Does anyone know how to understand SCT logs?

Discussion in 'SN95 4.6L Mustang Tech' started by mat82284, Jul 18, 2010.

  1. Thanks guys. As for the maf wires those were extended but were soldered and professionally wrapped. Those wires your looking at in the photos are for my hids lol.

    As for those water spots, I actually sprayed starter fluid all over my car looking for a vacuum leak. I keep water away from my engine bay. Good eye though.

    I just cleaned my maf sensor yesterday with electrical cleaner. I also cleaned my air filter and the pipes.
    As for the fuel pumps it still seems weird. When I did the 6k pull I ran out of fuel at 5k could the maf cause this? I used to have enough fuel to hit 7k and still had lots left over.

    I remember a while ago when my fuel line came off in the tank and it caused me to be stranded. Is it possible that the fuel line could be kinked somehow causing the fuel pumps to rais there pressure to keep up with demand? and since the fuel line is kinked it could theoretically cause me to run out of fuel at the end?

    If the mass air is causing this, is there any way to check to see if the actually meter has gone bad? Volt test or something? or would i need to swap it out to test it?

    I've probably had this problem for say 6months ish. I've noticed rpm stumbling for a while, but I dont drive to often and like i said before I rarly do WOT. I've only done it twice this year and once was in January and once was to log. This could be a good or bad thing lol maybe I would have noticed sooner.

    Rear 02 replacement on order. Check.

    Those black zip ties were there to help hold the pipe up. In the beginning the weight of the filter and Anderson pipe wanted to pull the blue elbow away from the supercharger causing a huge leak. The zip ties helped keep the pipe from moving and has worked for at least 8 months now. Eventually I'd get a piece welded to it to stop moving.

    As for the bypass valve. I'm only running 1 bypass valve and thats after the intercooler. Should I add another one before the intercooler? I also ran the mini race when I had the tune done. It exited the same pipe and same diameter tubing though. I figured since the tubing was the same size id be pushing the same amount of air out either way? When the car was originally tuned the car didnt have any maf blow back.

    Thanks again chris and don!
  2. mat82284:

    Thanks for the explanation of the "stuff" on the Power Pipe and confirmation that the MAF wiring was done properly. Nothing wrong in those departments.

    Was any physical change made to the engine 6 months ago?

    You're right about the fuel system plumbing: it is possible that something has popped off in the tank and is swimming around rather than sending the fuel forward to the rails. "We" are left with two problems: fuel supply/delivery and MAF signal stability. You have plans to look at the pumps and FPDM/wiring and Don's given you a great suggestion about the addition of another bypass.

    I think you'll be in tall corn soon.

  3. Thanks.

    By physical change do you mean the bypass valve? If so then yes. I didnt get a re-tune when i swapped from the mini race to stock bypass valve. As for the engine it was done about 15 months ago and tuned after driving it 2k miles. After that nothing has been changed except that bypass valve recently because of a California smog ticket. :(

    I'll try to add another bypass, but that will take a little while since i'll have to order parts online. Is there anyway to physically check the mass air sensor to see if its gone bad? I wish there was a simple test to check the mass air to see if the sensor is going bad on its own.

    I'll be removing the gas tank this Saturday in hopes its something as simple as a hose being kinked or something. If everything looks ok. I'll check to make sure both pumps are actually working. If one pump failed this would also account for this issue.

    You guys mentioned adding a possible block to force the air away from mass air meter so it wouldn't read bad. Has anyone done this? Is there any guides on how to do this? I was thinking of trying it out to see if it makes a difference and if it does I'll make sure to toss on that second bypass valve asap.

    I'll keep you two updated. Thanks again for helping me figure this problem out and locating possible issues.

    I forgot to mention that I've always had this huge airfilter on the car, and it worked fine when it was originally tuned.
  4. I kinda had an idea to test out. I took this metal piece from my stock mass air. Then just used a rubber band to hold together. I was thinking of using jbweld and screwing in 2 screws into the mass air plastic piece not the whole piece. Do you think this would help? Is this the type of barrier you guys were talking about?

