Never done a cylinder compression test before, but I'll be replacing my valve covers soon and figure it would be a good time to do it (having some power issues, roughness, etc.). Did a search here and also checked the FSM, but didn't see a mention of using an extension (OHC extension) with the compression gauge. Is it trivial to thread the end of the hose into the cylinders AND tighten it enough to do the compression test, or is it suggested to use an extension due to the length of the spark plug tubes? I'd hate to tear everything apart only to find that I don't have all the necessary/recommended tools. While at the same time, I don't want to buy more crap I don't need . Thanks.

 

Yeah....it needs to be tight. I'd use the extension. First, of it just runs a little rough and misses some, try some solid copper "cheaper" plugs gapped down to .030. With the inherant problem of these crappy coilpacks the NGK's takes the load off. Don't be nervous about yanking the intake, its easy. No new gasket is required. Try the plugs first.

Also, pinch the PCV line off with your fingers while it is idleing. Make sure you can hear it "click" to make sure its working and your not driving around with a vacuum leak.

 

Thanks. I replaced the NGKs a year ago (20k miles ago), so I vaguely remember the process. Have only ever had one noticeable misfire problem which threw a code for cylinder 4. It corrected itself , so I ordered a new OEM coil to keep in the glove box and swapped the coils around from cylinders 2 and 4 to see if the problem follows the coil. Also, I have been neglecting a P0420 code thanks to some wonderful anti-foulers, so for now I'm suspecting my rear pre-cat may be causing the power problems. But since the car has 194k miles, a compression test is in order so I'll know whether to cut my losses now with the car. If some random cylinder shows up at 110 PSI, well then I might as well not bother with the other items on my to-do list . So are you suggesting that a copper plug with a narrower gap would help make up for a problem with the coil packs? Not sure I'm following...

 

I've never heard of gaping the copper spark plug other than OEM specs to fix a rough idle... So I would like to know where you got that idea lol.

As for the compression test. It's unnecessary to use an extension to get it tight. Hand tight should be just fine as long as the O ring is seated right. Make sure the engines hot because by the time you get everything off it could cool down and not give accurate results so try to work fast! So before you change the valve cover check compression asap.

I ran a dry compression test on my max and got cylinder # 2,3,5 at 155- 157psi, #4 at 147, and #1 at 175, #6 165. Wet compression got me an average of 220psi all around. Still runs like a champ.

Make sure you run a dry compression test first then a wet test. Drip like 2tsp of oil into each cylinder and then re test. Don't add oil to every cylinder at the same time because when you crank it most of the oil will spit out the spark plug tubes.

Brodie

 

Of course gapping the plug tighter helps the coils. I got that from years of Turbo, procharger vette builds, which is what I do...... I am here to help, I will post good tech advice from experience if you would like some help. Don't add any oil to your test. It gives false readings. It doesn't run with oil in the chamber, so don't test with it. Also, a low cylinder wont show as a miss, just low power. Power surging is usually a vac. leak through a PCV valve if fuel pressure is good. Check plug gaps, then vac. leak. If you compression test it, prop throttle blade open, and spin every cylinder roughly the same amount of times.

A copper plug with no coating and a smaller gap is easier to fire. That's why we don't run coated plugs on nitrous, boost applications. Frankly, other than lasting longer, they suck.

 

First off, yeah the plug gap is different for TURBO cars. Not on a farily stock N/A. You will just encounter more problems. So please tell me where you got that information for a maxima...

And obviously the engine doesnt run with teaspoons of oil in it but that's why they call it a dry and a wet compression test. If you get good readings with a wet compression test and poor dry test it means your rings are probably worn and you will be able to see if your valves are sealing good.

And funny how hes going to prop the throttle open with the entire manifold off.. Yeah you may claim to be tech savvy but I actually go to school for this. 6 hours a day. 5 days a week.

 

Lol....dude. Forgot on Max's the intake is off. Either way, you are full of bad information. I will bounce from this site soon if nobody wants help. You guys can get back to your lips and rims and Newb bashing. You don't even understand spark plugs...quit giving advice....and looking to UP somebody. My 14yr old son just finished his first Ls1 nitrous engine. You probably will never achieve that. Listen and learn.

 

Lmao okay go ahead OP and gap your spark plugs .014 under spec. That will surely fix these bag coils. And IM gaskets.. who needs to replace those This "Vette builder" clearly knows everything about maximas and all my information is farse.

 

 

Lol...MLS gaskets are reusable. probably goes against what you've been taught...Tight gaps FIX nothing, just helps diagnose. You're learning.

 

Okay guys, put your di*ks away. Why does the FSM say to depress the accelerator pedal fully to keep throttle valve wide open for the compression test if the IM is detached?

 

Don't really know....I don't think you can do it without removing the manifold. Maybe a generic procedure copied from another FSM kinda like my first thought.

 

Anyone else have any thoughts on this?