Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

[brettdawnj]

I just bought a project boat and rebuilt the engine. The engine ran great out of water and was scanned by a dealer for any potential problems prior to putting the engine back in the boat. Serial Number is OW344362. It uses a ECM 555 as the computer controller to run the engine. I launched the boat today only to find out that it won't run under load. Originally, in neutral, seemed to be perfect, but in gear, once up to 3000rpm or so, starts missing and stumbling so bad it won't accelerate. Monitored with a fuel pressure gauge on it and it runs at 38psi steady under all conditions. Each injector is working via a crude pull the injector connector at 1500 rpm and feel and hear the engine not firing on the cylinder with the connector removed. Tested the tps and map sensors per the manual and they measure perfect over the complete range. When the engine starts to stumble or run rough, the Tach on the dash is dropping sharply with every miss. This made me think it was an electrical issue with the ignition. New coil, distributor cap, plugs, and took the coil driver to the auto parts store for a bench test. They assure me the coil driver is functioning perfectly. Original max smooth rpm was around 3000rpm and then as it was run longer the max smooth rpm dropped slowly over time to 1000 or 1200. Just kept getting worse and lower.

Let the boat set for 4 hours during a severe rain storm and then went back to take the boat out of the water. Much to my surprise, it ran with power for around 5-10 minutes (or until it heated up???) Running temp is at 165-170F. After this 5-10 minute time, it started running bad again with having to drop the rpms to get it to run decent enough to make it to the launch site. Still fuel pressure always at 38-40 psi. So now I am thinking stronger that the issue is heat related. Took the ignition coil driver module back the the auto store with a heat gun and applied heat while testing the module. It never fails their test bench equipment. Bench tested the MAP sensor also under a heat gun. Both modules never fail under heat.

Since Fuel Management and Timing is primarily controlled by the engine rpms and the MAP sensor showing the load at that rpm, now comes the painful thinking... perhaps the ECM 555 is what is failing under heat??? I wish I had another boat with a ECM 555 and I would just pop my suspected module in the new boat and see if the problems move with the ECM. Problem is I don't know anyone who has a Mag 350 MPI. I do have a friend in another state that has a 5.0 instead of the 5.7. Does anyone know if it is possible to run a 5.0 with a 5.7 ECM 555? All the wiring is the same and my guess would be that it would work well enough for testing a module to see if it was good or bad. I suspect that the fuel calibration would be off and run a little rich since it is thinking it is providing fuel to a 5.0. So the worst case would be that we possibly foul a set of plugs.

Can anyone out there confirm that this might work or perhaps have any other suggestion as to what I should try next?

Thanks so much for any help or suggestions you might have. If I wasn't currently trying to put triplets through college, I might either turn this over to a merc mechanic or buy a new module, but at this stage, it is not within out budget. So I will keep plugging away at this.

Brett

 

[r.j.dawg]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Any codes after the engine was put in the boat? Only asking as I had a 97 350 EFI/MP and it was a pig for recording problems. Most, if any, were under load in the water. Post your serial number.
Oh by the way.... welcome to iboats.

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Any codes after the engine was put in the boat? Only asking as I had a 97 350 EFI/MP and it was a pig for recording problems. Most, if any, were under load in the water. Post your serial number.
Oh by the way.... welcome to iboats.

No Audio Alarms after the engine installed in the boat, but I don't know if any codes were set as I don't have a scanner or at this point, any budget to pay for someone to scan it.

Serial number was posted above as OW344362.

And thanks for the welcome!

 

[Pete104]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

First, if what saying is true, that after it cooled down it ran better. Just make sure the ECM ain't locked in "service mode"! The only other temp related sensor is the CTS & will show a code when scanned.

From what your describing the engine is going into "guardian mode". That could be oil as well.

Another issue is are we Alpha or Bravo. Not knowing which, you may have shift cable adjustment issues.

Don't go switching ECM's! Distributor cap is clean, right?

Any code that is stored right must be cleared before a new component is going too correct the problem.

