Or, what am I doing wrong? I grabbed a compression tester at PepBoys loaner tool desk and attempted to check the compression on the 944 tonight along with changing the plugs. All plugs out, fuel and ignition disabled, throttle held open, engine cold (I don't want to pull plugs from a warm Al head). Crank motor about 8 seconds per hole. The tester is "OEM" brand and has a rubber hose with a 2-sized threaded and o-ringed end, along with a threaded longer adapter that screwed onto the hose end. No seal on the longer adapter. I tried it both with and without the adapter. Cyl 1 read about 10psi, the remainder read around 30psi. Huh? What am I doing wrong?
The car starts fine and runs well. It's a little gutless off boost but once the boost hits it goes just fine. The old plugs were gapped a bit wide and were covered in black soot with some oil on the threads, which fits with my nose telling me the car is running pig rich. She idles much better with the new plugs and doesn't hesitate off idle anymore.
Doing it cold can give you pretty low numbers but that's obviously very far off!
Can you have someone else crank the car while you check for any obvious leaks at the gauge?
Considering it's a loaner gauge, I'd assume it's been dropped (repeatedly?) and grab a different one.
pigeon wrote:
All plugs out, fuel and ignition disabled, throttle held open, engine cold. Crank motor about 8 seconds per hole. Cyl 1 read about 10psi, the remainder read around 30psi. Huh? What am I doing wrong?
I thought you pull and test one cyl at a time? But maybe that won't have any effect.
Why is the throttle held open?
Aside from that, if the car runs it has more than 10 psi, the gage is leaking somewhere. Recheck the set up.
Dan
914Driver wrote:
Why is the throttle held open?
You always hold the throttle open when doing a compression test.
Some motors are so (air) tight, you'll get a much lower reading if the throttle plate is closed.
sounds like its bleeding off a lot of pressure, like if the rubber ring round the threads aren't seating on the cyl head making a nice tight seal. or with the adapter extension between it and the hose end.
