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Thread: No Start, has spark, has fuel, what?

  1. #1
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    No Start, has spark, has fuel, what?

    1988 325ix won't start, sputters a little after cranking for a while but will not run. It was running fine two days ago, parked it overnight when it was below zero all night and it wouldn't start in the morning.

    Relays all test good, swapped with other car just to make sure, voltage is good at the junction block. CPS reads a little low, 480 ohms- that seems close enough, plus I'm getting spark so I assume it's good. Fuel pump runs when jumped, runs when cranking. Have not tested fuel pressure, don't have a guage. Exhaust smells like gas after cranking and plugs are wet. Cap and rotor are new.

    The resistance from the AFM is a little funny, but I can't really figure out where it's supposed to be. The Bentley doesn't give any specific range, just that it's supposed to smoothly increase through the motion of the flap. Mine starts at ~1100 ohms when fully closed, drops to ~400 and increases through the range until it drops back to 120-ish fully open. I don't really know what this means.
    I don't see the afm being the problem since they'll usually run with it completely unplugged. This one won't.
    I went through the whole table of tests at the ECU plug on page 49 of the Bentley and everything was good.

    I'm starting to wonder if the ECU is toast. It seems like the cold temperatures are what started this, I'm warming up the computer inside overnight on a whim to see if that happens to help.
    Will any m20b25 ecu work on an iX, or is it yet again something different?

    I can't figure out how I can have spark, fuel, and compression and it won't run! Any input? What am I missing?
    no

  2. #2
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    I'd be curious to know what fuel pressure is, just for eliminating one possible cause. Also wondering if any codes are present.
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  3. #3
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    I know, I need to check pressure- there is definitely fuel making it into the cylinders, I would think enough to fire, but who knows.
    No codes, 1444.
    no

  4. #4
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    Quote Originally Posted by Fraser View Post
    1988 325ix won't start, sputters a little after cranking for a while but will not run. It was running fine two days ago, parked it overnight when it was below zero all night and it wouldn't start in the morning.

    Relays all test good, swapped with other car just to make sure, voltage is good at the junction block. CPS reads a little low, 480 ohms- that seems close enough, plus I'm getting spark so I assume it's good. Fuel pump runs when jumped, runs when cranking. Have not tested fuel pressure, don't have a guage. Exhaust smells like gas after cranking and plugs are wet. Cap and rotor are new.

    The resistance from the AFM is a little funny, but I can't really figure out where it's supposed to be. The Bentley doesn't give any specific range, just that it's supposed to smoothly increase through the motion of the flap. Mine starts at ~1100 ohms when fully closed, drops to ~400 and increases through the range until it drops back to 120-ish fully open. I don't really know what this means.
    I don't see the afm being the problem since they'll usually run with it completely unplugged. This one won't.
    I went through the whole table of tests at the ECU plug on page 49 of the Bentley and everything was good.

    I'm starting to wonder if the ECU is toast. It seems like the cold temperatures are what started this, I'm warming up the computer inside overnight on a whim to see if that happens to help.
    Will any m20b25 ecu work on an iX, or is it yet again something different?

    I can't figure out how I can have spark, fuel, and compression and it won't run! Any input? What am I missing?
    My ECU did the same thing... i changed it out and its all good!! it also took a cold idaho winter to kill the ecu.. had spark and fuel wouldnt start.. changed the ecu and its all good!!!

  5. #5
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    Before you change out the ecu, i would check all the hoses and make sure something didnt crack because of the cold and create a vacuum leak big enough to not let the car start...


    1989 325ix-winter fun----1982 320i- 256k miles and counting ***for sale*** ---1993 325is-parted out

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    Quote Originally Posted by heartbreaker View Post
    Before you change out the ecu, i would check all the hoses and make sure something didnt crack because of the cold and create a vacuum leak big enough to not let the car start...

    That's the first thing I thought of actually. I gave them all a good once over, but I'll look at 'em again before I go throwing parts at it. My intake boot has looked rough since day one, but it's intact.
    no

  7. #7
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    Intake may have cracks. If so replace. Check little hose at the icv. Check the ICV is making noise in the start position. If your fuel pump hasn't been changed, look for it or the relay to be the problem. Cold weather aggravates marginal problems.
    Worst scenario, mine. The Oil sending unit wen't bad and shorted (burned/fused) the wires on my firewall harness, burned up the ICV wire which sent wrong stuff to the DME. Don't ask me what the bill was from my mech. Oil light and cel were both on. Stomp code results?

