# Misfiring



## gransport3800 (Jun 21, 2013)

I just bought a '98 Maxima for real cheap and it needs some work. It has a misfire on cyl # 3. It's getting fuel and spark. I pulled some codes out of the computer, one for the knock sensor bank 1, IAT sensor, O2 sensor which is probably because of the misfire and of course cyl 3 misfire. I'm thinking that a faulty knock sensor might lead to early or late timing. Is this possible on just the one cylinder? What are the resistance values for the knock sensor and the IAT in case that has something to do with it as well?


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## smj999smj (Jan 1, 2006)

A knock sensor will not cause a misfire. All it does is sense engine knock and signal the ECM, which in turn retards the ignition timing to help prevent engine damage. The fact that it is misfiring is probably the reason the knock sensor code is set. There's a very good chance that the oxygen sensor is bad, as they were a fairly common problem. Ignition coils and bad harness connectors for the ignition coils are fairly common problems as well. Another problem sometimes seen is wire breakage in the EGI harness in the bend between the engine and the firewall, which can cause a multitude of codes. A bad fuel injector could cause your misfire and isolate it to one cylinder. I've also witnessed a lot of rodent damage to the wiring of A32 Maximas. 
To test the knock sensor:

Disconnect knock sensor sub-harness connector.
Check resistance between terminal (2) and ground. Approximately 500 - 620 k Ohms [at 25°C (77°F)] .

It is necessary to use an ohmmeter which can measure more than 10 M Ohms.

For the IAT:
@68 degrees F., 2.1-2.9 k Ohms
@ 176 degrees F., 0.27-0.38 Ohms


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## gransport3800 (Jun 21, 2013)

What is the resistance range of the O2 sensor?


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## gransport3800 (Jun 21, 2013)

Also I checked the IAT, has a resistance of 1.80 on the 20k ohm setting and it's 78 degrees outside, is that right? It does have 4.8 volts to the sensor. The O2 sensor code is 141 bank 1 sensor 2, that's the one after the catalytic, correct? I also tested the resistance of all the fuel injectors and they were all the same.


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## gransport3800 (Jun 21, 2013)

Update, I think I've narrowed it down to a bad valve seal. I took it for a test drive and it blows quite a bit of blue smoke out the tailpipe, there is also a bit of oil on the end of the #3 cylinder spark plug. I did a compression test on it to rule out the piston rings, it has 150 psi. Has anyone ever changed the valve seals on this engine, how big of a pain in the ass is it? It is the V6 3000 DOHC.


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## smj999smj (Jan 1, 2006)

I've never heard of a valve seal fail on a VQ engine, but that certainly doesn't mean it can't. Replacing them would be a major pain! Labor guide time is 16.7 hours just for the right side bank, or 20.0 hours for both banks.


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## gransport3800 (Jun 21, 2013)

I've recently been told that a bad valve seal would only blow smoke upon start up and then go away, this car blows smoke going down the road and when you rev it up. If it is the rings or head gasket I wouldn't be able to get 150 psi of compression right? I also checked the PCV valve and that is good, I even ran the car without it after plugging the line going to it.


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## smj999smj (Jan 1, 2006)

You can test rings and the head gaskets by doing a cylinder leakdown test. I would recommend doing a fuel pressure leakdown test as I have seen some fuel injectors leak on the VQ engines; it could be the issue at #3 cylinder.


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## kxco111 (Aug 14, 2013)

Its main problem in the engine that create problem to misfire my opinion you must check the engine to the mechanic and change the oil of the engine its may be the factor of the misfire...


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## rogoman (Dec 16, 2004)

gransport3800 said:


> I've recently been told that a bad valve seal would only blow smoke upon start up and then go away, this car blows smoke going down the road and when you rev it up. If it is the rings or head gasket I wouldn't be able to get 150 psi of compression right? I also checked the PCV valve and that is good, I even ran the car without it after plugging the line going to it.


If the oil rings are worn, you can still have compression that's within spec. A very simple way to test for oil burning is to first fully warm up the motor. Stand behind the car. Have someone rev the motor to 4,000 RPM and hold at that RPM for about 15 seconds. If you see a lot of blue smoke come out of the tailpipe, the motor is burning excessive oil. If it's black smoke, then it may be leaking fuel injectors.


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