    P.S my dog was so interested in what i was doing lol that he made it into the photo.

    Attached Files:

  5. mat82284:

    Thank you for the info about the timing of the installation of the bypass valve. This coincides with some of your troubles. Also, it is good to know that the air filter is 'original' (so, not causing any trouble).

    A smog ticket. What is this world coming to? The administrators at CARB have not studied history (nor do they appear to be 'car guys') since California is the state that started the car craze. Nice weather out there but a difficult place to live, imho.

    The bypass air is coming in at pressure compared to the fresh air. The connection is a tee (90 degrees). The 'block' that Don mentioned is in the form of a 45- or 90-degree bend to send the bypass air towards the engine. (If the bypass hose connection stub is pointed towards the engine then that is good because it is guiding the bypass air away from the MAF.) At the moment, the bypass air mostly goes to the engine but there is a portion that heads towards the MAF or close enough to it to cause a disturbance. The second bypass valve will reduce the volume of air coming through the first bypass valve. Less volume flow means lower velocity and much less energy to send air towards the MAF. (This is basic fluid flow, nothing specific to supercharger bypasses.)

    If it would fit, you might try a temporary insert in the bypass inlet stub. The insert would have a closed end and have a cut-out on one side that would be open towards the engine. Copper pipe would be a good bet since it has thin walls and is easy to work on with a Dremel (lol).


    Do you understand my 'sketch'? Pop this in and collect a datalog or two and, if the MAF signal improves then you know that a 2nd bypass is the solution to the backwash problem. If it doesn't work, you'll need Don's expert opinion!

    I do not know how to test a MAF. A phone call to SCT Tech Support might be in order. You could try measuring the voltage while using a hair dryer (no heat setting!!) at low, medium, and high speeds. If the voltage is stable and increases with flow then you know the MAF is working OK. You won't know if it is accurate, just functioning as it should.

    I would not recommend installing the stock MAF plate on the SCT MAF. The stock MAF was designed with that piece and it needs it installed to work. For the stock MAF sensor, the plate probably helps to reduce the effect of backwash. The SCT MAF is not designed for the plate and you would have to adjust your MAF function or it would produce a rich condition (reason: (a) the plate reduces the cross-sectional area, (b) the MAF would sense higher air velocity, (c) translate it to a flow, (d) fuel (in closeed loop) would be adjusted for that false high air flow, thus, causing a rich condition).

    LOL at the look on the dog's face. He appears to be studying the MAF very intensely. He is definitely a Mustang hound.


  6. Haha yeah he loves the mustang. Every-time I take him outside he runs to the car and try's to jump in lol.

    As for the diagram. I'm a little confused. The bypass is already facing the engine. If you look at the photo with the red line. It showing the path of the tube. Could you use that photo, edit it and put a blue line showing me how you want the flow to go? I'm confused about the copper wire thing too. The air needs to be recirculated as well. The inlet on the Anderson power pipe is also facing the engine... Are you saying to let metered air escape to the atmosphere just to check to see if the mass air log changes?

    I'm eager to test it out, but I'm not quite sure when I need to do. Can you explain it a little differently?

  7. mat82284:

    Sorry that my sketch is not too clear. Has a cave drawing quality to it.

    No, do not vent that air. It is metered and the computer knows it is 'in the system' and is waiting to inhale it. Sending it to atmosphere would make the problem much worse, lol. Didn't mean to imply that path of action!

    That sketch is a copper pipe/tube, not copper wire. The idea was to use the copper tube as an insert that would direct the bypassed air towards the intake manifold and prevent the air from heading back towards the MAF. Before you do this, let's go back a step and I'll find out more about the Power Pipe.

    How is the bypassed air introduced into the Power Pipe? The external part of the bypassed air return connection looks like it is at 90-degrees to the PP. Inside the PP, is there any extension of the bypassed air return tube? If so, is the extension closed on the side towards the MAF but open towards the intake manifold? [This is what the copper pipe insert would look like.] This arrangement forces the bypassed air to join the fresh air in the same direction -- towards the engine. If the bypassed air connection is flush with the inside of the PP then the bypassed air enters the PP at high velocity, travels across the tube, hits the opposite wall, and goes towards the MAF (causing backwash) and towards the intake manifold (the way we want all of the air to go).

