosporttsi]

hmm... im not sure about the hfm voltage or not. thats what i took it as.

the scanner is not mine. it belongs to a shop and i'm not sure i am able to drive around with it.

the LT sensor values were pretty constant IIRC.... i dont know exactly what function they have. i just wrote down what i saw.

let me know what else i can try.

i should be going to RMS for tuning in like 10 days, but im trying to get a better idea of the problem. i'd feel pretty stupid driving 2 hours one way to finally get to RMS and find out that something simple is wrong.

[josemg]

I agree with dinans3m3. Your Long Term Fuel Trim from your sensor 1 is reading way different from your sensor 2. This is a trial and error situation where you need to troubleshoot, replacing, swapping sensors to achieve your problem. I personally swap the sensors (I suppose that they are the O2 and they are 2 for each manifold); front with front, rear with rear and check for the same results inverted. Also check for exhaust leaks, which can make your sensors reads erratic. Leaks in your exhaust will suck oxygen into the exhaust pipes and alter your O2 readings.

[paul e]

First, Forget the stft values, but pay attention to the LTFTs.

LTFT values dont dither, ie fluctuate sharply the way STFT values do.. And there should be no difference at idle or at cruise, or under boost, as these values tend to persist, and only will change after awhile. In fact, you can get valid LTFT values without even turning the engine on; just put ignition in position II and take your reading.

I would assume that the LT sensor 1- -8.6 is the LTFT for bank 1, and the LT sensor 2- -0.8 is the one for bank 2.

Its pretty unusual to see this big a discrepancy between your banks.. In addition, the -8.6 is a higher neg value than youd normally like to see. IT means that the mixture is rich by 8.6%, and the ecu corrects for that by removing 8.6% of the fuel, hence, the negative value.

But of equal concern is, why is there such a large disparity between the two banks? Perhaps one of the O2 sensors is going bad? As Josemg suggested, how bout swapping your two O2 sensors, and see if the LTFT values follow the sensors... But remember, its going to take you probably over 35 miles of driving for you to reach some kind of equilibrium wrt your adaption values so you can even make a proper evaluation.. good luck.

[marc1119]

Did you check to see if the O2's are crossed?
those 99's..make me think that perhaps this is so...:)

[turbosporttsi]

no, i didn't marco. my buddy and i specifically remember marking them and making sure when we replaced them. by 99's do you mean the rear sensors? it seems to me that sensor 2 would be the downstream O2s. if it is, it doesnt matter if they are crossed, as they have no bearing on fuel trims. i will double check the front O2s hopefully today, just to make certain. hell, i'll just swap the connectors and see what happens. that should tell me real quick.

josemg- i shouldn't have to swap sensors around. the fronts are new. like, very new. the CEL only started after the s/c install, not after the O2 replacement. and i have looked around the headers looking for signs of leaks, but didnt see anything.

[marc1119]

no, i didn't marco. my buddy and i specifically remember marking them and making sure when we replaced them. by 99's do you mean the rear sensors? it seems to me that sensor 2 would be the downstream O2s. if it is, it doesnt matter if they are crossed, as they have no bearing on fuel trims. i will double check the front O2s hopefully today, just to make certain. hell, i'll just swap the connectors and see what happens. that should tell me real quick.

josemg- i shouldn't have to swap sensors around. the fronts are new. like, very new. the CEL only started after the s/c install, not after the O2 replacement. and i have looked around the headers looking for signs of leaks, but didnt see anything.

OOPs sorry..those were voltages.....my bad

The idling HFM voltage of 2.0V seems high..Are you running a scaler?

[dinans3m3]

First, Forget the stft values, but pay attention to the LTFTs.

LTFT values dont dither, ie fluctuate sharply the way STFT values do.. And there should be no difference at idle or at cruise, or under boost, as these values tend to persist, and only will change after awhile.

