compression testing q's - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

phrozen · 06-24-2004, 03:40 PM

Sorry for this post and not searching but i have to go compression test a motor today and im wondering how id go about doing it. The thing is the harness is not hooked up to the car and there is no intake and exhaust piping but the manifolds are there. The motor has 75k on it i just want to make sure theres nothing wrong. Could someone explain to me how i would go about jumping the starter and if it would work without the harness or antyhing hooked up

DuffMan · 06-24-2004, 03:46 PM

The starter is controlled by the lower harness, not the main engine harness, so if you have the lower harness you should be good.

Otherwise you need to jump it by sending +12v to the little terminal that the plug plugs onto.

phrozen · 06-24-2004, 03:53 PM

so all i have to do is hook up the lower harness and i should be good? what about the injectors? im trying to run the motor till it gets hot so i can get an accurate reading.

kandyflip445 · 06-24-2004, 04:23 PM

I don't know if you can do that then if the ECU is unplugged.

TheTicTac · 06-24-2004, 04:44 PM

Like Duffman pointed out all you have to do it get the starter to work. You are just testing if the piston and it's rings can compress air in it's cylinder. If the numbers come out good then there is a high percentage that the motor is acceptable.

kandyflip445 · 06-24-2004, 09:18 PM

But with the engine cold the numbers may come out lower than normal. I don't see him getting it to run without it hooked to the ECU. But, yes you can get the test done without it.

*fliprayzin240sx* · 06-27-2004, 10:44 AM

Well cold will get you a general idea. May not be 100% accurate but its something. you doing a comp check on ur KA jason? Like everybodys saying, all you need is for the starter to kick off. Listen to the engine and let it spin 5 times and thats should give you some number. I cant remember whats the minimum you should be getting for the KA but if its your KA...itll probably be lower than its supposed to be *170 ish i think maybe higher* but if you get something lower and they are all within roughly 15psi of each other thats aites for now.

BlackS14 · 06-27-2004, 11:26 AM

I don't think the numbers will vary much when concerning whether it's hot or cold......doing it cold will give you a really good idea on what the number would be when hot...I did a compression test on my Ka (with a brand new tester mind you) recently (has 120,000+ miles) and got 180 across the board......those numbers work for me....haha

-Bill

06-24-2004, 03:40 PM	#1
phrozen Zilvia FREAK! Join Date: Apr 2003 Location: Bay Area Posts: 1,352 Trader Rating: (0) Feedback Score: 0 reviews	compression testing q's Sorry for this post and not searching but i have to go compression test a motor today and im wondering how id go about doing it. The thing is the harness is not hooked up to the car and there is no intake and exhaust piping but the manifolds are there. The motor has 75k on it i just want to make sure theres nothing wrong. Could someone explain to me how i would go about jumping the starter and if it would work without the harness or antyhing hooked up __________________ This box is 400x200: Please do not put your sig pic back if it exceeds this. -Moderation

06-24-2004, 03:53 PM	#3
phrozen Zilvia FREAK! Join Date: Apr 2003 Location: Bay Area Posts: 1,352 Trader Rating: (0) Feedback Score: 0 reviews	so all i have to do is hook up the lower harness and i should be good? what about the injectors? im trying to run the motor till it gets hot so i can get an accurate reading. __________________ This box is 400x200: Please do not put your sig pic back if it exceeds this. -Moderation

06-24-2004, 04:23 PM	#4
kandyflip445 Post Whore! Join Date: Sep 2002 Location: Arden, NC Age: 40 Posts: 4,460 Trader Rating: (1) Rides Gallery: kandyflip445 Feedback Score: 1 reviews	I don't know if you can do that then if the ECU is unplugged. __________________ My 240 vBgarage

06-24-2004, 04:44 PM	#5
TheTicTac Zilvia Junkie Join Date: May 2002 Location: CA Posts: 449 Trader Rating: (0) Feedback Score: 0 reviews	Like Duffman pointed out all you have to do it get the starter to work. You are just testing if the piston and it's rings can compress air in it's cylinder. If the numbers come out good then there is a high percentage that the motor is acceptable. __________________ GorgeousGarage L.oose S.ocks D.aisuke !

06-24-2004, 09:18 PM	#6
kandyflip445 Post Whore! Join Date: Sep 2002 Location: Arden, NC Age: 40 Posts: 4,460 Trader Rating: (1) Rides Gallery: kandyflip445 Feedback Score: 1 reviews	But with the engine cold the numbers may come out lower than normal. I don't see him getting it to run without it hooked to the ECU. But, yes you can get the test done without it. __________________ My 240 vBgarage

06-24-2004, 03:46 PM	#2
DuffMan Post Whore! Join Date: Oct 2001 Location: in a cardboard box Posts: 2,517 Trader Rating: (0) Feedback Score: 0 reviews	The starter is controlled by the lower harness, not the main engine harness, so if you have the lower harness you should be good. Otherwise you need to jump it by sending +12v to the little terminal that the plug plugs onto.

06-27-2004, 10:44 AM	#7
fliprayzin240sx Man w/ CTSV & a Car Seat Join Date: Aug 2002 Location: Tampa Posts: 17,998 Trader Rating: (19) Rides Gallery: fliprayzin240sx Feedback Score: 19 reviews	Well cold will get you a general idea. May not be 100% accurate but its something. you doing a comp check on ur KA jason? Like everybodys saying, all you need is for the starter to kick off. Listen to the engine and let it spin 5 times and thats should give you some number. I cant remember whats the minimum you should be getting for the KA but if its your KA...itll probably be lower than its supposed to be 170 ish i think maybe higher but if you get something lower and they are all within roughly 15psi of each other thats aites for now. __________________ If you think Zilvia has too many assholes... CLICK HERE!!!

06-27-2004, 11:26 AM	#8
BlackS14 Zilvia Junkie Join Date: Mar 2002 Location: Palm Bay, FL Age: 45 Posts: 384 Trader Rating: (0) Feedback Score: 0 reviews	I don't think the numbers will vary much when concerning whether it's hot or cold......doing it cold will give you a really good idea on what the number would be when hot...I did a compression test on my Ka (with a brand new tester mind you) recently (has 120,000+ miles) and got 180 across the board......those numbers work for me....haha -Bill __________________ Once you go black you...well...you know.....lol!!!!