# Need help with missfire problems



## iservealot (Oct 23, 2009)

Hi Guys I need your help!

I have a 2005 Nissan Altima 3.5SL with roughly 122k miles.
My car is in $8,000 of repair work - and they still can't get the car to run right!
My car shakes/misfires when idling either in park or drive and all shops that I've taken it too can confirm this, but cannot pinpoint why.

So far the relevant work done to the car just for the idle problem are as follows:
-Replaced entire throttle body (thinking the idle air valve was bad)
-Replaced "Air Flow sensor" and "Air Flow meeter) (aka 02 sensor?) bank 1
-Replaced 2 leaking fuel injectors

The work listed above was done by the Nissan dealer. With my most recent visit, I was told that they had to call the Nissan tech support hotline to ask what to do next. They advised them that the car needs to have bank 1 catalytic converter replaced. (the car has had a check engine code for this). 

The dealer is recommending that after doing all of the above work (knowing the cat was "bad") the cat converter needs to be replaced. The thing that makes me most frustrated is that all technicians working ont he vehicle, including the Nissan dealer, specifically advised me that the cat converter would not cause the car to misfire or idle bad. It seems that now that they have replaced parts and the idle has only gotten worse - they recommending that I replace the cat.

Can someone please advise me what to do next? I did some research and I cannot find anywhere that says a bad cat would cause a bad idle or the car to misfire. The dealer has tried to explain to me that the bad cat can cause the car to read incorrect figures from the oxygen sensors causing the car to run too rich or too lean in turn causing the car to misfire. I have no idea if this theory is accurate, but if it were true then wouldn't there be a check engine light for too lean/too rich? Why would they replace the airflow sensors with a bad cat too begin with?
Why the hell is the cat even bad to begin with?

I need some guidance from the smart people on this forum to see what my next action should be.


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## jdg (Aug 27, 2009)

iservealot said:


> My car shakes/misfires when idling either in park or drive and all shops that I've taken it too can confirm this, but cannot pinpoint why.


I find that hard to believe...along with the $8,000 bit...but I digress...

-->


> The thing that makes me most frustrated is that all technicians working on the vehicle, including the Nissan dealer, specifically advised me that the cat converter would not cause the car to misfire or idle bad. It seems that now that they have replaced parts and the idle has only gotten worse - they recommending that I replace the cat.


I agree with the dealer (for once) about the cat not causing a rough idle. And of course they'd recommend replacing the cat...it's all about the $$$.



> I did some research and I cannot find anywhere that says a bad cat would cause a bad idle or the car to misfire.


And you likely won't find it either, so I think you're good to go there.

-->


> The dealer has tried to explain to me that the bad cat can cause the car to read incorrect figures from the oxygen sensors causing the car to run too rich or too lean in turn causing the car to misfire.


Here I think the dealer is talking out his ass...unless the cat is totally plugged up. But, if you had a totally plugged up cat, any half-ass decent mechanic would figure that out quickly.

And the quote above totally contradicts 2 quotes above...
Which one is it? Maybe the 'dealer' isn't the only one talking out his ass?



> I have no idea if this theory is accurate, but if it were true then wouldn't there be a check engine light for too lean/too rich?


Not necessarily. OBD2 lies all the time. At best, the check engine light and it's associated code, is an educated guess, a description of the 'symptom' the ECU thinks it's encountering. For instance, if you've got a massive exhaust leak right before the front O2 sensor, the computer might tell you that the front O2 sensor switching rate is too low. And based on that, you'll replace the front O2 sensor and not do anything about the massive exhaust leak...because the computer told you something about the front O2 sensor.



> Why would they replace the airflow sensors with a bad cat too begin with?


Which leads me to think your cat is actually plugged. If the exhaust can't get out, fresh air can't get in. If fresh air can't get in, your airflow sensor might read low. If your airflow sensor is reading low, you might not get enough fuel. If you're not getting enough fuel, you'll get a misfire.



> Why the hell is the cat even bad to begin with?


Hell...the engine *only* has 122K miles on it. Cat's usually last a lot longer than this, but, it isn't a requirement. One really bad tank of gas, a few miles of a really rich air/fuel mixture caused by a failed sensor, any number of things, can poison a cat, cause it to break down, overheat, whatever, and, BAM! It's done...



> I need some guidance from the smart people on this forum to see what my next action should be.


Find another dealer...
Find a real mechanic...
Replace the cat...
Also, you never did say exactly what those 'codes' were, or told us how many mod's you've done to the vehicle, etc.