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

First, if what saying is true, that after it cooled down it ran better. Just make sure the ECM ain't locked in "service mode"! The only other temp related sensor is the CTS & will show a code when scanned.

I don't think it is possible for it to be in a "service mode". The difference in running was like the engine being a bucking bronco when it gets to stumbling vs a normal smooth running engine. From my experience with automotive ecm's, the manufactures would never let the controller do that to an engine as it must be more destructive than just backing off on fuel supply and timing to make the customer smoothly but controlled way to get home...

but if one is locked in service mode, how do you get it out of this mode? Disconnect the battery for some period of time or something?

From what your describing the engine is going into "guardian mode". That could be oil as well..

Don't think it is "guardian mode" as my alarm is working. No alarms other than the one beep at ignition on to tell you it is functioning. I also tested the alarm by disconnecting the outdrive oil bottle leads and then the alarm starts going off as designed. Oil pressure at 40 psi per my gage.

Another issue is are we Alpha or Bravo. Not knowing which, you may have shift cable adjustment issues.

Bravo 3. Can't be a shift cable issue as it shifts from forward to neutral and reverse perfectly. Also the neutral start switch works correct.

Don't go switching ECM's! Distributor cap is clean, right?

Why not try this ECM in another boat designed for the ECM 555? This would tell me if the ECM works great in another boat, I can avoid spending $1600 or so on a new ECM (and this is what I really can't do at this point).

Any code that is stored right must be cleared before a new component is going too correct the problem.

How do you clear these codes? Is this true for any code set or just critical ones? With no alarm sounds going off, my speculation would be that if there are any warnings or code in my unit, they would "self" clear themselves since they would be rather minor in nature (because they are not setting off any alarms).

Thanks so much for your thoughts and ideas. I keep learning through these problems by the moment.

Brett

 

[undercover]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

The ecm555 stores a fault code history, but only shows active codes during runtime. Said another way, active codes are cleared when the ignition is cycled but remain in the history. I recently replaced a bad iac and did not need to clear anything to get the warning beeps to go away. You need software such as rinda's techmate or diacom to read codes/clear the history.

 

[scoflaw]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

You didn't mention your fuel system. You could be getting fuel pressure without enough volume. Tank, lines,gas valves, filters,tank vent.
Try to borrow a scanner, very valuble tool with the 555

 

[NHGuy]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

You have tested some of the sensors, if you don't have access to a scan tool maybe test the rest. Does that motor have a crank sensor? Car motors do that stuff when crank or cam sensors act up.
I think if this boat is a keeper you either want to get a scanner or pay the man to pull the codes. There is nothing intelligent about guessing on a $1600 part.
Stinks to pay, but on the other hand EFI uses less fuel to make more power. So you get it back in operating savings

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

I don't think it can be the fuel system as the pressure is not dropping during any of the normal or bad running. If the ECM was telling the injectors to supply more than they could, I think the pressure would have to drop.

Unless someone can teach me something different.

Note the pressure is always 38-40 psi on my gage. I think above 35 is ok on this engine???

Thanks for your thoughts as I am really searching for it to be something other than a $1600 ECM.

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

The engine only has a crank sensor. No cam sensor according to the wiring diagram... But I will check this when I can get to the actual boat... I remember having having effect sensor on the distributor (which would mean that it has a camshaft sensor... But I suspect Chevy put a standard distributor away and mex just didn't use it in the ECM 555 generations).

Does anyone know if a Mercmonitor is sophisticated enough to also do all of the diagnostics I would need? Perhaps this might be a good way to get a scan type tool that will also add value to it having everyday use. I think they are around $500 or so, but that is only around 4 hours labor at the Merc shop... So it might be worth it in the long haul.

 

[Fun Times]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Your engine is a 2005, So yes you do/should have a cam sensor located under the dist cap the parts catalog shows.

Your fuel pressure regulator specifications is 42 psi. Does the fuel pressure move when you remove the vacuum line?

