Seriously doing my head in....Can alternator cause misfire?

Discussion in 'Technical' started by A-Bris-Z, Mar 13, 2012.

  1. A-Bris-Z

    A-Bris-Z Carcraze

    As many of you are aware I've had a very bad misfire problem for some time now that I cant seem to fix. I was talking to someone the other day and they suggested (with confidence) that it is probably my alternator. I didn't think an alternator could cause a misfire, am I wrong? I thought as long as my battery was still being charged, that meant that my alternator was fine??

    For new readers, here is what's been done so far:
    Fuel System

    • New fuel pump
    • FPCU bi-pass (no change)
    • Change injectors
    • Fuel filter has done only 1500km
    Ignition System

    • 6 new coil packs
    • 2 new AFM (now back to OEM)
    • S2 PTU x 2
    • CAS swapped in another one (no change)
    • All electrical connectors cleaned and checked

    • New engine, turbos, radiator and hoses (boost tested - no leak)
    • New copper plugs (no change)
    • Replaced ECU
    • ECU not throwing any errors
    • TPS (checked and fine)
    • New Coolant temp sensor
    • Air/Fuel mix altered by 5% using Conzult (up and down) - both made problem worse
    Car starts first time every time and idles well. Quickly then develops a misfire that can be heard best through exhaust. While warming up car is almost un-drivable, struggles to get revs up under load. At about 4500rpm it starts to pull again and then boost comes on and your off (at least until you change gear :rolleyes:). This state improves the hotter the engine gets until its presence is only felt in the lower revs as low power and lack of response from the pedal when the engine is at 95 degress Celsius. (Yes I know that's a little high but I have another clutch fan coming soon). She usually runs at around 85degrees Celsius.

    I've just pulled the loom back from the PTU to inspect wires etc and couldn't see any issues at all there (relocated PTU at the same time). Next I'm going to do the same with loom going to ECU. The car has an engine immobilizor and is most likely spliced into the loom near the ECU. Does anyone know if the immobilizor could be the problem? I thought they were either on or off??

    Now for those of you with a weak stomach ....stop reading because I'm going to start begging :bow2:. Somebody, anybody please help me!!!!!:lame:
    Seriously, I've had this car for two years and it's only been running properly for probably one week during that time, so I'm willing to listen to any suggestions no matter how ridiculous.
    Last edited: Mar 13, 2012
  2. rob260

    rob260 Administrator Staff Member

    Have you checked the alternator? Takes less time to put a meter across your battery than it would have taken to write that massive post!
  3. frysie

    frysie FRYTECH

    +1 ............ lol
  4. kakaboy

    kakaboy New Member

    I always thought the car (ecu) ran off the battery . But in the 300's case its off the alternator . I only found that out when I jump started the car and it ran without the battery :eek:

    So I guess its plausable . If your alternator is having intermittent issues which may not be noticeable on the battery end as it takes time for it to lose charge . So you never know .

    But like the other guys have said a meter will tell you :D
  5. Chilledpain

    Chilledpain Z Reaper

    Maybe try:

    Unplug your o2's, disconnect your battery, reconnect battery after 10 mins and leave o2's unplugged. - Any difference?

    If no ->

    Try another ECU - Any difference?

    If no ->

    Compression test - Readings? All good?

    If so ->

    New harness or known good one. Can wire it up outside car.

    After trying the above, let us know if anything changes...
  6. A-Bris-Z

    A-Bris-Z Carcraze

    I have ECUTalk in the car which gives me a voltage reading, what range should I expect it to sit in?
  7. mungyz

    mungyz Well-Known Member

    Check the cam timing, they will run quit flat and gutless then pull like a school boy at higher revs if the cam timing is out by a tooth.

    No offence to whoever built the engine but who was it? someone who really knows Zeds?
    Stock belt or aftermarket? I've seen an after market belt with the markings incorrect (needless to say I did not fit as if they can't get that right.....).

    As the others said though absolutely check the voltage in the system when the engine is running, anything less than 13V and you have a problem for sure (allowing for crappy multi meters that can read low some times).

    I worked at a garage that spent $4000 chasing a missfire on a Holden Commodore before I started there, one of the guys had rebuilt it and after that it always had a missfire at idle and ran poorly down low.

    I checked the plugs they were new, changed leads and coils etc for known good ones & it was no better, then I checked the part number of the plugs against what was recommended by Holden - it had the wrong plugs in it.
    Fitted the correct plugs (after a massive argument with the boss as he didn't want to buy new ones as it had them already) & problem went away.

    So yeah check you have the CORRECT spark plugs and gap as well.
  8. kakaboy

    kakaboy New Member

    When being charged (running) should be about 13v . When not its about 12v .
  9. mungyz

    mungyz Well-Known Member

    13 - 14v
  10. A-Bris-Z

    A-Bris-Z Carcraze

    Thank you for your idea's

    Sorry I forgot that......already swapped ECU's (x2). No change. Also replaced both O2 sensors. Could O2 sensors really cause this large a problem?

    I haven't done a compression test because its a new motor (1500km), and because it does intermittently drive well (rarely now).
    Hmmm......that might be beyond my skills, but it would be a great diagnostic test.
  11. A-Bris-Z

    A-Bris-Z Carcraze

    Thanks, I'll double check my voltage but I think that is where it sits. So can low voltage cause a misfire?

    Engine should be good as it was build by A2Zed and I use the copper plugs he recommended. I've also tried Iridium plugs (no change).
  12. mungyz

    mungyz Well-Known Member

    Yeah low voltage weakens the spark output and reduces the power to injectors etc - it generally screws things up BUT the voltage needs to drop down to around 10V before you will see any serious issues.

    What oil are you running? stupid question you might thing but it's important, if the valve springs are getting on a bit and the seats have been cut, valves refaced and then you run nice and thick oil the whole lot can combine to cause valve seating issues due to the followers holding the valves open.

    We proved that on the dyno with my car, the only thing changed between a mint run with good power and a crap run down on power and mixtures all screwed up was the engine oil. That was at the top end under boost though rather than at the bottom at idle. I replaced the valve springs and problem solved, it never had an issue down low though so put that suggestion in the further down the track box LOL!
  13. Chilledpain

    Chilledpain Z Reaper

    much a misfire, but I have heard of cases (local member) using aftermarket/incorrect O2's and for whatever reason, caused a massively lean condition. Coughing, spluttering etc.

    Could also be timing as mentioned by Mungy. Check base timing with a timing light. Also, get the timing covers off and have a look at the timing marks etc. Count the teeth if you have to.

    I'd still do a compression test tho. Just to rule it out and it's a nice feeling knowing all the figures are up to scratch.

    Regarding the misfiring, I'm starting to wonder if you have 2 issues?

    One more thing to check/replace would be the FPR and dampener. Unlikely, but if its a fuel starvation problem, fuel pressure could be to blame.
  14. dieseldave

    dieseldave Well-Known Member

    It can be a faulty voltage regulator or weak battery that does it too. You state that it only happens when cold, which indicates to me that these are the cause. And, yes a low system voltage can cause a miss fire and normally on No6 first. The changing areas of concerns from hot to cold has to do with the voltage and spark generation. I suspect it is the alternator's regulator, especially noting when it is happenning.
    Check your voltage, first (at idle and 3000RPM ) and it should be 13-14V, before you start dropping oil and changing piston rings.
  15. awgazm

    awgazm Active Member

    Have similar issue with my 4wd... Is a turbo related issue.. In that case :)
  16. ivan129

    ivan129 Active Member

    Is the misfire consistant with one cylinder?

    Have tried disconnecting the coils (unplug the connector on top of the coils) to one coil at a time to see if the problem is with a specific cylinder? This method should help to identify if the problem is with one cylinder.

  17. Chilledpain

    Chilledpain Z Reaper

    Interesting. Never would have thought to check the alternator regarding a misfire issue. Another useful piece of info added to the arsenal :)
  18. ezzupturbo

    ezzupturbo JDMAutomotive

    sounds timing related ay.
    does it run hell fatt before it starts to miss?
  19. Mongrel 295

    Mongrel 295 89 Z32 TT 2+0 J-spec

    now this may seem wierd but could it be exhaust system...? i freed mine up a bit and that fixed the problem
  20. pexzed

    pexzed Forum Administrator


    A blocked exhaust chokes the engine, as the volume of exhaust gases increases, this chokes down low and free's up at the top end.

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