Mercruiser MPI Won’t Stay Running

[BradsBoat]

Just completed a total gasket job on perfectly good running engine with 300 hours on it - head gaskets included. New Delco 41-993 plugs, cap, rotor, CPS, and Cool Fuel pump. The engine starts and runs smooth for a few seconds, then stalls. By feathering the throttle, it’ll try to stay running, but it struggles and pops. Rechecked the distributer position which is pointing directly at #6 while at TDC, rechecked the firing order, and rechecked the valve rocker arms adjustments. The fuel pressure is 38-43psi. Vacuum is stable and in range. The Mercruiser/Rinda scan tool shows no codes. Tested the following using the Mercruiser/Rinda scan tool:

Ignition Coil

Injectors

IAC

All seem to be good since they all made noise as the scan tool cycled through. Also pulled the coil wire and watched it throw a strong spark. Put the old cap and rotor back on, and it still has the same issue. Added 15 gallons of fresh marine fuel to the approximately 12 gallons that were in the tank from last summer. Still, no change.

What am I missing?

NOTE: It’s a 2004 and the serial number is OM69XXXX

 

[Scott Danforth]

TDC is on cylinder #1, not cylinder number 6

fuel pressure is a bit low

what lead you to changing head gaskets on a perfectly good and well running motor?

 

[BradsBoat]

Thanks for the reply. It’s the #6 embossed on the distributor, the Mercruiser Service Manual #31 page 4C-15 says to align the rotor to there. The motor had rusted due to saltwater exposure. There was some rust at the interface between the head. Seemed logical to replace the head gaskets.

 

[alldodge]

Thanks for the reply. It’s the #6 embossed on the distributor, the Mercruiser Service Manual #31 page 4C-15 says to align the rotor to there. The motor had rusted due to saltwater exposure. There was some rust at the interface between the head. Seemed logical to replace the head gaskets.

It says to align the motor to point on distributor and number one is at TDC (mine is 4B-13, 4C is charging system)

 

[BradsBoat]

The picture is almost the same. I put the rotor right on the mark while at TDC.

 

[alldodge]

That is an index mark, it doesn't mean to align number 6 when its there, it has to be on number one when pointing to it

 

[BradsBoat]

Thanks again for the reply. The engine was at TDC and the rotor was aligned to the location in the picture which happens to have a #6 embossed on the distributor. Since the cap is off when doing this, the #1 cylinder location is on or about that position.

 

[alldodge]

The on or about can be the issue. The HVS is real touchy so far as position. May need to remove valve cover to watch valves, or use stop bolt

The exact positioning is done using these bulletins

View attachment Bul 2011 11R2 HVS clocking.pdf

View attachment Bul 2003-06 gmefi-nostart HVS.pdf

 

[BradsBoat]

This is helpful. Seems I should revisit TDC. I noticed that on page 2 of Bulletin 2003-06 it indicates “TDC(firing)”. Is that the same TDC that would result from removing the valve cover and watching the valves?

 

[alldodge]

It should be the same, the difference is if timing chain and or gear has any wear.

The circuit is made in other bulletin is so timing can be set "dead on" where it should be

 

[BradsBoat]

The 2011 bulletin describes creating a position indicator light and setting the harmonic balancer at the 15 degree mark then using the light to make the final adjustment. I’m not sure if mine has ECT, I know it doesn’t have a connector for a Camshaft Position Sensor (CPS), although there is a receptacle where a CPS connector would plug into the distributor/HVS. Overall this procedure seems much more precise than the the one in Bulletin #31. So even though I may or may not have an ECT engine, should I make the position indicator light and set the distributor/HVS with the harmonic balancer at 15 degrees past the timing mark molded into the plastic timing cover?

 

[alldodge]

Damper is moved to 15 then dizzy is rotated to light at that location (or that's how I read it).

Yes forgot about Merc didn't use the cam sensor like VP until later years. Some Merc HVS dizzy did have the CPS just was not used

 

[BradsBoat]

The 2011 Bulletin procedure landed the distributor precisely on the scribe marks I made before taking it out. No change in engine behavior. Even though bad timing describes the observed behavior, it seems there’s something else causing the issue.

 

[alldodge]

Will it continue to run if its given a bit more throttle?

 

[BradsBoat]

Not very well. If I oscillate the throttle I can keep it running.

 

[alldodge]

Fuel pressure stays 38-43 psi the whole time its running smooth or struggling
Vacuum stays steady the entire time
Firing order and timing is correct
Valves are 1 turn further from zero lash
Compression is good (at least 130)

Did I miss anything?

 

[BradsBoat]

Would a failed circulating pump possibly cause this behavior?

 

[BradsBoat]

Would a failed circulating pump cause this behavior?

 

[BradsBoat]

Would the circulating pump possibly cause this behavior?

 

[alldodge]

Would the circulating pump possibly cause this behavior?

If your talking about the engine water circulation pump, then no, has no effect

Its sounds to me like a fuel issue, and I would think injectors first off