# Is there such thing as cheap diagnosis fro misfire code?



## solveet2011 (Sep 1, 2017)

My 2008 Versa kept losing power on the freeway, then the service engine soon light came on and smell gas here and there. But it still runs like a champ except for a sudden loss of power here and there at high speeds.

So I took it to a shop and said there is a misfire code. But he wanted $75-$200 just to diagnose it. But it's never $75 and none of the $200 would apply to repairs. Is there a non-computer or human method to pinpoint the problem? 

Then I called around and some places said it's probably the plugs and coil.

When I called other places they thought it's usually not the plugs or coil. That it's the vacuum or fuel injector etc.

Any hints will be greatly appreciated


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## Car guy (Mar 31, 2016)

The specific code would focus the answer.

But, sans that, you can easily change your spark plugs and coils yourself (assuming oil is not getting down past the spark plug tubes into the plugs contributing to the misfire).

And, given it's a misfire, you can swap the coil from the cylinder showing the misfire (code) with another one of the existing coils that is good (not misfiring), to see if the problem follows the coil - i.e., if the engine code changes to a misfire on that one. If so, it's that coil. You likely would replace all 4 then. Easily done.

If not (if the misfire does not move cylinders), check the plug in the misfiring cylinder. (You would check all the plugs anyway.) You likely would replace all 4 of these also then. Easily done.


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## solveet2011 (Sep 1, 2017)

THat's what I'm saying, if the scan says misfire, then why is the dealer saying it's usually not the plugs and coil. That it's usually fuel injectors or vacuums? 

So according to your method, I'd have to do the plugs and coil, only to find out, according to deal, that it's not the plug and coil. So is there a more logical method except spending $200 on diagnosis?
Thanks


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## smj999smj (Jan 1, 2006)

You need to start by getting the trouble code. Most auto parts stores will retrieve the code for no charge, or you can get a cheap, OBD II code reader and retrieve it yourself (I saw one for around $20 in the automotive section at Walmart a couple of months ago). Once you can give us a code, we can better help you. Spark plugs are usually good for 105,000 miles (always stick with original type, NGK spark plugs!). If they are due, it would be a good idea to replace them, regardless. Otherwise, ignition coil packs do fail at times. Fuel injectors can fail, too, but they are usually less common. If you get the code, you can also go to the "knowledge base-service bulletins" section at NissanHelp.com and see if there are any applicable TSB's for your code.


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## Car guy (Mar 31, 2016)

<Is there a non-computer or human method to pinpoint the problem? > Answered in post 2.
< ... is there a more logical method except spending $200 on diagnosis?> Below.

Our methods (SMJ's and mine, which are the same), given the available info, are logical and don't cost $200. They only involve a few minutes of time. Results/analysis are immediate. 

<So according to your method, I'd have to do the plugs and coil, only to find out, according to deal, that it's not the plug and coil.>
No, not necessarily. Post 2 should yield (expose) a bad coil or a bad plug. If (all 4 of) the coils and plugs were to prove to be good (following the advice in post 2) or perfect, there's still no out-of-pocket cost. So, yeah, again absent specific code(s) and limited info, it could be an injector or injector o-ring or pressure or flow issue (or other internal cylinder or clogged PCV valve - also easy and fast to check and remedy - or related issue); but, based upon what's been provided, collective advice is sound.

One also could check the resistance of the coils and injectors and check for power to them and ECU control of both. But, presumption is a DVOM is unavailable or unfamiliar.


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## solveet2011 (Sep 1, 2017)

Yes, the code is P0300 and this is what the google search says as below:

What causes the P0300 code?

Spark plugs that are damaged or worn
Spark plug wires and/or coils that are damaged or worn
Distributor cap that is damaged or worn (only if applicable to the vehicle)
Rotor button that is damaged or worn (only if applicable to the vehicle)
Fuel injectors that are defective
EGR valves or tubes that are clogged
Ignition timing that is off
Vaccum leaks
Fuel pressure that is low
Head gasket(s) that are leaking
Distributor cap that is cracked
Camshaft sensor that is faulty
Crankshaft sensor that is faulty
Mass air flow sensor that is faulty
Oxygen sensor that is faulty
Throttle position sensor that is faulty
Catalytic converter that is faulty
PCM is faulty

What are the symptoms of the P0300 code?