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## iservealot (Oct 23, 2009)

Thanks for your detailed response. The ball park $8,000 figure is not just for misfire diagnostic. It is also for repairs that were needed like new struts, timing chain job, tie rods, power steering pump, racking and pinion, both front lower control arms, engine mounts, alternator, battery, four new tires and the work listed below. I am sure I've forgotten something as that is all from memory.


jdgrotte said:


> I find that hard to believe...along with the $8,000 bit...but I digress...
> 
> -->
> I agree with the dealer (for once) about the cat not causing a rough idle. And of course they'd recommend replacing the cat...it's all about the $$$.
> ...


*I don't know the exact check engine code, but I was advised it was the code for a bad catalytic converter. There was only one code, and no additional codes advising that the car is running rich/lean nor any codes advising of a misfire on a specific cylinder. The car is also factory stock.*


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## jdg (Aug 27, 2009)

iservealot said:


> Thanks for your detailed response. The ball park $8,000 figure is not just for misfire diagnostic. It is also for repairs that were needed like new struts, timing chain job, tie rods, power steering pump, racking and pinion, both front lower control arms, engine mounts, alternator, battery, four new tires and the work listed below. I am sure I've forgotten something as that is all from memory.
> I don't know the exact check engine code, but I was advised it was the code for a bad catalytic converter. There was only one code, and no additional codes advising that the car is running rich/lean nor any codes advising of a misfire on a specific cylinder. The car is also factory stock.


Ok...should've included that much info in the 1st post...
But I still don't come up with $8,000 worth of work. Even at an expensive shop, I only come up with about $4,500 at most...unless you're getting crazy expensive aftermarket high-end parts that are gold plated.

Before letting them swap out the cat, I'd get something in writing that says something to effect that if the part doesn't fix the problem, you don't pay for it, however if it DOES fix the problem, you will happily pay for it, in cash, with a free dinner for all tech's involved 

Other thoughts...(I don't own this type of vehicle, so I'm guessing at best)
Does this car have 2 cats, one for each 'side'?
Sounds silly, but, take it to a muffler shop and have them swap the cats from side to side. If anything, at least it'll move the misfire code from #2 to #4, and help narrow down the problem.
Does this car have the type of coil pack(s) where 2 plugs are mounted on each coil, and there are 3 coil packs? If so, swap 2 of the coil packs with each other. This, again, _might_ move the cylinder misfire.
Did they change out the downstream O2 sensor (after the cat)?


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## iservealot (Oct 23, 2009)

jdgrotte said:


> Ok...should've included that much info in the 1st post...
> But I still don't come up with $8,000 worth of work. Even at an expensive shop, I only come up with about $4,500 at most...unless you're getting crazy expensive aftermarket high-end parts that are gold plated.
> 
> Before letting them swap out the cat, I'd get something in writing that says something to effect that if the part doesn't fix the problem, you don't pay for it, however if it DOES fix the problem, you will happily pay for it, in cash, with a free dinner for all tech's involved
> ...


Yes this car has two cats. I believe the term "bank 1" was used when they told me the cat was bad. As far as changing the sides, I don't think that will help with diagnosing the misifre. You see, the check engine code is simply telling that CAT1 is bad. There are no codes for misfire, let alone specific codes for specific cylinders. 

I have no idea what "coil packs" are. Does this have anything to do with the spark plugs? If so, I asked the dealer specifically if they had looked at the spark plugs to verify this is not at fault for the misfire and they responded with "Why would we do that? The spark plugs have nothing to do with this problem" ....?


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## pulsar86 (Aug 13, 2009)

Take the car to someone else and have them put it on a full engine analyser it should show up any missfire or rich or lean conditions. I personally would take the car to a dyno tuning shop [dynamometer] that works with high performance engines they will soon sort out the problems. It would be worth any cost involved, they are usually very knowledgable. You have already spent a lot for a car with relatively low kms.


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## midnightfallz (Oct 24, 2009)

check the timming and the tps if thats not it change the cats..


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## Nickaltima (Jan 11, 2008)

headers..cut out the cats off each manifold..mine were plugged and a piece of the comb was missing on the front cat..where did it go?? who knows probably back into the cylinder head..best investment ive ever made


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## Nickaltima (Jan 11, 2008)

o and "iservealot" theres 3 cats on the 3.5 not 2


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## Nickaltima (Jan 11, 2008)

mine also idles rough in neutral and shoots a 300 code which is random multiple misfires..i think its the coil packs..u might wanna check that out too ive got a 135k on an 03..only idles rough in neutral never when im driving


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## iservealot (Oct 23, 2009)

Okay guys, sorry for the delay (was in the east coast) but I have an update for you.

I took the car to a new shop and the advised me that after looking at the car it is blowing blue smoke from the exhaust.

He also advised that the engine is burning oil (For the same reason). Sure enough when we checked the dipstick, it barley even had a reading level. He recommends that a new engine/rebuilt engine be put into the car as the engine is ready to give out soon.

Ideas? Has this been the idle problem from the start? Should the Nissan Dealer have been able to determine this from the beginning?


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