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Discussion Starter · #1 ·
So my truck is not working well at all. Very reduced power so it just limps along. I'm getting this error code and dealership said to replace spark plugs. Did that and same problem persisted. Then they said replace coil packs. They wanted to charge too much so I got some aftermarket ones and did it myself. It still has the same problem and same error code. I took it back to dealership and they say they think the coil packs I bought are not good and that I need to use their guaranteed Nissan ones.

I don't see how that's possible though. If the ones I bought weren't good, then how is the truck running exactly as it was before I swapped them out? Wouldn't it now be not running at all if they were faulty? They are convinced it's the coil packs though so I suppose I will have to buy theirs, get them installed and see what happens because they just seem to refuse to look at other possibilities until we have ruled this out. Any advice would be helpful.
 

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PO300 is a random misfire. However you are saying that the truck is not running well. How is the idle. Smooth? Rough? I would think that it is running rough, and the random misfires are isolated to a problem cylinder. perform a balance test to figure out which cylinder is giving you grief. With the truck running pull (disconnect) one coil pack at a time. If the cylinder is a good you will have a drop in RPM and a stumble. If the cylinder was bad, then no change will occur.

no spark is not the only reason for a misfire. Read here on a 350z forum that a bad injector that was not closing caused an over rich condition that prevented a cylinder from firing.
I fixed my PO300 code! - MY350Z.COM Forums
That dealer guy would have had you change parts till half the truck was replaced.
 

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I have the same problem, rough idle, a loss of performance and lower fuel economy.
Through my research this can also be due to the vvt solinoid. These control the "phasing" of the intake valves. If they are not working properly they can cause too much valve overlap.
When these aren't working properly you can get codes for the misfire, timing advanced bank 1, catalitic converter code.
The solinoids are controlled by oil pressure. If your oil is dirty or of the wrong weight that can cause these problems.

I started by changing my plugs. The old ones looked worn but normal. Next I ran a cleaner in the oil and did an oil and filter change.
Now I'm using some injector cleaner.
If this doesn't work I'll check the solinoids. My local shop owner checked out my codes. He shut off each coil 1 at a time to no avail. He then went online and printed out the electrical specs for the solinoid. That will be my next step. All for free!
I'll keep you posted as to my findings.
Good luck
 

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Discussion Starter · #5 · (Edited)
I asked them to check the cats, air leaks and fuel injectors. They are stubborn though and just want me to get their Nissan certified coils and pay another $1000. I said that if they used theirs and the problem persisted that I wouldn't pay for any of it.

PO300 is a random misfire. However you are saying that the truck is not running well. How is the idle. Smooth? Rough? I would think that it is running rough, and the random misfires are isolated to a problem cylinder. perform a balance test to figure out which cylinder is giving you grief. With the truck running pull (disconnect) one coil pack at a time. If the cylinder is a good you will have a drop in RPM and a stumble. If the cylinder was bad, then no change will occur.

no spark is not the only reason for a misfire. Read here on a 350z forum that a bad injector that was not closing caused an over rich condition that prevented a cylinder from firing.
I fixed my PO300 code! - MY350Z.COM Forums
That dealer guy would have had you change parts till half the truck was replaced.
It idles just fine. Very smooth. Unlike other engines I can't do the diagnostics you are talking about. The intake covers up half of the engine so it has to be removed in order to check that side and then put back on every time. It's quite time consuming which is why they want to charge so much for labor.
 

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I have the same problem, rough idle, a loss of performance and lower fuel economy.
Through my research this can also be due to the vvt solinoid. These control the "phasing" of the intake valves. If they are not working properly they can cause too much valve overlap.
When these aren't working properly you can get codes for the misfire, timing advanced bank 1, catalitic converter code.
The solinoids are controlled by oil pressure. If your oil is dirty or of the wrong weight that can cause these problems.

