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Thread: Somewhat Functioning Turbo Car - Part 2

  1. #1
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    Somewhat Functioning Turbo Car - Part 2

    All, going to try to start diagnosing some issues that have been ongoing. Started a thread a couple years back trying to chase this but didn't want to continue on that thread since nothing I really did fixed anything there.

    Details on car:
    • 95 M3 chassis
    • OBD1 RK Tune
    • 3k ish miles on rebuilt S52 block (forged rods/pistons)
    • AEM Wideband (LSU 4.9 I think)
    • GT35R Turbo - SPA manifold
    • Exhaust built by CES Motorsport
    • Tuning done at CES by Jordan (remote)
    • Wahlbro pump is on relay direct to battery


    Old thread: https://www.bimmerforums.com/forum/s...urbo-Car/page4

    Long story short, from day 1, the car would always seem to drive and run fine with the exception of leaning out randomly while idling. It is an RK tune and I've had Jordan make me a handful of revisions trying to chase the issue. I'll include a list of things I've done/changed below that have not made a significant impact. I changed the MAF out at the end of last summer and that seemed to make things a bit more stable as far as AFR goes, and possibly a little more rich but that only really tells me the MAF wasn't the real issue but was possibly on its way out.

    After letting the car sit for quite a few months while traveling for work, I came home to an almost dead battery. Had some voltage inside but only got a click when going to start. After I jumped it and drove it the battery is holding a charge just fine, but I'm getting richer running conditions than before. Not that the dead battery was the cause, but I wanted to make sure I was clear on that.

    As of right now:
    • Every time I start the car cold it idles very rich, even when warmed up (about 12.5 AFR).
    • Driving around while cruising I'm getting 11s to 13s on AFR. THIS USED TO BE CLOSER TO STOICH before this year.
    • Highway cruise at 3600 rpm is about 11.8-12.5.
    • Every now and then when warm the idle will lean out really bad like it has in the past.
    • When turning the wheel while stationary (as to put load on the engine), it will cause the AFRs to shoot up (see second to last video below).


    Here is what has been changed/checked:
    • New OEM 3.5bar Bosch Fuel Pressure Regulator (6/25/18)
    • Brand new MAF from Jordan (8/2017)
    • Swapped Crank Pos Sensor (7/2017)
    • Swapped Cam Pos Sensor (7/2017)
    • Checked timing (many times)
    • Boost Leak Checked (albeit over a year ago - has not been apart since)
    • Replaced/check vac/boost lines
    • New DME O2
    • Swapped several IACVs
    • Checked IACV boot
    • Temp Sensors are hooked up to proper plugs (ohmed from plug to DME pins)
    • Swapped battery cable from battery to Engine Bay (previous one had some bad corrosion inside jacket)
    • Checked idle voltage to fuel pump - SAT
    • Tried 5 different revisions to last tune with more/less fuel at idle and adaptation on/off
    • Checked O2 relay and wire harness - SAT (have not scoped)
    • Checked Fuel Pressure at Idle - was where it was supposed to be.
    • Swapped alternator that was on car for another one and swapped back
    • New battery last summer


    Here are a couple running videos I took yesterday. Let me know your thoughts on what to look at. I have not checked fuel pressure while driving, but I have a new OEM FPR on the way. I'm thinking it's a fueling/voltage issue still.

    This is the car idling with the AC Compressor Off:


    Idling with AC on full blast:


    AC Compressor Cycling On/Off:


    Turning the wheel to produce load - leaning out:



    Older video (last summer) of the idle going from rich to lean inconsistently, this is still happening on occasion:
    Last edited by ty20404; 06-26-2018 at 08:33 AM.
    1995 M3 Coupe - Cosmos - CES Built S52 Bottom End - JE Pistons - Eagle Rods - S52 Cams - GT3582R - SPA T3/4 Manifold - RK Tuned - 513rwhp
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  2. #2
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    Tried a different throttle body yet?

