All - new to this forum, do drive a 2007 Sentra myself but all it has needed is oil changes. Trying to help out a really nice older lady I know who has a '95 Altima 2.4; she is getting ready to junk it and I said hold on. Couple people told her blown head gasket but I see no evidence of that at all. I guess it did get hot or overhead at one point. Ran compression test and got 150, 140, 120 and 120 in the 4 holes. It doesn't run too bad and she can drive it around town.

Although she says the CEL wasn't on originally when she started having problems, it is now. Scanned it and got P0325 (knock sensor), P0300 (random/mult cylinder misfire), and P0301 (cylinder 1 misfire). It also shows 3 'readiness not complete': catalyst, O2, and EGR and/or VVT. When pulling plugs for compression test two of the wires had the hard plastic section break off, and one electrode pulled off the wire and stayed on the plug. #4 wire boot also clearly wouldn't sit flush on the valve cover, even when you tried to push it down, but the plug end didn't show burning from arcing. Plugs don't look too bad, no coolant or major red flags. One of the hoses at the charcoal canister has a huge hole in it and I will replace that.

We're both on a budget. My plan would be to do the plugs and wires, cheapest way possible, and maybe cap and rotor, then see if the P0300 and P0301 codes go away. Is there a way to test the coil? Also I see many posts online that say that on these cars the knock sensor wouldn't set the CEL, but from my own experience on a Pontiac Bonneville, it absolutely did on that car. I won't touch the knock sensor unless I have to. Thanks for any help,

MT

Oh yeah, one key thing; #1 plug was hardly snug...might have been left loose by the last guy troubleshooting, and it might be the reason for the P0300 and P0301 codes! Might be why the CEL didn't come on right away. Guess I'll know soon enough but I have to get functional plug wires on it first,

MT

Fiddled with the car, got the plug tightened up and replaced the plug wires. Replaced that charcoal canister hose. It runs really badly. I cleared the codes and we'll see if the same ones recur. Right now the CEL is out, but I would expect that.

Went into live data mode and noted down some things that I suspect are flags. Right off, Fuel Syst 1 shows OL - Drive. Looking that up on another site, explanation was that the PCM is choosing to temporarily disregard the O2s and run the default fuel profile, as opposed to being forced to do that, in which case it would show OL - Fault.

Front O2 looks great but the rear O2 looks crazy - at idle, .03. Rev it up, it jumps way up, even above 1, then return to idle, and it goes back to .03. Fuel trim B1-S2 shows 99.4. I wonder if maybe either the catalytic converter or the rear O2 is bad. Catalyst and O2 are two out of the 3 tests that haven't run yet. I forgot to check that readiness monitor after the things I did today but might be able to tonight.

Any feedback welcome, thanks,

MT

Just scanned again, still 3 tests need to run but P0300 dropped off from what I did today. Wonder if the misfire in cylinder 1 could be vacuum leak or the injector.

MT

If your misfire is due to a vacum leak, check the intake manifold gasket. Very common on 2.4 Altimas. When my altima block cracked, the cylinder with the highest compression was the bad one. It was no 1.
Timing light is a great way to check spark.

Thanks much, Timothy. Best way to tell if vacuum leak? I think I have a gauge somewhere, not sure how to use it. Or old-school, spray carb cleaner around mating surfaces and listen for RPM? I'll grab my timing light tomorrow,

MT

Brake cleaner and idle speed changes should work on the manifold. I would try to fix the evap hose first. Also if you have a vacum leak, you will smell unburned fuel in the exhaust.

Couldn't find any air leaks. Then looked at the fuel injector in #1, tried my noid light but that didn't work even on a known good cylinder, so took a voltmeter to both wires and the signals are fine. Then took an ohmmeter to the injectors and #1 does appear to have a very different resistance. So I really think it's a bad injector. I tried my usual Pick N' Pull gig for pennies but couldn't get an injector out of the fuel rail. Those suckers are press-fitted tight. We are on a super tight budget here so I will wait for the 1/2 off sale the yard usually has at July 4th and buy a whole rail with all 4 injectors and I believe that will fix it. I'll close the loop in about 10 days,

MT

Oh, and I did slap my timing light on #1 and it flashed. Since I believe the plug is good I was really just trying to rule out dist cap,

MT

Haynes Manual says to remove two Phillips-head screws from the injector cap and pry the injector out of the rail with a flat-head screwdriver. It looks like this was hard for their technicians too.

Thanks, Timothy. I tried everything I could think of on the injectors at the yard, and they barely budged. They are also easily damaged. My best solution in this case is to get the whole rail with the injectors at a very attractive price,

MT

Grabbed a fuel rail with all 4 injectors at Pick N' Pull for $43...all 4 injectors ohm out at about 12.3...installed in about 30 minutes. Fixed the misfire, runs like a Swiss watch now, no misfire code. The bad injector in #1 wouldn't budge off of 1. Thanks all,

MT