can a broken o2 sensor cause the car to not start? - BMW Forum - BimmerWerkz.com
3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

 
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#1 (permalink) Old 05-29-2004, 06:45 PM
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can a faulty o2 sensor cause the car to not start?

how can I diagnose a bag ecu without swaping it with one that works?

what else can cause my car to not start?

Gap sensor, cold start vavle? how do I check these?

I am desperate for help... I have tried alot already! ghead

I am running out of ideeas and money.

PLEASE HELP!!!!
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#2 (permalink) Old 05-29-2004, 10:09 PM
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A bad O2 sensor won't make your car not start, it can cause you to get doo doo gas mileage and sometimes make the car run funny.

Now getting back to the no start prob:

First things first. Check all of your fuses.

Now make sure you are getting fuel, have someone crank the motor while you lay near the gas tank. (it's just under the rear seat) you should hear a motor running while the car is getting cranked. If you don't hear it you may need a fuel pump or have the power supply to the fuel pump checked (ie relay, fuse wireing).

Next, check for spark. Pull off one of the spark plug boots and stick in an old plug. Lay the plug on the valve cover so that it is touching metal (do not hold it, unless you want a new hair do) then have some one crank it, watch the end for a strong white/blue spark, if the spark is orangish and you can hardly see it, you may have a bad coil or pick up.

If you have both of these. Try pulling off one of the injector plugs, useing an automotive test light place the probe on one of the two terminals in the plug then useing a pice of wire touch the other terminal, then have some one crank it (don't worry you won't get shocked) the test light should flash on and off while cranking. If not you may have a bad CPS (Crank position sensor) bad computer, relay, fuse or wireing.

Good Luck
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#3 (permalink) Old 05-29-2004, 11:02 PM
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hey Starmavin,

Thanks for the hints!!! I figured it would be something like that. I'm thinking bad ecu. I had the injectors check by a shop about 1 month ago, the fuel pump/relay is new, the fuel pressure regulator is new. I have a bad oxygen sensor so it sometime runs kinda loopy but it usually starts. The coil dosen't look old but I can't open it so is there a way of testing it? and I will check the spark tommorow too. To ceck the injector, I don't know how to pull them off... I heared that if I put a srew driver on it I should hear a constant cliking as the engine tries to turn over. If it is the ecu can I get that fixed in canada...? And any certain way of knowing? And what about the gap sensor? how can I test that???

Thanks for the help, I'm really stuck here!

Bryce.
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#4 (permalink) Old 05-30-2004, 11:04 AM
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What car do you have?

The ECU is "normally" rather durable unit, and if it fails the car is dead. Rather, inputs into the ECU cause most of the problems. Testing it is tricky and requires special tools, I would suggest getting a bentley shop manual for more info on this and the rest of these items.

As far as testing the coil goes, you'll need an ohm meter. But I would just check the spark quality with the plug. Also check the plug wires, cap and rotor.

Checking the injector function with a screwdriver works to an extent, sometimes the "clicking" sound can be faint. A mechanics stethoscope works better, but the Noid or test light method is best.

Now a "gap sensor?" I'm unsure of what you mean, do you know if it is called something else?

If your car is running rough at idle, I would suggest cleaning out your throttle body and idle air control motor, crud builds up in there and causes rough idle, stalling when cold, and surging when warm. Carb cleaner and a rag gets the job done.

Also check the cold start injector (if you have one) by unbolting it from the intake leaving the fuel line attached. Give the engine a quick crank and watch the injector, it should spray a very fine mist, if not, it can be cleaned (with some effort) or changed. But this wouldn't cause a cut out problem, just hard starting, or stalling when cold.

Your garage "should" be capable of testing and fixing all of these. If not you may need to find another garage.....
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#5 (permalink) Old 05-30-2004, 11:39 AM
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ok,

By gap sensor I mean crank position sensor or something... the one that's on the flywheel. I read that that could stop your engine from starting. I also read that the ecu before going out usually the car is hard to start with intermitent problems like not starting at all, which is the case with my car, I alwas have a hard time starting it! I will check the spark right now and see if I can't get one of the injectors of, It's a motronic 1.3 I think, so I don't think there is a cold start valve.

I'll keep you posted on any news, yhanx again, bryce.
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#6 (permalink) Old 05-30-2004, 03:20 PM
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Checked the spark, seems ok to me, the park is bleu/white and constant. By the way it's a 1990 325 I with a (i think) motronic 1.3 system. my ecu # is motronic bosch 0 261 200 173. not sure about what to check next, the injectors are fine and I cleaned out the idle control vavle... What next??? any way of testing the sensor on the flywheel, I read that it could cause the car to not start if damaged...
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#7 (permalink) Old 05-30-2004, 11:26 PM
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Quote:
Originally posted by Starmavin@May 29 2004, 10:49 PM
Now make sure you are getting fuel, have someone crank the motor while you lay near the gas tank. (it's just under the rear seat) you should hear a motor running while the car is getting cranked. If you don't hear it you may need a fuel pump or have the power supply to the fuel pump checked (ie relay, fuse wireing).

Next, check for spark. Pull off one of the spark plug boots and stick in an old plug. Lay the plug on the valve cover so that it is touching metal (do not hold it, unless you want a new hair do) then have some one crank it, watch the end for a strong white/blue spark, if the spark is orangish and you can hardly see it, you may have a bad coil or pick up.

Those aren't good ways to check for fuel or spark.

A fuel pump can run but not supply adequate pressure or volume. You NEED a fuel pressure gauge. And the best way to check for power at the pump is with a light bulb across the power and ground. That way you verify both voltage and amperage.

You don't want to use an ordinary spark plug to test for spark. I've personally experienced coils that could fire a spark plug outside the engine, but not one inside the engine. It requires more voltage to fire a plug inside the combustion chamber then it does to fire one outside. You need a spark tester to verify that the coil is producing enough voltage.


A fuel pressure gauge and spark tester are not expensive tools and they will ALWAYS come in handy later in life.

Dan
1989 325i
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#8 (permalink) Old 06-03-2004, 10:13 PM
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The tests that I sujested are just basic tests, don't cost a thing to do, and give me an idea of what's going on.


But getting back to the no start problem, If I remember correctly the CPS or gap sensor as you call it wasn't working correctly you wouldn't have any spark at all. So that clears that as the suspect for now. One thing I can sujest to futher my understanding of what's happening is to spray some starting fluid into the intake then try starting it. If it starts then dies, then you have a fuel problem, if it doesn't start up at all, then we have a spark problem. After this very simple and basic "test" we can then focus on what may be causing the problem\s, rather than throwing money at it.

Good luck.
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#9 (permalink) Old 06-05-2004, 09:39 PM
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well, I got her going last week by jumping the puel pump relay and cranking it while flooring the gas four about 30 seconds... the strange part is when I jumped the relay and turned the key I could not hear the fuel pump at work... after it started and I turned the car back of to remove the wire I could clearly hear the hum of the pump... Could this mean that there is faulty wiring or something? It's done this to me a few times already... I wouldn't whant it to die on me while I'm at work or something... Anyways I changed the relay, It still takes a while to get started and I have to hold the gas full throttle to really get it started... I would really like to just turn the key And have her start up without any hesitations... I will try a supertune on the injection system this week end, maybe the engine is a little gummed up, it wasn't really driven before me, I think an old lady had it or something Anyways, thanks for the replies, they are od great help!!! I can't wait to get all the little mechanical bug fixed so I can start tunning it a little!!!
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#10 (permalink) Old 06-07-2004, 10:58 PM
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Possable ignition switch.
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