Thread: Misfire driving me spare

What about crank angle sensor and or cam sensor if fitted ?

Would that throw just a single cylinder off?
Is it a matter of changing for spares and seeing?

Alternator needs to be changed out first if noisy, can't believe that wasn't the first thing done, may have saved some money and time...
These crank and cam sensors are VERY sensitive to electrical noise, not saying it's a 100% fix in this case but electrical noises are first port of call.

Isolating the alternator (as in functionally removing it) lead to exactly the same misfire so it seems as a cause it is not likely. A new alternator is $6-700 for a Denso unit .

Originally Posted by Julian B

Isolating the alternator (as in functionally removing it) lead to exactly the same misfire so it seems as a cause it is not likely. A new alternator is $6-700 for a Denso unit .

Functional removal? Belt off? Reg unplugged, battery cable unplugged? My alternator was noisy, but not for long before it died. It's always cheaper and easier to completely rule out known problems when diagnosing. they won't always cause the issue to resolve but they will stop other problems during the search.
Mechanical faults such as a valve are unlikely for a misfire. Can be easily and cheaply tested with a compression test.
Test the ohms of each injector. You can also check the ohms of the coil but I think it'll only show the primary winding from memory.
With it running go through and shake the wiring "tug test" lightly pull the wires .
Have you confirmed that it is number five? Disconnect either the plug or injector on that cylinder, if the engine doesn't change note. Then it's the culprit. If does then move on to the next cylinder. When you get to the cylinder that doesn't respond to the injector or plug being disconnected. Swap one component at a time till the cylinder next to it becomes the problem. If nothing makes the cylinder number change. You need to test wiring using a multimeter and diagram for continuity. Unlikely though. Will usually through an open circuit code.
Coil over plug type coils don't live forever.

Just replace the alternator, regardless....🙄

Originally Posted by justinc

Just replace the alternator, regardless....🙄

I intend on doing so. I need to defer the cost for a week at this point.

Originally Posted by josh.huber

Functional removal? Belt off? Reg unplugged, battery cable unplugged? My alternator was noisy, but not for long before it died. It's always cheaper and easier to completely rule out known problems when diagnosing. they won't always cause the issue to resolve but they will stop other problems during the search.
Mechanical faults such as a valve are unlikely for a misfire. Can be easily and cheaply tested with a compression test.
Test the ohms of each injector. You can also check the ohms of the coil but I think it'll only show the primary winding from memory.
With it running go through and shake the wiring "tug test" lightly pull the wires .
Have you confirmed that it is number five? Disconnect either the plug or injector on that cylinder, if the engine doesn't change note. Then it's the culprit. If does then move on to the next cylinder. When you get to the cylinder that doesn't respond to the injector or plug being disconnected. Swap one component at a time till the cylinder next to it becomes the problem. If nothing makes the cylinder number change. You need to test wiring using a multimeter and diagram for continuity. Unlikely though. Will usually through an open circuit code.
Coil over plug type coils don't live forever.

Josh, yes I pulled the regulator cable so windings couldn't energise, and got a suitably grumpy chime and warning re no charging state and the AC voltage disappeared.

I agree that it seems unlikely mechanical.

Injectors were a completely different set professionally cleaned and flow tested accurately, all very close resistance. Fault remained following change. Manifold gaskets renewed with genuine at the time.

Coils each have 4 wires so not sure what values across what pins I am searching for. Also I swapped around coils and fault persisted.

Your check re isolating misfire by pulling components from cylinders sequentially is a familiar routine before I had vehicles with computers. Can I not trust the computer to tell me it is this cylinder?

Given that the misfire is not continuous, pulling spark to locate which one may not yield certain results as this is subtle at idle and making one cylinder dead will make it buck like a horse irrespective of the cylinder.

Any ideas about cause from someone who can read my process so far and advise next step. I am aware that the alternator is in need of replacement, as I listed the AC ripple voltage for this reason, but when this stray AC voltage is removed the problem is unchanged. Any further ideas from an electronics expert on these motors?

What type of scan tool are you using?

If it is a decent one you should be able to access the generic OBDII modes. You'll find misfire data in Mode$06. Have the unit plugged in and monitor it while you drive. Also check your long and short fuel trims and 02 sensor performance.

It could just be a vacuum leak. I've seen quite a few misfires caused by a dodgy hose or PCV.