Long term fuel trims issues

[Kurtomac]

did my first few logs and the Ltrims are through the roof...so from what i hear theres probably a leak inbetween the maf and tbody or around an injector...well anywhere past the maf basically...discovered my air bridge on my vette was crushed slightly so i RTV'd it a few days ago and it doesnt leak at all now...i was told to spray brake cleaner all around there and around the maf and all connections after the maf and if the idle change or better yet if i logged watch fuel trims. soooo....sprayed it all around the maf...the air bridge to bellow...bellow to tbody and at each injector and where the intake meets the head....no change in idle...and i was logging this...no change at all in LTrims.....now heres a question for you guys....I did long tubes and no cats a month or so ago....left the air pump and tubes connnected so i didnt have to take off the intake manifold to get the air tubes out....now the car was in closed loop...does the air pump run at all in closed loop?....if the air pump keeps running due to the fact that i have no cats and it never senses the cats are lit off so it remains on and pumps air into the exhaust...maybe my 02s are seeing this extra air and pumping in more fuel via the LTrims....also i reset my fuel trims before doing this....on up they went....BUMP guys thanks for your help looking to fix soon....Need be ill take out the AIR system and put block off plates on the headers

[joecar]

The AIR pump should run shortly after cold startup and runs for a specified time, and then shuts off.

You could pull the fuse and the relay for the AIR pump motor... and/or you could disable it in the tune.

But, when the AIR pump does not run, it's plumbing accumulates condensation, so you either have to pull the hose and tape off the pump, or remove the pump...

(the condensation flows down the hose into the pump and shorts the pump motor if you ever reactivate it -> dead pump motor plus blown fuse).

Cheers,
Joe

[Kurtomac]

any idea about the Ltrims issues?

[dfe1]

any idea about the Ltrims issues?
Not knowing what you changed when installing the headers, the air pump system could well be the problem. Although the pump only runs after start-up, prior to the system going into closed loop, (it doesn't know or care that you've removed the converters) it could be providing a path for air to enter the headers. If your long term trims are way off, you either have a serious calibration problem (bad data in any number of tables) or an air leak, somewhere in front of the oxygen sensors. The air pump on a C5 is electric, so all you have to do is disable it in the tune. However, I would disconnect the lines connected to the headers and block-off the openings with a plate. What air tubes are you referencing taking out of the intake manifold?

[Kurtomac]

the only change i made was LT's and Offroad x pipe....the pass side air tube runs behind the intake....dont see how it could be a path for air since they are hooked up like stock....since i added headers and theres increased exhaust flow....no keep in mind i havnt tuned it yet, just deleted rear 02s and cat protection crap and whatnot...now if i did the auto ve and tuned the maf accordingly would that possibly help my ltrims?....also keep in mind i got my tuning stuff around the same time that i got my headers on so i dont have any pre header logs so this could have already been a problem

[dfe1]

The first thing you have to do is determine whether you have a tuning or mechanical issue. Every time I've gotten involved with a car that has a really strange problem, the cause turns out to be something undocumented or a component that wasn't supposed to be what it actually was. In the case of fuel trims being out of whack, if the PCM had never been reflashed, (you know it hasn't?) I'd check fuel pressure and injector size-- actual versus claimed flow rate. Are you sure the injectors are the original ones? If you know they're not, what flow rate are they supposed to have and does that match the data in the IFR table? Is the MAF stock, or has it been modified? Make sure all the mechanical part are operating properly before you alter the tune.

[redhardsupra]

The first thing you have to do is determine whether you have a tuning or mechanical issue. Every time I've gotten involved with a car that has a really strange problem, the cause turns out to be something undocumented or a component that wasn't supposed to be what it actually was.
AMEN! i couldn't agree more

[Kurtomac]

The first thing you have to do is determine whether you have a tuning or mechanical issue. Every time I've gotten involved with a car that has a really strange problem, the cause turns out to be something undocumented or a component that wasn't supposed to be what it actually was. In the case of fuel trims being out of whack, if the PCM had never been reflashed, (you know it hasn't?) I'd check fuel pressure and injector size-- actual versus claimed flow rate. Are you sure the injectors are the original ones? If you know they're not, what flow rate are they supposed to have and does that match the data in the IFR table? Is the MAF stock, or has it been modified? Make sure all the mechanical part are operating properly before you alter the tune.


cars been tuned before (ie spark table adjustments(both low and high tables are identical...im going to change) fans and skip shift have been change)......checked the ve table with stock...same...check IFR table...its stock....per the previous owner he just did vararam....he didnt know it had been tuned until i downloaded the tune...ive flashed it with fan changes and turning off a few codes...the car only has 12k mils and appears to be stock....everything in the engine bay looks like it hasnt been touched...usually you can tell (i had a HC TA before this).....had the intake tract off the other day trying to see if i had an intake leak....it appear stock 85mm maf...no screen...

