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Thread: Turbo E36 Misfire Issue

  1. #1
    Join Date
    Apr 2024
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    Michigan
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    My Cars
    1998 BMW 328i

    Turbo E36 Misfire Issue

    I have just finished building my turbo E36 and cannot figure out why it is misfiring. It only misfires when switching to closed loop fueling. During warm up it runs fine. There are no codes either. These are the things I have checked already:

    - Ignition coils - tested hot and cold and resistance is within spec
    - Fuel pressure - tested slightly high (~4psi higher) from what I have found is normal for E36s
    - Spark plugs - using NGK V-power #4091 and swapped to other plugs and no change
    - IAT was faulty and swapped for a new one - no change
    - Oxygen sensors - swapped with spare sensor and no change - both worked fine before boosting
    - MAF is brand new - RK tunes kit
    - Injectors are brand new - RK tunes kit
    - boost leak tested - no leaks
    - have redone charge piping on cold side twice to get as straight as possible of pipe before MAF - 6 inches before and after MAF of straight pipe
    - Compression tested - low compression but 130psi on all cylinders
    - Leakdown tested - max of 6psi difference between highest and lowest cylinders
    - have checked all grounds and are good
    - DME - seems to have a slight discoloration on clip over one of the transistors - transistor itself looks fine
    - Ignition coil harness - checked and all have continuity
    - Checked timing - timing blocks slide over cams perfectly
    - Datalogged - seems to be trimming fuel more than I would think is normal


    I am suspecting that the discoloration on the DME coil driver is a red flag, however, I am not sure as the transistor itself looks fine. Compression testing low is also a concern. I am at the point of buying new cam, crank, and oxygen sensors and seeing if that will fix it. Or possibly a new FPR.

    I am lost on what could be causing this. Does anyone have any idea what could be causing the misfire in closed loop fueling?



    Sorry for the long post. Thanks!

  2. #2
    Join Date
    Jul 2004
    Location
    Houston, TX
    Posts
    12,662
    My Cars
    36 Cylinders
    What does you wideband sensor read when this is happening?
    -Abel

    - E36 328is ~210-220whp: Lots of Mods.
    - 2000 Z3: Many Mods.
    - 2003 VW Jetta TDI Manual 47-50mpg
    - 1999 S52 Estoril M Coupe
    - 2014 328d Wagon, self-tuned, 270hp/430ft-lbs
    - 2019 M2 Competition, self-tuned, 504whp
    - 2016 Mini Cooper S

  3. #3
    Join Date
    Jun 2005
    Location
    New England
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    F90 M5; E36 M3 Turbo
    Does the HFM require and special wiring such as bridging of grounds that you forgot?

  4. #4
    Join Date
    Apr 2024
    Location
    Michigan
    Posts
    4
    My Cars
    1998 BMW 328i
    The wideband reads 14.7-15.5. The HFM is wired how I was directed by RK. I checked continuity as well and everything checked out. I just retimed it last night following service manual instructions to a t thinking maybe I had installed vanos unit incorrectly or something. Started it up and still have the same issue. Will log and send to RK to see if he has any ideas. Doubt it is something with tune though as it targets stoic to 15.5 which is exactly what RK said it should be targeting at idle.

  5. #5
    Join Date
    Jan 2021
    Location
    Ny
    Posts
    91
    My Cars
    94e36, 00e39 532it turbo
    Every coil driver chip I have seen is discolored , ms41 ms42 and ms43. That's totally normal it's all gold and bubbly looking terrible on the dme board. I lost my vag smart coil piggy back box last year , and at first I thought the dme chip for the coil packs was suspect.... after researching and asking people who know more than me it's normal for it to look "hot"

    ( Smart coil box came from @turbothirty6 in Germany with r8 coils, he actually gave me a very heavy discount on the replacment even tho I think it was my over powered battery charger that killed the first one causing 2 coil packs to be inop. )


    What brand f.p.r, ?

    I know the radium f.p.r."'s were modified last year (a.k.a. recalled with out the recall part.) They originally came with different sizes aluminum for the bypass orface, a gold one a green one and mabye a silver one? . (That you can no longer buy) Then last year it all superseded to a new single steel bypass with a different flare on the seat. They also changed the diaphram so it has a bigger ball bearing that sits on the bypass seat. The original was with a ball that's too small/ design let fuel pass. In my case it lead to the diaphram tearing premature. (Brand new lasted only 2 tanks of pump gas) Do I think you have a fuel isue? No, not necessarily, more of a public service announcement.

    Did you replace your fuel filter? Do you have a inline mechanical fuel gauge ? They read differently based on temp. (Would be easy to set pressure low) I know mine on the rail seems to read lower at idol the hotter it gets,. The one under the car on the fpr tends to read more steady. (Im running Matching Radium gauges, -6 an line and return , flex fuel sensor on the return running x85 ape controller.)

    What pump? Did you use the correct hose between the pump and the lid inside the tank? Regular fuel hose can't be submerged. How did you wire the pump? Stock tiny wires?

    Your sure it's only in closed loop? Or is it under boost ? A.k.a, you have seen the same boost in open loop without issue? Is it misfires all the time even under light load? Your still seeing 15's on the afr under heavier loads? (Boost)

    Your fuel regulator has a dedicated vacum line running to the manifold ?

    Your sure you wired the 02 sensors right? The wires on my car were all black and yellow. It would be easy to wire one up wrong/or wrong bank by accident. You soldered your 02 wires? Or used solder shrink wraps? 02 sensors are sensitive, poor connections will cause issues and false readings. You calabrated your wide band if it calls for it?

