Low Compression??

[fast400]

Decided to change the plugs on my newly bought TTA. I figured while I'm at it, I'll do a quick compression test. So I did it with a cold engine and I didn't hold the throttle WOT either nevertheless it shouldn't have been this low.... 90 psi on #1-#5 and 85 psi on #6!!!
The car was idling a bit crappy, so I did the IAC procedure, and it's ok now, and power/driving seem good.
Should I be concerned??
The prior owner posted on turbobuick a year ago something about a bad plug and the cat glowing...so my worry is leaking exhaust valves.

Also #6 Sparkplug was really wet. The other 5 looked good. I'm thinking it's a leaky injector. I'm going to replace all 6 injectors...from memory of my last TTA I used 30lb Tomco's which seemed to work really well. Are they still available?

 

[JSTTA]

That's low compression, is your gauge accurate?? Did you have it tight in the plug hole?
If you plan on doing any mods to the car, you might want to consider different injectors. I would recommend an alky kit with 50 lb injectors.
Is your fuel pump stock?? alot comes into play. list as much info on engine and mods as possible.

 

[WS6]

You gotta block that throttle plate open and roll it over through 3 or 4 compression stokes to get an accurate reading. write down the compression of each compression stroke per cylinder and the lowest cylinder should be within 70% of the highest (that is debatable too).

 

[fast400]

Will opening the throttle blade make that much difference though??
The car runs really good that's the odd thing...no oil burning blue smoke, no loss of oilDontKnow:

 

[V6TA-MI]

Yes, it makes the test acurate. You need to follow WS6's directions. you should see 145-150 psi. One two cars I checked 90k mi had 150 psi +/- 2
124k mi car had 145-150 psi. the first comp stroke will be in the 70-90 range.
HTH
Glenn

 

[fast400]

I'll redo with throttleblade wide open...it'll be a shocker if it raises my compression by 30psi....but I'll try it.

 

[WS6]

Here's a quick, generic google search for doing a compression test
http://www.turbotbird.com/techinfo/Compression_Test/Compression_Test.htm

Okay, but to add to it. if the first full compression stroke is low and builds up on the following strokes it may be sign of worn rings. And adding a little oil in that cylinder should show a marked,temporary increase in pressure.

If it doesn't build up pressure after oil is added to that cylinder you have some leakage in the valves.

Headgasket leakage will show low readings between 2 adjacent cylinders and adding oil improves neither.

I understand why locking open the throttle plate my not make sense but it is what is required and factory suggested cylinder pressures are stated as normal with the throttle plate locked open.

I suppose it does not allow normal filling of the cylinder on what is just cranking speed for 4 full cycles.

I'd keep a battery charger on it too while testing to maintain noraml cranking voltage for all cylinders.