Page 1 of 2 12 LastLast
Results 1 to 25 of 31

Thread: 325i cutting fuel at low rpm. Video attached.

  1. #1
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i

    325i cutting fuel at low rpm. Video attached.

    Hi, I’m new to bimmer world and I have just purchased a 1993 325i coupe with 310.000 km on the clock. It runs fine and I feel there is no issue at WOT but sometimes, some minutes after cold start it cyclically cuts fuel when there is very low throttle input around 1800-2200 rpm. This makes driving in the city very annoying and uncomfortable.

    The interesting thing here is that if I restart ignition (see video below) the issue disappears and comes back after some minutes.

    What should I check first?

    For the moment I’ve disconnected the lambda sensor today and I will monitor how it behaves during the following days.

    Helpful data:
    - I recently had some problems with emissions and had to push it hard to pass the CO emission acceptance threshold. Not sure if this is an indication of a bad lambda sensor.

    - Cold start is not brilliant. It starts up but with some hesitation in the rpm..

    Video is not in English sorry, but it is quite comprehensive!

    https://youtu.be/8dhmNm7J7aA

    Thanks!!!
    Last edited by Billyescopetas; 02-05-2019 at 02:53 PM.

  2. #2
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    Saw the video. Unlike to be the o2 sensor. Plug it back in. Unplug the tps (throttle position sensor) and test it that way for a day or two. It can also be a bad maf not sending fuel in. Extra fuel needs to be sent to the chambers for the car to throttle up - nothing pushes the crank to turn faster except fuel combusting. This situation you have can only exist for devices that have a variable element built into them, like the tps and maf. The fuel pump, o2 sensor etc are either on or off. Variations caused by an o2 sensor cannot lean out a mixture so badly that you can't throttle up. So i would unplug and test both the tps and maf in turn. My money is actually on the maf, even though i suggested the tps at first.

  3. #3
    Join Date
    Jun 2010
    Location
    NY
    Posts
    9,066
    My Cars
    1997 328i
    I doubt its the MAF because it wouldn't be intermittent, it would either work or be bad. Another possibility is a bad fuel pump relay. TPS is also an easy item to test.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  4. #4
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    I've never heard of intermittent failure on a fuel pump relay. But as you said, all these three are easy enough to test.

    Especially since :

    Quote Originally Posted by Billyescopetas View Post
    Helpful data: - I recently had some problems with emissions and had to push it hard to pass the CO emission acceptance threshold. Not sure if this is an indication of a bad lambda sensor.
    A bad maf could do this for you too.

    Quote Originally Posted by Billyescopetas View Post
    - Cold start is not brilliant. It starts up but with some hesitation in the rpm..
    If disconnecting any of the two aformentioned sensors and swopping out the fuel pump relay does not fix this, then it is likely your icv. You'll need to remove it and clean it. That would be pretty tough on an M52 engine. There is another much easier way you can clean it out. Ask me if it becomes necessary and I will find the link.

  5. #5
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    lets add one more sensor to the list. Coolant temperature sensor on the cylinder head, might be blue tipped. So swap the fuel relay, test, swop the relay back if it wasn't the issue, then the maf, then the tps, then the cts. Keep the o2 sensor connected throughtout.

  6. #6
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Hi all! Impressed with the feedback! Thank you so much.

    I will check all of the ideas with o2 sensor fitted and update with results

    What is strange to me is why the issue appears after some minutes of driving (around 10m) and then restarting the ignition it runs fine again. If it was a sensor, I feel that it should continue reading “wrong” data as it was doing seconds before after ignition restart.

    Will keep you posted. Thanks!!

  7. #7
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    Intermittent failure, possibly also wiring related. Lets not speculate. The tests are real easy to do since you may be able to fix it at idle itself. Anyway ten minutes of driving is a short time. Could you do all the tests and reply today ? Best not to drag on the simple tests.

  8. #8
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Hi all,

    O2 sensor back in. The issue was reproduced without it so it is discarded 100%.

    Note that I have no way to test and discard every idea straight forward; the issue happens sometimes under conditions which are not clear to me yet, so very difficult to reproduce, but when it happens it stays there.

    So, current status is:
    - Already checked and swapped fuel pump relay, issue appeared again.
    - Now I’m running with disconnected MAF and for the moment it runs “fine”, but without MAF all is unstable so not sure if the scenario is representative.

