# My HB has error code P0303



## zazman (Dec 29, 2011)

I think this code is for cylinder 3 backfiring. I've had it before even though I've now got the timing right. I even checked my wires and the spark plug itself and both are just fine. This happens when I'm on the freeway after say, 60 miles of cruising at 60+ mph.
Can't exactly figure out what could be causing that and am hoping someone out there could help out.
My other problem is with the panel lighting. I checked all the bulbs on the instrument panel and changed one that was dead but that did not solve the problem. I thought maybe a fuse was blown but there's no fuse for this circuit. Anyone come across this and how did you solve it?


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## TheRepairMan (Jun 30, 2009)

It would help if we had some basic info on the truck, like year, engine, mileage and repair history. Zane will be here shortly to jump all over your azz.

-R


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## smj999smj (Jan 1, 2006)

P0303 is a cylinder misfire code for #3 cylinder. Essentially, anything that could cause a #3 misfire can cause this code, including a bad spark plug, ignition cable, distributor cap, fuel injector, engine valve issue, intake leak at #3 intake runner...to name a few. As mentioned, it would help to know which engine we are working with?

As far as the instrument panel lighting, have you checked the illumination switch (aka dimmer switch)?


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## zazman (Dec 29, 2011)

It's a 97 HB 2.4L 2wd. I just changed the timing chain and followed the write-up I got from this forum. Everything else seems fine other than this P0303 error. I set my timing at 10 deg BTC per specs.
I cleaned the distributor cap, checked my spark plug gap and checked that the spark plug cables. I could not replicate this error when the truck is not moving and like I said, it happens after about 60+ miles when I'm cruising at 65+ mph.
Regarding the panel lighting, I checked the dimmer switch but did not check whether the resistance changes when you vary it or not. If that will help, I'll try it again and see if I can observe any change in resistance.
I hope this info will help in the diagnosis.


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## TheRepairMan (Jun 30, 2009)

Okay, you said everything is fine except the code, but then you said "it" happens at speed. So, the check engine light is on all the time?

Describe "it" for us. And, there's a difference between backfiring and misfiring. Is it popping back up through the intake manifold like a cough, or a hard, jerking, dead misfire that shakes the truck when under a load? 

-R


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## zazman (Dec 29, 2011)

TheRepairMan said:


> Okay, you said everything is fine except the code, but then you said "it" happens at speed. So, the check engine light is on all the time?
> 
> Describe "it" for us. And, there's a difference between backfiring and misfiring. Is it popping back up through the intake manifold like a cough, or a hard, jerking, dead misfire that shakes the truck when under a load?
> 
> -R


I was implying that this is the only problem I have right now after changing the timing chain. I should have said cylinder #3 misfire not backfire. The CEL flickers then stays on when the truck is travelling at over 60mph and I can feel the truck shaking or running a little rough for a while until I slow down to about 50mph. At this speed it runs smooth again.
This happens when it is under load because when I tried to reproduce the misfiring when stationery it does not happen.


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## smj999smj (Jan 1, 2006)

Were there any signs of water entry or water corrosion when you had the distributor cap off? Nissan had a TSB for this issue. If signs of water entry are found, Nissan instructs to replace the distributor assy. with countermeasure part #22100-1S704RE, which has improved draining and a cap with an improved vent. If not...You mentioned cleaning the cap, but is the cap any good? If you have more than 60k. miles on it, I would replace it, regardless as preventative maintenance as well as the ignition cable. Always stick with genuine Nissan or NGK parts when replacing ignition components on Nissans. While idling, spray some carb cleaner around the #3 cylinder intake runner and see if the RPMs increase while you're doing it; if they do, you likely have a bad intake gasket. Check the fuel injector harness connector and the harness to it by the head; I had a #3 injector harness rub through its insulation and short again the edge of the cylinder head on my 97 HB a few years ago. After that, I would do a cylinder leakdown test on #3 cylinder to make sure there was no leakage past the valves. If that was okay, I would replace the #3 fuel injector.


