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air/fuel ratio + tuning question

22K views 22 replies 12 participants last post by  0lmytsi 
#1 ·
I recently installed a wideband in my car, and started playing around with tuning it. It seems that alot of people here agree that 11.5:1 is a good afr to run on pump gas at WOT. My car runs kind of lean, and I'm wondering if it is safe or not.

The car is a 95 GST, relevent mods are cone filter,fp intake, 14b turbo w/hard pipe smic +1g BOV, hallman pro mbc, stock 450cc with an SAFC2 and PLX m300 wideband to make adjustments. 93 octane fuel

During a third gear pull, turbo hits full boost by the late 3000rpm range and the car wants to run at 12.0:1 at first, then may lean out to 12.3:1 by redline. This is at 9ish psi (wastegate spring), it does roughly the same thing at 15psi, it might get .1 leaner. I can't log knock since I have a 2g, but the timing advance drops to 10 when I step on it, then steadily rises to 18 or 19 by 7000rpm. I also checked the plugs for any signs of damage and found none after several pulls at 15psi.

If I add fuel with the SAFC to bring it down into the 11.5:1 range, the car bogs and gets flat spots in the timing, which maxes out at 15* by 7k. Also to add enough fuel at 6500+ I have to set the SAFC to +19 or so, which seems to induce fuel cut.

cliffs : Car runs like crap at 11.5:1 afr, much better at 12-12.4:1, is this safe with 93 pump gas?

Any input is appreciated, thanks!
 
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#4 ·
You need a fuel pump and/or a set of injectors.

You are compensating for the AFR by having to turn up the AFC. So the ECU thinks you are seeing much more airflow than you are and is not advancing the timing to where you need it. If you run a larger injector then you'll be able to dial back the AFC, get the AFR in the right spot, but the timing will stay up better.
 
#5 ·
You will make more power with a 12 something AFR so of course it wont feel as good when you richen up the ratio, but anything leaner than 11.5 is too lean on straight pump gas....11.2- 11.4 is the best safest AFR that still gives good power from my findings with 93octane. 11.0 and richer starts robbing too much power progressively worse the richer you go imo.
 
#6 ·
When I got my car tuned in with the dyno, the person who tuned it actually found the most power at around 9.5-9.8 on pump gas. We tried a bunch of different AFR's, and the 9 range seemed to work best because of timing, knock and all that jazz.
 
#7 ·
It's not that it doesn't feel good at 11:1, it feels downright awful. The car surges like crazy, and feels like it has 75% of the power. When I zero out the AFC it runs so much smoother and give me 5* more timing..

I guess what Mike 99GSX is saying sounds about right, I plan on installing both a fuel pump and some 660s as soon as get my FMIC piping run.

I'm still wondering why I'm getting almost 20* of timing at redline with the 12.4:1 ratio though, I was under the impression that if the motor is knocking it will not advance/pull timing, which doesn't really seem to be happening? And am I really pushing the stock fuel system to its limits at 10PSI on a 14b turbo?
 
#9 ·
aworldsdeath said:
When I got my car tuned in with the dyno, the person who tuned it actually found the most power at around 9.5-9.8 on pump gas. We tried a bunch of different AFR's, and the 9 range seemed to work best because of timing, knock and all that jazz.
It probably only made more power because being that rich allowed more timing and or boost on your particular setup under whatever conditions the tune was in during the time the test was being performed.

Nobody should run around that rich, actually most cars will being knocking just because of being that rich. I know thats around factory level of richness, but 90% of us keep our pump gas tunes in the High 10, low 11 AFR range.

williillii said:
I'm still wondering why I'm getting almost 20* of timing at redline with the 12.4:1 ratio though, I was under the impression that if the motor is knocking it will not advance/pull timing, which doesn't really seem to be happening? And am I really pushing the stock fuel system to its limits at 10PSI on a 14b turbo?
I dont know why your car is doing what it is doing, you do need to make sure your fuel system is up to par though, But 12.4 AFR on pump gas is simply too lean. Theres nothing else to say about it than that.

How do you know the motor is not pulling timing, are you logging it correctly? It doesnt appear you have dsmlink, and you know that 2gs dont display knock on the logger, you have to look for any dips in the timing curve.

SAFCs have been known to increase timing advance and/or cause other wierd problems about a tune especially when you use them to hide airflow to run bigger injectors... I dont know if you have bigger injectors but what I do know is something is off with your settings, and you are way too lean with increased timing advance over what the stock map should give.
 
#11 ·
Black_ bullet said:
How do you know the motor is not pulling timing, are you logging it correctly? It doesnt appear you have dsmlink, and you know that 2gs dont display knock on the logger, you have to look for any dips in the timing curve.
Im logging with Evoscan. I would post a log, but Evoscan is utter trash for the EPROM ECU and only gives me like 5-6 samples a second, so it is useless for anything other than one parameter at a time. I'm watching the timing in real time on a graph, like I said it drops to 10 when I punch it, then steadily climbs to 19 degrees by redline.

Black_ bullet said:
SAFCs have been known to increase timing advance and/or cause other wierd problems about a tune especially when you use them to hide airflow to run bigger injectors... ...with increased timing advance over what the stock map should give.
I have stock 450cc injectors. The SAFC is zero'ed out in the aformentioned situation. What should the stock timing maps look like? 19 degrees is too much you say?

93_GSX said:
No, you shouldn't be maxing out your fuel system. If what you are saying is true, you basically have a stock setup, with stock-ish boost pressure.
Yep, it's basically stock. Which is why I'm wondering why its so lean.