  9. #9
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    Ah. All is not supposed to be unstable with the maf disconnected. What that means is that you have two damaged sensors, and the maf is probably not the one that is undamaged. These engines often run weird when two sensors are disconnected, or one good sensor is disconnected and one bad sensor remains connected (thus simulating two damaged sensors). Don't ask me why it works this way.

    No surprise on the fuel pump relay not being a driveability issue.

    You said the issue also happens at idle as well, which is why I asked you to test quickly. Anyway, for now, reconnect the maf, confirm the engine runs more normally, and go onto the tps and the ects (engine's coolant temperature sensor).

    Its probably a good idea for you to clean out your icv to rule that out. You can try this method it will work pretty good and is not a pain to do, will only take like 10 minutes. But you need to follow every single instruction there in sequence if not you'll have backfires.

    https://www.bimmerfest.com/forums/sh...d.php?t=759718

  10. #10
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Quick update!
    I’ve finally decided to remove the intake manifold and have a look. I will need to replace some cracked tubes (don’t se related the issue but worthy), also several rings and rubber seals of the intake.

    The only important fault I’ve identified is a cracked knock sensor:


    This might correlate with the unpredictable fuel cuts, don’t you think so? I will also replace the water temperature sensor.. but I see there are two sensors side by side. Which one is it?

    One more question please. When removing the injectors ramp, some of the green caps were broken.. some even felt inside the valves... any suggestion on replacement? Are they sold individually?


    Enviado desde mi iPhone utilizando Tapatalk

  11. #11
    Join Date
    Jun 2010
    Location
    NY
    Posts
    9,066
    My Cars
    1997 328i
    Replace all the vacuum lines while your in there. The tips on the injectors are called pintle caps. You best off getting a kit that has all new o-rings, pintles, filters. Check ebay for the kit, it should be less than $20, be sure to get the correct kit. The water temp sensors are color coded, I don't know what they are, but just search the forum and you will find the answer. Usually there are two knock sensors, but I don't know about yours, if there are two be sure to get two (if they are seperated). On the M52 there are two and there is only one plug. Cracked knock sensors are typical for the M50 engine. Be sure to put a new intake manifold gasket.

    When installing the injectors be sure to lube all the rubber o-rings with petroleum jelly.
    https://www.ebay.com/itm/6-set-Fuel-...0/331951385042
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  12. #12
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    If you want a thorough list of what you ought to do or at least inspect when the intake manifold is off, please see post #13 here :

    https://www.bimmerforums.com/forum/s...4#post30197174

    Add main coolant hose to that list, I forgot.

  13. #13
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Hi all,

    Sorry for not updating earlier. Issue still present after below actions:
    - New intake related vaccum lines
    - New gaskets (throttle body and 6x intake)
    - Cleaned ICV
    - New temperature sensors as suggested (the two ones located at the top of the block, one for coolant one for engine temp)
    - New knock sensor (it was cracked and not sure it was malfunctioning)

    Engine pulls strong and rides excellent.. the only issues have are:
    - Very random cut of at around 2000rpm. Issue dissapears if I start the engine again. It happens 1 out of 10 times I go from work to home.
    - Cold start: disaster.. no way it can hold the idle itself, have to press throttle for some time. Idle screw is already opening the throttle body a little bit but if I open it too much hot idle would run around 1.5k rpm.

    I can’t figure out if both are related or not... Do you think a faulty ICV can affect not only the idle but also affecting at 2.000 rpm making the engine go down to 1.000 rpm cyclically when throttle is slightly pressed?


    Enviado desde mi iPhone utilizando Tapatalk

  14. #14
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    Quote Originally Posted by Thomas525 View Post
    Saw the video. Unlike to be the o2 sensor. Plug it back in. Unplug the tps (throttle position sensor) and test it that way for a day or two. It can also be a bad maf not sending fuel in. Extra fuel needs to be sent to the chambers for the car to throttle up - nothing pushes the crank to turn faster except fuel combusting. This situation you have can only exist for devices that have a variable element built into them, like the tps and maf. The fuel pump, o2 sensor etc are either on or off. Variations caused by an o2 sensor cannot lean out a mixture so badly that you can't throttle up. So i would unplug and test both the tps and maf in turn. My money is actually on the maf, even though i suggested the tps at first.
    Did you actually do the disconnect test on the tps and the maf ?

  15. #15
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Quote Originally Posted by Thomas525 View Post
    Did you actually do the disconnect test on the tps and the maf ?
    Yes! Without MAF the throttle gets very difficult to regulate and keep around 2000 rpm... remember that the issue is very occasional and when it appears I need to avoid stalling the engine or I will loose the failure mode. Removing TPS while engine is running is something I tried and it nearly stalled it... i might give it a second try again and report back.

