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Thread: 1994 m50 Limp mode help!! 3500 rpm rev limit 5 speed

  1. #1
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    1994 m50 Limp mode help!! 3500 rpm rev limit 5 speed

    so! my trusty old 94 e36 is starting to give me some weird issues. I wanted to ask some people with possibly more experience before i tear it apart and just start throwing sensors at it. The car has run into an issue recently where it is running into a 3500-4000 rpm rev limit in any gear. in neutral just sitting at idle it usually lets me rev it out fine. This happened a few weeks ago and i coughed it up to being the maf. The car was driving normal again after disconnecting the dme (i was checking to see the condition). I thought it was maf because i disconnected the maf just after and it revved out just fine at the time but i was ignoring that i may have reset the computer by disconnecting it. So after a hard day of driving the car at the track(car drove great) the same issue popped up, 3500 rpm rev limit. It shows no cel or anything but with a stomp test it had the code 1222. disconnected the maf again to see if that was it and nope, even with maf disconnected it still had the rev limit.
    I have a large feeling that this is sensor related because of how it acted after disconnecting the dme. It drove fine for an extended period of time before just coming back into the same issue. The only video i could find that had the same issue ended up being the Knock sensor. I thought it may also be a possible cam/crank sensor but it idles fine tho the cold start is a bit slow at times. If there is anyone that has run into this issue before and can chime in that would be greatly appreciated. I do plan on taking the car apart soon to inspect the sensors and change out most of the gaskets.
    https://www.youtube.com/watch?v=Q7TZaxLPnUM
    this video is exactly like the issue i am having. Going to pull the intake and inspect everything. Most likely going to change the knock sensors. again just wanted to throw it out there to see if anyone has input. I will update if i resolve the issue!

  2. #2
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    Like most cars they run great until they don't. I would suggest checking the basics, before you start throwing sensors at it.
    Make sure there's no air leaks between the MAF and throttle body.
    Check fuel pressure at the rail.
    Pull some spark plugs.
    Fuel, air and Spark at the right amount and right time is what you need for combustion.
    A wise man from the Forum once told me, guessing gets expensive.

    Sent from my VS995 using Tapatalk

  3. #3
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    Quote Originally Posted by Greenday694 View Post
    Like most cars they run great until they don't. I would suggest checking the basics, before you start throwing sensors at it.
    Make sure there's no air leaks between the MAF and throttle body.
    Check fuel pressure at the rail.
    Pull some spark plugs.
    Fuel, air and Spark at the right amount and right time is what you need for combustion.
    A wise man from the Forum once told me, guessing gets expensive.

    Sent from my VS995 using Tapatalk
    Ive been looking and havent been able to spot any leaks. only connection i did not get a good look at was the hose that goes from behind the maf down towards the block. I did change the elbow that it connects to about a year ago to one with no tractioncontrol/abs throttle body. I did change the spark plugs recently because they were fouling out. some oil was dripping down onto them so i have all the gaskets ready to do that, just waiting for some rtv to arrive. they looked a bit rich but that was expected because of the oil. is there a place on the rail to connect a pressure gauge? I would be surprised if it was fuel considering how well the car was running at the track, the power didnt feel down one bit but its certainly not something i can rule out yet. Another reason i was thinking it may not be fuel related is because the car went back to complete normal after disconnecting the dme the first time. I would imagine it would still have fuel issues after that and it still wouldnt have run right but it drove great for almost a full 2 hours at the track before it started hitting the rev limit again. again i am not for sure just trying to explain my thought process. I do not think i have the right tools to test fuel pressure but i will look into it! I have noticed one of the wires going to the coolant temp sensor has been melted or cut but i cant imagine that would cause a limp mode issue. i will say the car drives just fine below the rev limit. It feels down on power but there is no breaking up or weird idle it still feels very smooth.

  4. #4
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    Ive done a visual check of all the hoses and everything seems to be in good condition and connected. The only hose i didnt get a good look at is the one that goes down towards the block just behind the maf, the top part looks fine just didnt get a good look down towards the block. I replaced the elbow it connects to about a year ago for one with no abs/traction control throttle body. Everything looked in good condition then. The car idles great and has no weird misfire or rough idle. It just feels lower on power and is hitting an early rev limit. I recently changed the plugs because they were fouling out and giving me a misfire. Most of the plugs looked rich and were coated in oil because i need to change the gaskets in the valve cover, just waiting on some rtv and ill tackle that. How would i be able to check fuel pressure? is there somewhere i can connect a gauge to? Not sure i have the tools but i cant rule that out. I had a feeling it wasnt fuel related because of the rich spark plugs and the car drove GREAT after disconnecting the dme. I imagine if it was fuel related the issue would still be there even after disconnecting the dme or i wouldve at least felt something a bit "off", i could be wrong tho, thats just how ive been breaking things down in my head. It felt awesome at track with no loss of power until the rev limit randomly popped back up on me mid lap. It was after about an hour and a half of hard driving the car.

