1998 Pathfinder P0300 code and injectors

[roncowpe]

This forum has been a great help to me in the past. I hope that this will help someone else out.

The back ground is that I've recently caught up on maintenance on a family owned '98. Started with a new distributor to fix a failed camshaft sensor. Followed up by timing belt change, drive belts, and plugs and ignition wires, and the upper plenum off to replace a collapsed lifter. The new distributor then failed, this time no spark, so now on the third distributor. it ran very well for a few days and then had a flashing Service engine soon light and the P0300 code. Multiple misfires!

I checked the usual suspects. No air leaks or split hoses around the plenum. Fuel pressure good when running. Checked fuel delivery volume and to make sure there was no contamination. As it was the multiple misfire code, I was convinced that it was another distributor problem, even though the sparks looked good, and the the cam sensor had good 120 and 1 degree signals. i bought and fitted a third distributor, this time from Cardone, in the hope that it would be more reliable. No change, still engine shaking at idle, and throwing the P0300 code. Once in a while a flashing SES light

I was now only running the engine while parked, and not driving it. There was an obvious misfire as soon as it was started. Cold starts were good, but sometimes it was slow to fire when it was warm, and the rpm was slow to pick up. Sometime the engine seemed to clear and run smoothly above about 2500 rpm. Once in a while it would pop in the exhaust, as the rpm wound down after revving it. Then it gave a P0306 code. I pulled the No 6 plug and it was dry and sooty black. I cleaned it off and swapped it into the No 1 cylinder. It was a new NGK, and I didn't really think it was faulty, but didn't want to have to change it out of No 6 again if it was.

Slow to start after the plug change, and missing almost at once. More throttle blips and some longer revving periods and back to the P0300 code. Clear that and try again. This time a P0302 code. Pull that plug and it looks perfect, just like new.

Now I'm really confused. P0300 is misfire on two or more cylinders. The 02 and 06 codes are for specific cylinders. I'm still thinking it must be some general fuel, ignition or air leak. But still can't find anything.

I started thinking about injectors, found a nice Youtube (https://www.youtube.com/watch?v=IYsfBWC4ilo) on how to check the injector ohms by accessing the two plugs on the passenger side valve covers. They all Ohmed out at 14.5 or so, and all clicked when I powered them with a 9v battery.

I'm struggling to think how a faulty injector on one cylinder can give a multiple misfire, but thinking about the sooty No 6 plug and the super clean No2, maybe No 6 has a leaking injector and the ECU was leaning off that bank and giving lean misfires and the multiple code.

I really didn't want it to be an injector, but I bit the bullet and lifted the plenum again. Second time around was easier. I just cut the vertical coolant hose at the back, and replaced it with a length of 1/2" coolant hose, 4 and 3/4 inches long. The 90 degrees hose was still pliable and flexible, so reused that. With a bit of lube they both went back on easily.

Back to the injector story. I bought three remans from the local Napa, for speed, price, and convenience, as I wanted to do the whole bank as I was in there. One was DOA, another had a sort of ringing tone when powered, and Ohmed at the bottom of the range, but the third one Ohmed mid range and had a nice click, so I fitted it in No 6.

It took twisting and a lot of pressure to get the new injector to seat, and I had to use the injector retainer, and the securing screws, to get it fully home. I jumped the fuel pump relay to pressurize the system, and there were no external fuel leaks at least.

Buttoned it back up, and it fired up pretty well first revolution, and ran smoothly, just like it used to.

So, a single leaky injector can give multiple misfires, as well as the cylinder specific code for the leaky one, and a cylinder specific code on the same bank.

If I'd gone more old school, and thought more about the state of the spark plugs, then maybe I would have got there sooner, and not wasted time and money on the distributor. With hindsight the clues were all there, I just let the codes confuse me. Oh, and check your injectors before you fit them.

Hope this helps someone.

[mdmellott]

... Oh, and check your injectors before you fit them.

I just bought a set of 6 Hitachi injectors that I plan on installing this weekend. #4 gave up the ghost last week after 230k miles. How would you check the injectors before fitting them onto the engine? Simply apply voltage and listen for a click sound or something more?

[roncowpe]

Hi, Yes. I used a 9 volt battery, and a pair of clip on leads. Pretty safe way to do it. You could use 12v from the car, but use a fuse in one leg if you do that. if they click they are good. A multi meter set to the Ohms scale will also show if the coil is the right resistance. From memory the range is 10 to 15 Ohms. Probably worth doing both, but do the click test for sure.

[mdmellott]

Thank you! I like the 9V battery method idea. I just checked the resistance spec in the FSM. For my '02, it says they should be 13.5 to 17.5 ohms at 68F. However, my Haynes repair manual says it should be 10 to 14 ohms and no temperature specified. I'll have to dig into that a bit deeper before I know for sure what's right. I appreciate the heads up on these prechecks.