  3. #3
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    Quote Originally Posted by Mklock View Post
    Tried a different throttle body yet?
    I have not. Do you think that would cause my AFRs to shoot up when the power steering gets loaded?
    1995 M3 Coupe - Cosmos - CES Built S52 Bottom End - JE Pistons - Eagle Rods - S52 Cams - GT3582R - SPA T3/4 Manifold - RK Tuned - 513rwhp
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  4. #4
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    Oh, I'm no expert and have no idea if that will help. I'm just another set of eyes and noticed that maybe you've not tried that. I'd say give it a go; one less thing you can cross off. (Careful with the throttle cables they have weak fittings)

  5. #5
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    I think I'm most curious to see if anyone can definitively say that this is a voltage/fuel pressure issue. I have no way to log fuel pressure or voltage. I've checked voltage at the pump (only on the outside of the tank) which was fine at idle, and I've checked fuel pressure at the rail (with a shitty gauge) at idle and that was fine as well. The AFR increase when loading the power steering pump is what has me confused/focused on voltage/pressure.
    1995 M3 Coupe - Cosmos - CES Built S52 Bottom End - JE Pistons - Eagle Rods - S52 Cams - GT3582R - SPA T3/4 Manifold - RK Tuned - 513rwhp
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  6. #6
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    http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf

    Download that. You more than likely have a lose/ corroded/ damaged splice in the cowl or at the fuse box or in the dme connector. There are lots of old and beat up wiring harnesses on these cars now, shorted relays that damaged a connector and it has taken 20 years to become a problem.

    Start with the 12v bus, check everything.

    I would start with injector wiring. I've seen the pins push back in the connectors more than once. I've also seen the pins loosen up and make poor contact. If those all check out good start on to the next thing. You need to be methodical and just go through everything.

  7. #7
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    Quote Originally Posted by Kevin325i View Post
    http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf

    Download that. You more than likely have a lose/ corroded/ damaged splice in the cowl or at the fuse box or in the dme connector. There are lots of old and beat up wiring harnesses on these cars now, shorted relays that damaged a connector and it has taken 20 years to become a problem.

    Start with the 12v bus, check everything.

    I would start with injector wiring. I've seen the pins push back in the connectors more than once. I've also seen the pins loosen up and make poor contact. If those all check out good start on to the next thing. You need to be methodical and just go through everything.
    I hate to say this but I've checked every connection on the engine harness. I've ohmed every connector back to the DME in hopes of finding either a grounded out power wire or just a broken or crappy wire. Literally, every wire. I suppose at this point I could entertain getting a "new to me" engine harness but that is a lot of work for something I've already somewhat ruled out.
    1995 M3 Coupe - Cosmos - CES Built S52 Bottom End - JE Pistons - Eagle Rods - S52 Cams - GT3582R - SPA T3/4 Manifold - RK Tuned - 513rwhp
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  8. #8
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    Replaced the fuel pressure regulator with a new OEM regulator today with no change in behavior. Checked voltage again at a few places.

    Voltage at Battery: 14.6
    Voltage at fuel pump connection: 13.7
    Voltage at auxiliary fuel pump relay: 13.8

    I swapped out a few relays into the connector for the relay and didn't get any real change in behavior. I'm going to probably swap out the relay wiring harness all the way to the battery and see what happens. It has been leaning out at idle w/o the A/C on and every time I kick the A/C on the AFR drops right down to 12.5.

    This doesn't seem normal to me to have this much voltage drop from the battery to the connection point at the fuel pump but I'm also confused as to why there is no change in voltage associated with the drop in AFRs when the A/C is turned on.

    Side question: does a properly functioning IACV buzz?
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  9. #9
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    u sure that gauge is accurate because ur maxing out lean i don't think it would even idle at least my car.

    i see you have the pump wired directly to battery what gauge wire is that?
    mine is 14g from pump to relay and 10g to battery reads the same as batt v.
    Last edited by Robocop; 06-26-2018 at 05:14 AM.

  10. #10
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    Quote Originally Posted by Robocop View Post
    u sure that gauge is accurate because ur maxing out lean i don't think it would even idle at least my car.

    i see you have the pump wired directly to battery what gauge wire is that?
    mine is 14g from pump to relay and 10g to battery reads the same as batt v.
    I'm fairly certain it is accurate. Was a PLX LSU 4.2 after I had the car tuned and I ended up swapping to an AEM LSU 4.9 setup in the midst of chasing this problem. No difference between them. I will say that when it leans out, it misfires and sputters pretty regularly... Then it corrects itself eventually and the AFRs come down, then it cycles all over again.

    Pump is wired directly and I want to say it is 12 AWG the whole way based off of my experience but I did not read the jacket. I've got a SPAL fan harness on the way that I'm going to potentially swap in. I need to ohm out the harness and see if there is an issue with that but even still 13.7V is what the Walbro pump is rated at (13.5V really). As long as it is steady this shouldn't be the problem???
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  11. #11
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    Notes from messing with some stuff last night.

