Even right after cat warm up mode is done it idles a tad rough until it warms up. Maybe just the nature of the beast but I am trying to smooth it out on my car.

 

When my car was new, you could hardly feel the idle. I remember taking note of that and how smooth the engine was. Recently I was having a vibrating idle, especially when cold but also noticeable when warm too. Sometimes my RPM would fluctuate at idle when coming to a stop (when I hadn't been idling for a while and AFRs were settling down).

Since solenoid disconnection, the vibrating idle is mostly gone and RPM fluctuations are gone. My guess is the ECU only allows the solenoid to open he valve when you have a fair amount of vacuum in the intake manifold, so that explains the AFR fluctuations at idle and vacuum. Once I got into light vacuum or in boost, the AFRs were much more consistant.

Thanks for the $.02. I don't know what I think about this, since it's basically saying that if somebody's purge solenoid simply goes out on its own then the engine could knock and burn itself up.

I haven't been having any knock/stumbling like I was having with it plugged in, so hopefully this'll get me by until I can get it fixed and/or get more information.

So far my wideband has been working fine and showing promising results. It makes sense that fuel trims would zero out if it has no O2 reading to go off of. It's probably running off of tables in open loop mode. My friend Pyros777 actually tuned the VE on his LSJ to run completely without his O2 (something that was very cool and helped smooth out open/closed loop transitions, but probably hard on the car to do and not good if something changed or happened). The LNF apparently works differently, with dynamically changing VE tables.

I'll be saving my logs tonight so if anybody is interested in them I'll shoot them you all's way or post them up somehow.

 

What was the variation in your afr while cruising?

 

Usually low 11s - mid 17s, though in some cases I got as low as 9 and as high as 18 (RPD won't show higher than that). It would be somewhat normal and then suddenly flip out, usually going way rich and then way lean, and then returning to normal, all in about three seconds. This would make sense if fuel vapor was released. It'd go rich and then the ECU would complensate and pull fuel... and then the fuel vapor would be cut off... and the ECU then found itself way lean and had to add fuel again.

Now it is 14.5-15.1, in some cases going as low as a steady 13.9-14.2 at a stop (probably for cat enrich) and high as 15.4 for a split-second when suddenly off the throttle.

Made a huge difference.

 

Wow holy **** that's bad lol.

 

needs some idle maf trimming done. I'm having that problem, but not as much of a variance at idle (go from (13.8-15.2), timing adjusts with it as well.

I'm thinking it's turbulence with the CAI (didn't happen with airbox mod and KN). Gonna probably try to seal up that fog light hole on the passenger's side.

 

When I cruise it's generally 14 to no higher than 15.5 very very occasionally dipping to 13.8 when I step on it very lightly.

 

What would acually casue this?

Intake? Catless DP? High Flow Cat? Bad Gas Cap?

I know I have pulled an evap code before, and just tightened the gas cap, and 7 cold starts later it was fine. Now I have one every 3-4 days. I clear it and it is fine, until it comes back. I noticed once I tripped it, my car seemed like it lost some power. What is the common denominator?

 

Evap code coming back over and over ended up beeing my HPFP+Purge. She have a hard time starting sometimes when you get gas?

 

It stalled once at the gas station, and thats because I didnt let the fuel pump entirely kick on. Other than that I have only had trouble during early morning start up. That has been discussed alot on here though. I had received a CEL code once when I was stock for the gas cap (not sure if this code is the same one as this one). Once I added the bolt-ons (exhaust, catless downpipe, hot pipe, intake) I have tripped the CEL 3 times now. The code I trip is a EVAP High Flow Purge.

I pulled the sensor wire and within 2 minutes I received a different code for Solenoid Error. I took off my purge solenoid, blew it out, cleaned the residue off, and checked my lines going back to the canister and could not visually see anything nor could I tell of any pressure leaks from the hose going to the solenoid, since it pops off its easy to check. I snapped the sensor wire back into place. I cleared the error code, and as of right now no codes, but I have only driven like 5 miles since that.

I imagine mine has something to do with recent modifications (more than likely intake, although I had not tripped it, until I put on my catless downpipe and exhaust, which was about 3-4 days later, then I tripped it that night), or the faint gas/exhaust I smell from time to time inside the car. I figured that was from the catless downpipe though, and it was just traveling back in the car when the fumes hit some down wind.

I am currently lost, and all I know is I pop the high flow purge code (not low flow), I erase it, and it comes back like 80 miles later usually when I am just cruising or at idle.

 

Either the solenoid is bad or something is wrong with the canister. I have similar mods to you and pop no codes.

 

Rode in Stamina's car today and did some logging. Holy wow is there a difference before and after!

Without even needing a log, the difference is very notable. The idle is so steady you question whether the car is even on, and the AFR no longer swings one bit. It stayed within .008 of lambda most of the time.

Here is the before log:
http://www.gmofhouston.com/download/EVAP_Before.hpl

And here is the after log:
http://www.gmofhouston.com/download/EVAP_After.hpl

 

Thanks for helping witness, log, and posting it up Pyros. I had fun this evening.







Fun experiment for one of the HPT guys:

Open up my "before" file under HPT, and choose to view it as a table. Notice anything of interest? (Hint: Column 1, Row 14)

Let's graph that in relation to AFR and STFT and see what we come up with. I'm not yet versed enough with HPT to do it myself.

