2004 4.3 MPI surging once warmed up. I don't know what else to try.

[SeaRayJosh]

Hi All, new to this forum, I have been scouring the internet for an answer to my unusual motor issue. Maybe someone here can shed some light on this.
Here is what is going on. I have a 2004 Sea Ray w twin 4.3 Mercruiser mpi’s. Engine serial # is 0M662545. Problem is the engine is surging. It’s a new reman. long block. Ran 3 hours perfectly first run during break-in. The next time I went out to start it the engine started surging once it warmed up. I have made 5 trips out to fix this now and unfortunately the boat is 1 1/2 hours away. Even after everything I have tried, each trip is same thing, runs fine until it gets warmed up then the surging starts back up. With more throttle it occasionally backfires as well. Once the engine manifests the issue, it still idles ok and starts right up. Fuel pressure is holding steady at about 38 - 40 psi. Last trip out, it ran perfectly, until it hit 156 degrees, then started surging/running poorly. I have run a compression test and all cylinders are testing between 160-165 PSI. I have also vigorously shaken the wire harness while running poorly to see if any difference. None noted.

Here is what I have replaced so far:

Fuel pump - New
Fuel pressure regulator -New
Plugs – New
Wires (from other motor)
Cap (from other motor)
Rotor (from other motor)
Distributor module (from other motor)
Coil (from other motor)
Map sensor (from other motor)
Tps sensor (from other motor)
Fuel filter - New
Ecm (from other motor)
Tested both switches at the shifter
Knock sensor (from other motor)
Both temp sensors (from other motor)
Injectors (from other motor)
Fuel rail (from other motor)
Iac and muffler (from other motor)

I have run out of things to try or parts to swap with the other motor. Any advice would be very welcome!!

Thanks,
Josh

 

[SeaRayJosh]

Another day on the boat without resolution. This time I swapped alternators and crank sensors. Ohmed out all the sensor plugs back to the ecm plugs. Bypassed the anti-siphon solenoid. I can’t come up with anything else to try.

Any advice or suggestions would be appreciated.

 

[Fun Times]

2004 Sea Ray w twin 4.3 Mercruiser mpi’s. Engine serial # is 0M662545. It’s a new reman. long block.

What specifics can you mention regarding the new block of what the inside components may have come with vs the older block.

Only curious to ask because of the following info,
Table 3: New ECM Required to use the New 58X 4.3 L V6 Longblock
Order the proper ECM when replacing engine serial numbers 0M324698 to 1A063239. Match the drive type and cooling system to determine the proper calibration...

NEW PART NUMBERS FOR V6 LONGBLOCKS | Service Bulletin | Crowley Marine

08-OCT-2007 - Manufacturer Service Bulletin: NEW PART NUMBERS FOR V6 LONGBLOCKS

www.crowleymarine.com

Your serial number is outside of this range so use the following linked info below as more of an example guide 'but since your HVS distributor assembly was disturbed it may not be phased in correctly as you don't set it with a timing light and it can be challenging to get it just right and set down correctly if you don't do it everyday/not paying attention... That or sometimes the cap bolt hold down thread holes ears tend to crack, etc. easily causing misalignments, miss fires, etc..

How are the plug wires on that side look? See or hear and sparking noises, changes in tone when shaking them? < Running the engine in the dark helps sometimes to looking for a light show.
Make sure all the black ground wires are nicely connected tight and not pinched or chafed of damage running to the studs of the rear of the engine.

See step 2 mostly but for giggles, you could try step 3,

V6 AND V8 GMEFI WITH NO START, ENGINE MISS-FIRE OR ENGINE SHUT-OFF CONDITIONS | Service Bulletin | Crowley Marine

25-JUN-2003 - Manufacturer Service Bulletin: V6 AND V8 GMEFI WITH NO START, ENGINE MISS-FIRE OR ENGINE SHUT-OFF CONDITIONS

www.crowleymarine.com

 

[SeaRayJosh]

Hi Fun Times, thanks for the info. The replacement motor came from ATK. This is the second longblock I have ordered from them. first one last year. For the first motor replacement, I swapped out all existing electronics including the ECM and did not have any issues. I would expect the same on this engine as well. While back out this weekend trying to fix, I did swap distributors (again) just to be sure. The distributor is new, and It was set correctly, following procedure, #1 at TDC compression stroke, rotor lined up to #6 as indicated on the distributor. New plugs and wires, and then swapped wires with the other motor. I spent a while following the wiring harness around, verifying grounds, and no pinched or nicks anywhere.