    If I was going to fire the parts cannon I would start with 02 sensors and or coil packs. (Sounds like you tested 02 sensors) fwiw I know tired coil paks can fail so they misfire only when under load . I know rk says ntk (ngk) o2 sensors over Bosch with his tune. What wideband / 02 sensor brand do you run? Second parts cannon choice would be crank/cam sensor, as they are know to go bad and not throw codes. Before parts I would pull the injectors and test them for flow pattern. I usually just pull the rail with injectors still installed, lay it into a empty 5 gallon bucket , and crank the car to watch them spray. I would also pull one coil pack at a time, with spark plug. Ground out the spark plug threads while still in the coil pack. Crank the engine watching for a bright spark that looks similar out of each coil pack. You can pull the fuel pump fuses so you don't flood the engine as you test coils.


    Maf would also be suspect in my world. Logs should be able to see the maf is working right. Your maf is in the same size tube as the pipes? Earlier today I saw a 3.5" maf adapted to 3" pipes cause tons of issues running rich with the maf thinking it's seeing a colum of 3.5" air when it's really a 3" colum in and out. (Air likes to go strait always )

    Your coil packs have grounds on them? Your motor has one ground on the engine ? (I ran a second engine ground, one from each motor mount arm. ) You torqued your knock sensors to spec?


    No dash lights? No other weird issues ( that may or may not be related ? ) if it's got no codes how do you know it misfires ? Pings? Bucks? You can see it in the log?


    Only other thing I would suggest and always suggest as it caused a lot of my isues... The brake booster on these cars only lasts 10 or 15 years. You can't easily smoke test or boost test them as they have a one way between them and the manifold. Pop the big hose off, is it all rusty inside? Either way I would test it. Mine leaking made it add fuel at idol and pull fuel driving.
    Last edited by Sio2crew; 04-15-2024 at 01:41 AM.

  6. #6
    Join Date
    Apr 2024
    Location
    Michigan
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    1998 BMW 328i
    Ok thank you that helps. It is a stock fpr so it is possible that its just old and there is an internal fault or something. Will try to test it and see if that tells me anything. I am using an AEM wideband that says it doesn't need open air calibration like a lot of sensors do. 02 sensor is a new NTK. I did find out the wiring on the cam sensor was missing pretty much all of the insulation on the wires under the rubber boot. I got a new one (Hella) and hooked it up and now the car runs pretty much perfect at idle. I also got a new Delphi crank sensor and will install that as well. Now it will idle without missing at stoic or near it but any throttle causes it to go super lean. Like 18+ afr. The gauge won't read over 18 so now I am suspecting a possible fueling issue, MAF issue, or vacuum leak. I will boost leak test again and see if that reveals anything. I will also check the brake booster in case it is the cause of the problem. MAF is a 3" in a 3" pipe. All grounds are good. I have discovered that it was not misfiring just in closed loop it was just more noticeable at stoic or close to it. I guess I am not certain it is a misfire but I am not sure what else to call it. It just seems like the coils are not firing randomly.

    Now that it runs good at stoic but with any throttle it misses and the afrs are very lean I am suspecting it just is not getting enough fuel. I have also found that if I unplug the MAF the car will die. I was under the impression that it should revert to a base map when it does not get any data from the MAF. Does it dying with the MAF unplugged mean anything? Tested at idle BTW

  7. #7
    Join Date
    Jun 2005
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    F90 M5; E36 M3 Turbo
    A lot of people have had trouble with aftermarket cam sensors, even ones from otherwise good companies. There was a post in the past year or two from someone with an RK tune and apparently the tune was not flashed properly. That seems like a one-off type failure.

  8. #8
    Join Date
    Jan 2021
    Location
    Ny
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    94e36, 00e39 532it turbo
    A 98 should have the 3/2 valve under the car aproxametly under the driver's feet. Did you delete this valve? known to cause fuel issues on occasion. I just left the wire clip zip tied up out of the way when I removed that valve assembly on my e39 build.

    https://www.bimmerforums.com/forum/s...ve-Information

    If you have not replaced the fuel filter I would do that asap.

    Are you resetting your adaptations after you made changes?

    I'm not sure about your maf.

    My cars run OK with the maf unplugged. My turbo s52 car is mid 14's to mid 15's afr with the car at idol or light load maf unplugged. I never tried to push boost with no maf. As far as yours stalling, I never tried pulling the plug while it was running. I always disconnected or connected it with the car turned off. (Stock maf on my m52, stock maf on my m52tu. Hpx brand maf on my turbo s52. They all will run with the maf unplugged. ( tested no maf troubleshooting in the past)
    Last edited by Sio2crew; 04-20-2024 at 08:25 PM.

  9. #9
    Join Date
    Apr 2024
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    1998 BMW 328i
    SOLVED

    The 3/2 valve is not deleted and the fuel filter was replaced about a year ago. Turned out to not be the issue. I have thought about it possibly being the purge valve for a while and taking the vacuum line off to the manifold but never actually tried it thinking that it was probably not the issue. Tried it today and the car runs MUCH better. Still a little bit of sputtering but I am thinking it may be the fueling on the tune just needs to be adjusted. Drove it and it has plenty of power and don't feel any misfires or anything.

    I am thinking the purge valve may have a vacuum leak which was causing it to run badly. It didn't show up when I boost leak tested it bc I have a check valve.

    Car runs 14.7-16 at partial throttle (still a little bit lean but thinking fueling just needs to be adjusted). Heavier throttle it runs 10-12 which I believe is about where it should be. VERY happy to finally have figured this out after about a month of testing just about everything I could possibly think of. Thank you very much everybody for all of the support in trying to figure this out!

    For all of the turbo guys that have tested pretty much everything else and are still having this issue I would suggest unhooking the vac line to the purge valve and seeing if that helps at all. Hopefully this will help somebody out if they are pulling out their hair trying to troubleshoot.

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