I have an 87GN with a TA49,009's,XP fuel pump,adj. FP reg.,ATR Cold air intake,3in TH DP,and i am running a Red's 93 chip (tailored for my combo of course). Im using Turbolink to tune it, but i cant get the 02 readings to drop below 890 at WOT. I can drop the fuel pressure to as low as 38 psi(vaccume off) and it still has little to no effect on the readings. A local GN guru suggested this is a problem with the chip commanding too much fuel to the injectors. Is that a possibility? If not, what else should I look for to fix this?
Thanks,
Bill Ritter
How much boost? Are you seeing retard?
If not, then start upping the boost carefully. If it's still too rich, then the chip probably needs some fuel taken out of it.
Yes i am seeing retard. I tried to chase the fuel with boost to lean it out. At 17psi of boost i am seeing 7.8 degrees of knock retard. that's as far as i dare to go. I will give Quad Air a call tomorrow. Thanks Ken!
Help! Here I go again. I need help understanding Bill and Ken's last post. I thought retard was caused by a too lean condition, which causes knock, which causes retard because the knock sensor hears the knock and sends a signal to the ECM to retard until the knock disappears. I thought if you add boost, you are adding more air which makes it even leaner which will result in more knock.
I always thought you had to raise the amount of fuel and/or add octane to get rid of knock without causing retard.
Where am I going wrong here? Is it the o2 count?
Thanks
If you have 17psi of boost and 7.8 knock retard bring your arm out 1/2-1 turn you are about at the limit. If you want to add more boost safely
race gas or alky system is the way to go.
Carl Ijames posted to the mailing list:
Quote:You are right that retard is the ecm's response to knock. However, knock can be caused by running too rich or too lean. The major factors that go into the knock threshold are octane, timing, afr, combustion chamber pressure, cc temperature, and overall "cc efficiency". The latter is determined by valve/port shape, cc shape, piston shape, etc, and is basically fixed. The rest you have some control over. It's true that running richer than optimum for best power will suppress knock, but running too rich will cause it. IMHO you should start with the boost turned down (that's cc pressure :-)), and whatever octane and timing you intend to run. Look at the O2 volts midway through 3rd gear if you are using a ALDL scan tool like TurboLink or Scanmaster, because in 1st and 2nd things change so fast you can't get a good number, and at the bottom of 3rd you have just made the shift so things aren't quite back to steady state yet. With DirectScan you can do this in 2nd, or even 1st if you aren't traction-challenged and your turbo spools quick enough, but remember that most chips turn the boost down a little in 3rd and the O2's usually fall some so be careful not to go too lean. Pick an O2 target based on octane and what your likes and what your combination is. On 93 octane my car with a small turbo and stock intercooler liked 800 mV, with a bigger turbo and frontmount it likes 780 mV. Most people with race gas seem to shoot for 770-780 as well. Adjust the fuel pressure to get your target O2 volts. Then start raising the boost 1 psi at a time, tweaking the fuel as needed to stay at your target O2. Eventually you will get a little knock or you will hit your personal "max boost" (about 25 psi for me - I just don't want to push harder). Keep the engine cool through all this and try to start each pass at the same temp, to make sure the cc chamber temp isn't starting to limit you. That way when you do get retard you can be pretty confident it is the octane/timing that's limiting you.
Also try a little richer and maybe a little leaner to see what your car really likes.
Thanks Ken and Carl! It's obvious I still have a lot to learn. I never realized that running too rich also causes knock. I always thought the only thing caused by a too rich condition was a lot of smoke and washing oil off the cylinder walls which eventually causes ring wear. I thought I understood the elevated o2s because I thought that was caused by the unburned gas or dirty exhaust. Can someone add some more info about what happens in the cylinder when you have a too rich knock? At what f/a ratio do bad things happen? As I loosely interperate Carl's post, 13.5-13.9 is good, 14.0-14.2 borderline lean, 14.3 mild lean knock, and 14.5+ severe lean knock. Conversly,13.2-13.4 borderline rich, 13.1 mild rich knock, and below 13.0 severe rich knock.