I would assume that the LT sensor 1- -8.6 is the LTFT for bank 1, and the LT sensor 2- -0.8 is the one for bank 2.
.
Wasnt sure what the LT sensor was recording? In dithering i meant the STFTs. What were the ranges that they accumulated (highs and lows) while you inspected them. Now LTFTs can change imediately depending on what chip you have. I dont recall what chip i had but whether it was the 28xxxF or 29xxx one of them reset adaptions every time i turned the key.
I dont think you were reading HFM voltage rather mass of air at idle. I agree 2.0 at idle i rather high. You would be maxing out that sucker in no time. All in all your tune may just be out of whack. One of my early RMS tunes projected fuel trim codes as well as O2 adaption limit codes, simply by doing a revision they never appeared. If you can wait it out and get a revision for elimination processing it could be that simple. Then again that could not resolve anything but its well worth it to start eliminating factors without spending money left and right.

[paul e]

Wasnt sure what the LT sensor was recording? In dithering i meant the STFTs. What were the ranges that they accumulated (highs and lows) while you inspected them. Now LTFTs can change imediately depending on what chip you have. I dont recall what chip i had but whether it was the 28xxxF or 29xxx one of them reset adaptions every time i turned the key.


Really? I always thought that what governed how LTFTs functioned on cars of his vintage was the OBDII Spec!! IF the specific ecu is obdii compliant, then I cant understand how its going to reset the value every time you reinitialized... doesnt make sense when you think about it.... does it? Not unless you believe that every ecu writer can do fuel trims however they want, and the OBDII spec be damned.. IVe never heard of an OBDII ecu that resets the fuel trims upon startup.

[turbosporttsi]

no, i'm not running a scaler. i was told they're not required for the later RMS kits. i have no clue what values the scanner recorded for the HFM. :P

i wrote the values in the first post.....regarding the STFTs. i just jotted down a couple that popped up. that was approx the range at idle.

update...... after readjusting the thermo intake yesterday....i got the CELs again today. :(

[dinans3m3]

Really? I always thought that what governed how LTFTs functioned on cars of his vintage was the OBDII Spec!! IF the specific ecu is obdii compliant, then I cant understand how its going to reset the value every time you reinitialized... doesnt make sense when you think about it.... does it? Not unless you believe that every ecu writer can do fuel trims however they want, and the OBDII spec be damned.. IVe never heard of an OBDII ecu that resets the fuel trims upon startup.
Odd isnt it? I sent out my ECU with outrageous 12% LTFTs to Marco to see if something was up with just my car. Well when he put it in the LTFTs at his house were only 1-3% after 20 miles or so. Then he sent it back to me. After putting it back in my car i immediately put in my car turned the key and the magical 0% LTFTs displayed. I then drove 30 or so miles and like usual it moved upwards into the 12% zone again. Ok so the following day i started the car and he LTFTs were zeroed out. Never complained about it but i couldnt get a consistent memory till i got another revision using the less sensitive chip which never zeroed out the LTFTs.

[josemg]

Is there a possibility that the sensors were twisted? The computer might be trying to adjust for the wrong O2 as if it was reading a post cat O2 in pre cat O2. Trying to read O2, but no O2 after the cat. After all, it will cel you because it is going out of spec and can't control the emissions.

165168

Did you benchmarked your O2?

I am meaning, tested with a voltmeter and a flame? It's the only way rather than connect an A/F gauge and check for variability of it. Using a torch, flame the tip of the O2 and check for Voltage varying intensity of the flame (flame, don't flame, flame, etc, etc, etc...). If the O2 readings fluctuates between 0v and .8v the O2 is oK, if not or if the reading keeps steady at any condition then your O2 is gone and there is your problem. Another thing is to check the wiring up to your ECU, but I think this will be a pain in the butt to check it.

[turbosporttsi]

no, that is not a possibility. the rear and front o2 sensor wires dont go near one another.....connector-wise.

plus i think that would throw a different code.

like i said. the CEL started coming on AFTER the S/C install. not after the O2 install. so they should be fine.

i think the only real options for fault are the tune or the S/C plumbing. they are the only variables.

the injectors are not because i get codes thrown for both banks every time, and the fuel trim readings between the two banks are not even similar.

what do you think?

