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Thread: E34 M20 No start, stumps 3 mechanics including myself

  1. #1
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    E34 M20 No start, stumps 3 mechanics including myself

    90 525i, manual with '87 e30 engine. M20
    So about a week ago, I went to replace my water neck gasket. I had the intake off. I put it back together and have been having problems ever since.
    The following things have been done to the car attempting to fix whatever I did to f-ck this up; chasing vacuum leaks and intermittent extremely high idle of 4 grand, surging, terrible running, running great, and then no start.

    Intake Gaskets
    TB gasket
    the fuck me tube resealed
    TPS swapped from one of the engines we have (We have piles of BMW engines/diffs etc...like 4 M20s all runners when pulled)
    Better distributor cap
    Better plug wires
    Swapped from yellow injectors to blue (Shop manager says "17's")
    New injector O-rings
    Sprayed all vacuum lines and intake ports w brake clean to find leak
    Done compression test 150 across the board
    Performed head gasket test with liquid tester
    Swapped fuel rail harness (Temp sensor plugs and injectors)
    Swapped CPS
    New rad cap....old one leaking
    New ECU temp sensor

    I'm sure i'm forgetting 1 or 2 things. I need some ideas...I'm keeping on it but another perspective could really help.

    My current situation is, has spark and fuel, will not start. No CEL on dash with key on
    Sounds like it wants to light off but only on one cylinder. I get a rythmic pop...pop...pop

    I love this car but we've tried just about everything which is crazy because we're BMW specialists...I'm more versed in japs and americans myself. My shop manager just finished dropping an S38 into is E30
    New ideas or questions are welcome. We've done a lot.

    Help

  2. #2
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    I am goin to assume you have check

    1. the cranks sensors

    2. the coil good and wires are on the right plug?

    3. Have you check the fuel pressure?

    4. Check the boot to the intake? Large vacuum leak?

    5. ECU might have cracks in the soldiering

  3. #3
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    Adding to the list: is the MAF connection clean and secure?

  4. #4
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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    Are fuel and spark present on each and every cylinder? Does starting fluid help? Any chance the cam timing is off?

  5. #5
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    You've got to start with fuel pressure as suggested, surely you guys can test that without throwing parts at it? It died after basic and maybe non related work, so fuel pump, coil and sensors are the type of thing that can fail unrelated to original work and you've tried sensors and ignition already.
    Though if fuel pressure isn't the cause, then who knows what new problems you may have introduced in frustration, time limits and parts swapping?
    Last edited by fo3; 01-09-2019 at 11:56 AM.

  6. #6
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    Check connector C191. I had a similar problem on an old E30.
    It's a big round connector located next to where the dip stick goes into the block. Mine was heavily corroded.

  7. #7
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    You mentioned that the intake has been off and a 4k idle.
    Only one thing that can cause an idle like that, AIR. Either the ICV is wide open or you have a big vacuum leak.
    No start? See the above but I'm wondering if you've lost a hose from the ICV. Any backfiring during all these tries?
    All the wire harness connectors in the right place?
    Last edited by ross1; 01-10-2019 at 06:43 AM.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  8. #8
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    Hey guys, thanks so much for all your replies. I was able to drive it home from our shop. Intermittent running

    I put a rad and a battery since it needed those things. I start it (runs rough) and I just barely make it there before she cuts off and won't start again. After some fiddlefucking with the throttle cable, I get her to start and run again. Runs fine, if a little surg-ey. On my way home two miles away...dies up a hill. Sucker won't start no matter what. I hoof it the quarter mile home where i'm typing this now

    Here's what we got.

    The crank sensor has been swapped to what should be a good one. They were both good but I figure I have a pile of M20's at my disposal....
    The wire is a bit shoddy in one place but I get fuel and spark. Some say oh it's getting those things so the sensor must be good but at the same time i'm not sure if it's one of those things that "kinda works" when broken or doesn't work at all.

    It's drowning in fuel. Last I pulled the plugs they were soaked. I'm 90% sure it's a vacuum leak because one guy rigged my throttle cable to stay open a bit and that fixed it...it was running perfect.