    I can work up a more formal sketch, if necessary. First things first: more info about that bypass return port, please.


  8. Thanks Chris.

    I have dyslexia and sometimes when im reading things online I miss read things like the copper wire instead of copper pipe. Now I'm understanding what your talking about. You saying to stick the copper pipe in the end of the power pipe that the by pass valve connects to. That way the air is thrown towards the propeller instead of the maf. Last time I looked at the power pipe was a year ago, but I dont remember seeing anything at all inside the pipe. If this is a problem and has always been a problem does that mean my tuner tuned my car around it without telling me? Sounds like a good idea to get that pro racer package and work on a new tune.

    Sucks though, I went to court over that mini race and I was fined 400 for having it. This is why I hate California. I cant wait to move out when I'm finished with undergraduate school, but it all depends where i end up for grad school.

    I have class in 30mins, but when i get back I'll go ahead and take the powerpipe off to double check the inside.

    The main question I have though, If I did stick a pip that fit inside, How could I get it to stay? I'm afraid of the pipe getting pulled into the power pipe then sucked into the propeller. If anything it can be just temporary that way I can get a log to see if it did anything then if my friend comes over this weekend or soon. I might just remove the powerpipe and see if I can get a 90 or 45 degree bend welded in instead as more a permeate fix then as well add another bypass valve asap.

    If anyone has any photos of something like this please post some. Whether there welded or not.

    Thanks again guys to helping out, updating, and being patient with me. You guys are great!
  9. Well after examining the power pipe i found oil inside of it. I also found the bypass valve air to being forced into the wall of the pipe like you described. Could the bigger bypass valve have somehow made it not as bad or is this something ive always had issues with and the tuner failed to acknowledge me about.

    Honestly, I'm just going to buy another bypass valve and stick it on the car and see what happens. I'm running a 2.87 pulley and its possible that even at low speeds im creating boost which explains why tons of air is being forced into the powerpipe causing the maf to go hay wire.
  10. mat82284:

    The smaller bypass valve is passing the same amount of air as the big one but the velocity through the little fella is much higher. The momentum of the air carries it across the pipe and it smacks into the wall, most going towards the propeller (LOL!!) but some heading backwards towards the MAF.

    The copper pipe would have coupling (sleeve) or reducer (3/4-to-1" or 5/8-to-3/4", for example) soldered on so it could not get into the PP. The rubber hose connects over the coupling or reducer and everything stays in place. Having a 45 or 90 welded on to the inside of the PP would be the best solution, imo. I didn't know if you had access to a welder so I figured a trip to the hardware store would be easy.

    Hypothetically (since we don't want to break, just bend, the law), you could install your old (larger) bypass valve for testing purposes. If the MAF signal settles down, you know that the little valve is causing you some trouble. Then, you can sort out your fuel issues.

    You're a busy lad: college classes and sorting out your engine problems. Too bad you can't get credit for the hours spent on the Mustang.

  11. I dont have access to a welder, but I just figured any exhaust shop could handle it. I went to the hardware store and bought this (picture below) except mine is 3/4in to 1in. the 3/4 in is the part with the threads. How would this work? The threads are backwards how could I get it in the whole? Do I screw it in from inside the pipe, is that what you were thinking?

    As for the piece, They had metal and plastic, but i figured if it ever came loose I'd rather it be plastic than metal. At least plastic would get chopped up by the propeller causing minimal damage to the engine at least. possibly saving the supercharger as well.

    I wish i UCDavis had a basic auto mechanics class. They only have stuff for engineer majors. Otherwise I'd be taking some of those to get more experience.

    I wish I had the mini race still. I actually sold it after I got that ticket. I figured since i wasn't going to use it why keep it. Now I wish I had kept it for testing purposes at least lol. Oh well. I'll give this idea you have a try. I wont be able to tear my pipe out until tomorrow, since I have a final tomorrow, but if you have anymore have any more tips id like to hear them.

