How do STFT and LTFT effect idle?

[Heat]

Hi everyone,

Sorry if this is long.

I've been doing a few things to get my car ready to convert to SD. During this process, the idle went from perfect to....well standard dsm idle issues.

I'm fairly certain it's not related to the usual suspects, for example what's listed in terry's talon guide etc.

Info: (Sorry mods are not listed in my profile, I've tried a few times but can't seem to get them set without it asking me for a bunch of personal info I'm not comfortable submitting)

50 trim @ 20psi
pte 680s
aeromotive AFPR
walbro 255
272s
OMNI 4 bar MAP sensor in place of stock MDP
Catch can installed in "race configuration" - meaning no pcv valve + vent filter on catch can
standard emissions vac lines removed
ceddy mods for engine management

TPS checks out
IAC - ohm reading within spec
BLT - holds firm over 20psi
throttle cable checks out
vac is a steady 20 at idle

The issue surrounding the idle appeared around when I installed the new MAP sensor and catch can. I say around because, the car runs fine after the ECU is reset. It's not until 20 minutes or so after ECU reset that the issue shows up (idle @ 2k rpms). I'm not 100% certain how STFT and LTFT operate although I've read up on it. STFT while the ECU is in learn mode and then it switches over to LTFT once enough data has been gathered? Speaking in regards to idle only.

I am throwing a CEL for the map sensor, will check the exact code when I get home.
I read in another thread a vented catch can with no pcv valve can cause idle issues, but this is a common way to set it up so I'm not sure how much stock I put into that theory.

Is there anything MAP related, or possibly not having a good base tune on my LTFT that would cause the idle scenario I described?

Appreciate any info or ideas.

 

[delta448]

Can you explain further the breather filter and the catch can setup?

Is there a check valve somewhere? Is the PCV inlet on the intake manifold plugged?

It sounds like you have a vacuum leak, possibly through that breather filter, but you said you have good vacuum at idle?

 

[gofer]

Since you've got ECMLink why don't you post a log too?

 

[Heat]

Can you explain further the breather filter and the catch can setup?

Yes, there is NO check valve in my catchcan setup. As per this thread http://www.dsmtuners.com/forums/articles-engine-fuel/366890-4g63t-pcv-system.html

On full race setups with no inlet pipe, crankcase evacuation options are obviously limited. Since there is no suction being applied to the crankcase, pressure will not be relieved until it exceeds atmospheric pressure plus any drops across the catch can(s), lines, and any filters. Because of this, you will want to run the largest-sized lines possible for the pressure to escape through, and use a large empty can with low-restriction filters open to the atmosphere.

That's how I have it setup. Both crankcase ports run to the catchcan with no check valve. Breather filter on top of the catch can.

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Yes 20 vac at idle.

@gofer. I will take a log tomorrow and post it. Evoscan log though, which from prior experience, doesn't get a lot of response (understandable as most people use ecm here).

Any theoretical idea on what would cause it to run fine in STFT but as soon as LTFT takes over the idle goes bad?

I'm pretty sure LoLTFT is negative which means adding more fuel at idle. Could this possibly cause the high idle? Usually sits around 13.0 afr @ 2krpms.

Just looked at one of my old logs, shows LTFTLo @ -7 and LTFTMid @ -9. That one is from July and used the default evoscan definition file. Should be similar for those values now I'd imagine, however, my more recent logs using ceddy's definition file for evoscan shows all my trims at 0

Thanks for the help.

 

[gofer]

Rather than trying to type a bunch of non sense, heres a good link about FT update points and the DSM ECU. Wiki: Fuel Trim Update Points

 

[Heat]

yeah i've read that page a few times before, in fact after I posted I just reopened it again and went through it.

ECU in learn mode (running off STFT only) = car runs fine.
Once LTFT gets it's first update = idles at 2k.

What can possibly cause this?

 

[gofer]

Is the car going into OL then too or its staying in CL and just idling high?