    Odd thing about this car. Whenever i hit the "recycle" button on the heat, the idle goes crazy. Hangs 2,3, 4 grand and stays wherever you blip the throttle, however high you rev it. When my buddy did the thing with the throttle cable, it stopped doing it. Weird. Jimmying the cable again got her to start but we didn't make it home

    It doesn't really sound like she's trying to light off. DME is probably flooding to compensate for the air leak

    Injectors have new o-rings, oil tube is quicksteeled at the top (don't hate me) and has a new o-ring at the bottom. I forgot the washer at the bottom....if it was leaking air i'd presume it'd be leaking oil too though. I remember soaking it with brake clean when i was running and no idle change. "new" (old intact one coated w RTV) tb gasket, actually new intake gaskets. It's just so strange it would run great sometimes and not at all other times. I'm about to go outside and blow cigarettes into the thing...see what I see

    - - - Updated - - -

    1. Getting fuel and spork so should be good
    2.Yes and indeed
    3. No....I know i'm bad
    4. intake boot is good, blew through it and no leaks
    5. Possibly probably if i can't find any more vacuum leaks. This car is on it's 3rd computer now

    6. My oilpan ground strap doesnt really go to anything. I'm told that's a big deal which i'm sure it is but the car's been fine up to this point.

    Not that it matters but this engine is out of an '87 E30. Good ole FrankenBimmer

    - - - Updated - - -

    It's an AFM on this car but indeed

    - - - Updated - - -

    Starting fluid doesn't help. It is possible the mechanical timing is off because I haven't checked it but I don't think that's the issue because I got 150 PSI across the board and she'll run pretty much perfect but only intermittently

    Pretty sure it's got fuel/spark on every cylinder. Plugs were soaked when I pulled them

    - - - Updated - - -

    I'm really suspecting this plug. The bitch plug. It doesn't seeeem corroded but it could still be my issue. I'm considering cutting the plugs out and using spade connectors to stick them together.

    I notice it runs like garbage (misses on at least one cylinder, not firing) when I go through a puddle and I know that plug is down that way so. Short of splicing them together, thoughts on di-electric grease? Some swear by it, other say it's not sh-t

    - - - Updated - - -

    I'm gonna re-asses when I can, going to make sure the ICV does the buzzy thing and do another smoke test. Definitely backfires. Connectors are right pretty sure

    - - - Updated - - -

    Sorry if this is tough to read, it's been years since I was a regular on any forum so I'm still remembering etiquette and format.

  9. #9
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    Quote Originally Posted by fo3 View Post
    You've got to start with fuel pressure as suggested, surely you guys can test that without throwing parts at it? It died after basic and maybe non related work, so fuel pump, coil and sensors are the type of thing that can fail unrelated to original work and you've tried sensors and ignition already.
    Though if fuel pressure isn't the cause, then who knows what new problems you may have introduced in frustration, time limits and parts swapping?

    This be true. To be frank, i'm a youngin. I've only got 6 years in and I'm used to American/Japanese junk. Ole 350's...Honda d16's...pretty forgiving stuff. BMW makes a fantastic engine but i'm still getting accustomed


    So basically I only have half an idea what I'm doing, and my buddies aren't too keen on helping me out. It's probably an air leak, and it's probably from my dipstick tube because the tube came with the dipstick when i went to pull it out just now. I'm gonna qwiksteel it in and that should fix what i'd imagine to be a pretty big vacuum leak

  10. #10
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    Quote Originally Posted by hoondog97 View Post
    This be true. To be frank, i'm a youngin. I've only got 6 years in and I'm used to American/Japanese junk. Ole 350's...Honda d16's...pretty forgiving stuff. BMW makes a fantastic engine but i'm still getting accustomed


    So basically I only have half an idea what I'm doing, and my buddies aren't too keen on helping me out. It's probably an air leak, and it's probably from my dipstick tube because the tube came with the dipstick when i went to pull it out just now. I'm gonna qwiksteel it in and that should fix what i'd imagine to be a pretty big vacuum leak

    I can't find the leak...no amount of blowing cigarettes into it and cursing makes the leak appear. Putting my tail between my legs and taking it to another shop to have it smoke tested

  11. #11
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    moroza is offline MORΩN ΛABIA BMW CCA Member
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    Quote Originally Posted by hoondog97 View Post
    The wire is a bit shoddy in one place but I get fuel and spark. Some say oh it's getting those things so the sensor must be good but at the same time i'm not sure if it's one of those things that "kinda works" when broken or doesn't work at all.
    What I've seen is that crank sensor failure is a black/white affair, but broken wiring can be intermittent and grey-area.

