1996 Pathfinder, 110K miles. Runs fine from cold start but misses in one cylinder when restart again when engine is warm. Spark plug in that cylinder looks like it’s never seen gasoline, like brand new.
There are other things that cause a misfire in a cylinder.
Bad injector, a bad plug wire, or a worn distributor shaft bushing.
Tester
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Thx. Injector was my first thought, but why runs great with no missing from a cold start?Plug wires have been replaced. I don’t know about worn distriibutor shaft bushing but again why runs fine from cold start? How do I diagnose worn distributor shaft bushing?
Run the engine until it starts to miss.
Remove the distributor cap and wiggle the rotor.
Tester
Thank you. I’ll give it a shot.
Misfire when warm, not cold, doesn’t seem like a faulty injector to diy’er me. Injector faults not commonly heat related. I’d guess the more likely cause is a problem with ignition system (e.g. distributor as mentioned above). Could be a problematic distributor cap or distributor rotor as well.
If I had that problem, since I knew which plug was causing the problem, I’d put a timing light on that plug’s wire, and see if the timing light behaved differently when engine cold vs engine hot. The other difference between cold vs hot engine is cold engine is running much richer mixture. So if ignition signal to that spark plug was weak, it might still be enough to fire with richer mixture, but not fire once mixture is leaned out due to warmer engine.
These all have been interesting thoughts. You’d think it boils down to only 3 possibilities - problems with 1) spark, 2) fuel, or 3) compression. In my case spark seems good in all 4 cables, compression checked out, leaving fuel. All injectors sound the same with a stethoscope. Haven’t checked resistance. Could resistance be off and injectors are purring along?
I can’t see that a distributor malfunction would always cause a specific single cylinder to misfire as long as cables are doing their job and cap isn’t cracked. Distributor cap has been replaced and plugs are good evidenced by switching them and miss stays in same cylinder.
This has been a mystery to me for over a year. Mechanics just seem to want to replace things without a diagnosis. Wish the even-numbered injectors weren’t so hard to get to.
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I presume you’ve ruled out shaft play. Does the electrode inside the cap corresponding to that plug look any different than the other 3?
It’s certainly possible you have a faulty injector. If measuring injector solenoid resistance is relatively easy to do, probably worthwhile doing. Correct resistance doesn’t necessarily imply injector is good though. Your shop might try a noid-light test gadget to make sure the electrical pulses to the injectors all seem the same.
Another unlikely idea, but when a used spark plug looks new, like it has been steam cleaned, well, maybe it has. Could indicate coolant is getting into the cylinder, faulty head gasket etc. Any other signs of a head gasket problem? Engine overheated shortly before this all started? With engine at normal operating temperature, is there white smoke coming out of tailpipe as you accelerate up a freeway on ramp? Ask helper to follow you, looking at your tailpipe. Do you have to add coolant from time to time?
Has your shop connected a spare spark plug to that wire and visually inspect the spark crossing the electrodes while cranking engine? It’s possible to have a spark, but it isn’t hot enough to properly fire the cylinder. A good, robust spark is blue-ish white. Any orange or red colors is suspect. I experienced the orange-spark problem on my truck a few years ago. Wouldn’t start until corrected. Seems unlikely given everything you’ve done, but fairly easy test to do.
Has a shop with access to a Nissan pro-level scan tool had a chance to offer an opinion? Have you had a battery/charging system test?
Remove the spark plug after running the engine, inspect for steam coming from that cylinder. Inspect inside the cylinder with a borescope for coolant entering.
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As soon as I saw this I thought the same thing. Burning coolant cleans spark plugs so they look like they are brand new…telltale sign…
No other signs of a cracked head gasket.
Healthy spark when I separate wire from plug about a centimeter. Have replaced plug wires and distributor cap. Distributor seems solid in mount. Never over-heated. No white smoke. No coolant loss except small amount from lower radiator hose. No “milkshake” in coolant. Haven’t had a pro-level scan tool. No sign of a battery or alternator problem.
Those observations are not relevant, it only takes a few drops of coolant seeping into a cylinder to cause a misfire during start-up.
Yes. Misfire isn’t upon start-up after vehicle has been sitting overnight when you might expect more coolant to have entered cylinder if there’s a bad head gasket. Misfiring occurs after warm-up and resting for 10-15 minutes before restarting.
No “wobble” whatsoever.