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Hi guys
I was running a Tech 2 scan on my 2005 C6 manual and noticed that when I accelerated to 3000rpm, my LTFT B1 went to 23% from 3%. And LTFT B2 19%
It also went into open loop fuel trim cell 38, and spark at 37°
But what I noticed was the MAF readings looked a bit high at 16.90g/s and 3870hz @ 2295 rpm.
I have attached a screen shot
Any advice on where to look next gratefully received.
Do you have an aftermarket cold air intake? If so, if not tuned for it this could cause ur problem.
was the car ever tuned? If so... well... that’s a can of worms.
if this is the stock MAF, it’s 14 years old, it has done its job for long enough, replace with a new OEM one.
Ive had a similar problem on my c5, replaced MAF and started running right again.
LTFT that increase like that is either a fuel delivery issue (fuel pump) or MAF sensor...what does your MAF read at idle ??...basic rule of thumb is grams/second equals the engine displacement...my ‘01 C5 roughly reads about 6.3 grams/second or so at idle and over 200 at WOT !!...you may have a dirty or faulty MAF !!...they usually are negative at idle.
I think you need to log more data instead of just looking at an instant moment. A five minute drive logging various rpm Andy load tells a lot more than this screenshot
I think you need to log more data instead of just looking at an instant moment. A five minute drive logging various rpm Andy load tells a lot more than this screenshot
At WOT, above 4000 rpm, the car is running open loop, purely based on the maf. That means there’s no closed loop fuel control, if the fueling is wrong there’s nothing fixing it. If the maf reads low, 5em the ECM will add more spark than needed because it incorrectly measured how much air is in the engine. Only think saving your engine are the knock sensors which only reduce spark (after it already knocks) there’s nothing saving the engine or cats from a hot, lean burn.
Sure, the other guys are right, you should collect more data, I could tell you to go buy hptuners or an equivalent, AND buy and install a wideband o2 sensor and collect more data, ... but that’s way more money than the maf sensor.
your car is 14 years old, likely still running the original MAF, you’ve gotten your moneys worth out of that sensor, just call it maintenance, hell, it’s cheaper than a set of front brake pads?
even if I’m wrong and you have to replace the fuel pump, it’s still nice having a new maf, and only what? 10% of the cost of replacing the fuel pump?
At WOT, above 4000 rpm, the car is running open loop, purely based on the maf. That means there’s no closed loop fuel control, if the fueling is wrong there’s nothing fixing it. If the maf reads low, 5em the ECM will add more spark than needed because it incorrectly measured how much air is in the engine. Only think saving your engine are the knock sensors which only reduce spark (after it already knocks) there’s nothing saving the engine or cats from a hot, lean burn.
Sure, the other guys are right, you should collect more data, I could tell you to go buy hptuners or an equivalent, AND buy and install a wideband o2 sensor and collect more data, ... but that’s way more money than the maf sensor.
your car is 14 years old, likely still running the original MAF, you’ve gotten your moneys worth out of that sensor, just call it maintenance, hell, it’s cheaper than a set of front brake pads?
even if I’m wrong and you have to replace the fuel pump, it’s still nice having a new maf, and only what? 10% of the cost of replacing the fuel pump?
The MAF is brand new as is the fuel pump. Both OEM. Air box is stock with brand new filters. My MAF reading at idle is 7.72 g/s 2962hz
Does that seem high for idle?
A faulty MAP sensor can sometimes skew the MAF sensor...that MAF at idle seems like it is “over reporting” a bit...when it does injector pulse is increased...the PCM thinks the MAF is getting more air than it actually is !!...baro at sea level should be around 14.7 psi and MAP around 4.5 psi...those numbers are for my LS1...what are your O2 sensors looking like from idle to WOT ??...can you graph that ??...at idle your load is 11 % ??....mine is around 1 at idle !!
Iv put a video up on YouTube of the data from Tech2.
Throughout the video I scroll through the parameters so worth watching all of it.
There is mostly idle but also up to 2900rpm will do another run to get a WOT over the next few days.
Iv put a video up on YouTube of the data from Tech2.
Throughout the video I scroll through the parameters so worth watching all of it.
There is mostly idle but also up to 2900rpm will do another run to get a WOT over the next few days. https://youtu.be/5ekCjLw0G0E
Fueling looks fine unless I just missed a bad section.. Not sure what you think the issue is.
Last edited by schpenxel; May 27, 2019 at 04:18 PM.
