Well its been awhile since I've posted on here, haven't even touched my tune in 6 months without issue, been concentrating on tuning my turbo R1.

A couple days ago, cold start was pretty bad. Started up ran ok for a few seconds, then idle start to hunt, bad, until you give it some gas, clears up. No misfires at all. As soon as you start to drive its fine from then on until cold start again. Today as soon as the closed loop kicks in i watched the interceptor have a very lean lambda until STFT corrected it.

Another issue, at idle, the STFT is more than what i like, i'm usually -5 or -5. LTFT is always -2 or -3. STFT is going nuts at idle either very neg or very pos (around 10-15% or more occasionally) until car is warmed up completely. Looks like the crazy swings don't happen long enough to affect LTFT bc its not changed with the crazy idle trims.

Cruising, and WOT have no issues, STFT are good and LTFT is -2. Just right around idle STFT goes crazy.

Now i can and i will log omw home from work today, but not having to touch the tune for so long, I'm thinking, what changed..... nothing that i can think of.

One possibility is that the one step colder plugs have fouled which i will check this weekend.

Car has 134,000 miles on it, valves may need cleaning too, never been done.

Relevant engine mods:
EFR6758
ZZP FMIC
ZZP upper CP
K&N short ram
alky/water inj
catless
one step colder plugs (approx. 10k miles on them)

 

Has anyone scoped the valves that has water injection?

Seems like they should be clean but they don't have the cleaning ability like gas does.

Also check your purge valve selenoid on the intake manifold. Mine is causing fuel trim issues because it's going bad.

 

purge valve was brand new from zzp beginning of the year, i thought that it would be unlikely for it to go bad that fast. I'm gonna try logging it and see what is up and if anything looks fishy.

 

Just did a log during lunch, everything is perfect and it started fine..... GD sometimes i hate this car. STFT is now just a bit too rich only at idle taking out -7% ish. I'll keep watching it to be sure, but I'm confused now. Damn cobalt. Love hate relationship definitely. Can't wait until next Aug., new engine to repalce the old beast. Then drive it until it dies bc i'm not getting rid of it.

 

With all of this said, the STFT should always be swinging.

As much as i tried to get my STFT perfect, it's the nature of the beast for it to swing with a spike to +-10% every once in a blue moon. As long as your LTFT isn't way off you will probably be fine.

 

Its been crazy again today, cold start was very lean when the wideband finally warmed up while it was stumbling (like a cammed idle), so in open loop at idle it was a lean stumble. Even until it warmed up while driving i was seeing +18% STFT, thats not cool. LTFT even climbed to +6%. Funny once it warms up, its normal for the most part, an occasional stupid large STFT swing at idle but instantly corrects itself.

I'm leaning towards a boost leak possibly or tank vent going bad since evap purge was just done this year.

Something is defenitely off, this car has been +3% LTFT for half a year now with minimal STFT swings and no rough starts, ever.

 

I'd start leaning to small boost leak. Do a pressure test on the system.

Make sure to check the intake as well. Clean your intake. Clean the MAF sensor.

Check you evap purge.

 

Is the engine missing with the idle also? Or just crazy STFT?

 

Pressure test I'll do this weekend definitely. Just lean on cold start causing the issue, no misfires recorded. If i bump the idle up on cold start theres no issue, but i don't like band-aiding things. Checked the evap purge just now, its fine, and cleaning the MAF in a few here at work.

I wonder if the ECU vents the purge solenoid on cold starts, the only other thing i can think of with that is the actual tank vent solenoid which has never been replaced. Car is at 134k miles.

 

But generally you get evap codes after a period of time. So if you don't have any then I'd say it's not those.

By your last comment it seems like tuning would fix it but that wouldn't explain what has changed. I see the temps in Houston are still warm so it's not cold air causing it.

 

Whats your cold start idle RPM set point?

 

was stock idle table, I've since played with it since this started upping it to 1400 until it gets to about 100* temp, then gradually down.

Used to get the low flow evap code, replaced the purge valve on the intake, never had another issue until now.

 

Just checked to see if any codes are pending in the ECU. Yup

P2188
Fuel Trim System Rich at Idle

I'm pretty confident this is a vacuum leak, where the numbers are terrible at idle and improve as rpm increases, cruising and WOT are right on the money no issues.

 

Plug the evap system and see if it corrects the issue. Disconnect the line and cap the solinode side

 

I'm going to try that next.

Progress....

I spent last night at the shop pulling plugs, did a boost leak test, looked for anything suspicious.

Came up with nothing, absolutely no air leaks anywhere. Plugs which are one step colder look great and very consistent.

I did a ton of logs and some pulls. Re-dialing in the MAF curve, I've got it down to -0.8 LTFT, I'm watching it at idle and it's prefect, then out of the blue, the STFT goes to -19% for about a minute, then settles back down around 0.8% again, then it'll stay like that until i start going again then come to a stop, and it won't do it all the time. Everywhere but that funky idle BS is perfect or darn near now, and I'm not even done with tuning it yet. I don't get what the ECU is doing during that time, maybe its venting the tank? IDK, but I'll try block off the evap lines and see if that changes anything, if that keeps it steady, then I'll get a new tank vent and intake solenoid.

 

Yeah try the evap system. Glad you got the LTFT dialed in. That tends to help a lot.

 

Has anyone deleted the evap system on an LNF yet? I think I might attempt this since I'm an engineer and have a shop at my disposal.

