Nissan Maxima SE 2007 shaking, poor gas mileage, engine codes in the message.

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Old 04-29-16, 07:24 AM
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Nissan Maxima SE 2007 shaking, poor gas mileage, engine codes in the message.

Hi everyone, my son's Maxima started acting out a little while ago. First, he noticed a leak. Had it repaired, was intake valve gasket. Then it started shaking at low speeds, but when you go faster, shaking would stop, and when slow down and stop, will shake real bad. My local mechanic thought it were bad coils so he replaced three rear coils. My son went back to school just to tell me that by the time he got there, about 3.5 hours it was worse. It didn't do it for a day or two that passed after repair that he was still home, but he didn't go anywhere, maybe a coffee shop next door. Check engine light was on again, he took it to read codes. That's what he got related to engine, there were some related to airbags:
P0725
P8026
P0300.
Now car is at his local mechanic, and they only got misfire code when checked. They said that two front catalitic converters are clogged and rear is rattling, so they want $1500 for that. Plus, they believe that the rear coils are aftermarket and want to replace again for 600 ( but i just paid the guy 600 to put them in???), and oxygen sensor wire has melted on the cat, and that would be another 300. Does any of this makes sense to you? I checked the prices on cats and O2 sensor, and it seems like 260-280 on the cats and 50 for the sensor. I don't know that shop, is this all reasonable at all? Plus my biggest concern, how is that going to fix misfires? Also, i cannot see myself spending 600 again to replace new coils. Because car was so bad, my kid barely used it, just tiny short rare trips, and both mechanics told him it was ok to drive. I was the only one telling him don't drive it at all.
Please, any thoughts? Appreciate any and all input. Thank you for reading this. Have to decide what to do quickly.
 
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  #2  
Old 04-29-16, 07:50 AM
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I only owned one Nissan. Aftermarket part prices were way too high compared to other cars. I'm not even talking about labor prices. I would not keep the car. Try to sell it one way or another.
 
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Old 04-29-16, 09:28 AM
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Could it be that bad catalitic converters and O2 sensor cause misfires

In Nissan Maxima SL, 3.5L 2007. Could that be the cause of misfires?
 
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Old 04-29-16, 12:33 PM
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I don't know why you started a new thread but the answer is yes. The moderators should combine the threads.
 
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Old 04-29-16, 01:19 PM
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Yeah, i guess. No one was replying and your answer about selling the car wasn't too helpful, lol. Just a last ditch effort, sorry. But thank you for confirming that it could cause misfires, i appreciate. Also, why then there were no codes foe converters or sensor for that matter? I looked them up, and they were for multiple misfires, engine speed, couldn't find anything on the third? Thank you.
 
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Old 04-29-16, 01:30 PM
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would probably get a second opinion would probably avoid the dealership and see an independent shop.
some exhaust shops can do a pressure test on the cats to see if they are plugged they also will likely have better price on replacing them if needed, but a plugged cat usually causes a power loss that will only get worse at higher speeds the shake at low speed and at stop is usually not a symptom of a clogged convertor would be more concerned about the misfire getting repaired first it could be ignition related.
 
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Old 04-29-16, 01:34 PM
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I would not keep the car. Try to sell it one way or another.

THIS ^
 
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Old 04-29-16, 01:45 PM
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You have at least two o2 sensors... one in front of the catalytic converter and one behind it. The one behind it is the one that would detect if the catalytic converter is plugged. That is its only purpose. However that rear o2 sensor does not give any data to the computer that would affect the fuel or spark, so if there is a misfire it has nothing to do with the rear o2.

A catalytic converter would need to be plugged / restricted pretty badly in order to cause a misfire. This is quite easily diagnosed with an obd-ii scanner by checking the live data. At idle and on the highway, the rear o2 sensor should have a regular sine wave graph, alternating from low voltage ( around .1V) to high voltage (around .8V) with an average voltage of around .42V. If the rear o2 checks out there is likely nothing wrong with your catalytic converter.

If your car is missing, an obd-ii scanner should surely give you a clue. Is your check engine light on? Have you had the codes read? If so, what are they?
 
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Old 04-29-16, 02:32 PM
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They told me that two front one are clogged, and rear one is rattling. The codes were P0725, P8026, P0300. But in the shop they only got misfire code. And it's not a dealership.
 
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Old 04-29-16, 03:21 PM
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No way I would be replacing o2 sensors or catalytic converter based on a misfire code. Misfires can be caused by SO MANY things. Sounds like they want to milk you.

There is no such thing as P8026. Do you mean P0826?

If it was my car I would definitely not stick money into the same parts... get it back from them asap. Have them clear the codes. Drive it until the check engine light comes on. When it does, take it back and have the most recent code read and diagnosed.

