My 2001 Fromtier 4 cylinder has a stumble between 1500 and 2000 rpm in fourth gear (automatic). It has 75k miles. The check engine light indicates cylinder 4 misfire (P0304). Gas milage is starting to fall from mid 20's to low 20's. I've changed the following: plugs, wires, cap, rotor, fuel filter, #4 injector, fuel pressure regulator, & EGR valve. The air cleaner is relatively clean (K&N). I've also had the injectors flushed. It still has the problem. Any ideas?
My 2001 Fromtier 4 cylinder has a stumble between 1500 and 2000 rpm in fourth gear (automatic). It has 75k miles. The check engine light indicates cylinder 4 misfire (P0304). Gas milage is starting to fall from mid 20's to low 20's. I've changed the following: plugs, wires, cap, rotor, fuel filter, #4 injector, fuel pressure regulator, & EGR valve. The air cleaner is relatively clean (K&N). I've also had the injectors flushed. It still has the problem. Any ideas?
Is the check engine light off now?
Have you changed the fuel filter?
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Jerry
2004 Frontier, King Cab, XE, 4x1, 4-cyl, 5-spd My Frontier Page
My 2001 Fromtier 4 cylinder has a stumble between 1500 and 2000 rpm in fourth gear (automatic). It has 75k miles. The check engine light indicates cylinder 4 misfire (P0304). Gas milage is starting to fall from mid 20's to low 20's. I've changed the following: plugs, wires, cap, rotor, fuel filter, #4 injector, fuel pressure regulator, & EGR valve. The air cleaner is relatively clean (K&N). I've also had the injectors flushed. It still has the problem. Any ideas?
The #4 spark plug looked no different from the other three. By the way, each time the MIL was reset it came back on in two or three drive cycles.
I'm wondering if the problem is really in #4 cylinder or if the ECU logic just detecys a change in crank speed from an overall misfire and "favors" cylinder "4" to report the malfunction.
Timing chain may not be the best next step (expensive). Though I know lots of Nissans in the past have had 60K replacement intervals.
Could also check the coil, replace the PCV valve, look/listen for vacuum leaks, dirty/wet MAF sensor or wiring issue to MAF/IAT, etc...
I cleaned the MAFS by dunking the sensing wires in denatured alcohol and mildly stirring. I aso replaced the K&N air filter with a Fram paper filter. The Titan guys indicate that the oil in the K&N may foul the MAFS sensor. There's no change in the truck operation (stumble still there).
The PCV valve is my next target (although I've yet to find the thing). Based on previous posts this is a somewhat time consuming job.
My 2001 Fromtier 4 cylinder has a stumble between 1500 and 2000 rpm in fourth gear (automatic). It has 75k miles. The check engine light indicates cylinder 4 misfire (P0304). Gas milage is starting to fall from mid 20's to low 20's. I've changed the following: plugs, wires, cap, rotor, fuel filter, #4 injector, fuel pressure regulator, & EGR valve. The air cleaner is relatively clean (K&N). I've also had the injectors flushed. It still has the problem. Any ideas?
How about the O2 sensor(s)?
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Jerry
2004 Frontier, King Cab, XE, 4x1, 4-cyl, 5-spd My Frontier Page
I'm not sure that the O2 sensor is the primary player here. My understanding (and PLEASE correct me if I'm wrong) is that the MAFS is the primary mixture control input at lower RPM's (< 2500 rpm's) and the O2 sensor is the primary mixture control input at higher RPM's. Since the problem is most evident at lower RPM's I'm guessing that the O2 sensor is not a factor (of course I've been wrong about everything else trying to fix this problem).
The problem has taken on an additional symptom. If you run at higher speeds (say above 60 mph) and back off the throttle the check engine light will flash indicating heavy misfiring. Giving the engine a little gas stops the flashing.
It's fixed. I cleaned out the EGR ports on the intake manifold per Nissan's technical service bulletin NTB04-044. The number 4 port was partially (approx 20%) blocked. The other cyliners were more heavily blocked with at least one port being almost completely blocked. I used gun cleaning brushes (.22, .45, and 20 guage calibers). a screwdriver, and Hoppe's #9 gun cleaning solution to clean the ports. This is not an easy job as it requires you to loosen the EGR valve and unbolt the throttle body to get access to the ports.
The engine runs smoother and the check engine light went out on its own after two or three drives. I'm guessing that the KA24 series engines have a problem in this area that explains a lot of posts on the EGR and rough running. You can get the text of the service bulletin at http://www.nissanhelp.com/Ownership/.../NTB04-044.htm.
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