[paul e]

Odd isnt it? I sent out my ECU with outrageous 12% LTFTs to Marco to see if something was up with just my car. Well when he put it in the LTFTs at his house were only 1-3% after 20 miles or so. Then he sent it back to me. After putting it back in my car i immediately put in my car turned the key and the magical 0% LTFTs displayed. I then drove 30 or so miles and like usual it moved upwards into the 12% zone again. Ok so the following day i started the car and he LTFTs were zeroed out. Never complained about it but i couldnt get a consistent memory till i got another revision using the less sensitive chip which never zeroed out the LTFTs.

I guess almost anything is possible.. Ive heard of tuners in our market who routinely program their OBDII ecus to totally de-program the vanos... I guess if you cant get the vanos to work properly with your code, or you can seem to get better FI results without it, even though its been shown that the vanos even with FI gives Positive results when programed properly, the easier thing to do is to deprogram it... So I guess its up to the tuner to do whatever he pleases.. However, we both know that the proper way to handle trims for OBDII is that they should persist, and survive engine startup.. Trims wouldnt serve much function if you had to start from scratch everytime you started her up.. the whole idea is that they are slowly modified over time as your equipment ages, filter conditions change, etc.. Plus, LTFTs will often take over 50 miles to reach a point of relative stability... If most of your trips are 25 mile jaunts in one direction, youll NEVER get a LTFT that is meaningful!!

[marc1119]

I guess almost anything is possible.. Ive heard of tuners in our market who routinely program their OBDII ecus to totally de-program the vanos... I guess if you cant get the vanos to work properly with your code, or you can seem to get better FI results without it, even though its been shown that the vanos even with FI gives Positive results when programed properly, the easier thing to do is to deprogram it... So I guess its up to the tuner to do whatever he pleases.. However, we both know that the proper way to handle trims for OBDII is that they should persist, and survive engine startup.. Trims wouldnt serve much function if you had to start from scratch everytime you started her up.. the whole idea is that they are slowly modified over time as your equipment ages, filter conditions change, etc.. Plus, LTFTs will often take over 50 miles to reach a point of relative stability... If most of your trips are 25 mile jaunts in one direction, youll NEVER get a LTFT that is meaningful!!


Angelo's trims were "0" on his ECM when he sent it to me because his trial chip was burned on a 29F200...If you use a 29F200 chip, when you take it out of the ECM. it loses the trims..permanently that were stored in it..

So even tho it came to me with -12's in it..I put it in my car it said "0"..
Adaptation was cleared..I drove it 50 miles and the LTFT's were ~ +1 and +1.

I take it out and send it back to Angelo..it now says "0" again..Angelo has a vac/boost leak on his car..which wreaks havoc on his tune in his car..Before you know it, his LTFT's are maxxed out again..and Adaptation is now inactive..

My car had no vac leak, so the trims stayed normal with his 29F200 chip..


Moral of the story...
A 29F200 chip does not remember trims if you disconnect the battery or take the chip out...
A 28F200 chip does..That is why we al now realize that a 29F200 chip is not a good choice for our cars..But 28F200 chips are proving to be more and more scarce....

[dinans3m3]

Angelo's trims were "0" on his ECM when he sent it to me because his trial chip was burned on a 29F200...If you use a 29F200 chip, when you take it out of the ECM. it loses the trims..permanently that were stored in it..

So even tho it came to me with -12's in it..I put it in my car it said "0"..
Adaptation was cleared..I drove it 50 miles and the LTFT's were ~ +1 and +1.

I take it out and send it back to Angelo..it now says "0" again..Angelo has a vac/boost leak on his car..which wreaks havoc on his tune in his car..Before you know it, his LTFT's are maxxed out again..and Adaptation is now inactive..

My car had no vac leak, so the trims stayed normal with his 29F200 chip..


