Compression Test questions

[LeonV]

I'm guessing the valves at #2 and #6 are tight. A lash adjustment is definitely the next step.

[Jennys280Z]

I'm guessing the valves at #2 and #6 are tight. A lash adjustment is definitely the next step.

Next indeed, Leon. Thanks for your help!

I'm hoping that #1 and #5 are a bit too loose also. If I can get all six to agree on 140+ ft-lbs when cold, I'll be happy with that!

[Jennys280Z]

Photos of my spark plugs, for brevity and posterity.

IMG_2226 on the right is Cylinders 1, 2 and 3, respectively

IMG_2225 on the left is Cylinders 4, 5 and 6, respectively

[jonathanrussell]

Looks to me like your #3 is dead.....running on 5 cylinders. Maybe this explains some of your performance problems? By dead I mean not firing...or not injecting....no combustion.

Also, personally I don't see any smoking gun in your compression numbers.

Edited April 30, 2013 by jonathanrussell

[FastWoman]

That would be my take, too -- dead #3 (far right on the second photo, right?). Does the exhaust make a regular, consistant "chugging" sound?

Aside from #1, the plugs look pretty lean. I'm guessing the plugs aren't very old. But still, the insulators are a bit chalky. Your #1 looks about ideal. You might have some partially clogged injectors. And these machines do sometimes tend to drift lean.

[Zed Head]

#3 looks so dry and clean that the injector might not be opening at all. Might be worthwhile to put it back together, start it up, and remove the injector connectors one at a time. Each one should cause a drop in RPM when it's removed. If #3 is "dead" there won't be any change.

Then, if you find no change with #3, swap 3 and 4 or 3 and 2 and do the test again. See if the problem stays on injector #3 or follows connector #3. It will tell you if it's the injector or cylinder, versus just the injector connection.

If it stays with cylinder #3, and the spark plug has stayed dry, the odds are good that it's an injector problem. If the spark plug comes out wet, it's probably a spark problem.

[Jennys280Z]

Hi guys,

Cylinder #3 is alive and well. At the time the photos were taken, I had only 15-20 miles on those spark plugs!

Zed Head: Swapping connectors and following the problem is great stuff! I have a digital tach on my timing light which would make it a cinch.

I have very little experience with reading plugs and next to no frame of reference here, but it just seems plausible to me that one can still have a brand-new looking plug after only ~15 miles.

#2 and #6 looked WHITE to the naked eye even though they don't look too bad in the photo. After only 15 miles and looking that bad already, something has got to be messed up. What about valve lash? If the intake valve is tight, I'm presuming the valve is opening too much/long allowing too much air into the combustion chamber? If the exhaust lash on the same cylinder is too loose wouldn't this compound the lean problem even further and perhaps even more dramatically?

I know what running on five cylinders feels like when I once lost spark in my #1 cylinder due to a fouled plug (and BTW, #1 looks too wet to me, it looks like evidence that could explain #1 fouling in the past).

The motor purrs at a steady 900 RPM when warmed up. It sounded great the last I drove it. Revved it to 5000+ for the first time this year and it was smooth all the way up and back down again. It had an infrequent front or backfire issue on a previous drive but even that was gone completely the last time I drove it.

Fastwoman: performance-wise, I get an occasional hesitation when I first hit the throttle. This symptom was more pronounced when my AFM was a couple teeth leaner, so I suspect that after adjusting valves I'll move the AFM another tooth richer. Oh and drive the car harder than just a lot of wimpy idling and stop n' go so I don't foul my plugs again I've replaced my coolant temp sensor but I may well have some "lean drift" in the circuit there, I dunno. What the heck causes that anyway? ECU? A faulty CTS resistance still wouldn't explain the differences in compression and plug conditions between the cylinders.

BTW I checked vacuum a few days ago and I'm only getting 15.25-15.5 inches at the intake manifold. Pretty steady but it fluctuates about a quarter inch back and forth.

So we have the compression #s, photos of brand-newish spark plugs, manifold vacuum, and #3 alive and well.

I am hoping that massaging the valves will bring vacuum to 17.5" or more. My expectations are rose-colored. I think I'm going to get 136+psi out of all of my cylinders COLD after my valve adjustment. Am I crazy? lolz

[Jennys280Z]

Okay here's an update. I know I'm already beyond the scope of the subject line here and I hope that's okay with the webmaster(s).

