the other day my cars A/F meter started creeping up sitting at a stop sign down the street from my house, its now idling at 16 to 18 A/F when I'm driving it is within completely normal range, however as soon as I let off the throttle it goes lean, not just under engine braking which is normal for the gauge to show lean or even off the chart A/F ratios, all the time if I'm not on the gas its lean like I'm engine braking and the injectors are off. I've noticed that at idle the Dashhawk shows that my throttle position is 2%, if I remember correctly, it used to be around 4 or 5% at idle, when I rev the engine up a bit to show 4 to 7% throttle it goes back to 14.7. 2nd, I tried moving my wide band from the left exhaust pipe to the right one and it was less lean. this makes me wonder if its my Cats that are the problem, one going before the other but I just don't know anything about cats and so this is just a shot in the dark, I just know that running rich can kill cats and my car is between 8 and 10.5 A/F at WOT, very rich! my wideband is behind the cats. thanks in advance for any help!
Have you changed or reinstalled your tune lately? What fuel rails are you running? Cross overs? If your cats aren't bad, it sounds like you're getting more fuel on the passenger bank.
My first guess would be an air leak? like at any of the joints past the header or at the bung weld. You said "less lean" when you moved it to the right side. Still lean over there or was it normal?
Behind the cat's??? Where is your a/f guage upstream from the cats or downstream?? You can't use a a/f gauge downstream from the cats.
?? my understanding is that behind the cats it might read (at most) 0.2 afr leaner. And that the cats will have a "damping" effect so changes in afr would not be as immediate as before the cats. They use a tail pipe sniffer for dynos right?
I've reinstalled tune twice, no difference, it acutally got worse after, it was around 16 before now its 18 at idle. stock fuel rails, not sure what cross overs are? still lean on the right side, but 15 to 16 and it seemed to show more movement to normal ranges then back up to 15 or 16. I've not checked for leaks, not really sure how I would do that...... downstream in the rear factory spot, I guess I could try putting it temporarly in one of the upstream spots, would removing one of those for a minute make the car freak out or would it run normal just triggering a CEL light? I've never had any problems downstream, its always showed 14.5 to 14.9 I was not there but I would assume they used a tail pipe sniffer. my intentions were to move it to a custom spot upstream of the cats but I have not gotten to that yet plus its never been a problem, always shown right at 14.5 to 14.9 before this came up.
With the kind of power you're running, you should really be running aftermarket fuel rails. We've found that most cars over 500 RWHP start showing some fueling differences between left and right banks. Its my understanding that the tune at idle is partially based off of your fuel trims, so reinstalling the tune will likely make it worse.
I've seen bigger differences then .2 between the tail sniffer and the a/f guage installed pre cat. As much at a full point. I don't trust it. If you remove your upstream O2 it will give you a cell right off. Check for leaks in the exhaust before you get too involved with anything else.
yea, I was definately planning on upgrading fuel rails, I've been running a few less lbs boost on the street but I know I would be better off with upgraded fuel rails. so I should not remove the front 02 sensor at all, not even to see if I get a significantly diferent reading? how do I check for exhaust leaks? thanks
Do not remove the front O2 sensor. The PCM uses that in closed loop operation to adjust fuel to 14.7. It sets the adaptives from that and those are used in open loop operation. Additionally the PCM is always monitoring the sensor control circuit for the heaters and to detect a short or open circuit. Not sure if it goes into limp mode or what but it won't be good, especially for checking A/F. Try this just for kicks. SWAP your front O2 sensors and see if the problem follows the sensor. (I really would not expect that to be it though, since it reads OK off of an idle). hmmm, do our cars even adjust fuel for each bank independently? Also, generally speaking, when narrowbands go bad they tend to start reading leaner and leaner so the PCM would adjust by making it richer and richer... So swapping sensors is even less likely to do anything, but heh, you'll feel better for the wrenching and trying something anyway :grin:. You can also look for air leaks and see if anything is loose or wiggles while you're under there.
Was this tuned in cold/cooler weather than you are experiencing now (as in is it warmer weather now??). I don't think it should be of concern if only doing this at idle. I assume it does the same coming off the loud pedal as well. Of course get it looked at including hardware as mentioned above as its better to be safe than sorry however as long as light/part throttle/under load readings are ok I believe it should be ok (hell mine went off the scale at idle after the 426 was installed). Best of luck mate.
Which would account for an increase in air (going lean). As the temps increase, you will see the A/F range go a little rich... My question is this, "is the gauge a steady number or is it bouncing around?" If it is bouncing around, and the goes steady while in throttle (WOT), this is typical behavior with an F/I application. My A/F gauge always bounces around when cruising or at idle, but once I go WOT it will maintian the A/F numbers I am tuned at. Once I let off the throttle, it will bounce to max lean and back down to the actual A/F I am tuned. Mine has done this for three years. Something about going from closed to open loop? Also, are you throwing any codes? I would think that if something was going bad or has stopped working completely, you would start throwing a code or two... And one more thing, it very well could be that the O2 sensor for the A/F gauge is fouled? Have you tried change this?