With these fuel trims are you experiencing any hesitation or stumble giving it “the beans” ??...at 3000 RPM my MAF is about 24 grams/second... under load your upstream O2’s are supposed to go rich...it seems like your O2’s are reporting lean...I have a Volumetric Efficiency program...if you give me at WOT your MAF grams/second, RPM, current Baro, temperature, humidity, and your upstream O2’s I can see if your car has a “breathing” issue (MAF or plugged CATS) or a fuel delivery issue !!...I’d also look at your MAF sensor ground...should be less than 100 Mv (.1volt) back probing the ground wire engine running !!
With these fuel trims are you experiencing any hesitation or stumble giving it “the beans” ??...at 3000 RPM my MAF is about 24 grams/second... under load your upstream O2’s are supposed to go rich...it seems like your O2’s are reporting lean...I have a Volumetric Efficiency program...if you give me at WOT your MAF grams/second, RPM, current Baro, temperature, humidity, and your upstream O2’s I can see if your car has a “breathing” issue (MAF or plugged CATS) or a fuel delivery issue !!...I’d also look at your MAF sensor ground...should be less than 100 Mv (.1volt) back probing the ground wire engine running !!
Power enrich mode has nothing to do with airflow. MAP/Throttle weren't high enough to get into PE, so it should stay in closed loop and continue to cycle fuel/trims O2 readings, just as it did
I still don't see anything wrong off of that video.
Pictured is your V.E !!....80% is “normal”...you’re at 51%...when you first mentioned your fuel trims went positive it’s either FUEL DELIVERY or MAF...your O2 went rich...you gave my sensor 2 not sensor 1 but it to went “rich” anyway...engine wasn’t starving for fuel...you don’t have a fuel delivery issue...most likely bad MAF... usually a dirty MAF’s or dirty filters fuel trims are negative at idle and go positive at higher RPM...you didn’t mention those numbers !!...also I’d check your MAF ground...less than 100mv back probing with engine running...that’s all I got for you !!
The datapoint at 5800 rpm was that at WOT? The volumetric efficiency comment only holds true at WOT. If it was part throttle 50% efficiency is plausible. What was the MAP at that same instance.
and like it was already mentioned, sensor 2 is downstream of the cats. Sensor 1 are the primaries, upstream of the cats.
Pictured is your V.E !!....80% is “normal”...you’re at 51%...when you first mentioned your fuel trims went positive it’s either FUEL DELIVERY or MAF...your O2 went rich...you gave my sensor 2 not sensor 1 but it to went “rich” anyway...engine wasn’t starving for fuel...you don’t have a fuel delivery issue...most likely bad MAF... usually a dirty MAF’s or dirty filters fuel trims are negative at idle and go positive at higher RPM...you didn’t mention those numbers !!...also I’d check your MAF ground...less than 100mv back probing with engine running...that’s all I got for you !!
Here are the numbers for sensors no 1 at the same point and also you can see the fuel trims on the screenshot.
I'll check the MAF ground wire as well.
Last edited by mazzerman; May 29, 2019 at 02:58 AM.
when i was looking at your video i noticed you have "MAF air flow" and "calculated airflow". that calculated airflow i think is likely the MAP based speed density calculation, converted to airflow.
when in steady state, those 2 values should agree. in the region where your fuel trims are high, check to see if MAF airflow matches calculated airflow. If calculated airflow is larger, and your fuel trims are high, that means there's something wrong with MAF, but speed density is right. if both values agree when fuel trims are high then you might have a different problem, like fuel flow.
all this only works at steady state, and the load must be low enough so that it stays in closed loop fuel control (not power enrichment), at 3000 rpm it should [edit *should NOT* ] be hard to do.
when i was looking at your video i noticed you have "MAF air flow" and "calculated airflow". that calculated airflow i think is likely the MAP based speed density calculation, converted to airflow.
when in steady state, those 2 values should agree. in the region where your fuel trims are high, check to see if MAF airflow matches calculated airflow. If calculated airflow is larger, and your fuel trims are high, that means there's something wrong with MAF, but speed density is right. if both values agree when fuel trims are high then you might have a different problem, like fuel flow.
all this only works at steady state, and the load must be low enough so that it stays in closed loop fuel control (not power enrichment), at 3000 rpm it should be hard to do.
Some good info there, thanks. 1st thing I'm going to do is check all the wiring to the MAF, with DVOM and my automotive scope. Then log a steady run around 2000/2500 RPM and look at those parameters you suggested. Iv got a shoulder OP in the morning so won't be able to do anything for a couple weeks. But will update the thread as soon as I can.
MAF sensor reading advice needed.