Check Engine Light that is on or flashing (It came on then when I left the car and battery died, the light went off. But it came back. Now it flashes and remain on as well)
Car may take longer to start up, or does not start up at all (not an issue at all)
Car dies while stopped (never)
Car idles rough (used to until I put some "Guarantee Pass" to do the emissions test. It idles rough very seldom now)
Car may hesitate while accelerating (it only hesitates at decreasing speeds from 60-70 mph down to 50 or less, but then the hesitation stops)
Lack of power while driving (again, it strangely used to have lack of power until I used the Guarantee Pass)
Increase of fuel consumption (I can't say I've noticed any)

Another thing I should add is that today I left it running in a closed garage and I heard a tapping noise from the driver side as my window was down and could hear. When I went back, the exhaust also had this tapping sound or sick sound)

So my reason for this question is to see if there is a process whereby I can go right to the point. Obviously I could pay $200 and have a dealer tell me it's fuel injectors or whatever. But I'm thinking that is not necessarily guaranteed either. That I could fix the injectors and another problem could still exist. Please don't get me wrong, I don't see a way out of paying the $200 and so I'm not asking for some sort of miracle. But I figured it won't hurt to see if someone has been able to consider the car behavior that I have stated and eliminate certain items on the list of to do's above. And thanks much for your efforts.


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## solveet2011 (Sep 1, 2017)

I just ran back to the part store because last guy told me it's ONE misfire but today's code showed all misfired. So he checked the history and the previous guy was wrong and it's been multiple misfire all along. So wouldn't it be nearly impossible that ALL plugs and coils would go bad suddenly? I'm thinking the dealer is right and it's something that's affecting the entire engine. Most placed I check on the net claimed that it's rare for fuel to cause p0300 and it's most often electrical. Then some of the placed I checked thought the Cam Sensor could cause this. I don't even know what it is and where it is and how hard it is to replace it or test it. But how does that sound? Thanks again


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## rogoman (Dec 16, 2004)

OK, so if the ECU code really is a P0300 which means a multiple cylinder misfire. If only one cylinder was causing a problem, the code might be P0301 for cyl#1 and so forth. The ECU might be posting more then one code so it's best to do an ECU code readout with a scan yourself. The tool can be purchased at most auto parts stores. The condition you're describing can be caused by a marginal crankshaft position sensor or a camshaft position sensor. If you're buying one or both of them, buy only OEM units from a new car dealer. Don't buy aftermarket types; they've been known to fail in a short time; some are even DOA. You can perform many of the diagnostic tests yourself which a dealer/private shop would do anyway. Here are the possible causes:

- Improper/dirty spark plug(s). 
- Insufficient compression.
- Incorrect fuel pressure.
- Fuel injector(s) dirty or leaking.
- Intake system vacuum leak.
- Lack of fuel.
- Air fuel ratio (A/F) sensor 1 malfunction.
- The camshaft position sensor (CMP) or the crankshaft position sensor CKP) may be defective.

To properly diagnose dirty/leaking fuel injectors, they need to be remove and tested on a flow bench tester. You can also do a quick leak test by teeing-in a fuel pressure gauge to the fuel rail input, then turn the ignition switch to the "RUN" position without starting the engine. If the pressure drops off rapidly, one or more injectors are leaking.

How long have you had the old spark plugs? If they are very old, then it's time for a set of new ones. When replacing the plugs, examine the electrodes for telltail signs that might point to what the problem in the engine might be. Always buy OEM NGK spark plugs, not aftermarket types which can cause drivability problems.

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The fuel pressure can be tested as follows:
Tee-in a temporary fuel pressure gauge to the fuel rail input. The reading at idle should be approximately 51 psi.

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To test for an intake system vacuum leak, use a vacuum gauge for good accuracy; most auto parts stores sell vacuum gauges. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source, usually somewhere on the intake manifold. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle body and at the MAF for cracks or loose clamps.


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## solveet2011 (Sep 1, 2017)

If doing a process of elimination, my most comfortable place to start would be your vacuum check and any other ELECTRICAL help you could offer. If my attempt fails, then I'd go into plugs/fuel etc. I mean it takes almost 2 hours to redo the plugs and coil on this thing, taking the intake and everything else off. Coils are $130 each. So to me vacuum and electrical seem cheaper at this time. Thanks for help


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