 

[mike96]

Fuel trims should not effect your idle like that, it should continue to idle the same no mater where your trims are at. Have you tried back tracking with your mods/tunes to see if it is something you have done recently that is causing the issue? If the problem started around that time period then it stands to reason that something you did either with a bad part installed or the ROM got goofed up on the re-flash that is causing the problem. Did you try re-installing the factory map sensor and see what that does. I don't know if you can or not on the 99ECU's but have you tried logging your ISCV steps to see what the ISC motor is doing?

 

[delta448]

Just want to say, I agree with everything mike96 posted above.

That's how I have it setup. Both crankcase ports run to the catchcan with no check valve. Breather filter on top of the catch can.

This? :

Yes 20 vac at idle.

What's your idle rpm?

Any theoretical idea on what would cause it to run fine in STFT but as soon as LTFT takes over the idle goes bad?

That sounds like an ECU malfunction or maybe an error in the ROM programming/reflashing. Possible?

I'm pretty sure LoLTFT is negative which means adding more fuel at idle. Could this possibly cause the high idle? Usually sits around 13.0 afr @ 2krpms.

Pretty sure negative means the ECU is seeing a rich signal and trying to pull fuel out. ?

Just looked at one of my old logs, shows LTFTLo @ -7 and LTFTMid @ -9. That one is from July and used the default evoscan definition file. Should be similar for those values now I'd imagine, however, my more recent logs using ceddy's definition file for evoscan shows all my trims at 0

Thanks for the help.

What ROM are you using?
Are you logging a wideband?

Post up your log, -for people who don't use Evoscan, it's just a .csv file that can be opened in a spreadsheet program.

 

[Heat]

Is the car going into OL then too or its staying in CL and just idling high?

I'll answer this the best I can.

When the ECU is reset, the car operates in what, open loop? STFT and LTFT ignored because there is no data there?

Once the car switches to closed loop, is when I imagine the problem starts. LTFT gets it's first update from learn mode and the idle changes to 2k. This happens about 20m after reseting the ECU.

After this point, none of the conditions are met to revert to open loop. TPS reads 0% and coolant stays in the closed loop range. The O2 cycles as expected.

If there is a way to know for sure which mode the ECU is currently running in let me know.

I will add that, approximately every 20 minutes thereafter, the idle does correct itself for a few seconds, drops down to 800 where I have it set, then goes back up to 2k. This would seem to coincide with a new LTFT update?

@mike96 - Right the mods I've done coinciding with the problem are the new MAP sensor and changing the catchcan setup to no longer be connected to the intake pipe for a vac source. The readings for the new MAP sensor in evoscan are dead on. I am throwing a P1400 code which is for the stock MDP but this is to be expected with the new sensor. I did try installing the stock MDP again which did not remedy the issue.

@delta

My setup is not like the diagram. I will take a picture when I get home from work. Meantime I will try to describe it. There are two barbs on the valve cover. A line from both barbs runs with no check valve in the line to either side of the catchcan shown above. That is it. It is not attached to a vac source, as I have it setup for SD.

My idle RPM is 2k 20 minutes after an ECU reset. Immediately after an ECU reset it idles at 800, where I have it set.

I think negative means it adds more fuel.

There are two definitions to use with evoscan. The default one that comes with Evoscan and the one built by ceddy to log different parameters. I have used both in the past. CURRENTLY I have the one by ceddy loaded into evoscan. I will take a new log when I get home and post it.

 

[gofer]

This might seem out in left field but let the car idle until it makes the jump to 2k, when it happens grab your 10mm socket/ratchet and loosen the two bolts on that hold the throttle cable to the intake manifold. I've got a feeling the cable might be a tad too tight and when things warm up it opens the the throttle a bit and raises your idle speed.

While doing the above you might as well grab a log too that way we can see it.

 

[Heat]

This might seem out in left field but let the car idle until it makes the jump to 2k, when it happens grab your 10mm socket/ratchet and loosen the two bolts on that hold the throttle cable to the intake manifold. I've got a feeling the cable might be a tad too tight and when things warm up it opens the the throttle a bit and raises your idle speed.

