UKKid35

Now I have my $10 Harbour Freight tool can someone suggest a site for me to find out how to use it, and what it will tell me.

Thanks!

GlenL

Search rennlist?

Idiots guide:

Warm up the car.

Remove all of the plugs.

Remove the fuel pump fuse.

Attach the tester to the holes, one by one.

At each hole, crank the engine and count to six, slowly.

Record the readings.

Look for consistency. The rings and valves fail unevely.

ViribusUnits

Rember unhook the coil, it's best not to load the thing up.

And also, rember to wedge the throtal open, other wise you'll get really low reading.

UKKid35

Am I right in thinking that the cranking speed will determine the readings, therefore I can compare different cylinders but the absolute figures won't mean too much?

GoRideSno

I'll add:
Do it w/ a fresh battery
Remove the Fuel Pump fuse
You may get a slightly lower reading from first cylinder tested to last because thee will be less oil on the cylinder walls for the last cylinder tested.
If you turn the motor 70-80 compression and exaust strokes (combined)before oyu start the test you mat get a more even reading from first to last.
HTH
Andy K

Garth S

Absolute consistency of method, cyl. to cyl. is the approach to give the best individual cyl. numbers, the goal of which is to compare the differential values - as in golf, the smaller the better. Motor to motor comparisons are less meaningful when differing gauges, operators, etc. are used.
BTW, perhaps not a bad idea to shut down the injectors along with the ignition.

Chris

I have the same $10 kit, beauty isn't it !!

As everyone else has mentioned but also pull connectors from the ignition module(s) at the front of the engine bay.

After my rebuild I was reading 160 on all cylinders, this is with new rings so one would expect (hope) this to increase.

Chris

Tony

< M. Python , Holy Grail voice over>


"Brother Maynard, bring me the instructions for the 928 compression check......"

"First shalt thou take out the Holy Compression tester. Then, shalt thou count to six. No more. No less. Six shalt be the number thou shalt count, and the number of the counting shall be Six. Four shalt thou not count, nor either count thou two, excepting that thou then proceed to Six . Seven is right out. Once the number six, being the sixth number, be reached, then one my read the gauge"


Sorry, i just got done watching disc 4, of what, 14, in my Python Box set. Several episodes per disc.

It was on my brain and i couldnt resist.
http://www.mwscomp.com/movies/grail/grail.htm

SharkSkin

155 ±5 is what I got on my low-compression 78... I sure hope yours improves!

Chris

Yeah, yeah, but with a $10 kit who knows what the accuracy of the guage is ... before the rebuild they were around 140-150.

Chris

GlenL

Gents,

Removing the fuel pump fuse is a good idea on fuel injected cars, except for true idiots.

Yea, verily brother Anthony. Six is the number to which thou shalt count.

European or African?

Yoiks and away!

SharkSkin

Just a thought here... why not save yourselves all of the trouble of disconnecting that stuff... get yourself a two-wire household extension cord or some 14 gauge speaker wire, 8-10 feet long, solder/crimp a momentary starter switch on one end and alligator clips on the other, and hook it to your starter. bring the switch up to the top where you can push it and watch the gauge. Saves you the trouble of disconnecting all that stuff. If you are super-paranoid about things, you could disconnect the starter solenoid wire so you don't feed power back into the system at all.

I learned that compression tests should be done this way(meaning you should have the gauge in your hand, and watch it closely), and that you crank until the pressure doesn't increase anymore but oscillates between the same two values on every compression stroke. Also, Andy's idea about cranking the engine for a bit sounds like a good plan. What I always do though is go back and check the first cylinder again when I'm done. If I get a significantly different reading I will sometimes go back and check them all again. Make sure the starter doesn't heat up too much while doing this though, as a hot starter will spin slower and affect the results.

ViribusUnits

Because pulling the fuses relays and connectors is as easyer than jacking the car up, and dealing with the starter.

Jim bailey - 928 International

it is not a bad idea to check 9 cylinders ....doing the first last , or is that last first ? That helps confirm that the the battery , starter etc can generate consistent readings by doing one cylinder twice , at the beginning and the end.

SharkSkin

Hmmm... on my Z, it's accessible from the top. On all of my mopars, there has been a point on the fenderwell where I could attach a switch(or use a screwdriver). On the shark, I haven't tried yet, but it seems that it could be reached from the side. Maybe not. Last time I pulled the starter I used ramps, but I think that if you just parked the car at the point where the driveway meets the street you could use the increased clearance to get under there and get the alligator clips in place.

Besides, what happens if you forget to disconnect one or more of those things, or pull the wrong fuse... you can get zapped, start a fire, or both...