Cold start this morning was fine with the new higher cold idle table i made yesterday too.

This was from another post and explains what I've been thinking the cause is:

"The solenoid is quite hollow inside the top half of it, in addition to not having a check valve until halfway up the evap line in the engine bay. That means that there's that much possibility for that volume to be backflowed and then pressurized when you go into boost. Higher boost levels or quicker hits of boost would seem to make it more prone to breaking.

There have been times when I turn off my car and a sudden spurt of air pressure was released by it a few seconds later. It also explains why we have sudden AFR wobbles with it sometimes. It builds up pressure between it and the in-line check valve and then releases it along with air-fuel vapor mix the next time it opens, causing the engine to get more air-fuel vapor then it bargained for.

If there's a way to install a check valve between the IM and solenoid, I believe the problem would be solved."

 

As far as I understand, you pull the line off the top of the selenoid, put a vacuum cap over it. For the other end of the line you can put a filter or a cap on it. Then you would need to delete the evap codes from showing up as a CEL.

I need to do it but haven't. I can tell you for sure that the STFT's are much better when that damn thing is unplugged. Very obvious when unplugging it to tune fuel trims.

 

That was going to be my suggestion also.

I would think though if you had a vacuum leak at idle that's causing trims to go crazy that it would be even worse when under a load and even worse than that when boosting.


Cleaning the MAF is the #1 thing I would do before touching anything else though.

 

So far:

Cleaned MAF
Boost leak tested
Vac leak tested
Checked plugs
Retuning the MAF curve
Plugged the EVAP solenoid and turned off the MIL codes


Taking the EVAP system out of the loop defintely made the car feel better and trims are much more consistent but on the long trip this morning, trims were awesome, see pics below. Only one hiccup this morning where STFT dumped to -15% then climbed back to perfect again shortly after at a stop light at idle. Other than that I don't know what else to check. Cold starts are fine now. I guess its fixed? Still boosting 26psi and the car is just ridiculously fun.

On boost trims are pretty much 0%, idle and cruising its around +/- 5% STFT, haven't even touched the MAF base multiplier table yet, so this should be pretty dialed in after tonight.

Last night:




This Morning:




EVAP plug i made:




Fun boost leak testing lol:

 

Well, just had another thought and i was right.

My alky injection kit. Haven't really tested it in about a year, never had issues with it. But i decided to pull it from the lower CP and see how well it sprayed or if it stuck causing rich spikes.

It dripped but didn't spray. The gd injector check valve was sticking partially open when the pump activated and dripped. I'm guessing that caused my rich spikes during high vacuum if it was dripping and stuck, plus my overall lean condition.......
****.... lol

I replaced the swelled up Oring inside the check valve and its good again. The alcohol must've done that over the 3 years its been on the car.

 

Yeah, thought it was good after logging today, was going to make the final trim adjustment to the base multiplier table.

Sat at idle for a few minutes when I got to work, and the STFT just tanked.... Stayed at -30%. Theres something else wrong, maybe sticking injector or something. I don't know what else to do or try, I'm out of ideas.

Seems to be happening after pulls at idle, I wonder if the meth is still sticking, I'll try plugging the alky injection and try again, if that's not it i'm leaning towards injectors.

 

How much is the o2 sensor for that car? If they're not too expensive it might be worth replacing it.

You can see it's trying like hell to pull fuel but still sitting at 12.9 afr at idle.....

Also your vacuum looks on the low side...I'll check some of my logs and see where I idle at.

Actually the O2 thing wouldn't make any sense. It would also act up in other areas on your tables......

I looked at my logs, i have not logged any vacuum so I can't help there.

 

O2 sensor is about a year old. Hell the ECU is only a year old too lol. Last one fried the O2 sensor circuit and caused all sorts of weird stuff but many error codes. I don't think thats it this time though.

I have tried everything i can think of. I'm convinced its an injector sticking. At idle it'll either be perfect one minute, +20% the next and -15% the next, then back to perfect. It varies each day too. What I'm doing now is running an entire bottle of lucas injector cleaner through the system to see if it clears up. Its starting to make a difference after one tank so far. We'll see after the next few tanks how it goes. If no improvement, I'm pulling the injectors and having a look at them.

Since staring the fuel treatment, I haven't had any issues like before where it would stick at -30%STFT at idle. For the most part its been much more stable, onlt the occasional a bit lean then fine or a bit rich then fine now too. Much better though.

Under load the trims are spot on.

 

THREAD REVIVAL.....

New built LDK, new opels, new everything. Same STFT issue and cold start problem occasionally. Got a p2188 this morning and my fuel trims never seem to want to stay dialed in after tuning them perfectly, so something is out of whack. No boost leaks, all sensors are new (<1,500 miles) I was reading that it might be the HPFP crapping out, it does have 150,000 miles on it, i swithced it from the LNF to the LDK thought it was fine. I'm going to get a low mileage used one for cheap from Mongorat to see if that the issue.

Checking logs, didn't notice before but as soon as the wideband and goes into closed loop, it's correcting -12 to-20 right off the bat each time low 12s to mid 11s afr then flattens out.. Attached is the FF. Keep in mind this maf curve tune was dialed in 2 days ago for the billionth time and keeps changing, has to be something mechanical and the hpfp is the only thing left over from the other engine.


edit addition:

after work i didnt didn't touch the tune, just cleared the cel and logged coming home and the trims are near perfect lol. Still got a low mileage hpfp from Jeff anyways.