6.2L MPI Horizon MIE: New Long Block. Runs rough above 2000 RPM Under Load

[Greg_E]

I had a 383 long block built over the winter by a reputable shop. The engine ran on the dyno for about an hour with a carburetor and ran great. The MPI intake manifold and TB was then installed, and my distributor set to #1 with #1 cylinder tdc. by the engine builder. I completed the assembly and it started right up and ran great at the dock.
I wanted to verify that the engine was properly timed, but found that a 2007 with the ECM 555 had no procedure to adjust/ check the timing, other than put it on #1, and the ECM will adjust to the 8* BTDC spec.
I have the Rinda Diacom software and at idle the timing seems to bounce around but as the RPMs increase it settles out.. When I took it out, everything looked fine on the gauges and Diacom, data log. When I reached about 2000 RPMs it ran very rough and at 2200 it sounded like like something could be damaged so I backed off and it ran fine. The noise seemed to be coming from the engine compartment, but it's hard to tell with the engine hatch down. I replayed the log file and none of the listed parameters looked out of the ordinary as far as I could tell and there were no fault codes set. Back at the dock I took it up to 2500 RPM's in neutral and it ran perfectly with no load.

I also installed a line cutter on the shaft , dripless shaft seal and realigned the engine to trans coupling to .003" before launch, so I need to verify nothing came loose, but I don't think that's it.

This was a new boat for me last year so I am not very familiar with Mercruiser inboards. I always had outboards. I'm not sure where to go from here.

Any help is greatly appreciated.

 

[Bondo]

The noise seemed to be coming from the engine compartment, but it's hard to tell with the engine hatch down.

Ayuh,..... Check the Contents of the fuel filter for anything, but clean fresh gasoline,......

This motor has a knock-sensor, don't it,..??

I'd take the hatch, Off, if necessary,.....

 

[alldodge]

Assuming HVS distributor, and there is no timing adjustment. Is the cap and rotor is new?

Where the injectors cleaned and flow tested?

Is the fuel pressure at 43 psi and does it stay close to that as rpms increase?

 

[Greg_E]

Ayuh,..... Check the Contents of the fuel filter for anything, but clean fresh gasoline,......

This motor has a knock-sensor, don't it,..??

I'd take the hatch, Off, if necessary,.....

Thanks for the reply.
The filters and Cool Fuel 3 module and fuel lines are brand new. I can swap the port engine to run off the starboard tank next time I'm at the boat. I have not had any water in the fuel last season and the filters had very little dirt in them, but who knows what can happen over the winter. I'll check.
Yes there are two knock sensors but the ECM did not log any faults, Also when I replayed the Diacom log file the advance was about 24* BTDC @ 2200RPMs. I don't know if that offers any clues.
To run with the main hatch open I need to make a brace to support it. I don't trust a few screws holding the two actuators in place to hold that hatch up while running. I'll do that next time down.
Also, all the fuel injectors were removed and sent out to be professionally cleaned and tested, fuel rail flushed, and new fuel line from cool fuel to fuel rail installed when the engine was rebuilt.

 

[Greg_E]

Assuming HVS distributor, and there is no timing adjustment. Is the cap and rotor is new?

Where the injectors cleaned and flow tested?

Is the fuel pressure at 43 psi and does it stay close to that as rpms increase?

Yes it the HVS distributor. The cap and rotor look like they were changed fairly recently so I cleaned the contacts and put them back in. I do carry spares if needed.

Injectors were all cleaned and flow tested.

I don't have a fuel pressure tester but will probably invest in one. It is one important parameter that can't be displayed by the Diacom diagnostic software.

Fuel filters were still like new and no water found.

I Installed a timing tape on the harmonic balancer and hooked up the timing light and at about 1000 RPMs it was around 0* I marked the distributor and base so I could put it back to the same position if needed. I turned the distributor until I got 6* BTDC and took it for a test run. It ran good up to 4000 RPM's and for now that is as high as I wanted to take it.. I guess the timing was out far enough that the ECM could not adjust. When I reviewed the Diacom log file back at the dock I showed 8* BTDC @ 1200 RPMs, while underway. Advance looks like it maxes out at 28* BTDC I was expecting 30* BTDC max. Am I OK with that?

 

[alldodge]

HVS uses the CPS and timing using tape is not the way to go

The distributor caps are known to give problems and look great, just no way of knowing if they are an issue or not. Also many keep a spare on hand because they can start failing without warning

 

[Greg_E]

HVS uses the CPS and timing using tape is not the way to go

The distributor caps are known to give problems and look great, just no way of knowing if they are an issue or not. Also many keep a spare on hand because they can start failing without warning

i know that is not the proper way to set the timing but I needed some way to check if the distributor was indexed correctly.
The engine ran on the dyno with a different distributor, carburetor, intake manifold. The shop was not set up to run the engine with the MPI manifold.

I didn't have to move the distributor very much and it seems to be running OK now.

If there is a better way to to troubleshoot this please explain. This is all new to me. I had to search thru three different Mercruiser repair manuals just to find how the timing signal is controlled.

Thanks for the help.

 

[kenny nunez]

I was having a similar problem with the 383 MPI in my Donzi. After using a Rinda and doing everything you have also done It came down to the spark plugs. I replaced them with the most expensive ones for that engine and the firs time I punched the throttle it went to 5k @ 70. The marine scanners are not as sensitive as the automotive systems are at this time and in my case could not detect a plug misfire.

 

[alldodge]

With diacom you can make a recording from start, idle, run, wot and back to stop
Can vary the throttle under different loads and should be able to see what is happeneing