Compression check - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Gregs71 · 01-27-2008, 05:02 PM

I have never done a compression check on a fuel injected motor. I have a 1987 chevy 4x4 with the TBI. Do I just disconnect the coil from the dist., and start checking the compression???

I have heard that the coil can build up a high amount of voltage and cause damage to electrical parts. Is this true??? Do I have to ground the coil??

How do you guys complete a compression check?

Thanks,

Greg

ChevyTech · 01-27-2008, 09:56 PM

If you unplug the wires from the distributor module (not the plug wires) it will make it so there is no spark and it will also stop fuel from being injected because the ECM needs to receive a distributor reference pulse from the distributor module to trigger the injectors.

You could also just unplug the “primary” wires from the coil, which are the little wires, not the big one. Then you could also unplug the injectors so no fuel is injected.

As the vehicle gets older the plastic connectors get brittle. Use care when disconnecting whatever you decide to unplug.

01-27-2008, 05:02 PM	#1
Gregs71 Registered User Join Date: Nov 2006 Location: Amador County, Ca. Posts: 229	Compression check I have never done a compression check on a fuel injected motor. I have a 1987 chevy 4x4 with the TBI. Do I just disconnect the coil from the dist., and start checking the compression??? I have heard that the coil can build up a high amount of voltage and cause damage to electrical parts. Is this true??? Do I have to ground the coil?? How do you guys complete a compression check? Thanks, Greg

01-27-2008, 09:56 PM	#2
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Compression check If you unplug the wires from the distributor module (not the plug wires) it will make it so there is no spark and it will also stop fuel from being injected because the ECM needs to receive a distributor reference pulse from the distributor module to trigger the injectors. You could also just unplug the “primary” wires from the coil, which are the little wires, not the big one. Then you could also unplug the injectors so no fuel is injected. As the vehicle gets older the plastic connectors get brittle. Use care when disconnecting whatever you decide to unplug.



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