    I was thinking about the oil in my power pipe. I used to get a small amount of oil, but it was very tiny. Now it was like 80% more. The supercherger makes boost fine and im sure its not the supercharger. I'm thinking that the bypass air is flowing into the crankcase causing oil to get into the powerpipe from the valve cover hose. When I fix this issue, i'll clean it all out then look for an oil leak again afterwords.
  12. I forgot to ask. If I extended say the hose, wouldn't the pressure in the hose slow down that way it wont be as strong flowing into the pipe. I was thinking of adding 3 feet or so to help slow the air down. If the 90 degree elbow worked then I'd only extend the hose by say 1-2 feet as extra precaution. Unless you think that's a bad idea?

    The other question I have. I keep reading that the stock bypass valve sucks. If you put two of these would it flow enough to be equal to a mini race? A mini race is about a 2" pipe and two of the stock bypass valves are 1" each. Wouldnt it flow the same or is there more to it?

    Honestly, I'm thinking of buying another mini race or a mondo bypass valve and slapping it on. Since California is hell on smog, I was thinking of putting it near the inter cooler hidden from view. That is if this is the best option. If two stock ones flow the same I'd rather do that, but for some reason I feel its not possible.

    I just thought of a way to test your theory. If i cant use that pipe to turn the air, could I make a whole in that blue silicone coupler to run the air directly to the propeller?

    What about splitting the hose in two, one hose goes to the new inlet at the silicone and one at the old one? Or would it be best to plug the one in the Anderson pipe?
  13. mat82284:

    Longer hose generates pressure drop so it keeps pressure on the blower and this is not what you want (for mechanical reasons). Short hose is a good thing.

    The 1" dia. bypass valve has about 1/4 the cross-sectional area of a 2" dia. valve. (From geometry: area = pi/4 * D ^2 so 1" dia. is about 0.75 in2 and 2" dia. is about 3.14 in2.) The same quantity of air has to be bypassed but the smaller valve diameter means that the velocity of the air is much higher through the valve. Two stock valves will give a total of about 1.5 in2 vs. 3.1 in2 of flow area for the mini-race valve. Two stockers would be a good improvement over one but not as good as the bigger valve. Is the problem that the bypass valve has to have a CARB number? What other/bigger valves does Vortech offer that are CARB-certified?

    Good idea about adding a second port. This will give more flow area so the air will have a lower velocity at the current bypass connection into the PP. This would help to reduce backwash at the MAF.

    The fitting: I don't want to be Mr. Buzzkill but the reason I did not suggest plastic is because it is thick. The inner diameter of that fitting is small and the air velocity through it will be very high. It would definitely send the air towards the propeller (LOL at that term still) but it will also restrict flow and limit how fast the bypass could dump air. This means that the blower would remain pressurized when you don't want it to be.

    I like the Don's idea of the second valve (bigger, if possible) near the I/C. That takes most of the bypass flow 'load' off the little valve near the MAF and backwash would be eliminated.

    GL with your final. Don't worry too much about your Mustang. There will be plenty of time to sort it out after the important stuff is done. [/parental tone]

  14. Thanks, The only reason I bought plastic was that it was skinner than the metal one I seen lol. We'll anyways it sounds like I should buy another mini race or mondo bypass valve and run that and the stock one. I figured I'd hide it in fender righter after the intercooler. I talked to vortech and they don't have any carb approved by pass valves for CA. The only bypass valve that's legal is the black one and that's because the kit comes with it. Since the kit doesn't come with the others as a choice its not legal. It's stupid because a bypass valve does nothing to hurt emissions.

    I'm not sure if there are other legal ones, but from what I've researched I doubt there is.

    I have a question though, When my car was tuned the mini race was on. The tubing is exactly the same. Then only difference is the bypass valve. I basically took the mini race off and put the stock on in its place. Nothing else was changed. If that's the case, wouldn't the amount of air going to the power pipe be the same and flow at the same velocity?