    Would a faulty Vanos match with this issue at 2000rpm and restarting solve the issue?


    Enviado desde mi iPhone utilizando Tapatalk

  16. #16
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    Dont unplug anything with the engine running. Shut down and unplug (after reconnecting the sensor you unplugged just before this one) then startup and see. And as to your question about vanos, I have no idea, I wouldn't think so because vanos does not cause running problems in that way. However, it is also easily tested - just include that in the disconnect test. See if you post a question and if you don't get the exact answer within 2 posts and 2 hours max, then its not a common issue. The only way out is then to relentlessly test and accumulate results on a scientific basis. This is what mechanics do so you need to do the same, and you need to report quickly.

    Had another look at your thread. You can reproduced these symptoms at idle. So unplug everything one after the other, including the vanos unit (although that really cannot cause this issue, but its easily tested). I have a strong suspicion that it is your maf, because you can throttle up beyond 2k when it is unplugged. That said, you may have more than 1 sensor damaged - bmw engines become difficult when two good sensors are unplugged or one sensor is unplugged with a different sensor that is bad still plugged in.

  17. #17
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Ok understood Thomas, thanks. Will do this test sequence this weekend and report back.

    As the issue is not frequent and it goes away after ignition reset (key out key in) it is a very tricky test as I might need to run tenths of kms or even hundreds to make it happen. Just for information, I’ve been running around 500km and issue only happened once during city driving with light throttle.

    Thanks again. Really appreciate your suggestions and technical knowledge.

    I tried twice with two different mechanics and they simply said the car was running fine and couldn’t reproduce the issue.


    Enviado desde mi iPhone utilizando Tapatalk

  18. #18
    Join Date
    Jun 2010
    Location
    NY
    Posts
    9,066
    My Cars
    1997 328i
    Very common on the early e36 for the fuel pressure regulator to go bad. Hook up a fuel pressure gauge, when increasing the throttle the pressure should go up. If you do replace the regulator be sure to also do the vacuum line that connects to it.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  19. #19
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    Quote Originally Posted by Eric93se View Post
    Very common on the early e36 for the fuel pressure regulator to go bad. Hook up a fuel pressure gauge, when increasing the throttle the pressure should go up. If you do replace the regulator be sure to also do the vacuum line that connects to it.
    Would it go bad intermittently, like with the OP describes ?

  20. #20
    Join Date
    Jan 2018
    Location
    Argentina, Buenos Aires
    Posts
    8
    My Cars
    Fiat Palio S 1.3 MPI
    This might seem a little bit obvious, but have you checked your ICV? the issue you are describing could be dirt moving around and clogging it, or it getting stuck.
    Give it a good clean, and try again. It might not be fuel related after all.
    Edit: Missed the part where you cleaned it. Do you have a known good one? an ICV with so many KM can go bad. I insist this sounds like it's air related.
    Last edited by Elmachomostacho; 03-15-2019 at 03:36 PM.

  21. #21
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Ok I’ll add this to the list. Maybe after swapping the ICV

    Enviado desde mi iPhone utilizando Tapatalk

  22. #22
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    I have a feeling it may be the cause.. it’s the only item i didn’t change, and cold starts are a pita.

    I only cleaned it and I thought it would be fine after hearing the valve after spraying it. The electronics might be damaged but, how an ICV would affect light throttle? If it’s kinda closed it should not affect, if it stays open it will let more air in the intake-engine should increase rpm instead not decrease?

    I have a friend’s ICV that I can easily change and swap.

    Enviado desde mi iPhone utilizando Tapatalk

  23. #23
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i
    Hi all! This is an important update it’s mainly related to the Throttle Position Sensor, which lost some focus from my side in the begining.

    Yesterday the issue was reproduced (after many days expecting it) and what I did was:
    1- Make sure the issue was the same observed in the past: very light constant throttle input and revs go from 1000 to 2000 cyclically without changing throttle input
    2- Disconnected the TPS with engine still running: no change in revs, no reaction from the electronics—> issue still present and identical behaviour
    My hypothesis is that the sensor input is somehow ignored at some point and no longer trusted. That’s why plugging it back it made no change.