I got back under my sled this morning and poked around to see if eigher of the cats/headers felt loose, neither side moved when I pulled or pushed on it, I also started the car to see if I could smell a leak under the car, nothing in this department either.
the thing is, I've been driving my car is cold weather and its never been a problem till now. the gauge bounces a little bit, I notices this morning that it bounces in correlation with the cars idle (at least when the car is cold) and the spark advance also bounces from about 4 to 12 degrees of advance. My car has always had the same characteristics that your describing, under acceleration/WOT its steady, as soon as I let off the gas it bounces way up high, even off the chart but then it comes back to normal closed loop/idle 14.7 unless your engine braking and then it may stay high until the car slows and the revs lower lessening the load on the engine at which point it goes back to 14.7. now its having trouble reaching that normal 14.7 area at idle or coming off of throttle. I am throwing codes but nothing new: P0301 CYL 1 MISSFIRE, P0038 HEATER CONTROL CIRCUIT HIGH (BANK 1 SENSOR 2), P2000 UNKNOWN. I've had all these codes sense I got the car built. I'm NOT having any lean codes or anything. the only thing I'm surprised about is that now that I have both rear o2 sensors unplugged its not throwing a P0038 for bank 2 sensor 2. I have not tried changing the AF gauge o2 sensor, I only have the one sensor, I guess I should go down to summit and get another one.
Yes. Narrowbands only have a range from about 14.3 to 15.7 or something like that. Actually narrowbands only read 14.7, lean, or rich and they output a signal from just above 0v to just below 5v. In closed loop operation (idle, cruising, etc) the PCM monitors the narrowbands and constantly adjusts the fuel up and down. It makes it richer until the narrowbands hit the max and then leaner until the narrowbands hit their min and back and forth. Constantly. The current adjustment is sampled and stored in the short term fuel adaptive memory frequently. The short term fuel adaptive memory is sampled less frequently and stored in the long term fuel adaptive memory. In this way, the fuel adaptive memory will have an adjustment value very close to what will result in a 14.7:1 AFR for the current conditions. Altitude, ambient air temps, air filter/CAI condition, etc. You have some base injector pulse width in the tune which is a constant and then the adjustment from the fuel adaptive memory is added to it (or subtracted from it). This is why you will see the AFR constantly bouncing up and down in closed loop operation. If you're watching a guage you might barely see high 13 numbers and maybe low 16 (depends on your gauge). The long term adaptives will adjust in a matter of seconds or less. Short term adaptive memory is lost over a key cycle. Long term adaptive memory is maintained. In open loop operation (like WOT) the PCM will use (base + long term + PE table) for fuel. The Power Enrichment table contains fixed values for the additional fuel to be added in WOT operation. Short term adaptive memory is not monitored or updated in WOT operation (so long term is not updated either). With all the values fixed, you will see a fairly steady AFR reading in WOT. The tables have cells with different values so it can move as you enter different cells but will basically be steady compared to closed loop. The PCM can adjust over a fairly wide range so it shouldn't make a difference when and where the car was tuned (actually most all of that kind of tuning is only to the parameters that effect WOT/open loop). The car will adjust to 14.7 from a couple of miles up to below sea level and way below 0 to way above 100 degrees. Since the PE table (and WOT parameters) are fixed they will not adjust. At sea level the adjusted fuel might be 50. At Ron's place the adjusted fuel might be 30. Lets say you tune for WOT at sea level and the PE table adds 5. Idle or cruise the car will run at 14.7 in both places. At WOT the car will run pig rich at Ron's place.
I just switched the A/F gauge back to the original side. its getting different reading on each bank, the drivers side bank which is the original bank shows approximately 18 A/F, the passenger side shows normal or very close to normal. I'm completely stumped, why and how would I get such different reading from one side to the other? wow, that's a mouth full! I think I gathered that weather conditions should not have an effect on the A/F readout except at WOT! are the upstream and downstream o2 sensors the same type, both narrow band? would it make any sense for me to replace the drivers side upstream o2 sensor with one of the downstream ones as they are not plugged in right now? I'm just wondering if its at all possible that the upstream drivers side showing lean has to do with the factory sensor malfunctioning, getting incorrect readings and adjusting that side too lean.
The upstream O2 is what sends info to the PCM to adjust your fuel trims. You need to reinstall them. Down stream is for emissions reasons. Question, "Did you have a seperate bung installed for your Wideband or are you using one of the existing O2 bungs? You need to have a seperate bung installed for the wideband for accurate readings.
the upstream ones are installed, I have never touched them. I have the A/F guage installed in the factory downstream o2 bung, I was going to get it moved but never got around to it and now I am in the process of selling my modifications so I didn't bother. having the A/F gauge in its current spot has always showed closed loop A/F reading right around 14.7 untill now and WOT readings between 8 and 11 which it still is I think, I don't go WOT much as my trans is going.
Yes. Upstream and downstream sensors are the same. The upstream ones are used for A/F. The readings from downstream ones are used to compare to the readings from the upstream ones and tell how your cats are doing. If the comparison isn't right then it throws a CEL (it only throws a code, there is no action taken). I think you could swap in the downstream sensor but it depends on what you mean by "not plugged in right now". If they've been hanging under the car exposed to the elements they may not be in such good shape. If they've been in the exhaust but with the cable unplugged they will be fouled and won't work. The tips on sensors (both narrow and wideband) are made with very sensitive metals. They have to be heated (1500* ~ I forget) while in the exhaust stream to keep them from fouling. Your sensors have 2 circuits going to them. One is for the 0v to 5v signal indicating the O2 levels and the other is to control/power the heater which keeps the tips at some constant temperature. Note, for the same reason, getting stuff like anti-seize or grease on the tips will most likely ruin the sensor. If your rear sensors have been completely removed from the car and you think they're in good shape you might try swaping one of them in. (I forgot -- the right side front sensor is almost impossible to get to right?) When putting in a different sensor you should disconnect the battery briefly to clear the PCM memory since it "learns" the heater sensor control. Your narrowbands are torqued to 22 ft. lbs. (I don't think that's critical)
