So, I decided to do a compression test. hasn't had one done for about 2 years. 1995 SE Maxima with 110,000 miles.

Starting from left to right counting across the Front and then across the back, here are the results: 192, 255, 195, 200, 230, 197

So, all looks somewhat OK (maybe a little carbon buildup), except for those 2 center ones. They are much too high. now those are the 2 that had oil on plug (not the threads) and on the coil pack when i took them out.

the plugs all looked AOK, tan/brown/the tip is more grey. Nothing stood out about those 2 plugs. The car seems to run great. Milage is , so-so, low 20's for city driving. No blue smoke when driving, so i don't think the oil in those two is also on the threads, because i would think i would see the burning oil during the combustion process, as blueish exhaust smoke. Since the oil is above the threads, I m guessing the Valve Cover O-Rings/gaskets for those two.

What's got me stumped is really the fact that the car seems to sound fine, exhaust looks and smells fine, and the car runs great. plenty of power, and drives pretty consistent across the spectrum. I have another 1995 SE which i haven't done the compression test on, but both cars run just a good. The other car has 245,000 miles on it.

So anyone have any ideas? Do you think i am headed in the right direction with the following assumption:
Since the oil is above the threads, I m guessing the Valve Cover O-Rings/gaskets for those two with the oil and the high compression.

Can the high compression be caused by Valve Cover O-Rings/Gaskets being bad?

Thanks in advance for all your help

 

Your test results are out of spec.

If I recall correctly, you can't have more than 14psi difference between the highest and lowest compression cylinders.

My first guess is that you must have tons of carbon buildup in the cylinders. Might explain the oily residues you notice.
Carbon will take away from the volume of the chamber and would make your compression results higher. I'd be suprised that your car doesn't knock and ping quite a lot.

I would try cleaning the throttle body and then add some Chevron fuel system cleaner for the next 5 tanks of gas and test the compression again.

You may have some sort of extra oil leaks going on in those two cylinders, but even all your cyclinders are past the max specs. If I recall correctly, 185-190psi is the maximum compression range specification in the service manual. So not only do you have all your cylinders out of spec on the high side, you are also out of spec for the variation between cylinders.

All that high compression may in fact give you some more power. But it doesn't sound too safe. What octane gas do you use?
In california, we only got 91 as the highest. I know in the northeast states one can get 93 or 94 octane.

If you use gas that has the MTBE additive (common in CA), you absolutely must use fuel system cleaner on a regular basis. Once every three or four tanks would not be over-doing it. MTBE additives leave lots of carbon build up in engines.

 

Without taking the upper-manifold off I am guessing that there is massive carbon buildup just by how dirty the throttle body is. As far as gas goes, i use 94 octane.

Can the Valve Cover Gasket/plug Seal leak be causing the Higher Compression readings for those two that are so out of spec? If so, and we remove that issue from the scenario, then it is probably just a case of carbon buildup causing the higher readings across the board. What was interesting is that the 2 with oil had the messed up readings.

i am trying to find the correlation between the plug/coil having some oil in there and the higher compression test results for those with the oil. The other 4 are a little high, but as stated I am guessing that is just carbon buildup. Whatcha think?

 

the specs are aout right but the two high ones are weird. Normal range is only 10% difference. A oil leak can cause higher compression becuase it will seal up the piston chamber better then running it dry. Honestly I wouldnt even bother with any work on this. if the car is running fine and you have no oil burning then let it go.

 

So, I forgot about warming the engine up this time. lol

So, put everything back together, and warmed up the car for awhile. then pulled everything and re-ran. here are the numbers from both:

Engine Cold Engine Warm
1. 192 180
2. 255 185
3. 195 180
4. 200 190
5. 230 185
6. 197 185

So, The numbers are a a little better and also more consistent. They are still also a little high for a car with this mileage, so i am guessing Carbon buildup, as the gentlemen who replied before kindly pointed out (Also thanks to the search feature).

Now, since there was oil in the 2 & the 5 (the way i count them, lol), when i did my first run, I still think I have a problem with either the Valve Cover gasket or with the o-ring/Seal around where the plugs go through the Valve Cover. But also, the oil in there on the first run was pretty dark, and no new oil on the second run. I recently changed my oil, so i am guessing that it takes awhile for the oil to build up on top of those two plugs. which does buy me some more time before replacing the Valve cover gaskets and seals.

Any new opinions / insights? Also, thanks gain to everyone who helps the gang out:-)

 

Are you pulling all 6 plugs and removing the fuel pump fuse? From what I have heard a dry test i.e. no fuel is the most accurate test. Your warm tests seem to show an engine in excellent condition for its age.

 

The only difference between the first and the second time, was the second time the engine had been warmed up.

Step 1 - Pull Fuel Pump fuse and start car (warm run, it died pretty quick, cold run, it didn't even start)
Step 2 - Tie Throttle body open
Step 3 - Remove all coil cables from coil packs
Step 4 - Remove all coils
Step 5 - remove all Spark plugs
Step 6 -test compression, with above removed from all during testing


So, it appears the instructions that the engine MUST be warmed up, make a pretty big difference. I did happen to get a look in the throttle body, and there was a ton of carbon. So I am sure that the numbers are a little high due to carbon buildup. Any one know how to get the necessary areas clean to remove the carbon that is affecting the compession test?

So, the game plan is, get new valve gasket, and seals/o-rings. then Remove and clean throttle body and intake plenum. Then on goes the Wet Direct Port NX kit. Then, it is "GAME ON"

 

FYI

3M makes a really nice fuel system/throttle body/intake/carbon removal system. Your not going to find this kit at Pep Boys, it's distributed by 3M to mechanics and dealers. The kit comes with adaptors to hook the system up to your car. There's a couple of steps to the cleaning process and one includes running the vehicle with the cleaner injested in the intake while the car is running. It cleans everything deep down into your intake manifold and your cylinders, removing a lot of carbon deposit. It all gets burnt up and comes out the tail pipe and believe me, you can see it!!! The stuff works!

Check around at your local automotove repair facilities or even Nissan to see if you can find somebody with this system. It restores vehicle performace, stops pinging, bla bla bla, my cusion has this setup at his Getty Station. Next spring with I hit the 60K mark I will definately be including the 3M cleaning system in my tune up!

 

njmaxseltd I think your talking about the products on this web page.

http://www.ontool.com/store/category...1/7002/7002/-1

Some of the products are very expensive but than again they are selling in bulk. It definately would be something you would want to do at a repair shop and not have to buy all of this stuff yourself. If anyone else has used this before, please post I am definately interested in the results of these products. I'm just wondering how useful it would be to me since I only have 57K miles.

 

Calling Nissan to get the Gasket sizes, and also to see if they can give me a break on the cleanng. They usually give a discount as my family brings them a bunch of business as well as they let my dad hang out there now that he is retired. lol

 

You can pick up the 3M throttle body cleaner from your local Napa, that is where I bought my bottle from.