'94 Sentra ignition misfire

OK,

1) Replacing rotor & cap did not help. 2) Wires were "lifetime" so they are now replaced this did not help. 3) Replaced plugs on outside chance it was an internal defect in the plug. No help.

Symptom is the same, noticeable power loss and feels like engine miss. When plug wires are removed with engine running, no loss of speed when #4 is removed. Noticeable idle speed loss when 1, 2 or 3 wire is removed.

I did notice 1, 2 and 3 plugs looked normal but with a light carbon deposit. #4 looked cleaner, almost no carbon buildup. Plug itself did not show signs of cracks or any damage.

I took off the oil filler cap while the engine was running and noticed somewhat of a light "chugging" sound, with a pretty good volume of pulsing air coming from the hole. A little bit of oil vapor not too much. I don't have any smoke in the exhaust.

Any ideas on what diagnostic to run next? Maybe a compression test? I'd suspecting a broken or worn valve spring but I've never seen this on an engine myself so I don't know what it the symptoms would be.

Thanks in advance,

Mark

If you still suspect spark misfire, then hook up a timing light and watch the strobe. Its pretty easy to see a misfiring plug that way.

Codifus advice is also good to check large connections like battery and grounds.

Did you chack the plug gap when you installed them? (doesnt apply if you bought good platinum or iridium styles. Also avoid Bosch plugs. They are the only ones I have seen used up in a few thousand miles.

-SP

Mark Fields wrote:

Thanks for the response.

I didn't know about the electrical connection thing so I will check it out.

The way #4 behaves (i.e. no loss of idle speed when the spark plug wire is removed) was the same before and then after all the items were replaced. I noticed the probelm with #4 and after changing rotor, sap, all spark plugs and spark plug wires the result is the same.

The spark plug wires were Bosch 09814 Wire Set (Stainless steel Mag winding,

100% pure Silicone jacket, Kevlar reinforced core. Lifetime warranty. I first started using them on this vehicle April 2001 when the car had 150K miles. I replaced the Bosch set with the exact same part number in March 2006 at 250K miles because wire #1 developed a small hole in the insulation. It was that set which was on the car Monday. Tuesday I replaced it with a third set of the same part number (no charge replacement) thinking perhaps there were breaks in the wire.

The spark plugs removed were Bosch Platinum FR8DPX. These plugs were installed July 2007 and had only 5,000 miles on them (all local town driving). They looked good but since it seemed like an ignition problem at first I figured it was worth replacing them. The set I installed Tuesday was the NGK BKR5ES-11. They are copper cored plugs. I think they are very close to OEM plugs.

The gaps was checked and all were at 0.044" as they were installed.

I of course kept the Bosch plugs since they had little miles on them. #1, #2 and #3 look almost identical with carbon buildup. Just a little though. #4 seems to actualy have less carbon buildup. If needed I could post a photo I suppose.

Mark

Thanks to all who offered suggestions.

It turned out it was not an ignition problem though the old method of pulling plug wires one by one coupled with the 'miss' seemed to indicate this.

Compression was checked and found to be consistent and good for an old car with 265K miles.

The real reason turned out to be a malfunctioning fuel injector on the bad cylinder. I had already dropped the car off for diagnosis (I don't have a compression guage) before looking through the repair manuals and figured possibly the fuel injector was to blame. the repair shop called and said they suspected the same thing after the compression check and replace it with a new one. Now the engine is running fine again.

Thanks again for the ideas. Time to put the car back in service and keep racking up the miles.

Mark