# Piston misfire P0303



## Vdubs (Aug 6, 2013)

I've got a 1997 Nissan Sentra GLE and I'm having some issue with piston misfire (code: P0303).

I feel like I've tried everything and I'm not sure what else to do.
I've...

Confirmed EGR value is functioning
Replaced spark plugs
Inspected spark plug wires for damages. They look good.
Swapped ignition coils on two pistons. The misfire did not transfer to the other piston
Added fuel injector cleaner (SeaFoam)
Replaced fuel filter

None of this seemed to have any beneficial effect.
The car is idling heavily and when I turn on the A/C it really shakes. When accelerating really hard the Check Engine Light blinks.

Any help would be appreciated.
Thanks!


----------



## Vdubs (Aug 6, 2013)

*Extra tube??*

While looking around in my car I noticed this tube that only was connected at one end.
Photo Album - Imgur
I can't seem to find where it goes. Any idea if it's needed/where it goes?


----------



## smj999smj (Jan 1, 2006)

The hose is a vent hose for the automatic transmission; it's not supposed to be connected to anything. 
Just because an ignition wire "looks" good doesn't necessarily mean it "is" good. If the wires have more than 100,000 miles on them, I would replace them, regardless, with a set of NGK or genuine Nissan spark plug wires. Did you check the distributor cap...especially the towers for corrosion? Like the wires, if it has over 100,000 miles, I would replace it and the distributor rotor with genuine Nissan parts. Is there any oil inside the distributor cap? If so, this is a sign that the internal shaft seal is leaking, which can contaminate the cam sensor and plate and cause misfiring; if the seal is leaking, replace the distributor. It's also possible to have a bad fuel injector or a burnt valve, but if the MIL is flashing when it misfires, most of the time it's an ignition issue.


----------



## Vdubs (Aug 6, 2013)

I'm still having problems with this piston misfire.

Since, I've...


Tested fuel injectors with multimeter. Piston 3 had a very high resistance and appeared opened. The others were around 11ohms.
I replaced the fuel injector on piston 3 thinking that would solve the problem, but it didn't
Replaced distributor cap and rotor with brand new ones (There was no oil on the inside of the old one)

The symptoms I'm getting are bazaar. The car runs fine while idling with the A/C off, but the second the AC turns on the RPMs drop from 750 to 500 and the car begins to slowly die. It also shakes pretty heavily with the AC on, but its more of a consistent rhythmic shake, rather than a wild jerky shaking. Only once it's about to die does it kind of jerk like it's struggling to stay alive.

I know the motor mounts are bad, but I that shouldn't cause a misfire in specifically 1 piston. So most of the shake might be from that

At high RPMs (5000-6000) usually before a gear shift, the check engine light will flash, indicating a misfire. But it only ever flashes at these higher RPMs. While sitting at a stop light it will never flash.

Without the A/C and driving at a normal pace the check engine light won't usually come on. But I can almost consistently make it come on by turning on the A/C and putting the pedal to the medal. But when the light flashes the car never jerks or shakes. It feel pretty normal, just the light flashing.

On a side note, after I just replaced the fuel injector, and drove it around the block a little and I noticed the smell of gasoline, from inside my car! I haven't had time to drive it very much to confirm this again, but I just thought it was odd. I opened up the hood and I could not find any leaks around the fuel injector. I also didn't smell any gas under the hood.

I'm completely lost. Not sure what else to do...


----------



## BeyondBiscuits2 (Jan 18, 2006)

Two questions I have for you:

1. You said you swapped ignition coils between cylinders and the problem didn't transfer with it. How did you achieve this when you have a single coil for the entire engine, and it is located inside the distributor? Just curious...

2. If your symptoms persist when your A/C is engaged, ever thought of checking out your A/C? It could be as simple of a problem as a bad bearing or malfunctioning clutch in your compressor, or the compressor itself going bad. That is where I would check...


----------



## Vdubs (Aug 6, 2013)

From my understanding these are the ignition coils. Maybe there are different ones I should be checking out. I thought the ignition coils connect to the spark plugs from the distributor. On this car it seems that the cables and the coils are connected together.

http://i.imgur.com/wiWT9Pv.jpg

I swapped two of them and didn't notice any changes, I got the flashing checking engine light, and checked out the codes again. Still P0303.

I haven't checked out the A/C, but if there is something wrong with the A/C, that shouldn't give piston misfire right?
I'll check it out anyways and see if I notice anything.

I'm worried my car is running on borrowed time.

Thanks for the help.


----------



## BeyondBiscuits2 (Jan 18, 2006)

Do you mean the spark plug leads, or spark plug wires? If that is the case, that makes a great deal more sense.

