Mercruiser 350 Low WOT and poor running w/video

[fishngolf]

Hi All,

Got a ‘94 ski boat with 5.7 350 EFI last fall. Had sat for 10 years but seller got it running and would idle and go up to 2500 rpm no problem. When I got it I Cleaned out the vst tank and got the rpm up to wot no problem in the driveway. Never got up to temperature and found that the thermostat was installed improperly and was getting water all the time. Straightened that out and now gets to temperature. Did a compression check and was getting good consistent numbers for all cylinders except #8 which was at 45. Was advised by mechanic to rev engine and see if it was a stuck ring. Ended up freeing that up and now have 150ish accross the board. Took it on the lake for a run and would get to about 3500 rpms and that’s it. I replaced the fuel/water filter already no change. Start of the year I filled the tank with fresh gas after winter. Maybe less then 5 gallons were in it previously. Ran through a lot of that and then cleaned vst and new filter again. Boat honestly seemed to run better when the thermostat was installed improperly and was getting cold water all the time. Had the E

Serial 0F230168

Sent the ECM out to OBD diagnostics and it checked out fine. He was able to pull the engine hours 724 and logged codes which he cleared. M43 ESC M42 EST M33MAP M21 TPS M14 Coolant. Said it was good on harness with injectors and all sensors and relays and IAc was good. He did mention a lot of dirt in J1 and J2.

I borrowed a scan tool and was getting error code 42 even after ECM was cleared. I also took the below video so you can see the timing jumping around as well as some of the other readings.

https://www.youtube.com/watch?v=nqMt...ature=youtu.be

Any help or suggestions would be great. Thank you

 

[Bt Doctur]

The timing will look like that until you place the engine in "base timing mode" Whats the fuel pressure?

 

[fishngolf]

I was just able to get my hands on the GM TBI fuel fitting so I can take a look. First thing I will be checking after de-winterizing. What should the readings be?

 

[alldodge]

Here is a good read about code 42

https://www.offshoreonly.com/forums/general-q/316782-need-help-code-42-v6.html

 

[fishngolf]

Thanks for the information. I went through all the grounds on everything and cleaned all the contacts. No difference. Also tried a different ignition control module and that changed the WOT down a couple hundred and idled a little differently. Not sure where to go from here.

 

[alldodge]

Are you setting timing in base timing mode?

Looked closer and you have a ski boat (you did say that in first post), showing fuel pressure should be 30 psi running if regular ski, if Black scorpion then 43 psi

Pull some plugs and see if they all look the same, nothing lean or rich

If your loosing one cylinder that would be enough to cause your issue.

 

[fishngolf]

Thanks guys. I took it to a local marine mechanic and got my first update today. He checked out the timing and found that it was not advancing. He’s taking a look at the distributor to see if that’s the problem. I had the e tested which checked out so not sure what it could be if not the distributor.

 

[fishngolf]

Meant to say ecm tested in previous post. He found the white wire connector to the ignition control module was bent and when he repaired and reconnected and checked the timing again it actually moved. Will be testing tomorrow in the water under load to see if we can break 3400 rpm. Thanks

 

[fishngolf]

Tested tonight and first pass I was able to get it past 3400 rpms. Second pass it capped out at 3400 again. I unplugged the knock sensor and it still capped out at 3400. Any suggestions? Thanks

 

[alldodge]

Compression is 150 across the board, timing is right.
Might need another prop, might be over propped

 

[fishngolf]

Another thing that’s interesting is when I’m pressing full throttle and at 3400 rpm if I pull back on throttle a little it actually seems to catch itself and increases rpm 100-200. Not sure why that would be.

 

[alldodge]

I would think this may be from the MAP sensor seeing the change in air pressure leans fuel (along with TPS) and when it runs lean some power can increase. If you have bungs in your exhaust could get air fuel ratio readings and could tell a lot about what is happening.

 

[fishngolf]

Hi Guys,

Mechanic had me replace the temperature sensor to see if that would change the low RPM issue. Unfortunately, no change.

Here's a video of a engine in water in neutral at idle. Seems to have a clicking noise back by the direct drive and a whine up by the TBI.

https://www.youtube.com/watch?v=uYVx_CmiBgc

Is this normal?
Any suggestions on next step?

 

[Rick Stephens]

I think your video is not public. Unavailable.

Just wondering how well you cleaned out the fuel tank. Sitting for 10 years, what was in there is no longer gasoline. Even a couple gallons left over will do a number on fresh gas poured in with.

 

[fishngolf]

Sorry about that. Video should be all set now. I had run out what was left. Went through a couple filters and had to clean VST twice.

https://youtu.be/uYVx_CmiBgc

 

[Rick Stephens]

Is there exhaust shutters to prevent water inversion?

 

[fishngolf]

There are rubber flaps on the rear and when I look down them I believe I can see the shutters just after the y pipe muffler. They seem to both be fully intact however the exhaust doesn't seem uniform between both sides. Here's a quick exhaust video on the fake a lake.

https://www.youtube.com/watch?v=CyGNNTBjslk

 

[fishngolf]

Was able to get the fuel guage adapter installed on the fuel line. What readings should I be getting at idle and WOT? This is a TBI. Thanks

 

[alldodge]

Looking at your vid the motor pressure should be 30psi
serial number would be best

 

[QBhoy]

I’d still be worried about that original low compression number. There is a chance you have a valve occasionaly not doing its job perhaps.