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Discussion Starter · #1 ·
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.
 

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I would say that shop's diagnosis is correct. Ford MAFs are known for going bad and having incorrect barometric pressure readings. I will say it is a little odd that is only throwing a p0174 not with p0171 but I have seen much stranger things. I would start with replacing the MAF. As for which MAF to go with, depends on your power goals. I think lightning MAFs are good to about 450rwhp (don't quote me on that). The ba-2600 is good for 600+rwhp. So if you plan on making more power down the road I would just buy the ba-2600 and be done with it. Either one you buy will require a re-tune.
 

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stft's are only useful if you look at the ltft's at the same time, since the total correction being done to the fueling comes from both of these trims, not just one. If you have a vacuum leak of any kind upstream of the manifold, and if severe enough, it would throw lean codes for both banks, not just one. An exhaust leak or misfiring would be more likely IMO.

Also, the SCT BA mafs can support more power because the electronics are calibrated differently from the 90mm LMAF, even though the housings are identical size.
 

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Discussion Starter · #4 ·
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?
 

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Discussion Starter · #5 ·
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.
 

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My 0.02 worth.

A bad MAF or a vacuum leak at the MAF should affect both banks. With only one bank (driver's side #2) affected, focus first on the things that could cause one bank to be affected. For example:
  • An exhaust leak.
  • A leak in the EGR system. Either the EGR value itself or the DPFE sensor.
  • A bad O2 sensor.
  • A clogged fuel injector.
  • An intake vacuum leak directly above one cylinder.
  • A base engine problem.
I get the feeling the car runs fine at WOT. To me, that rules out many base engine issues. So I would focus on the things that could affect "closed loop" PCM operation such as exhaust leaks and such.

The difference in the data log values in caps vs lower case is one is a direct PCM PID where the other is a calculated value. For example, load is a calculated value.

Yes a value of 1.25 for LTFT means adding +25% fuel.
 

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Discussion Starter · #7 ·
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.
 

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The "thrt_pos_absol" counts value of 214 is analog to digital value from the sensor. Usually it is expressed as a ratio of 1024. Which in this case is 20.89%. FWIIW, 20% is a reasonable TPS value as 20% is considered "closed throttle".

The other "strange" values (counts) are the same kind of binary units.

Regarding the TPS values. Remember that the TPS closed throttle is "learned" at each start up. The PCM keeps track of this "ratch" value. Hence the reason for all of the different "thrt_pos_*" PIDs.

Check out the following for more information on how the PCM uses the TPS on 96+ model years.

Is your mustang stumbling, dieing at idle or idling rough? - Page 14 - Ford Mustang Forums
 

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Discussion Starter · #9 · (Edited)
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.
 

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Discussion Starter · #10 ·
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.
 

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Discussion Starter · #11 ·
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.
 

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My .01 on the strange data: I've never heard of translating it into a percentage - but I'm a Diablo guy and maybe that is an SCT thing. Still, this could come in handy.

Yes the PCM does use "A/D counts," typically for various sensor data. And again typically such sensors use the 5 volt reference. Same concept that wmburns mentioned, but a translation of - divide counts by 1024 and multiply by 5 - gives you volts. So when you see people giving voltages for MAF or TPS or whatever, that is how you can get to it and compare.

Your datalog of 214 counts is therefore 1.045 volts. Seems handier to me as voltage is the sensor output, and is pretty much what you would find if you backprobed whatever sensor is in question with a multimeter. I'm a bit dubious as to the usefulness of a percentage, especially as to TPS, since I'm fairly sure it doesn't mean your throttle pedal or even the TB blade is "open" by 21%.

---

As to your code, I am perplexed. Could be O2 as you say. Also I think we are talking bank 1 - passenger side? Guess there's a few potential reasons why your PCM may be thinking lean and adding fuel. Do you still have a skittish IAC valve? You might want to log and check that out. Always good to eliminate known problems, as multiple issues going on at once can make diagnostics a bear. 1.045 volts closed throttle seems a bit much but I think is still within spec. Still, did you have to mess around with your TB set screw, possibly in light of IAC issues? Kinda wondering if you or somebody found a middle ground with that which is keeping bank 2 within limits but not bank 1. In case it might be making a difference here, if I remember correctly the KB bypass valve dumps into bank 2.

Again, just my random penny's worth. Good luck and keep us updated.
 

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Discussion Starter · #13 · (Edited)
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.
 

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FWIIW, the ONLY way the IAC value can CAUSE a lean condition is if it's the black vented type AND the engine starting vent is not closing when the motor is running. This same black vent must also open to provide air to start the motor.

Sooooooo. From a datalog prespective, a vacuum leak is a vacuum leak. The data log is not going to tell you WHERE the leak is.

IMO, one of the best ways for the home mechanic to find a vacuum leak is with a propane based leak detector. The propane will not harm gaskets like carb/choke cleaner can.

Note, the black vented IAC works off of a pressure difference. I could see a case where the supercharger bypass valve could "fool" the IAC and the IAC vent not close as it should. HOWEVER, based upon your report of difficult starts, to me that implies the IAC vent is NOT opening as it should. During starting, the KB bypass value shouldn't have any role to play.

At the end of the day, if the black vented IAC is not opening or closing as it should, the only fix is to replace it.
 

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Hmmm, well I may have got my speculating backwards lol. Too much Bailey's in my coffee.

I was going on the assumption that the IAC was not opening and so somebody had cracked the TB blade more to "help" things out. I also thought I had read that some KB guys could go sometimes go lean at cyl #5. Again, just my WAG and like wmburns says it is probably something else. That's why it was only my .01 ha ha.

The bypasses work via a vacuum actuator. Normal vac holds the bypass open. Go WOT and the bypass shuts, allowing boost to build. Get out of the throttle and it opens back up, boost falls off. Basically when it's open the cylinders only ingest the N/A air it needs, and any excess in the manifold pushed there by the rpm of the screws can flow out of that bank 2 intake runner and back into the inlet.

Wideband is a good idea, I have one myself but haven't installed it yet. However unless you have two of them I think it's only of sure help for general system issues. Anything that is bank to bank and you're left with a 50/50 shot of catching it, since you have to pick one side to put the sensor bung in.
 
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