We all know 4 cylinders at idle struggle to run the A/C. It is many times more likely for a misfire to occur or emerge at idle while putting a load on the engine, i.e. running the A/C. For example, you may have a fuel injector that is just spraying enough fuel for normal operating conditions, but when under load, cannot deliver enough fuel to the cylinder. Or, a spark plug that has just enough spark to ignite the mixture at normal conditions, but is too weak when strained.

Also, I have heard of misfires caused by vaccuum leaks under load. Perhaps the intake manifold around cylinder 1 is leaking slightly when under load, and not when at normal conditions? A quick fire way to test this is with a can of starting fluid (ether) or a water bottle. When the engine is idling, spray along the seem between the manifold and cylinder head. If your engine suddenly idles up (with ether) or bogs down (with water), that is your culprit.

P.S. on Nissans, I am pretty certain they only throw a cylinder misfire code, not specifically a piston misfire code. This is often improperly diagnosed as a bad spark plug or lead, and very little attention is paid to other potential causes of the misfire. Someone aforementioned a burnt valve, which is also an entirely possible culprit. How many miles (or k/ms) are on your engine?


----------



## Vdubs (Aug 6, 2013)

It's got about 155k miles on it.

It does have piston specific misfire codes. I'm getting P0303 (piston 3).


----------



## smj999smj (Jan 1, 2006)

Vdubs said:


> From my understanding these are the ignition coils. Maybe there are different ones I should be checking out. I thought the ignition coils connect to the spark plugs from the distributor. On this car it seems that the cables and the coils are connected together.
> 
> http://i.imgur.com/wiWT9Pv.jpg
> 
> Those are not coils you are switching; those are spark plug wires. You only have one coil on your engine and that's built into the distributor. You may want to start by rechecking your spark plug wires and firing order, because swapping the ignition wires will give you the incorrect firing order.


----------



## Vdubs (Aug 6, 2013)

Okay, yeah.

Sorry for the confusion.

I swapped the spark plugs wires on two of the spark plugs and the distributor connection points. So the firing order stayed the same and only the wire was changed. This didn't seem to change the problem at all.

This may be a dumb question, but if the coil is bad, could that cause single piston misfire? It seems like that would affect all of the pistons, but I'm not certain.


----------



## worthirt (May 21, 2013)

this may be a dumb question, but have you checked and/or replaced your cap and rotor? It is a part of preventive maintenance and both are pretty cheap, personally I would go with replace just to be safe.

Edit: I'm not awake yet, I missed the post about where you replaced them. I need more coffee...


----------



## rogoman (Dec 16, 2004)

Vdubs said:


> I swapped the spark plugs wires on two of the spark plugs and the distributor connection points. So the firing order stayed the same and only the wire was changed. This didn't seem to change the problem at all.
> 
> This may be a dumb question, but if the coil is bad, could that cause single piston misfire? It seems like that would affect all of the pistons, but I'm not certain.


Generally if the coil is marginal, it would affect other cylinders also. Apparently cylinder #3 appears to be weak. This could be caused by any of the following:
- Incorrect spark plug type. Use only the OEM NGK type.
- Marginal spark plug wires.
- Low fuel pressure. Tee in a fuel pressure gauge on the output side of the fuel filter to test.
- Excessive vacuum leak in the intake system. Use a vacuum gauge to test.
- Compression may be very low. Run a compression test on all cylinders.


----------



## smj999smj (Jan 1, 2006)

Low fuel pressure would also affect all cylinders, not just #3, but never hurts to check. I would definitely do a compression test.


----------



## BeyondBiscuits2 (Jan 18, 2006)

A compression check can never hurt, nor can a leak-down test.


----------



## Vdubs (Aug 6, 2013)

I took it in to a mechanic today to get it checked out. It passed compression and smoke test. But, it turns out the cylinders have oil completely caking all of the inside. Cylinder 3 just had the worst of it and the others don't seem to far behind.

I'm sad to say I think this means my baby is done for. I could either replace the cylinder or motor. Both of which would cost way more than it's worth to keep a '97 Sentra alive.

I think I'll spend the last of my cars life looking for a replacement.

Thanks for all your help!


----------



## EvilPotato (Sep 6, 2005)

mopar combustion chamber cleaner  
$11 at your local dodge dealer. we recently revived a neglected '89 corolla with that stuff. same problem, multiple cylinder misfire caused by baked oil, it was sucking oil really bad from the PCV hose, maybe a failed valve or the seal under the valve/cam cover had failed. you should probably check those things out if you have that much oil in the cylinders and you have good compression. the PCV baffle seal on the ga16de fails over time, it hardens then disintegrates, only a portion of mine was present when i took the valve cover off to replace a tensioner. its easy to replace, its on the valve cover itself.