    6/26/18


    • Started vehicle and voltage at Fuel Pump Terminals started at 13.63 then quickly up to 13.75
    • When voltage at 13.75V, AFR at 11.7ish, increased up to 13.82V.
    • After one minute or so voltage at Fuel Pump increased to 13.86V.
    • After five minutes or so, steady state voltage at FP was 13.88V.
    • Unplugged TPS, no change
    • Adjusted TB idle screw so it wasn't touching plate on butterfly actuator, no change
    • Adjusted TB idle screw open until it just barely changed idle - AFR went down from 12.5 to 11.7 and revs came up some.
    • Adjusted TB idle screw back to original
    • Unplugged MAF and engine died - should it do this?
    • Vacuum is at 19 inHg when idling through all of this


    Need to check what Voltage does when I kick on the A/C and or Aux Fan but from what I'm seeing everything is pretty steady. I'm starting to think I may have an issue with the Engine Harness in some capacity. I can't imagine why it would be so erratic in idle and why it over time has gotten to run richer and richer.
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  12. #12
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    It goes

    MAF -> ECU -> Injectors

    What I think is happening, mostly because of what I see in the last video,

    What you see is caused by the compressor buffeting the maf hotwire. The turbo compressor is gaining speed at idle and as the flow increases it becomes more than the engine wants. The OEM solution to this is to use a bypass valve that hangs open at idle allowing air to bypass back to the pre-compressor region (post air filter) which raises that region in pressure slightly and allows the turbine to gain momentum (rotating kinetic energy, The more of this you capture the less lag you have). On your car I am guessing you don't have a recirculated bypass (I mean, who knew?!) so what happens instead is as the compressor approaches flow values larger than the engine wants, this tries to create additional pressure (boost). if you look at the compressor map for this turbo you will notice that at idle flow-rates the map is wayyyy off to the left, in the surge region. So instead of creating boost the air flows backwards through the compressor (surge condition) and towards the maf hot-wire, which slows/changes maf airflow readings and causes turbulence between the maf and compressor. During surge the compressor is slowing down. Once it slows enough the process repeats, it gains speed flowing more and more until it overwhelms the engine again and the air "dumps" back out of the compressor and into the maf tube, "stalling" the air there and causing the lean condition.

    - - - Updated - - -

    I also notice an apparent lack or malfunction of closed loop. The computer can auto-correct high vacuum situation a/f ratio if a closed loop of some kind is enabled. With big injectors it may be necessary to keep closed loop "off" near idle. It depends on the injector quality (response/control/resolution for step size and transient delay which in some computers cannot be adjusted).

    What I usually do in my tunes is checkerboard the cruise regions with 14.8's and 15.2's, so it typically falls within those ranges and subtle alterations that closed loop would normally account for (.1-.3 a/f ratio) one way or the other put me either back to 14.7 or 15.4 which are also fine, because remember the checkerboard effect means it won't sit on either 14.7 or 15.4 it will wander between those values as you drive.

  13. #13
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    Quote Originally Posted by Kingtal0n View Post
    It goes

    MAF -> ECU -> Injectors

    What I think is happening, mostly because of what I see in the last video,

    What you see is caused by the compressor buffeting the maf hotwire. The turbo compressor is gaining speed at idle and as the flow increases it becomes more than the engine wants. The OEM solution to this is to use a bypass valve that hangs open at idle allowing air to bypass back to the pre-compressor region (post air filter) which raises that region in pressure slightly and allows the turbine to gain momentum (rotating kinetic energy, The more of this you capture the less lag you have). On your car I am guessing you don't have a recirculated bypass (I mean, who knew?!) so what happens instead is as the compressor approaches flow values larger than the engine wants, this tries to create additional pressure (boost). if you look at the compressor map for this turbo you will notice that at idle flow-rates the map is wayyyy off to the left, in the surge region. So instead of creating boost the air flows backwards through the compressor (surge condition) and towards the maf hot-wire, which slows/changes maf airflow readings and causes turbulence between the maf and compressor. During surge the compressor is slowing down. Once it slows enough the process repeats, it gains speed flowing more and more until it overwhelms the engine again and the air "dumps" back out of the compressor and into the maf tube, "stalling" the air there and causing the lean condition.

    - - - Updated - - -

    I also notice an apparent lack or malfunction of closed loop. The computer can auto-correct high vacuum situation a/f ratio if a closed loop of some kind is enabled. With big injectors it may be necessary to keep closed loop "off" near idle. It depends on the injector quality (response/control/resolution for step size and transient delay which in some computers cannot be adjusted).