 

I have a ss/sc and my car started throwin the P0496 code just recently. Everything I research has been leading me to this purge selonoid, do you guys know where it is on the sc models? In or around the same location in the engine bay?

 

Guys, concerning the rough idle and start up, that is the nature of the beast. Coming from my boss, who has tuned more LNF's than anyone on this board, it is an effect of tuning the car. We are not sure exactly what would be causing this rough idle, but the cars really do like to be up to full operating temp before being driven at all.

That being said, I have raised my idle speed as a bandaid to this. Its most certainly not a remedy to the issue, but I don't think we have the tables to fully remedy it. I believe the true remedy to it would be in the idle air control valve (or dashpot to some) control, which we do not have access to. I think the car in its cat warmup stage is loading the car some, and is not letting enough air past the throttle body to let it smooth itself out. If we could tame the cat warmup some, I think we could smooth it out as well, but again, no tables means no remedy. And, lastly, if we could control the idle timing, I think it would help some as well.

One with more time than I might play with the timing some, reducing it greatly in the low columns, just to see if it affects the idle at all. For instance, I notice a major jump (~11*) in my timing table at 974rpms/15% load, from the previous cell. I have my idle set to idle high at 900 rpms, so the engine is probably seeing this and jumping the timing alot. These are cells that would not be used in power production, so they may be able to be retarded to help this issue.

Writing this out is making me want to try it. If you look at the timing tables, the low load areas have very high timing. I may smooth the top right corner out and see how that affects the idle.

Lemme know your thoughts.

Well, I went ahead and made the changes to the low speed, low load timing cells. I will load the tune up before I start it in the morning, and report back with the findings. I don't see this hurting performance at all, and at the cost of a smoother startup, it would be worth it.

 

Could you get a log of your car after about a day worth of driving with the purge connected? No worries if its a hassle. Also any chance of you posting up a screenshot or something of your stock/tuned MAF Base table and MAF Airflow vs. Freq table? I'm curious now.

 

Pyros is across Houston from me, so I'm not sure if I'll be able to before I get it into the dealer. I'll do it if I can though. You're needing those tables after the solenoid has been hooked up for a day or more? Just making sure I understand.

Something I've noticed is that after an ECU reset, the erratic AFRs don't happen as much, but become more common and agressive over time until reset again. It's like a long term feedback loop.

As a note, both logs were taken while on "stock" tune of the Trifecta dual tune for consistancy and availability of stock tune information (and the fact the ground was all wet from the rain yesterday). The logs were also taken back-to-back with no ECU reset and only disconnecting the solenoid and restarting the car.

 

Just thought I'd add we can't get you those tables since HPT cant read Trifecta tunes. Its a totally different OS.

 

Just would like to browse a few minute datalog after a few hours worth of driving with it hooked up. Don't worry about the base and avf tables since you were rolling on the stock tune and it's trifecta.. What intake are you running?

Heh, yeah, didn't think he was trifecta'd. I'm bad at paying attention.

 

I'm rolling on completely stock intake box/snorkel with K&N Drop-in.

My bad. I thought the new beta was able to read a few things again.

 

Stamina, you may just be a genius!

My car has developed a rough idle and stumbles at cruise and full throttle, and with my Trifecta tune, the problems were magnified. I never knew what I would get when I floored it - sometimes it felt fine, and sometimes it bogged noticeably.

I unplugged the connector to the evap purge solenoid and, while I've only driven for 30 minutes or so, the car feels like new! Very smooth at idle and full throttle. I'm going to keep monitoring it, but if this is the cause of my poor performance over the past few months, I'm going to be very happy!

 

My test findings today...

One 40 mile trip this morning, but no ill effects yet and some possible tuning benefits for us.

I found that while the sol is disconnected, the LTFT's stayed at dead zero the entire commute. May help us tuning STFT's in the future.

STFT vs load & rpm histogram shows no major change on mine, fuel trims look to be the same.

Since going with the lightweight flywheel, I have experienced some chugging in second gear if I get down to 1000 rpm in traffic and accel lightly. This is gone as well.

As reported earlier, cold start & idle/smoothness were greatly improved.

No P2237 02 pumping ckt immature code today even after a very long DFCO.

Edit: No WOT run this morning, maybe tonight if I come across the right conditions.

Code for the purge sol ckt. showed pending/immature the entire trip, no CEL yet.

 

So I got a CEL on cold start this morning, not unexpected I guess. Car still seems to be running beautifully.

Are there any long-term implications of leaving this sensor disconnected? In my head I imagine fuel vapors building up somewhere and my car exploding

 

Yeah, I got my CEL on the second start after I disconnected it (first cold start after). It's just your car saying "Hey, where'd it go?".

Shouldn't be any reason. The only reason for the system's existence is to make the Emissions ***** happy. Many racecars for instance have no such system (they can do that since they don't fall under emissions laws). The fuel tank is still ventilated regardless.

Tuning could be another story. We'll see what the HPT peeps come up with.

Fun Emissions Factoid discovered during logging:
If you had the purge valve connected during last ECU reset and disconnected it since then, then the emissions counter will still say "Evap System: Complete". No emissions strike against you for evap.

 

So with the solenoid disconnected, fuel vapors will vent to the atmosphere instead of being sucked back in to the engine? It still makes me nervous that pressure is building up in the fuel tank.

The improvement in driveability has been really dramatic for me though. I suppose my options are to leave it disconnected, or to get the problem diagnosed and fixed. Without a CEL (when the system is connected), I doubt my dealer will do anything though.