Hi guys,

I need to do a compression test on my CRX, but I need to know which fuse to pull so that the injectors dont spray. Do I just pull the ALT/SOLENOID/VALVE fuse? I dont see a fuse specifically marked for the fuel system.

 

You will want to pull the 15amp ECU fuse.

 

whoa, quick reply!

thanks, I'll pull the ECU fuse that's under the hood.

 

or u can just disconet the plug at the distro, its easier imo

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nerologic &raquo;</TD></TR><TR><TD CLASS="quote">or u can just disconet the plug at the distro, its easier imo</TD></TR></TABLE>

 

or just unplug the clip that goes to the fuel pump under the rear seat... thats what i do
-Josh

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nerologic &raquo;</TD></TR><TR><TD CLASS="quote">or u can just disconet the plug at the distro, its easier imo</TD></TR></TABLE> Which still allows for fuel to enter the cylinder <TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Crimson_Tide &raquo;</TD></TR><TR><TD CLASS="quote">or just unplug the clip that goes to the fuel pump under the rear seat... thats what i do
-Josh</TD></TR></TABLE> Some of us have interiors

 

i have full interior also... lol but i can just reach under the rear seat and the plug isnt too far back... thats what i did when i did my compression test
-Josh

 

y crawl into the back seat of ur car when its as simple as pulling a fuse (ecu) from under the hood

 

Dont you want fuel and air mixture to be in the cylinder while doing a compression test? I just disable the ignition in my case with my rex i just disconnect the distributor.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 91 HONDAsaurus rex &raquo;</TD></TR><TR><TD CLASS="quote">Dont you want fuel and air mixture to be in the cylinder while doing a compression test? I just disable the ignition in my case with my rex i just disconnect the distributor.</TD></TR></TABLE>

why? that would just dump loads of fuel into your cylinders with nothing to burn it off

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 91 HONDAsaurus rex &raquo;</TD></TR><TR><TD CLASS="quote">Dont you want fuel and air mixture to be in the cylinder while doing a compression test? I just disable the ignition in my case with my rex i just disconnect the distributor.</TD></TR></TABLE>

No, because when you do a compression test you have to remove the spark plug and place the tester in its place. The plug wires aren't going to be hooked up to the sparkplugs anyways, and the plug aren't even supposed to be in the motor, so what difference does it make if your dizzy is unhooked?

Do yourself a favor, and next time you do a compression test disable your fuel system. That is the proper way to do it, other wise like tdocrx said you'll dump a lot of fuel into your cylinders with nothing to burn it off.

 

Generally when I do it on V-8 cars/trucks i dont take out all the wires at once when doing a compression test. I just asked my boss and he said it dosnt matter when you do this because when you release the pressure from the cylinder after a compression test it releases most of the gas. Its not like your dumping a lot of gas in the cylinders and you need the air/gas mixture to get the right compression #s. I dont really care what you guys say and you can do it your way. just my 2 cents anyways.

 

do what what you want it not going to change the test its ten times esaier when you unplug the dizzy. Ive never had a problem with dumping loads of fuel into the cylinders.plug the dizzy up and the car starts right up. what ever your beer is just drink up.

 

I'm just saying that safe work practices, like unsafe work practices are habit forming. When i'm doing somrthing like adjusting my timing belt I still read the instructions out of the FSM even though I have all the steps memorized. I suppose I'm this way because part of my job relies heavily on reading out of instruction manuals, and following the instructions to the letter. And as a result I am also a very safety conscious person.

I would think that if you work as a mechanic then it would be in you and your shops best interest to follow the FSM to the letter. If you dont, then you leave yourself open to possible legal action.

but whatever, do what you guys wanna do

 

[QUOTE=BlueShadow]I'm just saying that safe work practices, like unsafe work practices are habit forming. When i'm doing somrthing like adjusting my timing belt I still read the instructions out of the FSM even though I have all the steps memorized. I suppose I'm this way because part of my job relies heavily on reading out of instruction manuals, and following the instructions to the letter. And as a result I am also a very safety conscious person.

i dont see how you can claim that by unplugging the dizzy to do a comp test is a unsafe work practice. Ive even seen the dealership's unplug the dizzy. we can go on and on about who's right and wrong lets agree to disagree. I still look at the manuals thats a very good practice that everyone should use . hey everybody still gets brain farts every now and then

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dr_latino999 &raquo;</TD></TR><TR><TD CLASS="quote"> Which still allows for fuel to enter the cylinder</TD></TR></TABLE>

Nah, it will cut fuel and spark... the ECU has no input as to when to fire the injectors... so no fuel.

 

why dont you just use a piece of wire with a momentary switch and connect it to the battery from the starter input? that way you dont have to run back to crank it from inside. you will have no fuel or spark to worry about.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Crimson_Tide &raquo;</TD></TR><TR><TD CLASS="quote">or just unplug the clip that goes to the fuel pump under the rear seat... thats what i do
-Josh</TD></TR></TABLE>
Dont do that. The ignition system needs to be disabled too, or you run the risk of damaging your coil.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bunger &raquo;</TD></TR><TR><TD CLASS="quote">

Nah, it will cut fuel and spark... the ECU has no input as to when to fire the injectors... so no fuel.</TD></TR></TABLE>

Nope...fuel will still go into the system

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nerologic &raquo;</TD></TR><TR><TD CLASS="quote">Nope...fuel will still go into the system </TD></TR></TABLE>
With the distributor wires disconnected, The ECU wont get a signal from those sensors so it wont energize the injectors.

 

Just wanted to add that if you don't disable the fuel system, you could very well get yourself hurt.

I'll explain... since you're doing a compression test i would assume:
1. Something is wrong with the engine (unless doing baseline... but why? that's in book).
2. You don't know what's wrong with the engine (the whole reason for compression test is to figure out what is wrong).
3. You're doing it yourself harry-homeowner style.
4. You're doing the test with engine at N.O.T. or otherwise hot.

So ya get a little hotspot in the combustion chamber (could be due to bad valve, bad rings, bad cylinder, bad piston, or anything else that would warrant a compression test, or even just normal engine design). Then while you're turning the engine over Blamo inside the chamber, and your engine is running (like a diesel) with flames, gas, smoke and everything else blowing out of the spark plug holes (so if you're using a remote switch to test don't lean over the engine for a look-see while doing it).

Just thought i'd share one of my past screw ups with ya... i learned the hard way, now you don't have to.

g'day.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">
With the distributor wires disconnected, The ECU wont get a signal from those sensors so it wont energize the injectors. </TD></TR></TABLE>

i was talking about the distro plug, not the spark plug wires...

 

unplug the dizzy...BOTH plugs

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nerologic &raquo;</TD></TR><TR><TD CLASS="quote">i was talking about the distro plug, not the spark plug wires...</TD></TR></TABLE>
So was I.