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Chris(aka-Moose)
Chris(aka-Moose), Nissan Technician
Category: Nissan
Satisfied Customers: 46481
Experience:  16 years of experience
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I have a 2002 Nissan Maxima 3.5v6. I have a P0300 multiple

Customer Question

I have a 2002 Nissan Maxima 3.5v6. I have a P0300 multiple misfire code present. I have installed a new maf sensor, all 6 injectors, replaced all 6 ignition coils off another known good vehicle, ngk oe spark plugs and still get a P0300. I have removed
the pre-cat o2 sensors and still have the P0300. I checked the fuel pressure and with the gauge installed I have 52 psi and the misfire is gone!! I remove the gauge and the misfire returns. Can someone please explain why?
Submitted: 1 year ago.
Category: Nissan
Expert:  Chris(aka-Moose) replied 1 year ago.

Welcome, I'm Chris (aka Moose) I'm an independent contractor here at Just Answer.

When it is misfiring is the scan tool showing all cylinders misfiring?

Where did you connect the pressure gauge?

Did the pressure ever fluctuate while monitoring it?

Thanks for asking your question and letting me try to help you.

You should see a rating screen if I have posted an answer, not for an info request.

Your rating is my feedback. If I don't get feedback from customers, I will not be able to continue helping customers here.

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Customer: replied 1 year ago.
now even with the fuel pressure gauge attached the vehicle misfires. It only misfires at idle and not under load or high rpm. I performed a power balance test with my scan tool and each cylinder is affected each time one is disabled plus I have 6 new injectors installed. I am leaning towards ignition coils but I don't see how all 6 are bad. I also checked my vacuum using our gauge and I have 20in of vacuum and the gauge is steady. Any ideas as what I am missing. I also checked compression I have 150-170 on all 6 cylinders.
Customer: replied 1 year ago.
Also if you bring up the idle to 1000 rpm's the SES light will stop blinking but if you allow the engine to idle the SES light will come back on and start blinking. I also installed 6 ignition coils from another vehicle so this is the second time changing the coils from a known good vehicle with no misfires and the engine still misfires! I am running out of ideas and hair!
Expert:  Chris(aka-Moose) replied 1 year ago.

It appears its not an engine issue but a signal concern from the computer to the coils and injectors. Do you have access to an oscilloscope to check the coil and injector signal? Will your scan tool monitor the cam and crank sensor signals to see if there is a hiccup in there reading? What is the idle speed?

Customer: replied 1 year ago.
The idle speed is 650rpms.Yes I do have an O scope. The vehicle already has both new cam sensors and a new crank sensor.
Customer: replied 1 year ago.
The battery negative cable is new and the positive battery cable is very clean. I have also already removed the throttle body to clean it and I also performed the throttle relearn procedure. I have also already smoked the engine with my evap smoke machine to locate any vacuum leaks and none found.
Expert:  Chris(aka-Moose) replied 1 year ago.

If you monitor and increase the idle to 800 does the miss go away. 650 is a tad low for hot idle speed.

Customer: replied 1 year ago.
I have not tried 800 but at about 950 the light stops blinking. Another point is that the small coolant hoses just underneath the throttle body have no hoses to them they have been bypassed. I looked to see how this is routed and it appears it just has an inlet and outlet. I don't see anything there that may be affected by coolant passing thru.
Expert:  Chris(aka-Moose) replied 1 year ago.

Coolant to the throttle body is to prevent condensation from freezing. If this concern is occurring above 32 degrees then that is not to blame. Let me know the results at 800 and the CKP and CMP monitoring and oscilloscope test to see which is dropping out. So far a throttle body concern or computer concern looks to be to blame causing low idle and this miss.

Customer: replied 1 year ago.
I installed a new throttle body and performed the idle relearn procedure. Idle at operating temp is 750-780 rpms. Set idle to 800 and misfire occurs (SES light starts blinking). I can raise the idle to just above 1000 rpms and the light stops and misfire stops. Can only 1 or 2 cylinders actually be misfiring and still set a p0300 and not an individual P0301-306. I also looked on Nissan's website to check the Ecm part number and there is an update but it does not say for what. I have looked for TSB's and did not find any.
Expert:  Chris(aka-Moose) replied 1 year ago.