I will look into the bulletins you sent, those are both great information. I will post my next attempts.

 

[SeaRayJosh]

Finally! Problem fixed.

After replacing or swapping every single sensor on the motor including the ecm itself, tried that twice by the way to no avail, I hired a local guy who came out with a heat gun, rpm gun, and timing light. Unfortunately he didn’t have a computer. After his tests he said the engine wasn’t overheating, but timing was wildly all over the place. I had told him I was suspicious of something temperature related as it wouldn’t act up until motor came to op temp for the first time, but I had swapped sensors already.

He said he didn’t know what to do, I should get it hooked up to a computer. Well since merc has their own property ecm’s, you can’t easily get a computer. There is only one shop in my area and they are super friendly, but also very backed up and I really want to striper fish with the kids this fall/winter. So I found a guy on eBay that rents one out. You basically get a very expensive cable. The software is free so you put it on your own laptop. You have to specify what adapter you need. It was $45 to rent for a week. Worth its weight in gold. Software reported that the engine was experiencing an over heat condition, even though the dash temperature never went over 158. It was a brief enough reading that the dash didn’t register it, but the computer did and changed the timing from +8 degrees to -14 degrees. Then in would quickly decide the temperature was fine and go back to a forward state. Hence the surging. That led me suspect an issue with the seawater in contact with the sensor. I pulled the thermostat housing and found some scaling but not terrible. I had replaced the gasket, pvc sleeve , and thermostat on the motor setup in the winter and cleaned out the housing then. I scraped out all of the scaling again, and put the housing back on and problem fixed!!! I believe some scaling in the housing was causing an air pocket around the sensor. That’s my best guess anyway. Did a 1 hour sea trial to confirm. I have been working on motorcycles, cars, and boats for 40 years. Based on the symptoms I was having I would have never even considered that as a possible suspect. My advice to anyone having issues that are hard to troubleshoot: either rent, buy the cable /software, or take it to a shop.

 

[sandkicker]

Thank you for reporting back the solution to your problem. Much appreciated... Far too many folks never report back the final results.

 

[AllDodge]

I believe some scaling in the housing was causing an air pocket around the sensor. That’s my best guess anyway.

Thanks for reporting back

Merc uses a thermostat gasket which has brass rivets in it. The rivets are there to ensure there is good electrical contact with the sensors. If you used a standard gasket then this could be the issue
Gasket

 

[kghost]

Thanks for reporting back

Merc uses a thermostat gasket which has brass rivets in it. The rivets are there to ensure there is good electrical contact with the sensors. If you used a standard gasket then this could be the issue
Gasket

Careful suggesting this. Not all thermostat housings have sender or switch in them. That gasket is Only used if sender and switch is threaded into the thermostat housing. If installed in manifold or other location a standard gasket can be used ( non brass rivits)

 

[AllDodge]

Be careful, used his serial number

 

[SeaRayJosh]

Took the boat out this past weekend to finally put the remaining break-in hours on the motor after a very long process of fixing. Got out of the creek, started the stbd motor up and problem back. Unbelievable. Pulled back to the dock, and switched the thermostat housing with the port motor. Went back out and same issue. Started playing around with the throttle trying to get more of a specific identifier. I could stay in gear up to around 700 rpm, anything over started the surging, which I now know is from the computer quickly advancing and retarding the timing. I then found if I incredibly slowly increase the throttle just a few hundred more rpm, it would hold. Any more than that and it would surge. Once it would surge, I could pull back down, then quickly back to the last rpm just before surging. By doing this multiple times, it eventually went over 1500 or so, then lo and behold, it ran fine. Put 2 hours on it with multiple rpm settings and problem never surfaced. Took the boat back out Sunday. Same thing, surging as soon as I gave it any gas, then after the slow process as described, it went away again and I was able to put another two hours on it. So problem is still unsolved, but at least I managed to finally put the 10 hours of break-in on the motor. If anyone on this board can read Rinda diagnostics please let me know. I would love to have someone who knows what they are doing interpret the data I collected. In the meantime I guess I can use the boat as long as I go through the painstakingly slow throttle process.