I started by changing my plugs. The old ones looked worn but normal. Next I ran a cleaner in the oil and did an oil and filter change.
Now I'm using some injector cleaner.
If this doesn't work I'll check the solinoids. My local shop owner checked out my codes. He shut off each coil 1 at a time to no avail. He then went online and printed out the electrical specs for the solinoid. That will be my next step. All for free!
I'll keep you posted as to my findings.
Good luck
What ended up being the fix for you? I just had a cat replaced and getting O2 codes for a week or so now P0300.
 

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Amazing that in his case the dealer is guessing when they should be certain of what is wrong. I agree if their guess is wrong the customer shouldn't have to pay for any of it.

Clint
 

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What ended up being the fix for you? I just had a cat replaced and getting O2 codes for a week or so now P0300.
Phaser on bank 1 was not working properly because the oil press was very low going to the vvt solenoid, about 3 lbs at idle. Comp was also low in 2 cylinders so I opted to just put in a low mileage engine.
Problem fixed.
 

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Phaser on bank 1 was not working properly because the oil press was very low going to the vvt solenoid, about 3 lbs at idle. Comp was also low in 2 cylinders so I opted to just put in a low mileage engine.
Problem fixed.
Hmm well I have it going to shop tomorrow not sure I can justify replacing the engine at this point in time, so hoping its something simpler.
 

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Phaser on bank 1 was not working properly because the oil press was very low going to the vvt solenoid, about 3 lbs at idle. Comp was also low in 2 cylinders so I opted to just put in a low mileage engine.
Problem fixed.
Often the loss of oil pressure on the VQ40DE engines is due to a gasket failure on the back side of the rear timing cover. There are two plates bolted on the back of it. You can't reseal them, so the fix is to replace the rear timing cover, which is not an easy job. The front timing cover and the timing chains, gears and guides have to be removed. If I'm not mistaken, the oil pan may have to be removed, as well.
 

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Often the loss of oil pressure on the VQ40DE engines is due to a gasket failure on the back side of the rear timing cover. There are two plates bolted on the back of it. You can't reseal them, so the fix is to replace the rear timing cover, which is not an easy job. The front timing cover and the timing chains, gears and guides have to be removed. If I'm not mistaken, the oil pan may have to be removed, as well.
Exactly! Didn't make sense with 220k on the engene. That's why I changed out the engine.
Runs great now.
Thanks
 

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Often the loss of oil pressure on the VQ40DE engines is due to a gasket failure on the back side of the rear timing cover. There are two plates bolted on the back of it. You can't reseal them, so the fix is to replace the rear timing cover, which is not an easy job. The front timing cover and the timing chains, gears and guides have to be removed. If I'm not mistaken, the oil pan may have to be removed, as well.
How would I know the gasket is failing? Would I see a leak in a specific area, or would there be gasket material in the oil?
 

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Last week, the SES light began flashing and the engine started running rough on my '05 with 202K miles. My code reader displayed a P0300 code: "random multiple misfire". My indie shop traced it to a bad #2 coil that wasn't firing the #2 spark plug. Despite the un-burned fuel passing through, the cat survived, and only the coil and plug (fouled-up) needed replacing. The truck runs normally now.
 

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Last week, the SES light began flashing and the engine started running rough on my '05 with 202K miles. My code reader displayed a P0300 code: "random multiple misfire". My indie shop traced it to a bad #2 coil that wasn't firing the #2 spark plug. Despite the un-burned fuel passing through, the cat survived, and only the coil and plug (fouled-up) needed replacing. The truck runs normally now.
Cool, mine was a loose seal around the header gasket. I had replaced the catalytic converter on the drivers side and the aftermarket cat I think had the angles off ever so slightly. It was not a huge leak at first but eventually it blasted out more of the gasket and when that happened I got it fixed and the misfire went away also.

Sent from my SM-G920W8 using Tapatalk
 

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Cool, mine was a loose seal around the header gasket. I had replaced the catalytic converter on the drivers side and the aftermarket cat I think had the angles off ever so slightly. It was not a huge leak at first but eventually it blasted out more of the gasket and when that happened I got it fixed and the misfire went away also.

Sent from my SM-G920W8 using Tapatalk
Good to know!
 
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