Carl, is what you're saying, when you are too rich, the o2 sensor does not pull out fuel through the ECM. It is the knock sensor retarding spark because of rich knock?
I guess because my car is in such good tune all the time, I've never experienced this condition.
Thanks in advance!
Well, the A/F ratio depends on engine load, temps, etc. Under boost, the car runs richer (~12.5:1), due to the fact that the cylinder pressures are high (as are EGT) and the extra fuel is keeping things cooler.
Richer than that (11.5:1) may be required under certain cicumstances ... but too rich, and you start loosing horsepower and beyond that point you can actually induce "rich knock" ... too much fuel causing possible uncontrolled burn.
The O2 sensor is not really used much for WOT fueling corrections (as in not at all) ... thus, the ECM doesn't try to guess whether it's rich or lean knock. It just sees an EST event that indicates knock and retards the timing according to the chip parameters (and adds timing back in at the recovery rate).
Ken, Thanks! It's starting to make sense now. Is there a logic tree, in the archives somewhere, where I can follow the function of the sensors under WOT? The idle circuit is pretty well known to me, but I'm still not comfortable with how everything all works together when you're kickin' bootie.
Thanks for sharing your knowledge. Knowlegable people like you make the GN family fun. I can only imagine what it would be like for us newbies without you guys.
Try downloading the TurboLink manual at:
http://www.turbo-link.com and go to UPGRADES.
It's PDF, so you'll need Adobe Acrobat.
Read section 8 (all the sensor nominal values and functions) and "Tuning with TurboLink" section. That ought to get a few questions answered (and maybe spark a few more too!
)
Posted Carl's response from the mailing list (hey Carl, over hear!
On the BBS!)
Quote:Where did you get those afr's? You surely can't take the narrowband O2 voltages that I posted and convert them like that - the sensor just isn't accurate up there. It is fairly reproducible once you find a voltage range that your car likes, so we can use it for tuning in a relative sense but not in any absolute sense. From what I've read, somewhere between 12 and 12.5:1 is a good target for a turbo motor, 13:1 is lean (note that this is lean of 12:1, not lean of stoich at 14.7:1), and as a guess I'd say you need to be richer than 11:1 to get rich knock, depending on the other factors.
> Carl, is what you're saying, when you are too rich, the o2 sensor does
> not pull out fuel through the ECM. It is the knock sensor retarding
> spark because of rich knock?
At WOT the ecm ignores the O2 sensor and doesn't know or care how rich or lean the motor is. It calculates how much fuel to squirt using: injector pulse width=maf*blm*int*injconst*far*(1/rpm)*trims
In PE mode (power enrichment, lots of throttle) the int is set to 128, the far is taken from a table based on coolant temp instead of the normal closed loop value of 1/14.7, and the trims are PE-tps and PE-rpm. In closed loop the O2 sensor feedback is accomplished by twiddling the int so setting it to 128 is how the ecm ignores the O2 in PE mode.
--
Regards,
Carl Ijames ijames@netaxs.com
My car is also running pretty rich right now. It is an 86 GN and my setup is 9" K/N, Walbro 307 with Hotwire, adjustable FPR set at 40lbs at idle with vacuum line off (32lbs with vacuum connected), PTE Delphi 37lb injectors with matching 93 octane chip with 20 deg timing, boost set at 18lbs, stock manifolds with no leaks and a 2 1/2 inch Flowmaster catback system. I dont have a scantool (Turbo Link is ordered and on the way) so I haven't made any adjustments. My biggest problem right now is with a backfire (from intake) when under acceleration. The car seems to run fine....idles smooth, drives nice. It only happens when I get on it hard or even when slowly getting into it and boost builds to around 10lbs. Fuel pressure is good, all new components, new plugs CR43TS set at a tight .035, new wires, new O2 sensor....Any ideas?
Taken directly from my Trouble Diagnosis Manual;
Engine backfires;
Intermittent fuel supply, dirt or water in system.
Stuck intake valve.
Improper timing.
Moisture in coil boots.
Flat lobe on camshaft.
My own thoughts;
Sticky injector/s.
Worn valve spring/s.
FPR set too high.