----------



## smj999smj (Jan 1, 2006)

I agree^^ Before you condone the engine, pull the valve cover and check the PCV baffle seal. Refer to part code "13270N" on the part diagram linked below. This seal has a tendency to get hard and/or get sucked in, causing oil to be pulled directly from the cylinder head, pass the PCV valve into the engine causing oil burning and could very well cause the caked-up oil inside the combustion chamber, especially since it passed a compression test. 
Part Detail


----------



## Vdubs (Aug 6, 2013)

So today I went to my local autoshop and bought some Seafoam to see if I could clean my engine up. (I looked for Mopar, but they didn't have it)

I put it in through the brake booster line, using the instructions provided by a guy over at ******** (http://www.********.com/archives/how-to-use-seafoam-to-clean-your-engine-the-right-way.html) (*edit: n i c o c l u b, cannot be referenced for some reason??)

I just finished the whole process and I can say that my car is running significantly better. It doesn't shake or die out with the A/C on at stop lights. And it feels like the car is much more responsive. This stuff works!

However, it only seemed to have fixed some of unrelated issues. My check engine light still flashes at the higher RPMs right before shifting. Maybe it's worth another dose of Seafoam, but I'm not confident.

Thanks for the help, even though my problem isn't fixed, I don't feel like my car is going to die any second anymore!!

The mechanic said the cause of the check engine light was from the dried on oil in my cylinders, but that doesn't seem to be the case. He said he did a compression and smoke test and that the car passed, but I wasn't there to see him do it.

I don't know what else it could be....

I'll check the spark plugs and spark plugs wires again to make sure nothing got fouled, since I replaced the spark plugs before using Seafoam.


----------



## EvilPotato (Sep 6, 2005)

the mopar i think would only be available at a dodge dealership, and it works MUCH better than seafoam cause it actually has solvents in it. i've used both. the mopar stuff makes a less impressive smoke show tho.

have you checked timing? changed the plug in #3? and do you really need to shift at 6k?


----------



## Vdubs (Aug 6, 2013)

Okay, now I thought I should check out my timing, and in doing research I found a lot of B14 sentras have issues with the Timing Chain Tensioner. So I went ahead and replaced that, not confident it would fix the issue, but it needed to be done regardless. My old tensioner looked like this, but not quite as bad (http://i559.photobucket.com/albums/ss37/MoenOner/IMG_1853.jpg) . Now my car is making a bad rattling noise and the misfire seems unchanged. 

To try to fix the rattle, I reinstalled the tensioner again. Everything appears to be good and correctly installed, but it still rattles... Not sure what to do. Maybe it's better to keep the old tensioner if it doesn't rattle, even if it is worn down.

While opening everything up I checked the spark plugs again and noticed the third one was fouled (http://i.imgur.com/ECMZpBv.jpg). These are the same spark plugs I replaced just a week ago. They are practically brand new.

To recap.... So far I've:

Changed spark plugs
Tested spark plug cables. Confirmed they are good
Replaced distributor cap and rotor
Replaced fuel injector on cylinder 3
Put Seafoam thru gas tank and intake manifold thru brake booster line.
Confirmed EGR valve is functioning correctly
Mechanic performed compression test and smoke test. Passed both.
Replaced timing chain tensioner


I'm really drawing at straws here. I can adjust the timing, but the more that I think about that, wouldn't I expect to see misfire in all cylinders if the timing was off? I have misfire only in cylinder 3...
The misfire now occurs randomly when I'm accelerating, not just at higher RPMs any more. And never at idle. I think it's important to note that when the Check Engine Light flashes, indicating a misfire, my car does not slow, jump, or jerk in any way. The misfire wouldn't be noticeable when it happens, without the check engine light. The car does has a rough idle and seems like it struggles to stay alive while idling.

Maybe I'm praying to the wrong car gods....


----------



## rogoman (Dec 16, 2004)

If plug #3 is oil fouled, then that cylinder is burning excess oil caused by either bad rings or worn valve stem seals. If the plug is only carbon fouled, then there is an ignition misfire or the fuel injector may be leaking. Always buy new fuel injectors; reman'd injectors many times are DOA.


----------



## Vdubs (Aug 6, 2013)

Good news everyone! :thumbup:

I adjusted the timing and now the check engine light doesn't flash any more while driving.
The car is now less shakey while stopped and the RPMs aren't as wild.
I've only eyeballed the timing for now. I might buy a timing light later to make sure it's spot on. :fluffpol:

I'm resetting the check engine light right now and will drive again later to see if it comes back on.

So far so good!

Thanks for all your help!!!!!


----------



## Vdubs (Aug 6, 2013)

Driven car around more and confirmed the issue was related to the timing.

The check engine light has not come back on.

Thanks again for all your help.


----------

