[hangwire]

P0174 Came on for the first time about a month ago. Didnt do any work at all on the car leading up to the code. I cleared it and drove for a week when it came back on. Cleared it again and from there noticed gas mileage plummeting, 15MPGs as of today(yikes). Came on a 3rd time this week I got time off from work today to bring it to the shop.

Shop offers to do diagnostics service for $70 including exhaust leak check I say go for it. Mechanic tells me that the MAF is reporting barometric pressure at 5,000+ when it should be reporting 150ish(could have been 1500 forgot). There is also a vacuum leak at the MAF which is due to me breaking it a while back. I tried to unscrew the MAF from the housing and stripped both screws/threads. This prevented it from tightening back down so I wrapped duct tape tightly around the housing as a temp fix. Everything seemed fine and I had no codes at the time, but I guess the duct tape is loosening from the heat. Mechanic says when he sprays starter fluid around the MAF seal that the short term fuel trims drop to 0 instantly. Bank 1 STFT is at a steady 4 and Bank 2 at a steady 12 otherwise he said.

Is it practical for only my bank 2 side of the motor to run lean enough to trip a code if its a MAF leak causing the issue?

Second question - I am under the impression that the SCT BA-2600 is capable of reporting more air and thus supporting more power than a 90mm lightning MAF. Is this true? And how so if it is also 90MM? I've heard different numbers about how much RWHP a 90mm lightning MAF will handle, any accurate numbers? Trying to decide if the SCT BA-2600 is worth it or not.

 

[hangwire]

Yeah I find it strange that my passenger side is not coming up lean enough for a code. I'm gonna start with replacing the MAF because I know for sure its got a vacuum leak issue, I broke it myself and you can see where its not sealing all the way as is. That and we know there is some sort of issue with it not reporting barometric pressure, unless the diagnostic test came up wrong.

Crazy thing is I went to the strip and ran two passes with this faulty MAF lol.

That was also a question I was going to ask. I am assuming that no matter what once you swap MAFs even if its the same type(90MM LMAF in my case) that you have to specifically calibration your PCM/ECU to that MAF. Its not a matter of just changing a few things on the existing tune and plug it in? I will for sure need to get the car back on the rollers and re-tune after the MAF swap?

I've got a very short data-log I did earlier this week its on my laptop i'm gonna go fire that thing up and post the log. The reason its such a short data log is because when I was logging all the needles on my gauges were sweeping randomly all over - couldnt even tell how fast I was going. I think it may be because I am data logging with LiveLink 6.5 without updating my firmware/tune revision on my handheld. Gonna try to get this fixed this weekend and datalog more. What parameters should I log to further diagnose this issue?

 

[hangwire]

Ok gonna attach the data-log file to this post. One thing of many that I am confused about with a SCT data-logging is I dont know why when I am configuring parameters to datalog it comes up with multiple parameters with the same description except one item will be in all caps while the other is lower case. Sometimes I found very similar or the same parameter descriptions in different sections. I tried to data-log what I thought was right. Some of the values that correspond to parameters dont really make sense to me. Like when it lists a value of "1.25" for long term fuel trim what exactly does that value mean? +25% Fuel? I need to call SCT......their site is useless.

 

[hangwire]

I do agree with your .02 and so did the guy I talked to at my dyno shop(Fastlane Motorsports) when I called him just now asking what MAFs they had in stock. I too agree that a leak at the MAF should only cause the entire system to run lean. I do still however happen to know for a fact that its got a problem and it is literally being held onto the housing by duct tape right now because I stripped the threads. Doesnt make much sense to drop a $5,000 blower on my engine and then leave the MAF taped to the housing - it needs to be fixed. So i'm gonna drive down to Fastlane MS tomorrow afternoon and pick up another 90MM LMAF to get that possibility out of the way anyways. I'll drive down there - swap the new MAF in, reset the computer and drive around for a while this weekend and if that fixes the problem then i'll just mark it up as a weird symptom from a leaking/faulty MAF.

I really don't know if this allegedly faulty barometric pressure reading has anything to do with this or if theres a problem at all. I'm gonna stop by the shop I had run the diagnostics test this afternoon and talk to them about what exactly they said it was reading and to ask them if they actually checked for an exhaust leak as I specifically asked for and was told would be done.

I have my money on a driver's side exhaust leak or bad o2 sensor, but we'll see what happens. It wont be that much more money to fix the exhaust leak if that's the problem anyways.