  5. #5
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    Quote Originally Posted by nkilburg View Post
    Not sure i have the tools but i cant rule that out.
    Just a note, please DO NOT work on something if you don't have the right tools - I'm sure you know the pump is a high pressure system already but can be devastating if it goes wrong..

  6. #6
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    Quote Originally Posted by Ghost129er View Post
    Just a note, please DO NOT work on something if you don't have the right tools - I'm sure you know the pump is a high pressure system already but can be devastating if it goes wrong..
    oh yea! i certainly dont plan on doing anything with the fuel system especially if i dont have all the right things. I havent done any work to the fuel system of any of my cars so im just not sure if i have anything for it. Those things can be pretty sketchy with all the high pressure lines.

    - - - Updated - - -

    Testing the lines right now is on the back end of my list of things to check off, i still have a feeling that it is sensor related and not fuel related. I may be completely wrong tho, no way to know until its fixed

  7. #7
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    I don't mean to hijack the thread but the amount of M50 related posts I'm seeing is rather odd, considering I own an M50 and am having issues of recent, but I don't intend on posting on your topic and derailing it. Let me know what happens, so far mine's just sputtering and backfiring from the intake but not as bad as what you're talking about.

    Hope you solve your issue and post the fix here, from one M50 bro to another.

  8. #8
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    i appreciate it! for sure will let you all know if i figure it out. Any issues ive had with this car sputtering out or misfiring so far has always come to plugs. Im sure thats something youve tried already tho. the intake side has so many little parts and old plastics, doesnt hurt to pull things apart sometime to just check condition. ive had plenty of old brittle wires that caused issues. most notable being the main engine ground. it was almost in 2 pieces when i found it lol.
    I hope the best for you and your m50!

  9. #9
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    I completely understand not messing with the fuel system, especially if you don't really have any experience. If I remember correctly, fuel pressure should be 43.5 PSI with no vacuum to the regulator. Lower with vacuum.
    Oil in the spark plug Wells can cause a misfire especially under load.
    Bad wiring on the coolant temp sensor, blue sensor with blue band on The Wire, can make the DME think that the engine is cold all the time. That will make it run rich, and depending on that tune, could have a lower rev limit at lower engine temperature.

    Sent from my VS995 using Tapatalk

  10. #10
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    interesting! yea i had that issue the night before the track actually, plugs started fouling out. swapped plugs and it was good enough for the day but the misfire returned a few days later. it for sure needs those gaskets but i would be surprised if that was the cause. ill fix that wire up when i get in there to do the valve cover gasket. It should be a quick fix it doesnt look bad.

  11. #11
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    Please let me know what the issue was whenever you find out what fixes it! I have the exact same issue with the exact same car. I've found quick fixes disconnecting the battery for 15 seconds or plug and unplug the speed sensor.. but once I hit 5th gear it limits at 3500 and after that the system relearns to shift at that low rpm afterwards. The battery disconnect is quick and easy but the relearn process is frustrating. Anything helps If any solution arises get back to me please 🤘

  12. #12
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    I certainly will do! havent had much time with the holidays and weather to work on the car. I have a few things i also need to do before i can continue diagnosing this issue. My list of things includes dropping the rear subframe, reinforcing the chassis and swapping all of the bushings in the back. Going to do a valve cover gasket and from there i want to start pulling the intake side apart a bit. I want to get a good look at the knock sensors, i will most likely replace those but that will be after i get the rest of those things done most likely. I will update this thread next time i get on it!

  13. #13
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    Little update because it has been quite a long time! I just recently got my e36 back on the ground after reinforcing the rear and changing out all of the bushings. Changed out the Valve cover gasket, spark plug gasket things, 1 coil pack, and i was also able to sneak my hand up under the intake and replace just the front knock sensor. Unfortunately when i hopped in the car after not driving for a bit, my clutch system took a poop. Looks like i need to replace the slave and master before i can drive it and properly test it. When i inspected the knock sensor it was super corroded and the plastic covering it all fell off when i was unbolting it, it was shot. Hoping i can get away with just the front one to avoid removing the entire intake but well see. Once i fix the clutch issue ill get it back on the ground and test to see if it can make it over 3500rpm!

  14. #14
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    UPDATE: Took the car for a ride today, i believe it was a success! the car revved up just fine to well over 3500rpm. I do now feel a slight vibration when revving in neutral but im going to imagine that it is just my new bushings all around(trans,diff,subframe). Im thinking the vibrations that used to get absorbed by those bushings may now be present. Hoping it is nothing more than that. I believe the culprit was the corroded knock sensor

  15. #15
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    Interesting and thanks for the update. Hope that fixed it up for you! Report back if it re-occurs, then back down the rabbit hole you will go

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