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13 Mazda speed 2.3 turbo. Car has a stored p0171 and p0300. Short term fuel trim at 25. Definitely running lean. Smoked tested and did not see any vacuum leaks. B1s1 A/F sensor under 1V witch I believe is a rich command from B1S2 witch is around .30 witch is reading a lean exhaust. I introduced more air into the system by pulling the boosters vacuum hose to watch for sensor change. B1S1 went Lean and so did B1s2. Introduced a flammable spray to watch for sensors to go rich. Witch they both did. That eliminates a stuck sensor. I believe. Now the car has gotten a new down pipe and aftermarket intake. The intake is much bigger then stock but has been tuned with a cobb stage 2 map. Witch should have taken care of that. I believe. But customer states he didnt have these issues before modifications. Im not sure what im missing. The MAF looks clean. Maf unplugged the fuel trims both go to zero. Not sure if thats a normal default. Also. On cold starts its a bit hard to get it running. Have to try a few times. But this time i unplugged the maf on cold start and it started first try. Not sure if i should shift my focus on the maf or not. I have some running captures. 1 snap throttle. 1 at idle. 1 introducing air. 1 introducing fuel. Please any help is appreciated. Thanks in advance.
Check for exhaust leaks at manifold (broken bolts/ blown out gasket) egr valve issue. Also when you did smoke test did your test include intake boot up to maf? Did you smoke test brake booster?
Hey thanks for your reply. I smoke the system through the vacuum hose going to the booster. It did resch the intake tube and maf. Im going to smoke the booster side today and check for an open pcv valve. Exhaust looked to be good but ill double check. Thank you.
Did you check freeze frame data to see when the lean code set?
Knowing if the code set at idle or higher rpm can help determine if there is a vacuum leak or a mixture issue.
I would check the LTFT & STFT at idle and up to 2500 rpm in park.
Be aware that relocating the maf, such as with an aftermarket charge pipe, can have a negative effect on its ability to measure air.
If it's possible, you could try reinstalling the previous intake tube, resetting the computer and watching to see if the trims continue to trend excessively positive.
Thanks for the reply. I didnt check freeze frame. I will check fuel trim at idle vs 2500 rpm. I suspect the code set at idle because at idle stft is 25. I did have a running capture where stft and ltft were both around 20. When i snapped the throttle they both drop to 0. Witch from what Ikno should indicate vacuum leak. Im going to check pcv valve and smoke the booster to see what i have.
One thing to remember is that at wide open throttle, the PCM usually will go from closed loop to open loop. So on a snap, trims might go to 0 as a default.
Depressing the clutch while driving will also usually put it into open loop.
It's a good idea to include loop status while you're watching the trims to make sure the trims are being used.
With some of the Ford and Mazda stuff, you may have to reset keep alive memory after you make a repair to get it to start back at it's base fuel map. You won't always see immediate corrections in fuel trims even if you did fix the problem until after multiple drive cycles if you do not. Disconnecting the negative battery cable and touching it to the positive for a minute or two will reset the keep alive memory if you don't have a scan tool that can do it.
Great information. Ill have to include loop status while watching my trims. Update on my booster and pcv checks. I plugged hose coming of the booster and no change. And pcv valve is tough to get to, under manifold. I realized if the pcv valve was stuck open i would have excessive vacuum if i remove the oil cap. Am i correct. Also i removed the filter and put a few fingers in front of the maf and my trims started dropping right away. I dont have access to the original intake and a previous shop changed the maf. The maf housing he had previous to the one that is on now had a honey comb in front of it and the one that is on now doesnt. Any thoughts.
Jalvrzjn wrote: Great information. Ill have to include loop status while watching my trims. Update on my booster and pcv checks. I plugged hose coming of the booster and no change. And pcv valve is tough to get to, under manifold. I realized if the pcv valve was stuck open i would have excessive vacuum if i remove the oil cap. Am i correct. Also i removed the filter and put a few fingers in front of the maf and my trims started dropping right away. I dont have access to the original intake and a previous shop changed the maf. The maf housing he had previous to the one that is on now had a honey comb in front of it and the one that is on now doesnt. Any thoughts.
From what I've been told that honey comb goes a long way to direct non-turbulant air over the MAF, but I have no real world testing to back that up.
The theory is that without that screen the air swirls around making it difficult to accurately sample the air coming into the engine, where as when air is directed through the screen, the air stream is "smoothed out", allowing for a more accurate sample directed to the MAF.
Edit: I'm not telling you all of that because I think it's going to fix the car! Just sharing my understanding of the theory behind the screen.
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