30 psi in 3rd

I have a Nissan 2010 Sentra with only 86,000 miles and shop replaced all coils and sparks cause original code was 3rd cylinder misfire then a multi-misfire so a day later same thing car was loud and engine shaking bad again with the blinking engine light so brought it back to shop and the mechanic put the code reader up which I also have one myself so knew it was the 3rd cylinder misfire so he tested my psi of the engine and said is was at 30psi not 100-150 which he said it should he should I just give up on this car cause at this point it would need a engine replacement he said my piston is cracked and it’s not worth buying a new engine but I put car started in new brakes new rotors and tires then all new coils plus the 2,800 I paid I feel like I’m deeply invested into this car any advice would be greatly appreciated ty

Walk away… This is called “sunk cost” Money lost that you are never going to get the value back from by tossing MORE money in. Walk away.


I am not a pro mechanic but just some thoughts…
why didn’t he do a compression test before just throwing on new coils?
how does he know the piston is cracked? a piston does not just crack.
get a second opinion. something is fishy, unless there is more to the story.


I too am curious why the mechanic believes #3 has a cracked piston.

If it is a cracked piston, or something requiring removal of that piston, then I do agree with Mustangman that your best option is probably to walk away.

If a competent mechanic determined it’s only a bad valve on #3, then I’d at least want to know the repair cost for that. Depending on the condition of the rest of the car, it may be worth considering.


Might be a serious problem now.
How long did you own it?
Ran fine till this misfire issue?
New tires, brakes. Runs fine.
Next week it dies?
A seller can’t easily hide a dead cyl issue. Is my point.

Yeah, something’s not right. Each time my Corolla has had a bad coil, our regular mechanic swapped two coils to see if the misfire moved. Then he replaced the one coil that was bad. Presumably, a cylinder with bad compression would continue to misfire after the coil swap. At that point, a compression test or other diagnostic technique would be in order. Get a second opinion. You might need a valve job. That might run under $1k. Way cheaper than a replacement vehicle. Worst case, my non-mechanic advice is to get a quote on having a used engine installed and you might as well have the new plugs and coils put in it.


The only place this car belongs now is the junkyard

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Another vote for calling it quits on this vehicle . Also the OP might want to upgrade their keyboard to one with punctuation keys and a space bar.


He probably did…At least this way he suck some money out of him.

Did this “mechanic” put any kind of guarantee on this work?
He should give you some $$ back, or buy back the coils, or something.

Ask the mechanic how he determined that the piston is cracked. While the spark plug was out for the compression test, he may have put a borescope into the cylinder for a quick look. He could have seen the cracked piston at that time. Don’t ask if he did that, just ask how he knows. If he says he used the borescope, then you can believe him.

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First off, your mechanic is wrong. Dead wrong.

Question. Did he check compression on all cylinders or just the balky No. 3?
In most cases very low compression (as in 30 PSI) usually means a cylinder head valve problem. That is much less expensive compared to a total engine replacement.
There’s also the outside chance that low reading could be due to a faulty compression tester. That is why when a serious problem is shown during a compression test I do a followup test with a second gauge. Better safe than sorry.

Now; why is he wrong?
Compression on a good engine should be 180-190 PSI.
He SHOULD have checked compression while the plugs were out and as part of the job of replacing plugs/coils.
He SHOULD have followed that 30 PSI check of No. 3 up with a wet test. Meaning a squirt of oil into the cylinder.
Number does not go up much; head valve problem. Number goes up a fair amount; ring/cylinder issue.

I would not buy into that cracked piston theory just yet. Unless he has bore scoped it that theory is a bad wild guess.


When cranking the engine a very noticeable difference in sound should be heard when the 3rd cylinder goes through its compression stroke. You don’t need a compression test to listen for this.

To fix requires removal of the cylinder head. How much other stuff is in the way makes a big difference in the labor cost. Exhaust and intake manifolds have to come off. Some engines require the over head cams to come out to access the head bolts. I’ve done it before, all by myself, on one of the more difficult 4 cylinder engines!