    What I usually do in my tunes is checkerboard the cruise regions with 14.8's and 15.2's, so it typically falls within those ranges and subtle alterations that closed loop would normally account for (.1-.3 a/f ratio) one way or the other put me either back to 14.7 or 15.4 which are also fine, because remember the checkerboard effect means it won't sit on either 14.7 or 15.4 it will wander between those values as you drive.
    Yes definitely don't have recirculated bypass... But wouldn't my TiAL BOV do essentially the same thing? Only allowing the engine to take what air it needs at lower RPMs and essentially vent any excess "boost" created by the compressor? Is the spring in my TiAL not the right size or strength? Maybe it's not open far enough to prevent this buffeting at idle?

    Jordan has sent me several versions of tunes with "O2 on" or "O2 off" which is his way of saying that adaptation is either on or off... I don't notice a difference either way. I'm running the Siemens Deka 60lb injectors. They were brand new in 2016, ordered from TRM.
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  14. #14
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    So I went over to my shop and checked. The BOV is open at idle. It is located 5" past the IC outlet so it is a good ways from the MAF. I had the piping from the IC to the throttle body reworked by CES 3 years ago as well as the TiAL BOV installed (had a Synapse before).

    Should this BOV be open at idle when pulling 18" of Hg a minute after cold start???

    I also have a new 60lb base tune from Jordan that I'm hoping may address something since I swapped my old (2012?) MAF for a new one last summer.
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  15. #15
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    I thought you have a maf sensor? Where are you releasing air to? If the maf "sees" air going in... and then you are letting it out to the atmosphere... the engine will run rich because it goes

    MAF -> COMPUTER -> INJECTORS

    Maf measures air, computers inject that much fuel. Any air you leak anywhere is going to be fuel injected that wasn't expected. This is why we pressure test our systems and bypass valves.

    The short answer is, lets just jump to a diagnosis here. To diag this issue immediately we need to:
    A: pressure test the engine to 20psi or whatever you intent to run for long as you intent to run it
    B: Setup a test on running engine which prevents the turbo speed from interfering with a/f ratio or verify shaft rpm with a/f ratio coorelations
    so,
    1. use a wheel speed sensor to coorelate a/f ratio changes with impeller rpm
    or
    2. stop the turbo from spinning somehow (hold it still) and see if idle a/f ratio fluctuations disappear
    or
    3. create a pressure leak (install a bypass that hangs open at idle) and verify it is open at idle and sends all air back into the pre-turbo inlet tube, which is post maf sensor. This way air is directed from intercooler plumbing to a post-maf location and won't be counted twice by the maf sensor. The circuit needs to be large enough to support the highest shaft rpm achievable necessary to prevent surging.

  16. #16
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    right now it sounds like you have a maf + atmospheric bypass which explains the constant changes and generally too rich behavior. Correct me if this is not the situation. stock-related Fuel system issues go either too rich a tiny bit or extremely lean and blown apart for whatever reasons. The rich problem is a subtle influence that gradually darkens spark plugs with carbon chain fragments "soot" that over time can cause misfires. Subtle misfires can be maddening and you can ruin an entire good fuel map chasing a misfire issue and all this time it was just the plugs. The NON-recirculated bypass cylinder wash phenomenon is sometimes clued in maf turbo applications where users upgrade to "better blow offs" and wind up with 120psi compression across the board down from 165psi after 7 years of cylinder bore washing. Do not struggle with this simply recirculate or go with a MAP.

