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Thread: Camshaft pos sensor output & coil failure (perhaps?)

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  1. Camshaft pos sensor output & coil failure (perhaps?) 
    #1
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    Hi, my A4 B6 1.6 developed a misfire on cylinder 2&3. It happens when the engine has warmed up and I have confirmed there is no spark, so an ignition issue rather than injector etc.


    It has a coil pack rather than a coil on each plug.

    Ignition Coils For Audi A4 From 2000 To 2004 | MicksGarage


    I did a resistance check on the high tension side, getting 17k between the 2/3 and 1/4 leads, I was hoping to find 2/3 open, so if it's the coil, it's either on the low tension side, or a crack causing the failure. Problem is, the coil is at the back of the engine near the bulkhead and it's a big job to get to, or even change the leads. So, I want to make sure it's the problem before I change it.


    To eliminate other components, I put a scope on the camshaft position sensor and am getting a nice stable square wave (while it was just running on 1&4). The crank sensor was replaced last year (unrelated) so I didn't bother looking at that.


    The frequency of the square wave at idle, about 800rpm was about 6.5hz. So the camshaft was doing 400RPM, or 6.6 revs per second. So, 6.5hz would suggest the camshaft creates just one pulse per rev - I would have assumed it would be many more. Is this normal? Here is a pic of it, if the part I've circled is the sensor reluctor then it appears my sensor is OK.

    camshaft.jpg

    Am I missing anything before I go to replace the coil?

    Thanks
     
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  2. Re: Camshaft pos sensor output & coil failure (perhaps?) 
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    The G40 cam sensor only produces one pulse per cam revolution so as to provide the ECU with a cam position reference signal in conjunction with the G28 crank speed sensor so it knows at what position the engine is for sequential injection and ignition otherwise it is wasted spark and group injection which is wasteful.

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  3. Re: Camshaft pos sensor output & coil failure (perhaps?) 
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    That's great, many thanks for confirming that.

    Is there anything else I should check before committing to changing the coil/leads? Only DTCs are P0302/3.
    P0301

    Read more at: OBD-II Trouble Code: P0301 Cylinder 1 One Misfire Detected
    Copyright OBD-Codes.com

    P0301

    Read more at: OBD-II Trouble Code: P0301 Cylinder 1 One Misfire Detected
    Copyright OBD-Codes.com
     
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  4. Re: Camshaft pos sensor output & coil failure (perhaps?) 
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    I recently had a similar problem of a misfire when the engine was hot, which eventually became permanent Please Help My A4 B5 is not firing on cylinder no. 1

    Although my A4 does not have the same engine, it does have sequential ignition and injection, but with a separate coil pack for each cylinder.

    I don't have a wiring diagram for your engine, but I think it is likely that the circuit is similar.

    My problem turned out to be a fault in the Ignition Power Output Stage, N122, which is a small component containing 4 "power amplifiers", actually just switches, which convert the low voltage pulses from the ECU into 12 volt pulses to the coils.

    After removing the fuse supplying the injectors, I cranked the engine and tested the inputs and outputs for each channel with a test light consisting of a small LED in series with a 1/4 watt 330 Ohm resistor.
    I guess you could also use your 'scope to check them.
    Did this forum help you? Help make sure it's here next time! Follow the instructions at the top of the page to make a suitable donation using PayPal .
    1996 A4 B5 (S2) Avant 1.8T (petrol) 150 bhp code AEB automatic with 79,125 kms = 49,450 miles on 30/07/23
    VW T25 Camper, Alfa 33 1.4 ie, 2 Alfa 33's for parts.
     
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  5. Re: Camshaft pos sensor output & coil failure (perhaps?) 
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    Hi, many thanks for that.

    I read your old post, I'm not sure if we have the same setup, you seem to have an individual coil for each cylinder? Mine is a single module (pic in link in my OP) with one 4 pin connector going to the ECU, I assume, plus the 4 HT leads. I'd love to go putting my scope in the input connector, but the problem is access, you need to remove the throttle body etc to get to it.

    In any case I just ordered a coil and leads an hour ago! I really hope this is it! I will report back.
     
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  6. Re: Camshaft pos sensor output & coil failure (perhaps?) 
    #6
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    I have looked again at the pic in your OP.
    I'm guessing that the wiring from the connector goes straight to the ECU with no other component between, and that the heat sink on the top is for the Power stage, as coils don't need a heat sink.
    It might be available as a separate item, but as the price shown is close to half what I paid for a Febii Power Stage, probably not worth bothering.
    Did this forum help you? Help make sure it's here next time! Follow the instructions at the top of the page to make a suitable donation using PayPal .
    1996 A4 B5 (S2) Avant 1.8T (petrol) 150 bhp code AEB automatic with 79,125 kms = 49,450 miles on 30/07/23
    VW T25 Camper, Alfa 33 1.4 ie, 2 Alfa 33's for parts.
     
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  7. Re: Camshaft pos sensor output & coil failure (perhaps?) 
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    Yes, I think/hope the control module is built in. I can't find the site now, but in one of the suppliers the description said something like that.

    I ended up getting an NGK unit and leads from another motor factor for €125, I'd rather go for a brand I know. Got the old one out today, big job due to a rounded allen bolt!
     
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  8. Re: Camshaft pos sensor output & coil failure (perhaps?) 
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    It was the coil/module. Replaced it Tuesday and no misfire since. I compared resistance readings of old vs new on the low tension side, on the new, all 4 pins were open circuit to ground, on the old, one was zero ohms to ground, so that seems to have been the issue.
    @FrenchAudi, yes it seems the power stage, or some electronics are build in, see pic:

    coil.jpg
     
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  9. Re: Camshaft pos sensor output & coil failure (perhaps?) 
    #9
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    The 1.8 B5 had a separate power stage module for only a couple of years around 1996, after which a power stage was built into each individual coil pack, which are located immediately above the plugs.
    This means that an entire coil pack has to be replaced if its power stage fails.
    Good for ease of diagnosis if paying for the work, bad for the pocket if DIY.
    Even later models had coil packs above only two plugs, with an extra HT lead on each supplying a second plug on the "wasted spark" principle.
    I see your ignition works on this principle, which is why you had misfires on two cylinders.
    At least my car is still driveable with only one cylinder misfiring. I disconnected the connector for the relevant injector and drove gently home, about 200 km, without any problem.
    Did this forum help you? Help make sure it's here next time! Follow the instructions at the top of the page to make a suitable donation using PayPal .
    1996 A4 B5 (S2) Avant 1.8T (petrol) 150 bhp code AEB automatic with 79,125 kms = 49,450 miles on 30/07/23
    VW T25 Camper, Alfa 33 1.4 ie, 2 Alfa 33's for parts.
     
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  10. Re: Camshaft pos sensor output & coil failure (perhaps?) 
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    Sorry for my late reply.

    Yes, it seems it fires two plugs at once, given that resistance readings on the HT side show that 1/4 and 2/3 are about 20k and no connection to earth. So, I assume, both plugs must be working to complete the circuit. I thought each coil might be tapped in the middle and grounded, but it seems not.

    Anyway, still working!
     
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