Cylinder Misfire

[bigtime]

How do I determine which cylinder is misfiring?

[goody90q45]

Assuming you have a 94Q your misfire is more than likely due to a bad injector rather than a bad coil as in the 97+ Q's. The easiest diagnosis is to ohm test the injectors with a digital volt meter. The bundle in the pic is on the end of the plenum, passenger side.

Pulling ECU codes would also give helpful information. If you plan on owning your Q long-term I'd recommend investing in a consult cable and (Blazt) datascan software. With this setup and a laptop you can shut off one injector at a time to narrow down the miss. Without the program you're going to have to unplug one coil/spark plug at a time which involves a couple of hours of wrenching to get there.

Ohm test your injectors first. Chances are good you'll find the source of the miss there.

[Q45tech]

Observe the O2 waveform ^v^v^v^.........4 cycles then repeats...compare to firing order...........extra rich = coils; extra lean = injectors.

Just like every V8 for the past 20-25 years ........the standard diagnostic method.
http://www.picoauto.com/tutorials/lotus-misfire.html
http://www.picoauto.com/waveforms/Sensors/

[Infinitiguy19]

Thanks for the info Q45Tech but there prices for hardware are a bit steep for the average DIYer. Its nice how they lure you in with free software though. If any local Infiniti dealerships close down I will be the first to there to get a Nissan Consult. I will even sleep there over night or even for a couple of days to guarantee me and some others one. I really really want a Infiniti dealer closes down after 2 local GM of all dealerships closed down. Why can't it be Toyota or Ford closing down, there cars have done nothing but kill people.

[Q45tech]

Anyone with a PROPER scientific education [even a 2 year trade certificate in electronic tech] would realize that all these electronic devices can be home built on the cheap, bought used on ebay, or emulated in some inexpensive way.

OLD Laptops or desktops on wheels with suitable test cables.

[Q451990]

If it's a dead miss you might be able to diagnose it by measuring the temperature difference on the exhaust manifold with an IR thermometer. Those are available at Harbor Freight and other outlets and are relatively inexpensive.

Still, the easy method on the models prone to injector failure (90-96) is to measure the injector resistance. We see very few coil faiures, so it's a good bet that your problem is an injector.

Heath