  17. #17
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    Quote Originally Posted by Kingtal0n View Post
    right now it sounds like you have a maf + atmospheric bypass which explains the constant changes and generally too rich behavior. Correct me if this is not the situation. stock-related Fuel system issues go either too rich a tiny bit or extremely lean and blown apart for whatever reasons. The rich problem is a subtle influence that gradually darkens spark plugs with carbon chain fragments "soot" that over time can cause misfires. Subtle misfires can be maddening and you can ruin an entire good fuel map chasing a misfire issue and all this time it was just the plugs. The NON-recirculated bypass cylinder wash phenomenon is sometimes clued in maf turbo applications where users upgrade to "better blow offs" and wind up with 120psi compression across the board down from 165psi after 7 years of cylinder bore washing. Do not struggle with this simply recirculate or go with a MAP.
    Itís a blow thru setup that most people on this forum run. Itís dumping air prior to the MAF. Trying to figure out why itís open at idle as it should not be. Also MAP means not stock DME which Iím not about. Standalone is great and everything but in todayís age these guys are good at tuning the stock DME. I appreciate the insight and Iím definitely utilizing this info to help troubleshoot but Iím not going away from the stock computer or my mechanical configuration as it works for just about everyone. Just need to figure out where the gremlin is and get rid of it.
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  18. #18
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    Air can still flow backwards through the maf. For example if there is no bypass during surge it would. The action of compressor discharge into the intake plumbing changes the atmosphere there dramatically, and maf sensors are not designed to work well in those conditions. This is my perceived diagnostic report, my sole conclusion is that blow-through maf setup without extensive stand-alone tuning is prone to situations like this. It only takes a slight change in voltage, perhaps .14v or .24v to make the a/f swing from 15 to 13 at idle air speeds. The size of the tube which is capable of some MAX HP determines the resolution of a MAF. This is why OEM tends to size a maf with a max HP value as low as possible, to get the most resolution from the maf tube. The compressor wheel provides a fairly wide range of streams, streamlines or pathlines, velocity vectors in fluid mechanics along a streamline in a fluid for example can be turbulent or laminar. There are a bunch of words engineers use, the key I am providing for your door is that the maf sensor is extremely sensitive, like very very sensitive to all the whipping around, back and forth, of liquid air in a tube between a compressor wheel and a breathing engine that pulls frequently on an manifold reservoir behind a throttle valve simultaneously pulling on the same tube. It is unlikely the maf sensor will experience many smooth flow situations, except perhaps ONLY when it is accelerating nicely through a gear. This type of gradual and smooth flow is what MAF sensors are famous for being extremely easy to tune well with, and is perhaps their one and only 'payback' for all the headache at every other situation.

    FWIW
    The bypass should be open at idle. It should feed a precompressor reservoir of pressure behind a filter. The filter should be large enough to fill the 'surge tank' of air reservoir behind which rests the compressor wheel. The pre-compressor reservoir gains positive pressure because the bypass feeds it an excess from the intercooler tube allowing the shaft rpm to rise with no surge. As the shaft rpm rises with no surge the bypass would open more and more and eventually shaft rpm is a maximum and the positive reservoir behind the air filter and in front of the compressor wheel will be well above atmospheric pressure. It "pre-boosts" the compressor wheel inlet region. And because shaft rpm is allowed to rise completely idle steady state there will be minimal lag.This is typically how turbo cars are from the factory. Sometimes the bypass gets "old and weak" and can hang open near part throttle when you want it closed, it lead to many owners installing aftermarket bypass valves on their 10+ year old turbo cars.

    I don't blame you for wanting the maf, they are great. But if you want it to behave you have some tuning to do. There are many ways to limit idle and part throttle MAF issues like this.

    For example SAFC-II has a setting that below some TPS You can limit max MAF voltage. That would put a clamp on idle fueling no matter what the maf says, no matter which way the air blows or how much leaks out. Ten years ago I used one of those to prevent cylinder washing on an atmospheric bypass MAF car with great success. In your case it would lock the a/f where you wanted it.

    to verify all of this, one need simply verify the maf voltage swing at idle when a/f dips into 13's. Check that the maf voltage is increasing simultaneously. If the maf voltage doesn't change then we look at other things like weird fuel pressure variations or something else. Poor closed loop algorithms. I would say repeat the test with the O2 sensors ALL unplugged.
    Last edited by Kingtal0n; 07-01-2018 at 01:34 AM.

  19. #19
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    I understand everything you're saying and you're right about a lot of it. What I'm trying to figure out is how a setup that most people are running on here is so problematic for me. I have a mechanical engineering degree and I agree that while most manufacturers utilize a recirculated setup, the tuners on this forum have been able to properly tune this engine on OBD1 to idle much better than what I'm experiencing.

    Either way my BOV should not be as wide open as it is.

    I converted over from 3.5mm ID line to 1/4" ID to the BOV. I also changed the location it was pulling from to another dedicated nipple (1/8" NPT to 1/4" barb). It seems as though the BOV is even more open than it was before. I removed the spring from the BOV per John's (CES) suggestion to make sure it was the correct spring. It was the natural silver color which has both of us stumped. I pull 18-19" Hg all the time unless it is falling flat on its face so why is the BOV open as far as it is? Regardless open or closed it isn't making much of a difference as I pinch off the line and it doesn't seem to make an impact.

