2004 5.0 Mercruiser down on power

[Kevin C]

Hello, I am working on a 2004 5.0 MerCruiser that is down on power. When I check for a down cylinder I throttle up to around 2000 rpm. I pull each plug wire one at a time. #1 and #7 there is no change in the rpm. I just performed tune up. Cap, rotor and plugs. I checked fire on both suspected cylinders and I have fire. Could this be a fuel issue? Any advice would be appreciated. Thank you. Kevin

 

[fastjeff]

Suggest you do a compression test on the motor.

Jeff

 

[bondo]

Could this be a fuel issue?

Ayuh,..... Pull the filter, 'n examine it's Contents for anything but clean fresh gasoline,.....

 

[Docksidemarineservices]

Compression test/Leak down test.

 

[Kevin C]

Thank you for the information. Will perform a leak down test.

 

[Kevin C]

I did a compression check and leak down test. both passed. While checking the timing I noticed the spark plug wires weren't in their proper place. I broke out the service manual to verify. Normal firing order for this engine is 1-8-4-3-6-5-7-2. This is the firing order of the engine I am working on 1-2-7-8-4-3-6-5. I don't know how this engine could be running. I removed all the plug wires and ran them the correct way. Engine would not run at all. Put them back the way they were. Engines runs but had a slight miss. I am wondering if this could be a counter rotation engine?