What service manual are you using? did you follow the special instructions in the manual when installing this style distributor assembly?

Your friends ECM may not yield the exact running info your looking for there for not being a good valid test.

This could be many things before suspecting a bad ECM.

Have you verified "all" the ground wires to the engine harness were installed after engine instalation to the boat?

Also, there is no service mode to worry about with this style distributor.

Even a misadjusted shift cable linkage could make the ecm think it's still in neutral gear while you're trying to get past 3000 rpm. that is just a few reasons why i say it could be many things.

 

[Bondo]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

I don't think it can be the fuel system as the pressure is not dropping during any of the normal or bad running. If the ECM was telling the injectors to supply more than they could, I think the pressure would have to drop.

Unless someone can teach me something different.

Note the pressure is always 38-40 psi on my gage. I think above 35 is ok on this engine???

Thanks for your thoughts as I am really searching for it to be something other than a $1600 ECM.

Ayuh,.... Water, 'n Crud can be pressurized, yet they still won't burn.....

What's the contents of the fuel filter,..??

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Fuel filter was clear and the screen in the bottom flowed gas through it without hesitation when poured into it. I even ran the boat with the tank line disconnected and the filter lid off to watch the flow on the return line. Tank was emptied and out for engine install, so it was starting clean with new fuel. I suppose I can test the real flow capabilities by connecting a hose to the fuel test port and see how much really flows out.

Anyone know the flow rate I should get out of this engine?

I am a little nervous about volume of flow now that some one mentioned I should be getting 43psi and my gage shows 38-40. Could be a gage calibration issue?

But this wouldn't explain why when it is cold it runs strong for 5-10 minutes and then it starts to severely stumble and convulse after it seems to warm up. And the longer you run it the lower the I need to move the RPM's to make it run smooth (unless I am really at the borderline of fuel pressure and the longer I run it and the pressure is just dropping enough to make a huge difference). Within 10 more minutes I could only run it at 1000 RPM's without it stumbling and bucking.

Next time I have it out I think I will run a hose onto a small portable gas tank and use it to supply fuel to the system without the check valve and pickup tube. This way I can rule out any tank related suction problems.

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Your engine is a 2005, So yes you do/should have a cam sensor located under the dist cap the parts catalog shows.

Your fuel pressure regulator specifications is 42 psi. Does the fuel pressure move when you remove the vacuum line?

I will check this the next time I get to the boat. I didn't test this.

What service manual are you using? did you follow the special instructions in the manual when installing this style distributor assembly?

If my memory is right, it is a Selmar for Mercuisers 2001-2008 or 9. I tried to follow the special instructions on setting this... hope I didn't follow the wrong instruction. It was a few months ago I was at that stage, and I think it had you set #1 to top dead center and then align the rotor to the #1 plug conductor on the cap. It also stated this didn't have to be perfect as the timing is controlled by the computer. I tried to make it really spot on to the #1 TDC I think.

Your friends ECM may not yield the exact running info your looking for there for not being a good valid test.

I was actually thinking just the opposite... send mine to his boat and he just plugs in the 2 connectors to his boat instead of his. If his boat then runs reasonably well without major stumbling and bucking (after a total run of 10-15 minutes), then it will be clear that I have something on my boat that is causing the major problem... if his boat then doesn't run right at all and exhibits major running problems similar to what I am experiencing, then we can conclude that the problems are moving with the ECM and then it will be clear that I need to somehow bite the $1600 bullet.

This could be many things before suspecting a bad ECM.

I really like your thinking here... the thought of $1600 is killing me.

Have you verified "all" the ground wires to the engine harness were installed after engine instalation to the boat?

I thought I did, but I will go back and verify this by measuring all ground wires back to the ECM and the devices. Good point, but I am still confused why the boat runs OK cold and then gets continuously worse rather quickly (within 5-10 minutes it can't run over 3000 rpm's and within another 5-10 minutes it can't run over 1000 or 1200 rpm's.