    It's drowning in fuel.
    Intake leaks would make it run lean, not rich.

    6. My oilpan ground strap doesnt really go to anything. I'm told that's a big deal which i'm sure it is but the car's been fine up to this point.
    Is there another ground strap to the block? A big healthy one with clean tight contacts? If not, fix this regardless.

    Starting fluid doesn't help.
    Consistent with soaked plugs, that means it's getting fuel, though not necessarily in the right pattern.

    It is possible the mechanical timing is off because I haven't checked it but I don't think that's the issue because I got 150 PSI across the board and she'll run pretty much perfect but only intermittently
    The compression number matters less than the intermittent condition. I'd check timing anyway; 150 is low.

    I'm really suspecting this plug. The bitch plug. It doesn't seeeem corroded but it could still be my issue. I'm considering cutting the plugs out and using spade connectors to stick them together.
    What plug?

    I notice it runs like garbage (misses on at least one cylinder, not firing) when I go through a puddle and I know that plug is down that way so. Short of splicing them together, thoughts on di-electric grease? Some swear by it, other say it's not sh-t
    That suggests electrical problems. Fix your sketchy ground and other wiring first. If that doesn't help, the next things I, in your situation, would check are: fuel pressure, ignition timing (old-school light), cam timing, in whatever order feels convenient.
    Last edited by moroza; 01-18-2019 at 05:38 AM.

  12. #12
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    Quote Originally Posted by moroza View Post
    What I've seen is that crank sensor failure is a black/white affair, but broken wiring can be intermittent and grey-area.
    -Fair, i'll probably end up replacing it with a new-new one.


    Quote Originally Posted by moroza View Post
    Intake leaks would make it run lean, not rich.
    -Fair again. It took this shop forever because they didn't really wanna touch it but they've smoke tested it and she came back leak free. They also said it needs an alternator so i'm looking into a new one. I want to put the 140A in but i'm not sure if it's a direct bolt on to the OE bosch one. Any idea about that?
    Quote Originally Posted by moroza View Post
    Is there another ground strap to the block? A big healthy one with clean tight contacts? If not, fix this regardless.
    -The engine is out of an '87 E30...to my knowledge that ground strap has never been hooked up in this car. It probably should be.


    Quote Originally Posted by moroza View Post
    Consistent with soaked plugs, that means it's getting fuel, though not necessarily in the right pattern.
    -Exactly. I haven't checked fuel pressure or injector pulse.


    Quote Originally Posted by moroza View Post
    The compression number matters less than the intermittent condition. I'd check timing anyway; 150 is low.
    -I've been told 150 is optimal for these m20's but i'll still check


    Quote Originally Posted by moroza View Post
    What plug?
    -The ole c191 plug. The one that goes to the injector harness and two temp sensors. People are saying that where the twist plug connects to the main harness gets corrosion and causes all kinds of weirdness.


    Quote Originally Posted by moroza View Post
    That suggests electrical problems. Fix your sketchy ground and other wiring first. If that doesn't help, the next things I, in your situation, would check are: fuel pressure, ignition timing (old-school light), cam timing, in whatever order feels convenient.
    -I'm gonna put the new alternator in and go from there. For one it's not charging and I know any kind of voltage drop will cause weirdness in these cars. Fix ground strap, new alternator, then see what we got. I'm happy there's no vacuum leaks ( My old shop manager was swearing up and down it's an air leak...he was wrong)
    Last edited by hoondog97; Yesterday at 04:41 PM.

  13. #13
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    moroza is offline MORΩN ΛABIA BMW CCA Member
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    Ok, you're getting somewhere. My hunch currently is that your injectors are misfiring, probably due to electrical problems. Your notes about corrosion and voltage drops causing all kinds of random gremlins is correct; hopefully that'll lead to the solution, too. Your next step sounds good.

    Regarding compression: 150 is servicable, and I guess for an older engine like the M20 it's ok. Bentley is useless here - specifies 142-156 minimum for all engines. As if two numbers could both be a minimum, and as if that applied to everything between the 8.8:1 M20 and the 10.5:1 M50TU and M60B30 The FSM is nearly worthless - as usual - as well: specifies 143-156 for the M20, and for the others either omits reference altogether, or plays Bureaucrat and says "refer to specifications" or "refer to E36 manual".
    Last edited by moroza; Today at 04:29 PM.

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