    If thats the case then my tune is probably not the best, would the computer adjust accordingly when the maf backwash dissapears?

    Thanks again, The final went well :)
  15. We'll I just purchased a Mondo Unit. I remember last time when I had the mini race I still heard fluttering sounds. I plan to mount this in front of the intercooler, hidden away in the fender. I will also run two bypass valves. I'll get a new hole welded on for the mondo. Should I still worrry about trying to turn the air towards the propeller with the mondo installed. I was also thinking that maybe I should dissable the stock bypass somehow and just make it look hooked up. Like, putting a plug where it connects to the powerpipe and connect the hose to the plug to look like its working. Would that be ok, or should i just let them both be hooked up?

    Sucks though. I would have rather spent that $300 on a pro racer package :( I'll definitely get that package here soon hopefully. I still have to pay my stupid $450 ticket too.
  16. mat82284:

    Glad to hear your final went well.

    LOL about the elbow. Usually, a copper elbow (like the ones found under the sink) are pretty thin-walled so the inner diameter is not too much smaller than the outer diameter. Bigger ID means more area for flow and lower velocity. Plastic is fantastic so maybe the manuafacturer has been able to put his fittings on a diet.

    The amount of air being bypassed is exactly the same regardless of the size of the bypass valve installed. The difference is the inside diameter of the bypass valve and the connecting hose to the PP.

    As the bypassed air enters the PP, it has momentum to keep going in a straight line. Momentum is the product of mass times velocity, MO = m*v. Using our example of bypass air in a 1" vs. 2" valve/hose combination, the air in the 1" valve will have a velocity of about four times higher than the air in a 2" valve. The momentum of the air in the 1" valve is about four times higher than the air in the 2" valve. The air in the little valve and hose has a lot more momentum to smack the opposite wall and travel backwards down the PP towards the MAF. It also has a lot more momentum to smack the opposite wall and travel forwards in the PP towards the propeller (LOL!).

    Using a larger valve, or a valve in parallel with the black valve, allows the bypassed air to enter the PP at a lower velocity and momentum, and little, if any, backwashing of the MAF.

    Now before you get your PP modified, what size of hose/tubing was connected to the mini-race valve? The black valve is not at the inlet nozzle of the PP: there is a length of hose connected to the discharge of the vlave and then to the PP. I can't see the hose connection clearly at the PP. Is the hose slipped over the PP stub? Having the hose slipped over the stub will make the stub the "thin spot" but Vortech has sized this nozzle for the expected maximum bypass air flow (so the velocity should not be excessive). It looks (to my old eyeballs) like there is something that is not just the blue rubber hose at the stub. Was any of this area changed any when the black valve was installed? Can you take a close-up picture of that nozzle, please? (I am trying to see the connection detail at the PP.)

    If you get your PP modified, have your welder the new stub in at 45 or 60 degrees instead of 90 degrees. This reduced angle will direct the bypass air towards the propeller and away from the MAF.

    Last thing: you may want to discuss all of this (single bypass valve or two in parallel, PP mods, etc.) with Don before proceeding. He can help you with exact locations and routing and hose sizing. (I don't know if he is still keeping track of this thread.)

    It is a pity that Vortech has not (yet) gotten the larger bypass valves approved. As you said, a bypass valve, big or small, performs the same function.


  17. The mini race was connected to the blue hose before. The blue hose goes below the PP then does a 45degree turn into the PP. The blue hose has a metal pipe inbetween to connect the blue hose to the black one. There is already a 3/4in plastic piece going into the PP on the outside. The hose connects to that, so it doesnt go over that piece on the pipe. I tried to install the 90 degree elbow I bought, but the threads on the reverse side are messed up so it wont screw in. I couldn't get it to fit so i bought the mondo valve. I was trying to think of another way to test, but I can think of any. I wish the threads were fine at the end. When it was welded up the end has weld spots on it that are bigger than the threads which is why it wont screw in from the inside of the pipe.

    As for the location, I pretty much have no choice but to toss it in after the intercooler. I need it hidden from plane view. That way If i get pulled over again the cop will see the plastic one and not see the other one hidden in the fender from view since you'd have to remove the bumper to access it.