  8. #8
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    Quote Originally Posted by Fraser View Post
    I know, I need to check pressure- there is definitely fuel making it into the cylinders, I would think enough to fire, but who knows.
    No codes, 1444.
    It may be getting too much to fire. You need stoichiometry.
    9/2004 Chevrolet Suburban Z71, black, purchased March 2016, 270k miles.
    6/99 740i Cosmos Schwartz M Sport, 214k miles, purchased May 2017
    2001 740i OrientBlau M Sport, purchased March 2023
    1984 MasterCraft Stars and Stripes, Blue/White, PCM Ford 351W, PowerSlot, 912 hours, purchased September 2012 (not a car )
    4/99 323is/5. Titansilber, 211k miles. Straight body project.



    past BMWs: 5/1994 325isa (Arktisgrau), 3/1997 328is/5 (cosmosschwartz), 9/1990 535i/5 (calypsorot), 9/1990 318i/5 (brillantrot) 7/93 325i/5 convertible (samoablau) 2/92 325i/5 cabriolet (lagunengruen).
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  9. #9
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    +1 ECU.
    Though, try to find a known good one to test the theory first.
    Also, let it be known that my ECU didn't COMPLETELY poop itself. It just pooped itself in cold temperatures. Try heating it either inside, or with a hair dryer or something and seeing if it works then.

    My car is a beater of catastrophic proportions, so I have no problem pulling my ECU every night to ensure my car starts (i just leave it dangling in the glove box).
    In any case, I recommend the above test because it may keep more options open for you.
    Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies.

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  10. #10
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    Cool, ECU's been sitting inside all night, I'll try it this afternoon. (I'm in my other car in another town at the moment.)
    Anybody know if any old m20b25 ECU will work with an iX? My ECU ends in 380...

    Edit: nevermind, just read up on the ECU info. A guy local on CL has a 153 for dirt cheap. Does anyone think it really matters to "downgrade" to that from the 380 that's in it? I don't really care about the stomp test.

    Stuck the warmed up ECU in it today and still no start. Didn't have time to check fuel pressure before going to work, I'll check it tomorrow hopefully.

    The fuel pump is not turning on with the key in ON position, but seems like it is while cranking. I tried seeing if the car would run with the relay jumpered so the pump was on no matter what, and still no go. I'm assuming either the ECU is doing something strange, or the pump is not putting out what it should.
    I might try swapping pumps with my m42 car tomorrow just for grins, real OEM says different part number but I would imagine the pressure requirements are similar.

    Can anyone tell me if 480 ohms for CPS is out of whack enough to throw things off?
    Last edited by Fraser; 02-11-2010 at 11:12 PM. Reason: Automerged Doublepost
    no

  11. #11
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    Have you tried disconnecting your fuel return line and seeing if any fuel comes out when you crank?

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    Quote Originally Posted by Paul G View Post
    Have you tried disconnecting your fuel return line and seeing if any fuel comes out when you crank?
    Yep, fuel comes out. Checked pressure today, constant 43-45 psi. So....pump is good, FPR is good. I have good fuel pressure, good spark. I'm trying a new ECU tomorrow.
    Any chance the CPS is off just enough to let it start? It's a little low (480 ohms). I know if it's totally dead you won't get spark.

    I can't think of anything else that would cause this.
    no

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    The "153" motronic 1.1 that the 1988 ix's came with where s**t. Mine fired too, but in a different way. My car just decided to idle at 2K all the time. Changed the ECU to a motronic 1.3 "173" and it worked great.
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    Quote Originally Posted by 1988 325ix View Post
    The "153" motronic 1.1 that the 1988 ix's came with where s**t. Mine fired too, but in a different way. My car just decided to idle at 2K all the time. Changed the ECU to a motronic 1.3 "173" and it worked great.

    Mine came with a 380 ECU motronic 1.3. I just swapped in a good 153 for comparison and it didn't change a thing.

    Does anyone know if 480 ohms at the CPS is low enough to cause problems?

    I'm pulling my hair out with this thing, and I can't figure out what else could be screwing with it.
    no

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    Quote Originally Posted by Fraser View Post
    Mine came with a 380 ECU motronic 1.3. I just swapped in a good 153 for comparison and it didn't change a thing.

    Does anyone know if 480 ohms at the CPS is low enough to cause problems?

    I'm pulling my hair out with this thing, and I can't figure out what else could be screwing with it.
    It's supposed to have "153"

    And 480 seems right but I'm not near my bently manual right now.
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    Quote Originally Posted by 1988 325ix View Post
    It's supposed to have "153"

    And 480 seems right but I'm not near my bently manual right now.
    ?

    As far as I know, there's a whole host of DMEs that came in m20b25s- 153,173,380,524,525,526, etc... I'm pretty sure any one will work. I don't know what came in mine from the factory, but it has a 380 in it, and still won't start when I swap this 153 in it either.