 

[AllDodge]

First motor was replaced and had no issues

Old motor had no issues, trouble started with new replacement

I'm leaning toward a vacuum leak

Can you post some screen shots of the data when it's surging?

 

[SeaRayJosh]

Thanks AllDodge. I have attached 2 screenshots. I would think a vacuum leak would offer a consistent issue, vs one that appears and then disappears. I did try the stethoscope method with a piece of vacuum hose and could not identify any leaking areas around the intake or throttle body.

 

[AllDodge]

The throttle position and and throttle sensor voltage is not changing
The motor is warmed up but temp shows 78*
Throttle position is staying at zero

 

[SeaRayJosh]

I just looked back at it and you are correct. that is strange for sure. It shows voltage but not position. Since the problem had started, I had switched the TPS with the other motor, to no change, so I wonder if there is a connection issue, assuming if that could cause the problem. It could explain the intermittent and why an extremely slow throttle change can make the issue go away. Good catch, thanks!

 

[SeaRayzor]

Hey, did you ever find the solution to your problem? Im kinda having the same issue but with factory mercruiser 5.0 MPI.

Ill see if i can copy my post in your replies.

Thanks

 

[SeaRayzor]

Hey, did you ever find the solution to your problem? Im kinda having the same issue but with factory mercruiser 5.0 MPI.

Ill see if i can copy my post in your replies.

Thanks

Its a 2005 SeaRay Sundeck 200 with Mercruiser 5.0 MPI.
Last year it started running bad after launching in the water. Really struggled to get on step, like it was starving for fuel or too much fuel being dumped. But after a while, about 30 minutes of taking it easy and gradually giving more throttle, it finally started to run a little better and finally plained out. The more i would run it, the better it would preform. By the time we would get off the water, it was at peak performance.
Next time I took it out, same scenario…

I changed fuel/water separator and tried again…same problem.

Save boat for winter, (boat has always been in shop out of elements)

This spring, I pulled it out and tried a few different things. I cleaned flame arrestor, siphoned old gas out, put another fuel/water separator and put fresh gas (about 15 gal) with a stronger than recommended amount of Seafoam and Lucas Oil injector cleaner.
I put water through the muffs on the intake vents and let her run at about 1100rpms. After about 10 minutes, I heard the throttle gradually increase on its own, i checked it was now at 1600rpms. Hmm… did something break loose in the injectors? I let her run for about 4 hrs with small bursts of 3k rpms, all while monitoring temperature of engine.
Next day, I took her out on a small lake near home and she preformed alot better right off the get go but still had small hiccups until after about 30 minutes and then ran fairly good.

Two weeks later (Memorial Weekend Sunday) we took her out with 7 full grown people and full tank of fuel with recommended amount of Seafoam and Lucas Oil Injector cleaner. SAME ISSUES! Really struggled to get out the hole and took almost 2 full hours to start running good enough to pull skiers. Im in the middle of changing spark plugs and wires, real pain in the butt, but im still just guessing.

Any help would be greatly appreciated in diagnosis of problem.

Sincerely,
SeaRayzor

 

[SeaRayJosh]

Hey there sorry to hear about your issues. My problem turned out to be the crank sensor. It was intermittently bottoming out. I added a second o-ring and no problems since.

For your issue, I would suggest plugs, wires, and cap/rotor.

Good luck!

 

[SeaRayzor]

Hey there sorry to hear about your issues. My problem turned out to be the crank sensor. It was intermittently bottoming out. I added a second o-ring and no problems since.

For your issue, I would suggest plugs, wires, and cap/rotor.

Good luck!

Thanks Friend! That’s exactly what I did. Parts were about how I expected after 20yrs of use. Not quite finished yet but here’s a few photos of old parts.

 

[SeaRayJosh]

Hope that solves your problem! Happy boating.