    I'm just really tired of my car running badly. I hope after all this its back to normal or better than normal. I just bought a wideband 02 sensor kit as well. I figured I need to log my air fuel better, plus this is needed for the pro racer package so now im one step closer to that purchase. At the very letest i'll pickup the pro racer package in October. It all depends on my cash flow.

    I guess Don went on vacation or hasn't revisited this thread. Its possible he stopped getting e-mail notifications, I know i did. So I just recheck the thread a couple times a day.

    Your a very intelligent guy, Thanks for all the wonderful information. It's been very helpful and informative.


    I did want to ask though. That 1 bad rear 02 sensor, should I replace that asap? If its not working at all and its enabled on my ecu would that screw up my air fuel ratio?
  18. mat82284:

    A faulty rear O2 sensor is only going to say to the PCM that the catalyst is not performing well. No biggie (unless the CEL is on and you're due for an emissions check).

    Thanks for the description of the bypass plumbing. I have a better idea of what is there now. But I am a little troubled.... The bypass inlet tube has a 90-degree bend on the inside now? If it does then the bypass air is directed towards the propeller (LOL still). And, if there's a 90 inside then my theory of the flow going straight across, smacking the wall, and going down to the MAF and up to the propeller is a load of horse hockey. So much for your theory of me being 'intelligent', lol. Is there a 90 inside the PP? Is it possible to put the rubber hose on the metal stub rather than connecting it to the screwed-in insert? Like we discussed before, the insert reduces the inside diameter and increases the bypass air velocity coming into the PP. Eliminating the insert allows the full inner diameter of the stub to be used and the air velocity will be lower (so less momentum of the incoming bypass air).

    The WB is a great idea with a blower car, imho, and ought to be standard issue with a supercharger. That's a good investment and can save your engine from an untimely death.

    Hey, don't get discouraged about the current running condition of the car. It will get better. Think of the sense of satisfaction (perhaps, bordering on smugness?) you will have when your Mustang is running great in the near future.

    Post an update of your fuel tank/fuel pump investigation, please. (Not pushing, just interested.)

    We're getting there!

  19. Oh ok sounds good. I might not get to the tank this weekend. I still have a full tank I havnt been driving lately. If anything it'll be a little in the week. As for the PP. The bend I was talking about is in the tubing not in the power pipe. Its what allows it to fallow that path of the red line In that photo. The plastic piece fits into the socket on the power pipe. The hose is actually to small to fit over that part otherwise I would have removed the plastic piece and did it that way.

    What I meant to say eailer is that the plastic piece only screws in on the outside of the PP it doesnt screw in on the inside. I wish it would though then I can push it towards the propeller. Since it wont I have no way to test that theory. So your not wrong yet. I'm sure your theory is right. The plastic piece just directs the flow to the wall of the pipe causing it to split in two directions. One towards the maf and one towards the blower. I hope you understand my description. If not I'll see about doing a video since pictures wont help with this description. I don't know of any other way to direct the flow of air since I cant screw anything in from the inside of the pipe. Only other way is to weld in something, which I'll just wait since I need to weld my new wideband in, and bypass valve.

    I'll keep you updated. If you have anything else I could try let me know.

  20. mathew:

    Thanks for the info/answers.

    Another question: was the plastic insert part of the original installation? If so, I am worried about my theory! Here's why: the valve is far away from the entry into the PP so the size of the vavle won't have any effect on velocity. On the other hand, a larger valve or a second valve in parallel will reduce the pressure in the system faster. Perhaps the problem is that the blower is still seeing backpressure (generally, this is bad for a compressor since it can move the operating point into an unstable region known as surge). Now we have two theories.


    Did a little searching on Corral and found some interesting info. One fellow was using the stock Bosch bypass valve, p/n 0 280 142 102 for 7 psig. another poster suggested going to an Audi/Saab dealer and getting the 710N Bosch bypass, p/n 0 280 142 110 because it is rated up to 15psig and the price is right at $50.

    end of edit