I have a 2003 Maxima with 130k miles.
Car runs fine, except the pinging i hear around 2k rpm every day.

I decided to replace my spark plugs this weekend with a step colder NGK Iridiums.

I also decided to measure the compression for each cylinder. This is what i found. Let me know if i should be alarmed, worried, etc...

Front bank of cylinders - 130/120/115 psi
Rear bank of cylinders - 175/160/180 psi

HUGE difference between the front cylinders and the back cylinders. WHY?

I added a little bit of oil to the front cylinders but i did not make a huge difference at all.


What does this mean? Bad head gasket on the front? Or it's only a minor issue with the head gasket and/or something else?

Should i think about repairs and spending crazy $$$ on this problem or the numbers are not that scary?

Should i sell/trade in the car now, before it gets worse? And....will it get worse?

Btw, i do add one quart of oil every 3k miles or so. I use only Mobil 1 synth.


Thank you for any opinions!

 

Wow, that is way off. Sounds like a head gasket issue to me.

 

Any antifreeze in the oil? Does sound like a bad head gasket. I would however, do a leak down test of the cylinders to verify your holding pressure.

 

Absolutely do a leak down before jumping to any conclusions. I will say that it doesn't look good though.

How is the car running??

 

Well, this is the funny thing - car seems to run normal. Like i said, it only "pings" around 2k rpm.

- Idle is stable.
- Gas mileage is as always...around 22MPG.
- No leaks.
- No overheating.
- I have not seen any oil in the antifreeze.
- Power seems to be good. I do not feel any hesitation.

I have never timed my car on the track(never been at the track) so i have no numbers to compare against. I suspect that the car is not as fast as it used to be when i got it new but it could be only my imagination. After all, i have 130k miles on it. It still moves very very well around town and on the freeway.

I've never had blown head gasket before, but i don't think my car behaves like i have a bad head gasket. It has too much power and it is still too smooth.

Yet, i can't explain the low compression in the front bank.
Thanks!

 

How do i do the "leak down" test?

 

Searching?
http://tinyurl.com/d25obk

Basically:

1. Remove all plugs
2. Place whichever cylinder you're checking at TDC
3. Insert leak down tester, and open up the valve
4. Watch for leakage
5. Determine where leakage is coming from

 

 

if the cylinders vary a bit from eachother its fine but there shouldnt be more than a 10% difference between the cylinders

Low compression in one cylinder usually indicates a bad exhaust valve. Low compression in two adjacent cylinders typically means you have a bad head gasket. Low compression in all cylinders would tell you the rings and cylinders are worn and the engine needs to be overhauled.

 

I have low compression only in the front bank - all 3 cylinders.
Can i have bad rings on only 3 front cylinders and the 3 rear to be just fine?? Seems unlikely.

So, should we determine that the only thing left is the head gasket on the front bank? I have no oil in the coolant and no coolant in the oil. If the head gasket is not leaking and the car still pulls strong....is it really a head gasket issue??

The only thing i can think of now is that the engine was COLD when we did the compression test. However, cold or warm ....why were the rear bank cylinders so much better than the front ones?

 

Have you not done the leakdown yet? It's useless trying to diagnosis it without the leakdown being done, it'll show exactly where it's leaking from.

The coolant not having mixed with the oil has zero diagnostic relevance to a head gasket failure. Just because it didn't mix, doesn't mean a HG couldn't be blown.

Yes, it's possible to have one bank's rings bad. Just think if one bank of injectors were constantly washing the cylinders down with fuel.

Do the leakdown.

 

Can i do the leak down test only on the front 3 cylinders?
I guess, i am asking is.... do i need to remove the spark plugs from all 6 cylinders to do the leak down on the front bank only?

I read a lot of articles on the leak down test procedure and some said to remove ALL spark plugs, some said that it is not necessary.

As you know, on the VQ35, it is a major pain to get to the rear bank spark plugs.

Thanks!

 

It only takes about a half hour (if that) to get access to the rear bank.

You don't need to, but it would be best. Do the leakdown on each cylinder.

 

Was the upper intake plenum off when you did both the front and rear cylinders? In other words.......did you happen to accomplish the compression test on the front cylinders when the upper intake plenum and the TB were installed and the throttle was not at WOT? And........did you repeat the test on each cylinder? If the engine has had no performance issues and had the normal, nice smooth idle, and it is not using abnormal amounts of oil (for a VQ35), your compression figures for the fronts, could be bogus. Go ahead and accomplish the leak down check, but you could be chasing a red herring. And keep your appendages out of the accessory belt area in case the crank suddenly rotates on you as you apply the air pressure. This can happen if you are not at true TDC.

 

Good point, we're all assuming that the compression test was done correctly; battery charger, at WOT (or in this case, the UIM off), all of the plugs out, etc.

 

- Upper Intake plenum was removed. (i had to get access to the rear spark plugs, there is NO other way)
- A lot of vacuum lines, sensors and connectors were disconnected. (required in order to remove the intake plenum)
- Spark plugs on ALL cylinders were not removed, but they were VERY loose
- Engine was COLD (i could not warm it up if half of it was disassembled)
- I used the battery/starter to crank the engine
- Front 3 cylinders showed bad/low numbers, Rear 3 cylinders showed much better numbers.

 

Are we talking about the same VQ35 engine?