    Bentley says 540 +- 40 ohms for CPS if I remember correctly, just not sure how far off of that number will still work. I don't think it matters because I'm pretty sure I'd have no spark if CPS was bad.
    no

  17. #17
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    Quote Originally Posted by Fraser View Post
    ?

    As far as I know, there's a whole host of DMEs that came in m20b25s- 153,173,380,524,525,526, etc... I'm pretty sure any one will work. I don't know what came in mine from the factory, but it has a 380 in it, and still won't start when I swap this 153 in it either.

    Bentley says 540 +- 40 ohms for CPS if I remember correctly, just not sure how far off of that number will still work. I don't think it matters because I'm pretty sure I'd have no spark if CPS was bad.
    I read somewhere that the 1988's only came with 153's. And when you go to buy a chip for a 1988 325ix you only get offered a chip for the 153. So since I have a 173 ECU when I bought my chip I had to put in that I had a 1989 325ix so I could get teh chip for teh 173 ECU.

    Just going by past experience that's all. I may be wrong.
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  18. #18
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    Can anyone tell me the exact nature of CPS resistance readings?

    My CPS reads right around 540-550 ohms, which is correct apparently. When I move a ferrous object near it, it jumps around a bit and returns to 540-550 ohms.

    Isn't it really supposed to read a certain resistance when a tooth of the trigger wheel is in front of it, and a certain resistance when one isn't?
    no

  19. #19
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    iX started yesterday, if anyone cares. Replaced ECU again with a 3rd one I got in the mail yesterday and it fired right up. Goddamn these things are fickle.
    no

  20. #20
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    Quote Originally Posted by Fraser View Post
    iX started yesterday, if anyone cares. Replaced ECU again with a 3rd one I got in the mail yesterday and it fired right up. Goddamn these things are fickle.
    Strange that this was the problem... I've never heard of ECU failures like this.

  21. #21
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    Quote Originally Posted by ryan_george View Post
    Strange that this was the problem... I've never heard of ECU failures like this.
    Yeah, the story continues. That wasn't the problem.

    I thought it was interesting that it started up with the new ECU the other day, so I thought I'd see what would happen with either of the two old ones now that I had got it running. It started with those too. The temperatures have warmed up considerably recently, and apparently un-did whatever was wrong with it initially.
    It's been running fine for that last few days now.



    For the record, those 153 ECU's do suck- my car idles like garbage with that one in, 380 and 525 run make it run great.
    no

  22. #22
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    I wonder if the ignition coil is suffering with the cold... It might be powerful enough to produce a spark in free air, but not strong enough when it's in the combustion chamber.

    Another thought.... Could the AFM be sticking/freezing?

  23. #23
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    Quote Originally Posted by ryan_george View Post
    I wonder if the ignition coil is suffering with the cold... It might be powerful enough to produce a spark in free air, but not strong enough when it's in the combustion chamber.

    Another thought.... Could the AFM be sticking/freezing?
    We're on the same page. I threw a new coil in it today, that was the only other thing I could think of that was screwing things up. Fingers crossed right now, it should be below zero tonight so I'll see if it starts in the morning...

    AFM seems alright, but generally they'll run with it completely unplugged so I have a hard time believing a bad one wouldn't let it start at least poorly.
    no

  24. #24
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    Fuel and spark but still no start

    For the record in case anyone reads this later, this problem was likely a combination of three things:
    1) Cold temps-Its harder to start a cold engine.
    2) Flooded engine-On cold starts the fuel injectors will spray more fuel than normal. If you start your car and move it a short distance, say into the driveway and kill the engine, the cylinders will end up with more fuel in them than normal.
    3) No compression-Flooding the engine with fuel washes the cylinder walls of oil. This makes it difficult for the cylinder to make adequate compression especially if the rings are old and valves are dirty.

    So what happens is the cylinder will not make compression and thus will not fire. You should always check the big 3 when troubleshooting a no start. Fuel, spark, and compression. Throw a gauge on see what it gives you. Do a dry test and a wet test(adding small amount of oil to the cylinder). And in this case hold the gas pedal down to shut off the fuel pump thus clearing engine of excess fuel while you are conducting the compression test(killing two birds with one stone here).
    If your not making good or consistent numbers say around 150psi or better you should try coating the tops of the pistons with oil, assemble everything and see if it makes a difference when trying to start. When you turn over the ignition hold it while the gas pedal is fully depressed and then let off the gas pedal fully and then quickly depress it again. Try this a couple of times and this usually will get it to fire. If it works then you will be likely smothered in a cloud of smoke from the exhaust so open a window if your indoors.

    I hope this helps some restless, fed up, pushed to the breaking point guy trying to save a buck.

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