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Hello

I'm new to this forum and am looking for alternative solutions or at least confirmation that my mechanic is legit in what he is quoting me for my repair needs.

I have a 2009 Nissan Altima 2.5S that I bought in 2011. It has 98K miles and was previously used as an Enterprise fleet vehicle.

My problem started about 2 weeks ago when I was driving to work after filling up at the gas station (Exxon). On the freeway, my car started running so rough that I thought I blew a tire. Upon inspection, my tires were fine but my check engine light was blinking. After taking it to Autozone for code reading, I got a P0300 and P0304.

I switched out the spark plugs hoping that it would be a simple, and cheap fix, but it only helped out a little bit. I didn't drive it at all afterwards and just got back from my mechanic and was told that there is Zero compression on cylinder for, and the other three are running at about 85psi as opposed to the normal 120psi.

His master mechanic said that he could find no fault in the surrounding systems that would normally cause this to happen and is baffled as to what caused this. There was no rough ride leading up to this.

He gave me 2 options. 1. Replace engine with new one for about $5K including labor with a 3 year warranty. 2: Replace engine with used one for about $3K with 90 warranty. He said he only uses low mileage replacements if he can find one for a good price.

Is this reasonable or are the other avenues that I can explore? I've done some quick research and found used engines with about 30K miles on them for about $800 online.

Sorry for the long thread, but I wanted to give all of the details. Thanks in advance for all of the help!
 

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I would get a second opinion. Paying another diagnostic fee in hopes he is wrong is way cheaper than replacing an engine if it isn't needed.

Maybe there was miscommunication with the compression numbers, but there is no possible way three cylinders are at 85 and the engine is running. Normal compression on a 2.5 is around 200. Minimum is 185. The engine won't run if it gets below 130.
 

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Those codes are both for misfire (cylinder not firing) w.r.t. cyl 4 in particular.
It seems likely that this is the well known precat problem, where the contents of the precat are sucked into the engine destroying the cylinder walls.
I take it that the engine did not overheat prior to this event, you didn't find oil smoke and waves of heat coming from it when you stopped? If that had happened it would be a new head gasket set and top end overhaul. Actually you could check this by removing the dipstick and seeing if there is water in the oil.
If it is the precat problem I would buy a used engine online, at that price it's an OK deal for a low mileage motor.
 

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As far as I know the precat issue does not effect the 2.5l after 2006. If you replaced the spark plugs reset the ses light and the code came back I'd swap around your cyl 4 ignition coil to one you think is good clear the code and see if it moves to that cylinder. If so replace that coil. With the p0300 you might have another coil bad thats intermittent.
Also I'd change all the plugs if not done so yet and check them for oil just to safe.

I dont think that shop knows how to read a code. Was it a Nissan dealer?
Sent from my Moto X
 

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So where does the zero compression on #4 come from and the 85 psi on the others?
If the bores are actually OK, then it can only be either a blown head gasket or a valve issue. hmmm ... possible to get a TB screw loose on this model, sucked in and stuck on a valve seat??
 
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