    One thing that I may think you're right on is that the adaptation is getting thrown for a loop due to the BOV being open. Whenever I come down off of cruise, the car struggles to idle which I'm guessing it may be due to the fact that the BOV comes open and the MAF is not happy about the turbulence. After a little bit it will catch itself. This recent base tune seems to have the car idling more stoich than it was before but it is still exhibiting a lot of the same issues that the other tunes did.

    I will note that the first couple of times that I kicked on the A/C the AFR plummets from close to stoich (although swinging a good bit) to high 11-12.5, within a few seconds the CEL came on for a brief second then disappeared. It was code 1222 so I'm betting that the car wanted to see a much different lambda value than 11-12.5 when the A/C kicked on. I think it has finally adjusted fuel trim enough at this point so that the CEL doesn't kick on but I think the trims on idle are drastically different than what the tune wants to see. I'm thinking it is definitely possible that the open BOV may be the reason for this?

    I know last year when troubleshooting Jordan had me unplug the O2 to see how it behaved. I am going to try this again at some point here and see what comes of it.
    1995 M3 Coupe - Cosmos - CES Built S52 Bottom End - JE Pistons - Eagle Rods - S52 Cams - GT3582R - SPA T3/4 Manifold - RK Tuned - 513rwhp
    2008 M3 Sedan - Melbourne Red - 6MT - Bimmerworld Street Exhaust - Macht Schnell Intake - Daily Driver

  20. #20
    Join Date
    Jul 2005
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    California
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    Bima
    can't you just drive around with the bov disconnected see if that' the problem?

  21. #21
    Join Date
    Feb 2008
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    Wilmington, NC
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    95 M3 Turbo, 08 M3 6MT
    Quote Originally Posted by Robocop View Post
    can't you just drive around with the bov disconnected see if that' the problem?
    Per Jordan's suggestion I tried that once but didn't notice a huge difference. I think that if this is truly what's causing it, then it's so subtle it's just throwing off the fuel trims over a long period of time and simply taking it for a short (boost-less) test drive won't make a huge difference.

    I'm not even sure the BOV being open at idle is even really causing an issue... I'm going to swap coil packs out and see if that has any impact. I have 6 laying around from a different car. Will also try spark plugs to see if maybe that is the problem as well.
    1995 M3 Coupe - Cosmos - CES Built S52 Bottom End - JE Pistons - Eagle Rods - S52 Cams - GT3582R - SPA T3/4 Manifold - RK Tuned - 513rwhp
    2008 M3 Sedan - Melbourne Red - 6MT - Bimmerworld Street Exhaust - Macht Schnell Intake - Daily Driver

  22. #22
    Join Date
    Jun 2018
    Location
    Florida
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    My Cars
    240sx
    The maf sensor was never designed to run post turbo flow. It was also never intended to be run near an engine. Typically there are multiple curves between engine and maf, and the maf is placed in a straight zone with straight pipe to both ends.

    idle speed has the lowest flow-rate through the maf. This means maf sensor has the lowest resolution at low mass flow rates, this is it's least reliable situation to be in. Even the slightest change to airflow conditions can drastically alter maf output. Remember air can flow "through" a maf both ways; imagine the bypass is open between the turbo and engine somewhere. Air flowing in that direction means the sensor is getting "double the airflow" because air that already went through it is moving backwards now.


    The way I would tackle this (again but big picture)
    1. compression test if its easy enough
    2. inspect plugs or change them
    3. now that you have no misfires due to poor plugs and good compression go to #4
    4. unplug O2 sensors and take note of open loop a/f behaviors.
    5. If any issues arise in open loop, tune the engine properly and eliminate all air leaks from the maf plumbing. A maf sensor is an extremely reliable consist in operation when used properly, they require absolutely all air molecules going in only 1 direction with nice straight pipe on either side to alleviate turbulence.

    so,
    Good compression, no O2 interference, good tuning with no air leaks using a maf properly where there is no chance for reversion or leaking. Because
    MAF(used properly) -> ECU(tuned properly)-> INJECTORS (no leaks or seizures)

    If you see a/f variances or issues with a/f ratio, just remind yourself of the above

  23. #23
    Join Date
    Jun 2018
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    Florida
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    My Cars
    240sx
    I want to remind you that when issues with a/f changing occur the first step is remove closed loop operation from the equation. I just disconnect the O2. It is the first thing you should have done because it is the simplest and free. THEN get a video of any "issues".

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