Thanks for all the help guys!
 
#12 ·
You should definitely pick up a fuel pump soon, and look for a decent deal on some evo 560s. Check out evolutionm.net, I'm sure you won't have to drop more than $125, and it may be worth tossing them in before your fmic. Just a thought.
 
#13 ·
williillii said:
I'm still wondering why I'm getting almost 20* of timing at redline with the 12.4:1 ratio though, I was under the impression that if the motor is knocking it will not advance/pull timing, which doesn't really seem to be happening? And am I really pushing the stock fuel system to its limits at 10PSI on a 14b turbo?
The reason you're getting so much timing is because you are dialing back the airflow signal on the AFC (making the knob more negative) when it runs 12.4:1. The less airflow the ECU then the more it will advance the timing as long as the engine doesn't knock. You're getting away with running the car that lean and not knocking due to the low boost level.
 
#14 ·
Maintenance

Please check off the following if you have completed them:

  1. Boost leak test
  2. Checked your spark plugs/wires
  3. Checked/replaced fuel filter
  4. You are hitting right about 20 inches of vacuum at idle
  5. Perform a compression tesy
 
#15 ·
At WOT I run 22psi tapering to 16psi by redline on my 14b, My afr is 11.5:1 and my timing is set at 17 degrees, I have no knock anywhere and plan to try to reach 12:1. I have a FMIC and FRH intake manifold. I have found that the leaner I go with as much boost as the 14b is delivering, the more power I make. Timing and too much boost is a greatway to fuck your car up. Lean is mean, find your max acceptable boost level, dial-in your afr, and add timing until you knock. Or go fuel, boost, then timing. Timing is always dead last on my list.
 
#16 · (Edited)
Mike 99GSX said:
The reason you're getting so much timing is because you are dialing back the airflow signal on the AFC (making the knob more negative) when it runs 12.4:1. The less airflow the ECU then the more it will advance the timing as long as the engine doesn't knock. You're getting away with running the car that lean and not knocking due to the low boost level.
I understand that setting the SAFC in the negatives will cause higher timing advance because the ECU thinks there is less airflow. HOWEVER the SAFC is set to ZERO across the board. My car runs lean by default, if I want it to run at 11.5:1 or whatever, I have to richen it up.

So do you guys think the car is knocking even though I'm getting 19 degrees at redline? If its not, Im just going to run it how it is until I get new injectors/fuel pump. The car rarely sees over 30% throttle anyway.

Don Boosted said:
and look for a decent deal on some evo 560s.
I forgot to mention the car will be getting an Evo3 16g put on at the end of the month so thats why I'm going with something bigger than 560s. I plan on runing at least 20psi on that and I don't want to be seeing 95% IDCs right off the bat lol.

Laser-Fist said:
Timing is always dead last on my list.
I would if I could man, tuning with an SAFC sucks and I don't have the cash (or a laptop) for DSM link. I'm only shooting for 300-350hp to the wheels so Link seems like an unnecessary waste of money to me at this point.
 
#17 ·
Don't forget about your whole fuel system. If you get injectors and a front mount, you may wanna get a pump, but I think someone mentioned it already. Get a wally 255lph and be "done" with fuel pumps for awhile. If not that, then a 190lph would be alright. If you get a 255, then you should get an AFPR. If you get all this and the things your talking about, you'll be pretty well off for a good setup.
 
#18 ·
19 degs at redline? I thought the stock 2g timing maps peaked at like 16degs?
Someone clarify that, its been a while.
Also you say it starts at 10degs under wot, at what RPM?
I also recall the 2g timing map starting lower than that, more like 6 or 7 degs?

I realllly dont think the 2g timing maps stretch to 19 though,
so there is something going on. Maybe your safc isnt really zerod out like you think it is. The AFR your running could be related to that....?

Theres no way to tell if your knocking from the information you've supplied...
How does your timing climb, does it climb then pause for a while then suddenly jump to some higher number.

Does it climb and then dip down to a lower number than the previous rpm and then shoot back up, give more details.

If its still able to advance its not knocking horribly bad, but with your AFR i wouldnt doubt it was knocking.
 
#19 ·
Black_ bullet said:
I realllly dont think the 2g timing maps stretch to 19 though,
so there is something going on. Maybe your safc isnt really zerod out like you think it is. The AFR your running could be related to that....?
I'm pretty sure I've read that it is supposed to drop to about 9 or 10* as soon as you go WOT then, climb towards 20ish at redline. Search is broken right now or I'd try and verify this.

Yes I am sure the SAFC is set at all zero. I may be a DSM nub but I'm not an idiot, lol.

Black_ bullet said:
Theres no way to tell if your knocking from the information you've supplied...
How does your timing climb, does it climb then pause for a while then suddenly jump to some higher number.

Does it climb and then dip down to a lower number than the previous rpm and then shoot back up, give more details.
I start the pulls at about 4k. It immediately drops to 10* then, like I've said twice, climbs pretty steadily towards 18-19* with no flat spots or dips. I'll see if I can get away with logging timing advance and RPM so I can post a log...
I've got the AFR set at about 12 now and the car pulls hard as hell (for a 14b lol) and is butter smooth. We'll see what it looks like when I get a new fuel pump/injectors I suppose...
 
#21 ·
The wideband is behind the flex section in my downpipe, I'd say no more than 2.5 feet after the turbo. I am also using it to simulate narrowband if that makes a difference, which I doubt.

Also I'm pretty sure the wideband is reading correctly as I am seeing it cycle from 14.6-15.0 during light throttle cruising, it stays at 14.9 at idle.
 
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