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agent provocateur
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Discussion Starter · #1 ·
Compression Testing made a little easier and simpler...worth the read I think if you want to save yourself some time and work....that may not be needed in the first place.




I discovered this interesting little something with my fuel injected car I have, and interestingly enough the same thing I found also seems to hold true for the GL1800...well at least mine which is a 2010. I am sure it holds true with most, if not all of the 1800's.

This does NOT apply to any one to the bikes that have a Carb systems like the GL1000, 1200, 1500, so on and so on...

I bring this to your attention in order to save you a pile of un-needed work from having to be done over a simple thing such as a cylinder compression test. The Honda service manual states to remove the seat and to ( un-plug ) the gray plug that runs the fuel pump. This is in order so that the fuel injectors will not pump fuel into the cylinder while you do the compression testing.

However I have discovered one interesting thing that makes this step useless and just creates more work for you in the end. As the manual states...for a compression check, heat up the engine, remove seat and un-plug fuel pump wire, remover all spark plugs and then test each cylinder one by one, hold throttle FULLY open while crank the engine to read the pressure. Sounds simple enough....right?

However what I found is that you do NOT need to disconnect the fuel pump, in fact you do not have to take the seat off or any of that. What I found is that when you hold the throttle FULLY open right to the very end...it DISABLES the fuel injectors from firing gas in...!!!

Think I am BS'ing you...try it for your self. Try to start the engine...warm or cold...with the gas FULLY opened right to the very end. It will NOT start....! It seem the TPS ( throttle position sensor ) when it see's a fully open setting, will disable the injectors from opening and pumping fuel in. Try it for yourself and see if I am right or wrong...try to start it with a full open throttle...and you let me know if it started or.....not.

This by the way I have confirmed it with the sniff test...so I hear you ask what is the sniff test...? While doing the compression test, I DID NOT unplug the fuel pump at all. With the throttle wide open, and cranking I could NOT smell any hint of gas what so ever. However when I let go and let the throttle return to its idle position and I cranked it...you bet I could small raw un-burnt gas very fast.

So there you are...why do work that's really not needed. If there is any real logical reason for un-plugging the fuel pump...I would love to hear it, as it seem to be a step that's not needed when it seems the TPS automatically disablies the fuel injectors from firing in the first place.

 

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So there you are...why do work that's really not needed. If there is any real logical reason for un-plugging the fuel pump...I would love to hear it, as it seem to be a step that's not needed when it seems the TPS automatically disablies the fuel injectors from firing in the first place.
Manufacturers can't rely on people knowing how to read and follow basic instructions.

I've tried to tell people over the years to use a remote starter with the key off. Never a chance of accidental fuel or spark. On the 1000-1200, it's easy to access the solenoid. I can't speak to the 1500-1800.
Sparks and fuel don't mix.
 

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agent provocateur
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Discussion Starter · #3 ·
I know that is a great idea as that way you do not have the head light on as well to drag the battery down on top of all the cranking. Not sure myself on how easy it would be to get to the starter relay on the 1800's, but if I would be doing this for a living then I would find out and set up some sort of PLUG & PLAY thing so that I could do this. For me this bike is new, I bought it new and put like 48,000 Km's on it...and well wanted to see how the engine was doing when I did the test.
 

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That is good to know, I just pulled the FI fuse. On the headlight I turn the key off between cylinders and then hold the start button while turning it back on so the headlight never comes on.
 

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The throttle needs to be held open so that there is no restriction on intake to give false readings when doing a compression test.
 
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