The mere suggestion that they want to replace the same part and charge you again tells me it's time for you to find a new mechanic that's honest and trustworthy.
 
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Old 04-29-16, 04:09 PM
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Threads combined...... one topic stays in one thread.
 
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Old 04-30-16, 09:41 AM
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That's the code my son gave me, and i couldn't find it either, but i don't have the correct one. The shop where car's now is not the one that put coils in. They said that if nothing else would work, they would like to swap that for original parts instead of cheap ones that my guy here put in. Which is upsetting enough, as i trusted him to do a good job.
 
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Old 04-30-16, 10:00 AM
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Coils can be tested electrically to see if they are going bad. The primary and secondary windings can be tested... no way I would replace the coil again if it tests ok. I would look elsewhere... plugs and wires would be an obvious thing to check. Ot it could be injector related... the list goes on and on of possibilities for a misfire. The exact cylinder that the misfire is occurring on should be identified. This will narrow it down tremendously. It could be a variety of things causing it. With each obd code there is a long list of possible causes... a good mechanic will figure it out, not just replace parts or go on a hunch. If it's randomly occurring on all cylinders then there may be some problem with the exhaust, but I would not replace the converters without reading the o2 voltage, as mentioned earlier. The MAF sensor is another sometimes troublesome component. It can be cleaned easily as long as you don't damage it. The MAF sensor controls a lot of things and if it's dirty it can really hurt performance.
 
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Old 04-30-16, 10:18 AM
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Just for the sake of discussion, here are all the things that are likely causes of the P0300 code (misfire on random cylinders)

- Faulty spark plug (s)
- Faulty ignition coil (s)
- Clogged or faulty fuel injector (s)
- Intake air leak
- Fuel injectors harness is open or shorted
- Fuel Injectors circuit poor electrical connection
- Ignition coils harness is open or shorted
- Ignition coils circuit poor electrical connection
- Insufficient cylinders compression
- Incorrect fuel pressure

By testing the components they can often either be ruled out, or if the tests seem questionable or fail the testing, then replacement is warranted. Also, it's wise to replace some things if it's time to do so... for instance if the plugs and wires are original, it's probably time to change them anyway. Fairly inexpensive and fairly easy to DIY.
 
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Old 04-30-16, 10:25 AM
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How many miles on this vehicle?
How long has your son owned it?
Has the regular scheduled maintenance been done on this car?
 
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Old 05-03-16, 09:10 AM
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you said you had a intake gasket replace, for a leak? did the miss fire start after the intake gasket replacement? if so I would guess there is a leak. does the car try to die at idle but run fine at highway speeds?
 
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Old 05-03-16, 09:20 AM
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A vacuum leak (such as from a leaking head gasket on the intake) would show higher than normal fuel trim readings, especially at idle. Those readings can be had with an obd-ii scanner that shows live data.
 
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Old 05-07-16, 04:50 AM
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My son had the car for two years ( almost), it was regularly maintained. The converters are done, he said they were bad, but with my luck, car still misfires. They did change the back coils again, without talking to me (#1, 2,3 i believe ). He's telling me that the codes change between #2 and #3 coils. Car still misfires. Runs fine cold, as soon as it heats up, starting misfire. He told me he checked everything, injectors are ok, and the way wires are melted on O2 sensor it overheated at some point badly. Sparkplugs and wires were replaced and are good. Now we ere down to either head gasket or block crack. He thinks it could be between 2 and 3, because of the lost compression. Is there a way to tell without opening it up? Not sure about the intake valve gasket initiating the misfire, will need to ask my son and think about it too. That was chronologically first thing. And yes the car would run at highway speeds fine, but shake violently at slow speeds and idle, not really dying though.
 
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Old 05-07-16, 05:19 AM
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Sounds like a vacuum leak.
 
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Old 05-07-16, 06:19 AM
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"He thinks it could be between 2 and 3, because of the lost compression."

What are the compression test numbers??
A vacuum leak won't screw up compression.
 
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Old 05-07-16, 06:46 AM
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I don't know what the numbers are. But it all definitely started after the intake gasket replacement. Should i ask him to check that?
 
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Old 05-07-16, 07:02 AM
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I agree, definitely look into the lost compression. The O2 wires are fixed, and the O2 is working, I assume? If not, it would be a fairly easy diy repair. I didn't see you mention any code having to do with the O2, so it must be working. The wires may have touched the exhaust at some point. If there is no code it probably is still working just fine.
 
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Old 05-07-16, 07:33 AM
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Yes, i believe it does. Just melted from touching exhaust
 
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Old 05-07-16, 10:21 AM
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You can also use a vacuum gauge to check the vacuum level at idle.

After going back and re-reading thru this thread.... your problem sounds very much like a sticking EGR valve... although that usually sets a code.
 
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