    Today I didn’t reproduce the issue but I had this behaviour:
    1- I made sure the issue wasn’t reproduced by applying light throttle —> OK
    2- Disconnected the TPS: engine tried to stall for a second and reved up again idling.
    3- Observed that with TPS disconnected the issue reappears with identical behaviour (revs between 1000 and 2000 cyclically with light throttle input)
    4- Reconnected the TPS—> issue disappeared

    So which is the outcome of this???
    I believe the TPS becomes not functional under some specific conditions (temp, vibrations, etc) and engine management ignores it. Engine management thinks throttle body is closed and as rpms are increasing, it cuts fuel to go back to idle.

    MAF is the remainig element to calculate needed fuel. I also noticed some laggy response with the TPS disconnected, maybe this was not noticeable to me when the issue ocurred, because I quickly restarted the engine to make the issue disappear.

    I read somewhere that Bosch systems cut injectors (or maybe spark plugs) when throttle body is read as closed and rpms are increasing.

    I already checked today the resistance values of the sensor across all the throttle movement and they seem to be fine against Bentley manual and progressive.. but I checked it when the issue was not present..

    So, what I will do next? I will swap the TPS with a friend’s one and see if the issue goes with the TPS or stays in my car.

    I will keep you posted!


    Enviado desde mi iPhone utilizando Tapatalk

  24. #24
    Join Date
    Jan 2019
    Location
    HK
    Posts
    280
    My Cars
    525
    I told you about the tps weeks ago.

  25. #25
    Join Date
    Sep 2018
    Location
    Spain
    Posts
    16
    My Cars
    e36 325i

    325i cutting fuel at low rpm. Video attached.

    Hi all, Thomas.
    I have news. I tested with a known-good TPS and issue is still present, no change at all, same low idle, same “random” rpm issue at light throttle.

    I’ve managed to find a way to reproduce the issue: in cold start (it actually is a bad start since it has always stalled unless I press the throttle for some time) if I keep pressing the throttle to keep rpm around 1000 for 2-3 minutes, immediatelly after the issue appears! This is good since I had to wait some days to make it visible to me while driving.

    As I know I’m extending too much in this investigation and I might be even confusing you with my comments.. I’ve recorded a couple of videos today to show exactly the behaviour and you’ll see me testing TPS and MAF sensor disconnections and engine reactions. Hope this helps.

    1st video: issue present
    Steps shown:
    0m 0s: Interior view of the RPM issue demonstration with constant light input throttle. You’ll see cyclic rpm change from 1000 to 2000 rpm
    1m 5s: Same as before but now acting directly at the throttle body manually
    1m 17s: Test disconnecting MAF-> very unstable, engine almost stalls with light throttle input. Can’t reproduce the issue but might be masked
    2m 05s: MAF reconnected -> issue still present as in the beginning
    2m 20s: TPS disconnection and MAF connected-> no change, issue still present
    2h 47m: TPS reconnected-> issue still present
    https://youtu.be/EqYg6sBGilY


    2nd video: same kind of test sequence as video 1 but this time issue not present. I’m able to get same failing behaviour disconnecting the TPs
    https://youtu.be/zJlhDH8q3XY

    I’m very confused.
    - Can I discard the TPS or any of the throttle body elements?
    - Cold start has always been dramatic, but when engine is warm, idle is perfect and no oscillations seen. Is ICV (it was cleaned but not replaced) still suspicious of the rpm issue?
    - Sensors not changed yet: MAF, air temp sensor (the one located at the intake manifold), ICV..
    - Is Vanos a potential cause?

    Thanks again. Appreciate your time and help with this. Hopefully this ends soon with a kind of troubleshoot guide that might help others!

    Eric
    Last edited by Billyescopetas; 03-27-2019 at 06:06 PM.

Page 1 of 2 12 LastLast

Similar Threads

  1. 92 325i lacking power at low rpms
    By dannyE36 in forum Engine Conversions
    Replies: 2
    Last Post: 12-02-2011, 11:58 AM
  2. 96 328i cuts out at low rpm under load.
    By cars in forum 1991 - 1999 (E36)
    Replies: 11
    Last Post: 07-09-2010, 08:12 PM
  3. Engine cuts out at low rpm
    By pacecar78vette in forum 1983 - 1991 (E30)
    Replies: 6
    Last Post: 02-06-2007, 01:54 PM
  4. 91 318is revving itself and cutting out at low rpms
    By CodyB in forum 1983 - 1991 (E30)
    Replies: 7
    Last Post: 10-31-2006, 05:57 PM
  5. '92 325is feels sluggish in low rpms
    By BAZ in forum 1991 - 1999 (E36)
    Replies: 23
    Last Post: 02-08-2005, 04:42 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •