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Engine Missfire


danielbrookes
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Absolutely spot on, answered my questions before I even asked them :). It’s doing it again now on the drive, I’ll see if I can get some logs for you.  Thanks for your help.

For info at the moment if I holt throttle at 7% it will sit at 1.7k RPM and start to fluctuate, struggle and eventually stall.

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Brumster my brother has just turned up with his wife so apologies if I go quiet.  Here are the logs, the engine stalled at the end of the first log and almost stalled end of second.  You will see I kept the TPS constant.

Any insight or tips would be great.  My thoughts are to replace the crank position sensor next, £25 from europarts unless you think that isnt the issue.

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Nothing seems at odds with the sensor values, on both of them it seems the revs drop first and everything else is 'as a result' of that, rather than being the source of the problem. The only thing it's hard to make a call on is the MAP, but I'd guess it's more effect rather than cause. You close the throttle towards the end as it's about to stall, and that recovers it a little, so it does suggest *maybe* it's related to inlet manifold vacuum (or boost in your case)... just as it's nose-diving to stall it's loosing inlet pressure, you close the throttle and it picks up again.

So I think this is a dead end. This map hasn't changed right, the car was running fine on these ignition advance numbers and injector timings, you've not fiddled with it in any way?

Given what you've done on the electrical side of things, I wonder whether it's worth turning attention towards air leaks or injector connections? The ECU is telling the injectors and the ignition the right thing but maybe they're not DOING the right thing because of bad connections, bad fuel pressure, etc etc. If you can get it running long enough you can go fiddling/wobbling connectors to see if you can trigger it, other trick is spraying brake cleaner around the various hoses/inlet manifold/etc and listening for a change in engine tone (it'll pick up if it's pulling the cleaner in anywhere), helps you narrow down where it might be.

It's probably also worth someone for knowledgeable about forced induction (STU!) commenting here as there may be other parts to the puzzle I'm unaware of that might cause this... you lot and all your dump valves/etc ;) ;)

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Edited by brumster
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Replaced crank sensor (£25) no different, testing old one it looked fine anyway resistance within tolerance and voltage produced when I chucked some metal past it....not exactly a scientific test I know.  But for £25 it was worth a go.

Anyway I am wondering if this is alternator\battery related.  Reason being the battery is now flat after idling for a few minutes.  I am getting 3V per injector (should be 12V right?) but the battery is flat, starter no longer turns.  So its in the garage charging.

I did notice the battery voltage was low even thought engine was running (11.7V) so before I do anything else I am going to fully charge and confirm its up at 14.5V when idling.  It certainly was from memory before all this started.

Looking at the logs I sent does the battery voltage look OK or seem low?  If I dont get anywhere after a full charge and the alternator putting out the correct voltage I may take it to a specialist.

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One of my (many) problems discovered while trying to fix my misfire was the wiring to the alternator - at one point, one of the wires dropped out of a spade terminal. However, not sure that would be the cause of a misfire - you'll just kill the battery.

At idle, my battery gets about 13v and up to 14.2v when driving with revs. Too much is as bad as too little and 14.5v sounds a bit high (what I have discovered is that 0.1v is quite a lot in battery-speak 🙂 ).

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Looking at your logs, you're getting 11.8v at the start but I assumed that's during cranking? Which is not bad - once she's fired up you've got just over 13v, although it does fluctuate with engine revs, anything from 12.3 to 13.3v. If your battery is flat then it may well be the alternator responsible, because in none of those logs are you getting anywhere near 14v to charge a flat battery - but if the battery was in tip-top condition then you wouldn't expect it to be. But if you've been doing lots of starting of the engine for short period, trying to diagnose this, without good long runs to charge it back up - then it may just be what it is; the battery has drained from all the repeated starting.

That might be an unrelated issue - I can't see any suggestion that the voltage drop is causing the stall, more the other way, but remember that's only what the ECU is seeing, it's not necessarily what the coil, injectors, etc. are (although it's normally a fair indication, if not, I would say it's a wiring issue). Either way, I don't think it's the cause of your main problem with the engine just cutting out.

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Just skimmed so apologies if I have missed something, but it’s a misfire at cruise right? Have you got an overrun fuel cut? If that is set incorrectly you can have that cut fuel at cruise. 
 

Another thing, I can’t see the logs but dans comment seems to suggest map reading goes up when throttle closes? If so that suggest map reading is wrong side of the throttle body. 

Edited by theduck
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As the revs drop (as it starts to presumably cut out, although in this instance he saved it/it picked up again) the MAP reading is going down on the graph but in reality it's a negative reading (negative pressure) so it starts off at -0.67 bar (rpm @ 1400) and goes up to -0.24 bar (rpm @ 500) as it starts to stall. Assuming it's all calibrated of course, I would take the actual pressure readings with a pinch of salt but that's what the values on the graph show as.

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Hey, thanks for the help. It started at Missfire are cruise, went to two cylinders constantly misfiring and tow home.  

Repeatable after heat cycle and cold start next day, two cylinders down. Checked spark at all 4 plugs (I have one) and now it’s misfiring and stalling at constant throttle (the logs are 7% throttle and no load on drive).  I’ve ran out of juice in the battery and it’s on charge now.

MAP is getting its vacuum from plenum behind throttle.  It’s a strange one, I’ve just replaced Crank sensor which made no difference - but to be fair the battery died.  

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