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## zazman (Dec 29, 2011)

I checked the harness and the insulation is fine and the carb cleaner did not increase the idling. I did not observe any signs of the presence of water in the distributor. The reason I cleaned it was because there was some dirt build-up on the rotor contact points, otherwise it looked ok.
I have no clue what a cylinder leakdown test is so I won't even attempt it. I'm just an ordinary Joe. The last option would be to replace the #3 injector then if there's no other likely cause?


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## TheRepairMan (Jun 30, 2009)

zazman said:


> I checked the harness and the insulation is fine and the carb cleaner did not increase the idling. I did not observe any signs of the presence of water in the distributor. The reason I cleaned it was because there was some dirt build-up on the rotor contact points, otherwise it looked ok.
> I have no clue what a cylinder leakdown test is so I won't even attempt it. I'm just an ordinary Joe. The last option would be to replace the #3 injector then if there's no other likely cause?


Don't rule out trying another spark plug or wire just yet. I got an engine finished today with brand new Bosch Platinum plugs in it and it would NOT run on two cylinders. I changed those two new plugs out with a different brand just as a test and she purred like a kitten. Sometimes the simplest things don't make sense. You could even swap a plug and wire from a known good firing cylinder to see if the miss moves with the #3 set. ALWAYS do redundant tests to rule out ignition problems first!

-R


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## smj999smj (Jan 1, 2006)

Nissans don't like Bosch Platinums!


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## TheRepairMan (Jun 30, 2009)

smj999smj said:


> Nissans don't like Bosch Platinums!


It was a 528i BMW, but it didn't like BP's either, and neither do I. I don't know how many cars I've seen come in on a rollback that had those same plugs in them and all they needed were something else that would light to get them running again.

-R


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## smj999smj (Jan 1, 2006)

The guys at the auto parts stores love to sell 'em (Bosch plats)! I use NGK's in everything I own from my cars to my lawn mowers and weed trimmer and have never had a problem!


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## zazman (Dec 29, 2011)

I'm back again with the same #3 cylinder misfire. I took out injector #3 to check its condition and swapped it with #2 then installed new plug wires, distributor cap and rotor and that did not make a damn difference. When I pull the #3 wire off while the motor is running, it reacts the same way as the other wires when pulled off and I can see and hear the spark when I bring the wire closer to the plug. Only now the sound of only three cylinders firing is audible and when you give it gas it's even louder and shakes more visibly.
I'm desperate to find a fix for this problem without taking the truck to a shop. Currently unemployed and will have to fix this with any help I can get from here. I need all the help I can get.


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## TheRepairMan (Jun 30, 2009)

I don't know all that's been done, but I'll add...

Pull plug number 3 again and make note of what it looks and smells like (I'll cover that later). Then run a compression test if you haven't already. If #3 is way below the others, you will need to run a cylinder leak down test (unless doing a major engine repair is out of the question anyway) then it wouldn't matter about the results of either test. Post up the results.

Another real simple test of the electrical side of the fuel injectors, and this is important... listen to each injector with either a mechanics stethoscope (they cost like $4.00 at Harbor freight or some autoparts stores), or you can improvise with a section of rubber hose or just a long screwdriver put up to your ear and the other end on the body of the injector. With the engine at idle each injector should make a clear audible click.

If all the injectors don't have the same (click-click-click), even though you have swapped a couple, there is likely a problem with either the connector on injector #3, or like smj said, a possible problem with the wiring harness somewhere.

Normally a technician would use either a NOID lamp or a Power Probe to check for power (a pulse) in the circuit at each injector, but not everyone has those tools at their disposal, so you do what you can. Sometimes with older cars it's just a matter of doing a wiggle test with the connector or harness to make that injector fire again... that's if you're lucky.

If all the injectors do sound the same, at least you ruled that concern out... the possibility of an electrical problem within the fuel system controls.