I don’t know. You’ve got a miss indicated on the computer, not sure a compression test would be the first thing to do. In fact no one has ever done a compression check on my cars except me. If in fact there is low compression, you either got valves or piston issues, no way around it, and you don’t do valves without serious thoughts about the bottom end.

So go ahead and get a second opinion to sink more money in it if it makes you feel better. But usually that’s the way things work out-you put a lot of money in a car and someone runs into it for you. Lost money is lost money so ya just got to brush the dust off your pants and move on. Girl friends and cars. What can ya say.

It sounds like regardless of whether or not you keep this car, you need a different mechanic, or better yet, you need to start working on the car yourself. A 2010 is rather young to give up on, especially if the body and interior are decent. However, if you are paying thousands of dollars in repair costs, which are not fruitful, that money would be better spent on the down payment toward a new car. If you go that route, you could still sell this 2010 Sentra, which runs but has a misfire, for $1500 to $2000 as a “mechanic’s special” on Craigslist.

I do not believe the diagnosis of a “cracked piston” unless this was visually verified by the use of an inspection camera. Nor would I accept a diagnosis of “worn piston rings” unless an inspection camera shows wear to the cylinder bore.
Otherwise, it is much more probable that the head gasket is leaking, or one or more valves are bad.

For someone who can DIY, this is not terribly expensive to diagnose or repair. I bought the Maddox deluxe compression tester kit, Maddox deluxe cylinder leak-down tester kit, and a portable air compressor at HFT for less than $300 including the tax. I used these tools to diagnose the engine problems with my car, which ended up being the head gasket leaking between two cylinders and an exhaust valve leaking on one cylinder. Buying the tools was cheaper than paying a shop for several hours of diagnostic time, and now I own the tools and can use them as many times as needed in the future.

BTW, I ended up fixing my car (DIY) for less than $2k–including the money spent on tools which I didn’t already own, and were needed to diagnose the problem and complete the repairs.

I would start by either buying the tools and attempting a DIY diagnosis, or simply taking the car to another reputable shop and asking them to diagnose the problem. Do not mention anything about a “cracked piston”. Just say that you had ignition coils and other repairs performed due to a misfire on one cylinder, and that the problem has not been solved. Then see what they find, and what they recommend.

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This is another consideration. I had a 1991 Toyota Tercel, and the engine failed at around 78,000 miles. The car was 11 years old at the time. We had it towed to the Toyota dealer where my father had all of our cars serviced (except for the one non-Toyota car in the family) and they suggested putting in a low-mileage used engine from a junkyard, which would have included a 1-year warranty. I believe they wanted about $3k to do this, which was a good deal. A factory-new engine cost about $5800, and I opted to do that since I really liked the car. They did an excellent job, and the car ran great.

Unfortunately, I only got another year or so out of the car, because an idiot in a Ford Windstar van ran a stop sign and I slammed into her at about 55 MPH. The Tercel was destroyed, as was the van. Her insurance only paid a paltry $2300 or so for my car, so I lost thousands of dollars. The only good thing is that I walked away with no injury, and the idiot who caused the accident was injured, and had to pay for my losses in pain, though I would have much rather had the money.

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CPK, Hello. You have all the symptoms of a bad Crankshaft Position Sensor.

Now back to your real problem, you are approaching car repair like a student who goes tot he teacher for answers. It is not an academic transaction, it is a business transaction.

Good business practices require second opinions. If you don’t want to be a mechanic, then at least be a good businessman. Solicit opinions on local mechanics from friends and co-workers. Do google searches for reviews on local mechanics. Then get a diagnostic done by one of the leading candidates.

I suspect that the compression test was not done correctly (read BOGUS) and done with the intention of cleaning out your wallet. Get another, or better yet, just take it to another mechanic with a good reputation and let them look and listen to the problem. They may tell you that all you ever needed was a CPK in the first place and that is jsut a couple hundred $.

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Careful with the abbreviations:
Creatinine phosphokinase (CPK) and myoglobin (MB) help healthcare providers measure heart damage from a heart attack

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Yeah one costs $125 and the other $125,000.

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It’s CKP, by the way