Getting access to rear cylinder bank and all 3 spark plugs requires removal of the intake plenum and a bunch of vacuum hoses, connectors, etc.
Doing this in 30 min or less would be... *impossible*.
I am sure that it is a lot easier to do this on the 3.0L engine.

 

Yes, the VQ35. Otherwise, the statement wouldn't make sense; no reason to remove the UIM on the VQ30 to access the rear bank.

Saying that it flat out can't be done is completely incorrect. If you know what you're doing and have the proper tools, it can be easily done in a half hour. Hell, with no brackets, the UIM can be taken off in under 10 minutes.

And why didn't you just remove all of the plugs, instead of just loosening them?

 

OK. I am not going to argue with you. I am really glad that you can do a full spark plug swap on a VQ35 in 30mins or less.

I work from my own garage/driveway. I've replaced the spark plugs on my car 3 times already and without any special tools (no air and no power tools) it takes significantly longer to ... remove strut bar, remove engine cover, remove all vacuum lines, disconnect electrical connectors, clear the way, remove 5 IM bolts, remove IM, remove coils, etc. Then, I have to put everything back together, use the right torque specs, etc ,etc. At the end - it takes me a lot longer than 30mins. Either i am retarded with two left hands or i need to invest in some "special" tools.

I am not a mechanic, yet i have done a lot of DIY projects by myself on variety of cars (Audi, VW, Ford, Acura, Hyundai) and i can state with confidence that replacing the spark plugs on a VQ35 Maxima is a time consuming, kind of painful, project. Just my opinion. On top of that, my Maxima is the first car i've had that "fails" a simple compression test on half of its cylinders. Never had such problem on any of my other cars and i am puzzled.


Oh, I did not remove all spark plugs from the wells because i did NOT want crap to fall in the cylinder(s) while i was working on the other cylinders. I removed the plugs one at the time.

Would a loose spark plug in a neighboring cylinder cause false compression test results?

 

The plugs likely didn't cause a problem, was just wondereing.

I never said a spark plug swap in 30 minutes (although that is possible, would just be slightly fast paced), I said get access to the rear bank.

And granted, if you don't have much experience, I could see how you'd think that it's some huge job. I suppose it's a lot easier and quicker for me because of my background. For me it's around an hour, hour and a half job to swap out the clutch on a Z33, if that says anything.

 

i have pulled all the rear plugs, coils and reinstalled all that in under 30 minutes using the correct torque specs practice makes perfect. once your used to doing this job you learn shortcuts. But, i want to learn to do a clutch in around an hour and a half thats pretty impressive.

 

It's not too bad, maybe a dozen or so bolts to remove, trans slides right off.

Granted, this is with air tools and a lift. On jackstands with hand tools, can drop a Maxima 6MT and crack it open in ~45 minutes.

 

i see you re adding oil every 3k miles and low compression in front three cylinders is a sign of bad piston rings...does it show bluish /black smoke during accelrating..if it does then it s burning oil and rings are worn,,

 

I am wondering if I am starting to have this problem. I notice black soot on my muffler tips...What the hell is it..

 

like everyone said if you did the test correctly, theory says that if your precat were to start falling apart it would get sucked back in the engine due to valve timing overlap (remember no EGR) and score your piston walls. And this makes sense since it is all 3 of your cylinders that have more or less exact readings. If that is the case you may need new short block or try to fix it with honing and using oversized pistons. If that is the case you may want to consider headers at the same time.
it won't be headgasket issue unless it was one or 2 cylinders besides eachother and if u pull plugs out those pistons if coolant was present would be shiny new. very small chance H/Gasket would fail in 2 different spots especially on these motors.

 

one bank of injectors? Do u mean 3 bad injectors? They work independently and it is a returnless system with only one regulator (on a33). What are the chances of having 3 bad injectors on the same bank.

 

maxima 6MT on jackstands on 45 min? how about if i give you a 6th gen 6 MTwith a subframe? haha

 

Here is an update...

I did a second compression test on the front bank of cylinders.

This time is made sure the engine is WARM!!! First time i did the compression test, my engine was completely cold.

Here are the new numbers:

Cylinder 1 - 150 psi
Cylinder 2 - 140 psi
Cylinder 3 - 145 psi

I added some extra 0w-40 oil in all three cylinders and i re-tested:

Cylinder 1 - 165 psi
Cylinder 2 - 175 psi
Cylinder 3 - 180 psi


What do you think?
These numbers do look better than last week's results. At least all 3 cylinders now gave me 140 psi or better compression. For the VQ35, this is the "minimum" level at which compression should be, correct??

Clearly, adding oil helped. Bad piston rings, i am guessing?? Should i be worried with these numbers or for a 130k miles VQ35, they are kind of "expected"??

Thanks!

 

At least they're all right about the minimum now:


Yes, most likely rings. Nothing really to worry about IMO. Just your quart usage per oil change.

 

After the new numbers, the only thing i am planning to do is to switch to thicker oil. I am currently using Mobil1 10W-30 ... i may go to something like 15W-50 or at least 10w-40. ...and i may switch to a different oil brand. I started to hear some not so great things about Mobil 1 lately.

 

I switched from Mobil1 to Castrol Sytech, haven't noticed any difference, oil consumption (1 quart every 1800 miles) hasn't changed. Still using 5W-30 though.