Moral of the story...
A 29F200 chip does not remember trims if you disconnect the battery or take the chip out...
A 28F200 chip does..That is why we al now realize that a 29F200 chip is not a good choice for our cars..But 28F200 chips are proving to be more and more scarce....

Nicely stated Marco. I can count on you for better informing the situation. Good thinga bout that was that teh CEL never flashed because the trims were always resetting everytime i started the car, but the problem always persisted.
Now onto the problem. I have some possible suggestions.
1) If you lean on the thermo or pull on it does it disconnect from the blower? I had that issue plenty of times. I took it off and put lithium grease on the lip and stored the thermo in my icebox overnight clamped firmly to narrow the diameter. The ehat makes it expand. So when i took it out of teh icebox in teh morning i slid it on the blower lip with quite a bit of tension. I didnt even have to put a clmap it stayed still. Putting on the worm clamp was of great ease, although you still need to apply pressure on the clamp with one hand while tightening with teh other (Marco's advise helped along with my idea). Thatw ill resolve if its teh thermo.
2) Another cuprit can be if your running the M50 manifold which tends to always be an issue somewhere along the line.
Im not doubting your install or experience just trying to help by binging up some common issues people overlook.
3) Are you running an aftercooler? MAke sure the clamps grab the TB correctly and straight rather than angled because it can miss tightening teh bottom of the TB since its an akward. Mine slipped off one time due to improper tightening down.

[marc1119]

Nicely stated Marco. I can count on you for better informing the situation. Good thinga bout that was that teh CEL never flashed because the trims were always resetting everytime i started the car, but the problem always persisted.
Now onto the problem. I have some possible suggestions.
1) If you lean on the thermo or pull on it does it disconnect from the blower? I had that issue plenty of times. I took it off and put lithium grease on the lip and stored the thermo in my icebox overnight clamped firmly to narrow the diameter. The ehat makes it expand. So when i took it out of teh icebox in teh morning i slid it on the blower lip with quite a bit of tension. I didnt even have to put a clmap it stayed still. Putting on the worm clamp was of great ease, although you still need to apply pressure on the clamp with one hand while tightening with teh other (Marco's advise helped along with my idea). Thatw ill resolve if its teh thermo.
2) Another cuprit can be if your running the M50 manifold which tends to always be an issue somewhere along the line.
Im not doubting your install or experience just trying to help by binging up some common issues people overlook.
3) Are you running an aftercooler? MAke sure the clamps grab the TB correctly and straight rather than angled because it can miss tightening teh bottom of the TB since its an akward. Mine slipped off one time due to improper tightening down.


All great advice..Angelo..You have been there..done that....:)

Now get back to the books and study!!!

[dinans3m3]

All great advice..Angelo..You have been there..done that....:)

Now get back to the books and study!!!

had a break thought i could shed some light since I've been down that road. ;)
and it not a fun road to be on. It can be very aggrevating :banghead: Best of luck , im late for class.

[turbosporttsi]

lol.... yup, it is aggravating. extremely.

ok, i dont think my thermo slips off, but i will def investigate that.

i dont have an aftercooler, but that connection at the TB can be checked out as well. i pull the discharge tube off all the time, but i guess it could be on wrong every time.... ???

and the M50 manifold shouldn't be a factor, as the problem has been going on for months and the M50 mani has only been on for a week or 2.

and i appreciate your bringing up common problems. because no matter your experience, the issue usually winds up being something common or stupid. in my case it always seems to be the latter. :rolleyes

[dinans3m3]

Did you plug off the oil air separator when doing the original install from the stock manifold?

[turbosporttsi]

i eliminated it. i used eric's (E36M3) adapter kit for the install. i had him make it so my oil seperator could be eliminated.

[turbosporttsi]

not sure how relevant this is.... but every day i drive side roads and its kinda stop and go between traffic and stop lights. i generally get a CEL with in 15-25 miles of driving.

last night i reset the CEL at a meet which is 30-40 min away, and didnt get a CEL the whole way home and then some. the 30-40 min was all freeway. i think my car likes the freeway.....

could this mean anything? help eliminate something or shine some light on something?