[joecar]

The first thing you have to do is determine whether you have a tuning or mechanical issue. Every time I've gotten involved with a car that has a really strange problem, the cause turns out to be something undocumented or a component that wasn't supposed to be what it actually was. In the case of fuel trims being out of whack, if the PCM had never been reflashed, (you know it hasn't?) I'd check fuel pressure and injector size-- actual versus claimed flow rate. Are you sure the injectors are the original ones? If you know they're not, what flow rate are they supposed to have and does that match the data in the IFR table? Is the MAF stock, or has it been modified? Make sure all the mechanical part are operating properly before you alter the tune.Ditto. :cheers:

[Kurtomac]

ok well i got a new stock air bridge....so if there was any leak in my rigged slightly crushed at the clamping point stock one...it will be gone...im throwing a bank 2 sensor 1 slow response...going to try new 02 sensors....after this is done and Im still logging high LTRIMS....would i be safe to start tuning? Will be using a LC1 still yet to intall
stock injectors so i dont need to change the IFR table
stock cam so no idle tuning will be needed
might tweek my timing tables
so i should start by tuning my Main VE table in SD
Reenable my MAF and tune the MAF strictly in MAF Mode....
then hit a dyno and spark tune?

[Kurtomac]

btw would the bank 2 sensor 1 slow response cause my ltrims to go wayyyy positive? Im thinking all this oils and crap in the headers after being welded at the factory on initial startup could have F'ed up my Sensor
btw this is for an 02 Z06

[Kurtomac]

ok i posted 3 times...im sure nobody wants to read back so here are all 3 at once

ok well i got a new stock air bridge....so if there was any leak in my rigged slightly crushed at the clamping point stock one...it will be gone...im throwing a bank 2 sensor 1 slow response...going to try new 02 sensors....after this is done and Im still logging high LTRIMS....would i be safe to start tuning? Will be using a LC1 still yet to intall
stock injectors so i dont need to change the IFR table
stock cam so no idle tuning will be needed
might tweek my timing tables
so i should start by tuning my Main VE table in SD
Reenable my MAF and tune the MAF strictly in MAF Mode....
then hit a dyno and spark tune?


btw would the bank 2 sensor 1 slow response cause my ltrims to go wayyyy positive? Im thinking all this oils and crap in the headers after being welded at the factory on initial startup could have F'ed up my Sensor
btw this is for an 02 Z06


question...the maf measures grams of air..and sends a freq in hertz to the pcm so does that kind of go to the PE table and thats what commands afr from the maf?....been doing a lot of reading this stuff is starting to make sense
if this is true...why do we tune the maf....the maf incoming reading shouldnt be different....just the amount of air....if we need to adjust AFR then why wouldnt we just tune the pe table b3618?....just poked around the tuning software some more...whens the 3605 used?

[dfe1]

I think you're starting to wander off the path of righteous data acquisition and table references. The MAF table relates HZ to grams per second and in a perfect world, what you see is what you would always get. But any number of factors (intake manifold or throttle body configuration, trick-of-the-week air cleaner assemblies, camshaft profile) can skew the MAF reading. Accuracy of the PE table is largely dependent on accuracy of MAF input and injector flow rate. Is you command 12.9:1 air/fuel, and the engine is using more or less air than is indicated by the MAF, you won't get 12.9:1 on your wide band. Obviously the same is true if injector flow rates are incorrect. It's important to get the base reference table data accurate so that all the computations based on that data is correct. If you're above 4,000 rpm, or wherever the switch point is to MAF-exclusive control, and your injector flow rates are correct, actual PE air/fuel ratios will match commanded only if the MAF table is accurate. Hope this helps.

[Kurtomac]

I think you're starting to wander off the path of righteous data acquisition and table references. The MAF table relates HZ to grams per second and in a perfect world, what you see is what you would always get. But any number of factors (intake manifold or throttle body configuration, trick-of-the-week air cleaner assemblies, camshaft profile) can skew the MAF reading. Accuracy of the PE table is largely dependent on accuracy of MAF input and injector flow rate. Is you command 12.9:1 air/fuel (stupid question where is this commanded ive hinted around in my previous post PE table or what?, and the engine is using more or less air than is indicated by the MAF, you won't get 12.9:1 on your wide band. Obviously the same is true if injector flow rates are incorrect.So if my injectors are stock leave this table alone? It's important to get the base reference table data accurate so that all the computations based on that data is correct. If you're above 4,000 rpm, or wherever the switch point is to MAF-exclusive control, and your injector flow rates are correct, actual PE air/fuel ratios will match commanded only if the MAF table is accuratelost me a little here..... Hope this helps.


help the dumb please

[Kurtomac]

ok maybe i need to have it broken down to me at a lower level....why do we tune the maf to get the desired AFR...why dont we tune the PE based on RPM?....looking at my logs (when im at 100% tp) at a given rpm commaded AFR in my log matches the PE based on RPM....im sure this might make more sense once i get my lc1 in and check out commanded vs actual....is that what were tuning the maf for? to get actual and commanded to match and then adjust PE from there?