While doing the above you might as well grab a log too that way we can see it.

I have tried messing with the throttle cable. Even when the car is cold (first fired up after not being driven 12+ hours) it immediately idles at 2000. It only idles at 800 when I reset the ECU and for 20 minutes thereafter.

I just logged it and have attached the log to this post. The file type opens in Excel.

For anyone who doesn't feel like opening it:

Idle - 1.5k-2k
FuelTrimLo -2.1
FuelTrimMid -2.3
FuelTrimCurrent -2.1
TPS - 13.3% - Is this normal? My in car TPS % displays 0 but evoscan shows 13.3%

 

[mike96]

When the ECU is reset, the car operates in what, open loop? STFT and LTFT ignored because there is no data there?

Correct. The easiest way to know you are running in close loop is to check your STFT in EVOscan. If the STFT is active and the ECU is compensating fuel than the car in running in closed loop. When the car switches from closed to open both the STFT and LTFT data in EVOscan will zero out.

Once the car switches to closed loop, is when I imagine the problem starts. LTFT gets it's first update from learn mode and the idle changes to 2k. This happens about 20m after reseting the ECU.

After this point, none of the conditions are met to revert to open loop. TPS reads 0% and coolant stays in the closed loop range. The O2 cycles as expected.

I will add that, approximately every 20 minutes thereafter, the idle does correct itself for a few seconds, drops down to 800 where I have it set, then goes back up to 2k. This would seem to coincide with a new LTFT update?

That is what sounds like is happening but it shouldn't cause any issues.The LTFT should have no effect on the idle what so ever. As the ECU compensated for fuel in the STFT if keeps track of the amount it is adding or removing and after having made a + or - correction for an extended period of time the ecu will make a change to the LTFT. It does that so that it can reduce the STFT correction. But like I said before that change shouldn't make and difference to your idle.

@mike96 - Right the mods I've done coinciding with the problem are the new MAP sensor and changing the catchcan setup to no longer be connected to the intake pipe for a vac source. The readings for the new MAP sensor in evoscan are dead on. I am throwing a P1400 code which is for the stock MDP but this is to be expected with the new sensor. I did try installing the stock MDP again which did not remedy the issue.

Well if you tried the stock MDP and the issue still persists then there is a very strong chance that something got goober-ed up when you flashed the ROM. I assume that the vacuum ports on the intake manifold and turbo inlet are sealed well enough? They should be, you said it holds BLT solid at 20PSI. When you get a chance reset the ECU and take a log. You don't need to do the entire 20 min just the min or two when the update happens. Log the following.. ISCV steps (or ISC if that what it is called in EVOscan), MDP/boost, MAF, RPM, idle switch (if that is an option) STFT and LTFT's, and whatever else you feel like and post it up. also post your ROM as well. Try Gofers suggestion as well just to rule out any physical issues.

I think negative means it adds more fuel.

Nope, Negative STFT or LTFT means that the ECU is removing fuel. Positive STFT or LTFT means the ECU is adding fuel.

This might seem out in left field but let the car idle until it makes the jump to 2k, when it happens grab your 10mm socket/ratchet and loosen the two bolts on that hold the throttle cable to the intake manifold. I've got a feeling the cable might be a tad too tight and when things warm up it opens the the throttle a bit and raises your idle speed.

While doing the above you might as well grab a log too that way we can see it.

There is always that possibility that the throttle cable is to tight. But being that he mentioned that every time the LTFT gets an up date the idle goes back to where it should be then goes back up again up again makes me think there is a problem with the ROM...

Heat, how long have you been running Ceddy mods, when exactly did you switch?

 

[Heat]

I've been running ceddy since February I believe. In July I started taking the steps to convert to SD. This is around the time the issue cropped up.