-R


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## zazman (Dec 29, 2011)

I just did a compression test and cylinders 2-4 are at 152psi and cylinder 1 is at 140 and just realised that this cylinder does not burn the gas. That's the one which I swapped the cylinder with #3. The injector seems to be stuck open and letting in too much gas into the cylinder hence the spark cannot burn it because of too much gas. It is even coming out the exhaust.
I tried the screw driver method to listen to the click-click sound and think I could hear it, though can't guarantee that, on all injectors but I doubt this one functions as expected.
I took it out and applied 12 to it to see whether I can hear the click and did hear a little click sound but can't verify if it actually moves or not. I've decided to buy a new one and it costs a whopping $79. I'll just bite the bullet and hope this wil be the fix. I'll update you hopefully tomorrow about the outcome. They have to order it. Meanwhile you can post your suggestion.


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## zazman (Dec 29, 2011)

Just installed the new injector for cylinder #1 and all four cylinders are firing fine but the initial problem (misfiring on cylinder #3) has cropped up again. I haven't had time to investigate this once again and hope to work on it fully this weekend.
I'll update then.


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## TheRepairMan (Jun 30, 2009)

zazman said:


> Just installed the new injector for cylinder #1 and all four cylinders are firing fine but the initial problem (misfiring on cylinder #3) has cropped up again. I haven't had time to investigate this once again and hope to work on it fully this weekend.
> I'll update then.


I'm sorry, but I'm not following you. The whole thread was around cylinder #3 misfiring, so why would you replace the #1 injector and expect that to fix anything. You've lost me, and I may not find my way back.

You know, one in six adults are mentally ill. Just replace every sixth one!

-R


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## zazman (Dec 29, 2011)

That was not my intention to lose you. What I did was swap injector #3 with #1 in order to rule out a fault with injector #3. After doing that I had a problem with injector #1 not functioning at alland after testing it uninstalled by directly putting 12v across its terminals and also realising that the small o-ring was not in good shape, I decided to buy a new altogether and installed it on cylinder #1. It is now functioning just fine but the initial problem with cylinder #3 misfiring is still there. Now I've ruled out injectors being the problem and am left with finding out what the problem is. 
I've checked the wire harness to the injectors and have not found any issues with it.
Thank you for taking your time to read this.


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## CMax03 (Jan 17, 2009)

It's a intake manifold leak at #3.....


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## TheRepairMan (Jun 30, 2009)

zazman said:


> That was not my intention to lose you. What I did was swap injector #3 with #1 in order to rule out a fault with injector #3. After doing that I had a problem with injector #1 not functioning at alland after testing it uninstalled by directly putting 12v across its terminals and also realising that the small o-ring was not in good shape, I decided to buy a new altogether and installed it on cylinder #1. It is now functioning just fine but the initial problem with cylinder #3 misfiring is still there. Now I've ruled out injectors being the problem and am left with finding out what the problem is.
> I've checked the wire harness to the injectors and have not found any issues with it.
> Thank you for taking your time to read this.


Oh, okay. My bad. I'm hanging in here to see how it turns out.



CMax03 said:


> It's a intake manifold leak at #3.....


Yep! Could be. It's hard to get to the bottom of the intake to hear or test for the air leak.

-R


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## zazman (Dec 29, 2011)

I'll see if I can figure out how to check that manifold leak. Why does it occur at 60+mph only and not at lower speeds though? This is one puzzler. I've already checked for vacuum leaks and found none so the manifold leak hopefully will be the culprit.
Thanks for the tip, I'm going to check it out tomorrow.


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## zazman (Dec 29, 2011)

Yep! you're right Repairman it's not possible to get to the bottom of the intake manifold. I sprayed carb cleaner to try and see if I can hear at least some kind of clue but couldn't. It didn't work.
The thought of actually taking the whole assembly off and then finding there's no leak makes me think twice, should I or shouldn't I.
I don't know at this point.


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