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Ducati Monster Forum
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(Moderator:
Speeddog
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Disabling fuel injector for compression test
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Topic: Disabling fuel injector for compression test (Read 1931 times)
EEL
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Posts: 1167
Disabling fuel injector for compression test
«
on:
July 18, 2008, 10:53:16 AM »
So as part of my through 15k checkup, I want to do a quick compression test to make sure that both cylinders are holding the same amount of pressure. That being said, I was planning on just using the starter to pump up the compression. I plan on disconnecting the sparkplug on the cylinder that I'm not testing but how do I disable the injectors? Can I just turn off the fuel pump or is there residual pressure in the lines. I'm assume there wouldnt be since the bike has a return loop on the fuel.
Any thoughts? I may want to run multiple tests but I dont want to flood the motor while doing them. Also for consistency I want to run the compression at the same engine temperature so I dont want to run the bike inbetween tests.
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hypurone
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Re: Disabling fuel injector for compression test
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Reply #1 on:
July 18, 2008, 11:16:59 AM »
I would go for the fuse(s)...
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'07 S4RS "Testatretta" (In the FASTER color)
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Hedgehog
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Re: Disabling fuel injector for compression test
«
Reply #2 on:
July 18, 2008, 11:23:09 AM »
Quote from: EEL on July 18, 2008, 10:53:16 AM
I plan on disconnecting the sparkplug on the cylinder that I'm not testing
You mean removing the plug; not just disconnecting the high tension wire, right?
+1 on removing the fuel pump fuse
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EEL
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Re: Disabling fuel injector for compression test
«
Reply #3 on:
July 18, 2008, 11:53:17 AM »
For the cylinder i'm NOT testing, all I'm doing is disconnecting the cable on the plug. Is there a reason I should take the plug out? I want to obtain real life compression results as much as possible. Unloading the cylinder that I'm not testing makes the test less valid for a real life scenario. But if there is a reason I should I would be more receptive
«
Last Edit: July 18, 2008, 11:56:18 AM by EEL
»
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Hedgehog
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Re: Disabling fuel injector for compression test
«
Reply #4 on:
July 18, 2008, 12:02:20 PM »
Quote from: EEL on July 18, 2008, 11:53:17 AM
For the cylinder i'm NOT testing, all I'm doing is disconnecting the cable on the plug. Is there a reason I should take the plug out? I want to simulate real like compression as much as possible. Unloading the untested cylinder makes the test less valid for a real life scenario.
I don't think you're looking at this correctly. Ducatis are 90 degree L-twins. The pistons aren't in compression at the same angle from each other. One piston fires 450 degrees (I think) after the other, while that one fires 270 degrees from the first. As a result, with the starter, one gets a bigger "run" at the compression phase than the other, if you leave the plug in. Does it make a measurable difference? I'm not sure, but I'm betting it does; especially with the smaller batteries. If you pull both plugs, then you get just the affects of the one cylinder's compression stroke.
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printman
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Check out my a.....
Re: Disabling fuel injector for compression test
«
Reply #5 on:
July 19, 2008, 07:16:47 AM »
By leaving in the one plug that is not being tested, and no fuel is being released, then I would think that it would put excessive pressure on the starter to turn over correctly. By pulling both plugs the starter can turn over freely giving you independent readings on your compression gauge.
I don't know if leaving in other plug would hurt the results, I always pull all plugs, unplug spark and fuel
But these were in carb'd bikes not FI
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I'll update this later at a convenient time Thank you for tuning in.....
Howie
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Re: Disabling fuel injector for compression test
«
Reply #6 on:
July 19, 2008, 08:45:45 AM »
Certainly no reason to leave a plug in, no advantage.
Both plugs out, throttle open.
Crank the engine over with the pump fuse out first to relieve residual pressure.
«
Last Edit: July 19, 2008, 08:47:58 AM by howie
»
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brad black
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Re: Disabling fuel injector for compression test
«
Reply #7 on:
July 20, 2008, 04:03:45 AM »
i unhook the rotation sensor. the ecu will do nothing as it doesn't know the engine is turning, and also that way it's not trying to spark unplugged leads.
a comp test is just a test. it bears little relevance to what is actually happening when the engine is running, it just tells you if something is wrong at a speed slightly higher than normal cranking.
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Brad The Bike Boy
http://www.bikeboy.org
WTSDS
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Re: Disabling fuel injector for compression test
«
Reply #8 on:
July 20, 2008, 06:58:02 AM »
Doesn't matter if the fuel injection is on ( or carbs are full ), there's so little airflow during the test even with the throttle wide open, and a bit of fuel vapour won't hurt the instrument. Pull the fuse if you wish.
Put the plugs back in the HT lead caps and tie them to something metal, not a good idea to mess with the flow of the green smoke..........
A normal comp test is reassuring.
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2000 Monster Dark 900 ie Stock except for low Staintunes and a centrestand. 15:39 sprockets make for excellent highway gearing
EEL
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Re: Disabling fuel injector for compression test
«
Reply #9 on:
July 21, 2008, 01:12:25 PM »
You guys are making sense.. I'll pull both plugs and pull the fuel pump. I'll probably just run the bike with the pump disabled and then measure when everything cooled down.
Thanks for the help
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