It's definitely possible I have something goofed up in the rom. I've changed the map sensor to omni 4 bar in the rom and also enabled the SD setup bits (I do not have the actual SD rom yet, this is all on the standard 1.9cMAF rom).

I guess I can try reverting to an older or unedited version of the rom to see if that clears up the idle issue. That will have to wait until the weekend though. I will also use the default evoscan definition so I can log more of the applicable parameters and post that up.

Much appreciated on the continuing help.

I have attached my current rom here. I know this is asking a lot, but if anyone feels like poking around in there, I'm willing to "return the favor" if you happen to find the problem in the rom itself.

 

[delta448]

I've been running ceddy since February I believe. In July I started taking the steps to convert to SD. This is around the time the issue cropped up.

It's definitely possible I have something goofed up in the rom. I've changed the map sensor to omni 4 bar in the rom and also enabled the SD setup bits (I do not have the actual SD rom yet, this is all on the standard 1.9cMAF rom).

I'd look at the ROM you posted but for some reason I can't seem to locate my copy of the definition file for that ROM. Ceddys site has changed a bit since I last visited it, and I can't locate anything there either.

When you say "changed MAP to Omni 4 Bar", do you mean the MDP sensor input? That sensor's input is used in conjunction with EGR. Do you still have functioning EGR on this car?

 

[Heat]

I'd look at the ROM you posted but for some reason I can't seem to locate my copy of the definition file for that ROM. Ceddys site has changed a bit since I last visited it, and I can't locate anything there either.

When you say "changed MAP to Omni 4 Bar", do you mean the MDP sensor input? That sensor's input is used in conjunction with EGR. Do you still have functioning EGR on this car?

I can upload the definition when I get home. Don't have my car laptop with me at the moment.

I forget exactly where, but

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is the screen. I think this is just for logging the SD calculations while building the SD map.

I DO NOT have a functioning EGR. It's blocked off and and vac lines are unhooked.

This should be the definition file.

Should go in:

Ecuflash/rommetadata/mitsubish/eclipse

 

[Heat]

Update:

Attached are 2 more logs including the ISCsteps.

First one is prior to reseting the ECU with the car in high idle mode.

The ISCsteps read anywhere from 94-100 (I was adjusting the BISS during this process to see if I could get the step down to a reasonable level). No success.

2nd log is after reseting the ECU.

ISCsteps go to 72-75 after the reset. Still high, but the idle is spot on. I drove the car for approximately 1 hour (not at once) after this reset before the idle decided to jump back up to 2k.

The only other difference in the log is that, the bad idle log has values in for fuel trims, whereas the log after the reset does not (obviously...).

I pulled the ISC out and re-tested it.

All coils resistance is dead on. I opened the ISC up to inspect the o-ring and interior chamber. It looks brand new (the car has low miles). With the ISC removed but attached to the harness, it operates as shown in the ISC test video in conjunction with keyturn.

Any ideas?

 

[jtmcinder]

I didn't have the same turbo, but I had the same catch-can hooked up the same way and all emissions deleted, etc. I had to move the 50Hz slider down quite a bit to get the car to idle smoothly and not shift the fuel trims. Does DSMLink still have those sliders? It was such an easy solution and it was verified by DSMLink's estimated AFR continuing to match the wideband.

 

[mike96]

I didn't have the same turbo, but I had the same catch-can hooked up the same way and all emissions deleted, etc. I had to move the 50Hz slider down quite a bit to get the car to idle smoothly and not shift the fuel trims. Does DSMLink still have those sliders? It was such an easy solution and it was verified by DSMLink's estimated AFR continuing to match the wideband.

That might work for him if he were running ECMlink but he isnt... He is using ECUflash...

OK. At first glance I would say your TPS needs adjusted... I am not sure about the 98/99ECU but I know that with the EVO ecu there is no Idle switch input so it bases idle off of actual TPS and that needs to be under 10% for the ECU to recognize that car is sitting at idle. I an pretty sure that I have read somewhere that on the 2G ECU's the TPS should also be under 10% if posible...