Mercruiser 350 Low WOT and poor running w/video

[fishngolf]

Serial 0F230168

Is it a leakdown test for the valves? Any thoughts on the whine noise or the noise by the rear transmission?

Noticed the ECM wasn't attached to the mounting bracket properly. Only a single bolt rather then the four it should have had. Does the ecm pick up ground through the bolts or contact with the housing itself or is there a ground wire in the harness? Could that be my source for error code 42. Going to the hardware store tomorrow to get the right size bolts and mount it properly regardless.

 

[alldodge]

Thanks for S/N and should have noticed on first post, my bad. Yes fuel pressure should be 30 psi

Leak down is for valves and rings, it tells how well pressure is contained, mostly for valves

The ECM gets ground by wires and should be bolted tight also

I'm not hearing a whine

 

[fishngolf]

Bolted down the ECM tight. Makes sense it’s grounded by wires as there was no change. Interesting enough the boat will get up to 3800 rpm on the first pass prior to engine reaching temperature. Trying to find an adapter to test the fuel pressure as the mercruiser adapter is a standard Schroeder valve and my gauge doesn’t fit.

 

[fishngolf]

Tested the fuel pressure and was getting over 30 both at idle and when attempting to go WOT but only getting 3400-3600 rpm. Mechanic had me replace ASV anyways as he said it was partially restricted when he took a look originally. Unfortunately, no change. Could the coil be the problem?

 

[alldodge]

Did fuel pressure stay at or above 30 psi during WOT?

Don't see it being the coil, its running so the coil is ok. Would think more the ignition and module or wires before the coil

How much timing advance are you getting?

Edit: Are you sure the tach is accurate?

 

[fishngolf]

Did a tune up including new plugs, wires, ignition control module, cap, rotor. Unfortunately no change problem persists. I believe timing is being controlled by ecm. Mechanic wants me to check the exhaust baffles in the fiberglass "silent master" muffler. He's thinking it could be restricting exhaust and causing back pressure. Need to get new riser gaskets before taking a look as I cant get the hoses off without taking the risers off first.

 

[fishngolf]

Tach is correct. I also reconnected the perfect pass which also reads rpm to make sure. Tach and perfect pass both measuring approx 3600 rpm at wot. Took apart the exhaust and didn’t see any issues there. This boat has a fiberglass “silent rider” exhaust. Attached are a couple pictures of inside. Only has small holes on each outlet leading to the exhaust hoses which I find really hard to believe those are the only openings. Could the distributor be the issue? Here’s a video of the the play it has. Not sure if this is normal or not.

https://youtu.be/Yn0KhHL0g-8

 

[alldodge]

I don't see an issue with the distributor play

 

[fishngolf]

Checked compression again. Ran on muffs for a few minutes and not sure it got all the way up to temperature or not but getting the following 8-133, 7-120, 6-147, 5-147, 4-148, 3-135, 2-148, 1-128. Any ideas? Previously all were 145+ except #8 originally was low at 50.

 

[alldodge]

8-133, 7-120, 6-147, 5-147, 4-148, 3-135, 2-148, 1-128

I see the issue with low power and WOT, your compression is low
Leak down test would be next

 

[fishngolf]

Was advised to get it fully up to temp and retest compression with throttle depressed. This time numbers are good with everything 150ish except number 4 cylinder which was around 170. Idle seems a bit rough now.

 

[alldodge]

170 is to high, there is some liquid in there

 

[fishngolf]

Plug looked clean. Checked oil and no issue. No water when I pulled plug. What should my next step be?

 

[alldodge]

I think you just have a worn or tired motor. Compression is low and gets better has it warms up and one cylinder is to high

May also be over propped. What is the pitch of the prop?