[joecar]

The PCM's operating sequence (simplified, no doubt):
1. the PCM calculates the airmass from the MAF (B5001) and/or VE (B0101),
2. the PCM determines the commanded AFR from:
- in CL: stoichiometric AFR defined by B3601,
- in OL: the richer of B3605 CFOL or B3618 PE (when PE enables).
3. the PCM uses airmass/AFR to calculate fuelmass,
4. the PCM looks up the injector flow rate from IFR (B4001),
5. the PCM uses fuelmass/IFR to calculate the injector pulse width.

You tune the MAF table (and/or VE table) to so that the PCM calculates the correct airmass (i.e. reflecting the true actual airmass)...

If the measured AFR equals the commanded AFR (i.e. BEN == 1.00) then the MAF is reporting the correct airflow allowing the PCM to calculate the correct airmass...

This means that the AFR you commanded is the AFR you see produced...

This is irrespective of the AFR you want to run.

You could just ignore the BEN's and simply look at the measured AFR and tweak B3605/B3618 until your saw suitable AFR's at WOT (irrespective of the commanded AFR or the MAF/VE)... but you still want part throttle "quality", and you want your tables to be a "true" indication of what the motor is doing (i.e. true airmass, true IFR), and you want your tune to work under all operating conditions.

The stock IFR may or may not reflect the true IFR (yes, it comes like that from the factory).

Oh, an airleak in the header (from heads and as far as 18" downstream from O2 sensor) can "influence" O2 sensor... or it could be fouled/bad.

Cheers
Joe
:cheers:

[jfpilla]

Joe,
Very nice! Thanks.
Joe

[joecar]

Joe,
Thanks;
I edited it a little to make my wording clearer; if I missed something let me know. ;)
Joe.

[Kurtomac]

awesome....did some more readling...everythings making sense

[Kurtomac]

anybody got a nice writeup for tuning the MAF...went over the AutoVe Tutorial again.......Do you just Reenable the MAF and make it strictly maf based fueling?....and the ben should equal PE table?

[dfe1]

As usual, Joecar did an excellent job of explaining things. but put his explanation aside for a while, and let him get back to counting lost bolts. While he's off counting, you ("you" being Kurtomac) need to start thinking more about your good friend the internal combustion engine, and less about Mr. Semiconductor and his band of lost electrons.

Your engine doesn't know and doesn't care why it receives fuel and air in the proper ratio-- it just feels good about itself and behaves properly when it gets about 14.7 parts of air for each part of fuel when it's loafing along, and about 13 parts of air to one part of fuel when it's being asked to deliver maximum power. By reflashing ECMs and PCMs, what we're trying to do is assure that these ratios are achieved. Alterations to original calibrations are required either because they weren't accurate enough for our liking, or because the engine has been modified. BEN is simply the difference between commanded and actual AFR. Ideally BENs should be 1.00 under all operating conditions, but alas, we don't live in an ideal world, so they rarely are.

PE (power enrichment) is the commanded, and hopefully actual AFR when an engine is operating under heavy load-- like wide open throttle. High load conditions create higher than normal combustion temperatures and richer mixtures are required to keep these temperatures under control.

When you go through the AutoVE process, you disable the MAF and tune the VE table. When you re-enable the MAF, you'll probably find that AFRs weren't what they were when running in speed/density mode (MAF disabled). That tells you that the MAF calibration isn't quite right, so you alter the MAF table as required.

As an example, if you had gotten the long term fuel trims to about -2% in speed/density mode, and found that they were +10% when you re-enabled the MAF, that's an indication that the MAF calibration is off. At wide open throttle, fuel trims don't apply, so if the MAF table wasn't calibrated accurately, you'd notice that the wide band O2 sensor is reporting different AFRs depending on whether you're in MAF or speed/density mode.

We now return you to your regularly scheduled program.

[Kurtomac]

Did my heads/cam/Ported FAST 92 and LS2 tbody swap....went to 36 lb injectors...changed my IFR table....Installing my Wideband saturday but as of now my LTRIMS are still sky high...+23 and +25....sound like it just needs tuned to get the ltrims back +-5%? Or are those abnormally high...they were that high before the swap