[roncowpe]

Hi, yes the 9v battery is simple. Your FSM will be correct. The '98 FSM has 10 to 14 Ohms, and Haynes probably just carried that over. My Haynes has a number of errors. As you have a set, then measure them all. My six all measured within half an Ohm. I don't think that the actual measurement is that important as long as they all click and are all similar.

[MisterH]

"I'm struggling to think how a faulty injector on one cylinder can give a multiple misfire..."


If you examine the intake design of the VG33 engine it then becomes apparent why one bad injector can trigger P0300 codes. You can isolate banks one and two in terms of ST/LT fuels trims but not individual cylinders. When I replaced all the injectors on my '99 I went the reman route, as I was unable to find new OEM Hitachi injectors anywhere. Two of the six turned out to be faulty, but luckily they were on cylinders one and three.

[roncowpe]

Thanks for the comment. Can you expand a bit on it please.
Here are the fuel trims:
SAE 0x06 Short term fuel % trim - Bank 1 -11.72 %
SAE 0x07 Long term fuel % trim - Bank 1 -10.16 %
SAE 0x08 Short term fuel % trim - Bank 2 -25 %
SAE 0x09 Long term fuel % trim - Bank 2 -10.16 %

This is the freeze frame at first occurrence:
Short term fuel % trim - Bank 1 -4.69 %
Long term fuel % trim - Bank 1 -3.12 %
Short term fuel % trim - Bank 2 -7.81 %
Long term fuel % trim - Bank 2 -10.16 %
In my case would that have been enough to give lean misfires on 2 and 4? I have the feeling that the no 6 injector took a little while before it fouled the plug enough to give the p0306 code. Any idea how it got to the P0302 code either?

[mdmellott]

Thanks for the comment. Can you expand a bit on it please.
Here are the fuel trims:
SAE 0x06 Short term fuel % trim - Bank 1 -11.72 %
SAE 0x07 Long term fuel % trim - Bank 1 -10.16 %
SAE 0x08 Short term fuel % trim - Bank 2 -25 %
SAE 0x09 Long term fuel % trim - Bank 2 -10.16 %

This is the freeze frame at first occurrence:
Short term fuel % trim - Bank 1 -4.69 %
Long term fuel % trim - Bank 1 -3.12 %
Short term fuel % trim - Bank 2 -7.81 %
Long term fuel % trim - Bank 2 -10.16 %
In my case would that have been enough to give lean misfires on 2 and 4? I have the feeling that the no 6 injector took a little while before it fouled the plug enough to give the p0306 code. Any idea how it got to the P0302 code either?

Yikes! These are really bad numbers indicating a serious rich condition, not lean. These negative numbers indicate your O2 sensors, S1 on banks 1 and 2, see too much fuel so the ECM is backing way off on fuel delivery, hench the negative numbers. All it would take is one injector on each bank to be leaking badly enough to throw out these kinds of numbers in your fuel trims, with misfires I would expect to see on any one or all six cylinders at random.

The freeze frame data is not terrible on bank 1 but it is bad on bank 2. The first set of data, which I assume is live data, is horrible, indicating a very serious rich condition on both banks.

[mdmellott]

Either that (leaking injectors) or the timing is way too far advanced, not allowing for a complete burn before the exhaust stroke expels the unburnt fuel. This too would be a rich condition witnessed by the O2 sensors which would cause the ECM to back off on fuel delivery.

You already mentioned checking the obvious suspects so I'm assuming you're getting a spark. It just might not be happening close enough to the right time.

[roncowpe]

Thanks for the comments. The fuel trims are all just a bit negative now, and it is running well with no codes.

[mdmellott]

Thanks for the comments. The fuel trims are all just a bit negative now, and it is running well with no codes.

That's good to hear.

Once again, thank you for the precheck function test tip using the 9V battery. That just saved me a whole bunch of pain by not installing three DOA injectors. I purchased six brand new Hitachi injectors from Rockauto. Three of them had the same lot number printed on them and neither one of them worked. I applied the 9V, but nothing happens. The other three work just fine.

[roncowpe]

Pleased that it helped. That was a pretty high failure rate. Hope it all works well once you finally get it done.

[mdmellott]

Hope it all works well once you finally get it done.

It all went well enough. Rockauto sent me 3 replacements. All with different lot numbers printed on them, and all initially failed to work with the 9V battery test. However, when I double-checked them using the car battery, which I did not do with the three I rejected, they all worked. Checking them again with the 9V battery, they all finally worked with the lower voltage test. I'll just write this off to the difference between OE, Genuine Nissan branded tighter tolerance specifications for their injectors, versus OEM aftermarket injectors. They were both made by Hitachi Unisia Jecs but not necessarily to the same exacting tolerance specifications, a difference in pricing between $150 and $50 each. I guess these injectors needed a good swift kick to wake them up and the ones I returned were likely just as good.

[roncowpe]

That is interesting. Maybe they do get sticky with standing. My DOA one was open circuit.