I measured all the lashes and I'm pretty disheartened at the results. No smoking guns, and they're all WAY too tight. These were the biggest gauges I could fit in each:

Lash (inches)

Cyl 1

E .009

I .005

Cyl 2

I .005

E .008

Cyl 3

I .004

E .007

Cyl 4

E .007

I .004

Cyl 5

E .008

I .004

Cyl 6

I .004

E .007

I wonder if any of you guys have ever seen (cold) lash this tight before? The clearances are pretty consistent across cylinders, but 3/1000ths or 4/1000ths of an inch too tight?? Seriously? I'm not going to start dramatically loosening everything until I hear back from you guys because it just doesn't seem like a good idea.

Attached are photos of my timing sprocket with Cylinder 1 just past firing position (cam lobes just past 10:00 and 2:00) to check for timing chain stretch. I see the "location notch" through the "window" easily enough but I don't see the "oblong groove" to line it up with. There's supposed to be a little dash above the notch (according to img_2281). Can anyone advise what to look for here? Did I turn the motor a little bit too far perhaps? Is the groove obstructed by that bolt? Is there a different kind of marking on this one? Is it just dirty and hard to see? *shrugs*

Edited May 1, 2013 by Jennys280Z

[Zed Head]

You're looking in the right spot but it looks like you might have turned things too far. You should set the notch on your damper pulley to zero (where you look to set your ignition timing) to be at TDC. The cam lobes will be up if you're on the compression stroke.

Sounds like you're almost there. Back the pulley notch through zero, and down to about the first or second mark (5 or 10 degrees) on the timing marker. Then reverse rotation and move the pulley notch back slowly through 10 and 5 degrees to zero and stop. If you accidentally go past, try again. This will stretch the chain in the direction of rotation, as it would be in operation. The groove should be visible then, close to the V notch in your pictures.

[Jennys280Z]

You're looking in the right spot but it looks like you might have turned things too far. You should set the notch on your damper pulley to zero (where you look to set your ignition timing) to be at TDC. The cam lobes will be up if you're on the compression stroke.

Sounds like you're almost there. Back the pulley notch through zero, and down to about the first or second mark (5 or 10 degrees) on the timing marker. Then reverse rotation and move the pulley notch back slowly through 10 and 5 degrees to zero and stop. If you accidentally go past, try again. This will stretch the chain in the direction of rotation, as it would be in operation. The groove should be visible then, close to the V notch in your pictures.

Yep you're right Zed, the notch on the damper pulley is at 12 o'clock.

I might be able to see the groove shining a flashlight and looking through the window at an angle. If I am seeing that groove, it's really close to the v-notch when lined up. A lot closer than that drawing/diagram shows. When you say "back" the pulley notch, do you mean turn the motor backwards (counter-clockwise)? Also, I'm using a remote starter switch to turn the motor and even with the plugs in, it turns fast with even a blip of the trigger. I'm not going to get the precision I need to line it up that good, it'll be hit and miss, and most of all luck. So I don't want to keep turning it that way, I need to turn the motor by hand and slowly to get it right. What's the best/easiest way for me to do this? The bolt on the front of the camshaft?

[EuroDat]

Also, I'm using a remote starter switch to turn the motor and even with the plugs in, it turns fast with even a blip of the trigger. I'm not going to get the precision I need to line it up that good, it'll be hit and miss, and most of all luck. So I don't want to keep turning it that way, I need to turn the motor by hand and slowly to get it right. What's the best/easiest way for me to do this? The bolt on the front of the camshaft?

Its best to use a socket on the bolt in the crankshaft pulley. That way you will keep the chain under tension just like when the engine is turning the camshaft.

I cant remember what the size is, but it should be in the FSM.

My friends Z gained 20hp by adjusting the cam timing on a dyno test bank. A little can make a big difference in top end hp, but he had no problems down low.

Chas

[Zed Head]

Yes, I meant turn it backwards. I didn't know you were using a remote starter. Doubtful that you'll get it to stop on the spot with that. 12 o'clock is pretty good.

I think that the damper bolt is 27 mm. It's difficult to get to though, at least on my car, from the top.

Another way to do it is to put the transmission in 5th gear, then nudge the car forward or backward while watching the mark. Probably easiest with the plugs out. You can fine tune the movement by grabbing a tire and turning it. You might have to go forward and backward a few times to get it on the spot since it's easy to go too far.