As for the data-log parameters I get what you're saying but i'm still somewhat confused. For example it offers to log fuel trims as both an upper and lower case parameter. So which is it, a calculated value or a "direct PCM PID"? When we say "calculated value," does this mean were safe to assume this is a value that the PCM has calculated based on data it has before we log it? That is what this sounds like to me. Since my "thrt_pos_absol" parameter is in lower case, there is presumably a calculation already done to present the values that I am logging, such as "214" at idle. What calculations have been done by the PCM to come up with the "214" number and how do I go about translating this "214" number into a real world value that I can use? Does this mean .21% throttle? seems like a bit much for idle. Same for MAF counts, how do I make sense of that? Sorry about all the SCT questions its just so so hard to find this info anywhere on the internet. You almost have to be in tight with somebody whos already experienced and knowledgeable to even get started with this stuff without dropping tons of cash on tuning software.

 

[hangwire]

So all of these "strange" values/counts can be interpreted by using this binary system? They are all values based on a scale with 0 as a minimum reference and 1024 as a maximum reference?

Good info there. You may have solved one of my few small problems with the car with that lol. Its kind of weird but my IAC starting making notorious noises months before putting my KB on but then just stopped. I never ever had eratic idles even though it was making the honking sound, not too bad at least. It would maybe jump 100-150 RPMs. Ever since I put the KB on and got it tuned the car doesn't like to start especially when cold. It just stumbles around for a few seconds below 1000 RPMs then just dies. Most of the time it takes a second or third re-fire to actually get started and it still usually barely starts itself up. Yesterday morning without using throttle it wouldnt start on its own until the 4th crank and barely at that. If I tap the throttle though while its stumbling the engine picks right up and runs perfect. It usually starts right up when warm. Its never bothered me enough to track down but i'm pretty sure its just a bad IAC now which is what I suspected.

 

[hangwire]

Fastlane motorsports came through for me and got the lightning MAF I needed quick. But im pretty sure it didnt fix the issue. I drove ~25 miles after swapping MAF and clearing KAM. Then I stopped the car and data logged for about 2 minutes at idle. LTFT started out at 11% and crept up to 20% within those 2 minutes. Obvious still dumping fuel. Gonna take it by the shop as soon as they open tomorrow and see what they say - I'll bet they didnt exhaust leak test it like I requested. I'll find out.

 

[hangwire]

Talked to the shop this morning. They did in fact hook the exhaust up to the smoke machine and found no leaks. So its not an exhaust leak, not a vacuum leak at the MAF, and not a faulty MAF sensor. Gonna drive it until I get another code then bring it back. This probably is gonna end up being a lot more expensive as I foresee I lot of money getting dropped into labor and guesswork now........ugh.

 

[hangwire]

As for the SCT stuff I'm just not positive how to translate these raw values into something applicable. I'm gonna call SCT and try to find out this week.

As for the IAC as far as I know its the same one that came on from the factory. I've owned this car since 53,000 miles and it has about 103,000 now and its never been changed. I have also not touched the throttle body set screw since owning this car. However I am not sure if Fastlane Motorsports changed the TB position in the process of tuning it. I doubt it - but I guess its a possibility. I do have a funny startup issue that was described earlier in this thread.

What should I data-log to check for indicators that my IAC is causing my lean condition? And I am running lean on bank 2 - drivers side. Same side that the KB by-pass valve dumps to....interesting. Though i'm not sure how a funny IAC would cause the by-pass system to run my drivers side bank lean. Since you mentioned these things I went back and looked at the data log that I posted on this thread. It appears that my system is only running lean at idle. If you look at when I'm actually idling the LTFTs are just sitting maxed out at 25%. But if you look as soon as I start driving and getting the RPMs up going through the gears the LTFTs STOP adding fuel and the value is stays right around 1.00(no additional fuel). And it just so turns out that my all four times this code has come up has been on startup/idle, never while driving. I think I may have an idle issue.

I will be installing a wideband A/F kit either this week or this weekend. Hopefully it will help solve the issue if it isnt solved by then.

How does a KB by-pass valve physically re-circulate the boosted air to the inlet under idle/low throttle conditions? When I look at the bypass valve it appears to only be able to physically dump the air to the bank 2 side of the engine when the butterfly valve is open. But somehow it is able to re-circulate the air evenly back into the inlet according to KB. I understand how the air is forced into the engine when the bypass valve closes. But i'm confused on how the system works when the valve is open.