Nothing is said on how random misfires need to be to set the random misfire 0300 code. How did you come out on the oscilloscope tests and speed sensor monitoring to find out why its misfiring?

Customer: replied 1 year ago.
I scoped the crank sensor and both cam sensors. Found nothing dropping out or erratic. I cant remember where I saw it but I think there is an update for the ecm and replacement of the front O2 sensors. I will look to see if I can find a description of the TSB.
Expert:  Chris(aka-Moose) replied 1 year ago.

I have looked over all the TSBs for this model and none are for the concerns you have mentioned.

Customer: replied 1 year ago.
I am at my wits end with this vehicle. I have no idea what can be causing this. I noticed that the vacuum lines at the vias vacuum switch were installed incorrectly. So I installed them and drove the vehicle home and no misfire so I thought well I guess this one is fixed even though I can't understand why I never got a P0171 OR P0174 lean codes. So we went to dinner and I wanted to make sure it was fixed and guess what P0300!!!!!!!! I just can't seem to understand what Nissan did when they engineered this POS. The only thing I can think of is when the vehicle warms up the fans are constantly running and never shut off but it is not overheating so in my mind maybe a small headgasket leak is present. Because now that is warmed up you guessed it no P0300 but the fans are running on high and the coolant temp on the scan tool reads 213 degrees. It is not overheating and has a new radiator and thermostat.
Expert:  Chris(aka-Moose) replied 1 year ago.

Is the temp staying at 213 or fluctuating up and down?

Did you ever monitor the coil and injector signals to see if any are dropping out, if not then we know its the engine to blame.

Customer: replied 1 year ago.
The bottom radiator hose is cold when engine is at 213. So I believe there is a coolant flow problem. Probably the water pump. No the temp does not fluctuate and yes I have monitored the injector pulse and coils and none of them drop out. I am going to check the coolant flow at the shop tomorrow. So far what are your thoughts?
Expert:  Chris(aka-Moose) replied 1 year ago.

Based on the most recent info, it is running warmer than it should normally. Although 213 is within limits, 200 is more expected. Does it misfire on cold start prior to getting to 213 degrees?

Customer: replied 1 year ago.
it does. But after it gets up to temp and the fans start running the misfire goes away. This is why is feel that there might be a small head gasket leak.
Expert:  Chris(aka-Moose) replied 1 year ago.

A compression and leak down test is needed now.

Expert:  Chris(aka-Moose) replied 1 year ago.

I like to stay in contact with my customers that appear not pleased, still working on the concern, or have not rated yet. I assume you were not pleased with my help. I hate that you have spent money to get an answer but left not happy. Can you tell me why, or can I help more. If its more help you need just reply and we can pick up where we left off.

Thanks Chris

Customer: replied 1 year ago.
The customer took the car Saturday. We conducted a compression test and leak down test with nothing abnormal. I don't need diagrams or info. We have Identifix, Motologic, Alldata and Iatn. I have been a technician for over 20 years and I am ASE Master certified. In all the years I have worked on Nissans I have yet to see one act like this Maxima. Most of the time diagnosing these vehicles has always been cut and dry with some exceptions. But nothing like this car. I have never seen a vehicle put up a P0300 multiple misfire if only 1 or 2 cylinders are misfiring. In this case compression is within specs no cylinders leaking (performed twice). Cleaned all the grounds and added a new negative battery cable. New injectors (performed a balance test/ passed). New spark plugs, maf sensor, swapped 6 used coils off a 2006 Maxima with no issues. Performed 3 smoke tests on the engine with no leaks present. Installed a used Ecm and still the same results. I am not a fan of throwing parts a vehicle but this car gave me no choice considering the problem and when it occurs. Scoped both cam sensors and the crank sensor with no drop outs or erratic signals (compared with known good signals).Also all 3 sensors are new. Used a vacuum gauge to check vacuum (20in) at idle with no fluctuations. Removed the front O2 sensors to see if there is a slight restriction that may be causing the misfire with no change ( still misfiring). Using a back pressure gauge we did not find the catalytic converters restricted. Oh yeah and we installed a new throttle body for the low idle which did not have an effect on the misfires at idle. So in the end I thank you very much for your time and efforts but the customer wanted their vehicle back and could not leave it any longer.
Expert:  Chris(aka-Moose) replied 1 year ago.

Thanks for the update. Keep in touch if needed.