Also, there is no service mode to worry about with this style distributor.

Even a misadjusted shift cable linkage could make the ecm think it's still in neutral gear while you're trying to get past 3000 rpm. that is just a few reasons why i say it could be many things.

This is not possible in my case because the guardian system will beep at you if you go over 3000 rpms and your in neutral. And I verified that this function works.

Thanks so much for your thoughts and making me think about more possibilities.

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Quick update on my problem... I was able to spend some time with Mercury Tech Support and they were very helpful. Because of the sharp drop in the tach when it starts to stumble, he strongly suggests the Crankshaft Sensor is the most likely cause. This is what tells the ECM 555 when top dead center is and also is the direct link to the tach on the dash and the tach test lead in the harness. If this sensor acts up at all, it rarely sets a code (because usually not running due to a complete CPS failure is rather obvious). But it can play havoc with the computer and shut off both the fuel and spark if the sensor is not sending the signal it needs to.

We also think it is very important to verify the actual flows of the fuel system. So when I can get back to the boat, I will run the fuel pump under 2 different conditions. 1st condition will be to run the pump and pull fuel out of the normal tank and the 2nd condition will be to run the pump and pull from an open 1 or 2 gallon tank (one you fill your lawn mower with). Attached to the test port on the fuel rail will be the outlet hose going into a measuring beaker. We want to verify that the pump is flowing the right amount of fuel in both an open tank condition and also the real fuel tank of the boat.

Oh, someone also asked about the manual that I was using. I was traveling and mentioned I thought it was a Selmar, but it is a Seloc.

I am one the road for business at the moment, and I can't wait to get back to the boat to see if the CPS could be my issue. Already ordered a new one so I have something to try that is not the $1600 killer computer.

If the Merc Tech Support guy is right, he will be my hero!!!

 

[Fun Times]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Just curious, Did you ask the merc tech support guy his thoughts about swapping ECM's of different engine models?

You probably would be better off ordering the OEM mercruiser service manual especially with everything you have done to this engine. Google Mercruiser part numbers,
90-864573001 - ECM 555 DIAGNOSTIC SERVICE MANUAL #36
90-864260T00 - SERVICE MANUAL #31 V8 ENGINES 5.0, 5.7, 6.2

Also for what your about to do with the fuel system,
http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/gen3fuelmoduletesting.PDF

Yes it very well could be the crankshaft sensor or it could also be your rotor is not pointing at the correct timing mark on the HVS housing since you just installed it in your engine rebuild.

Just in case, try step 2 on Page 2 / 3 as well.
http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/gmefi-nostart.PDF

I don't think you're having this problem but just so that you are aware you may want to google and read (Paint inside mercruiser gen 3 cool fuel module) just to keep it in mind when looking things over.

Good luck.

 

[NHGuy]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

I'd recommend retiring that Seloc manual and work from Mercruiser info.

 

[brettdawnj]

Re: Mag 350 MPI Won't Run Under Load - ECM 555 Failing???

Just curious, Did you ask the merc tech support guy his thoughts about swapping ECM's of different engine models?

Yes, I did. He didn't recommend this as a first step because he was confident that the Crank Sensor is what is really causing my problem. He told me about them finding bad connections there and also even cracked sensors. As for swapping computers, he stated the fuel mapping would be wrong and in my case of putting a 5.7 ECM into a 5.0, then it would not run right as it would be too rich. He stated going this direction couldn't cause much problems for a test, but he would not advise going with a 5.0 ECM into a 5.7 as it would run too lean and this could cause damage to the engine.

You probably would be better off ordering the OEM mercruiser service manual especially with everything you have done to this engine. Google Mercruiser part numbers,
90-864573001 - ECM 555 DIAGNOSTIC SERVICE MANUAL #36
90-864260T00 - SERVICE MANUAL #31 V8 ENGINES 5.0, 5.7, 6.2

I ordered the ECM 555 manual at this stage, and since my engine is completely rebuilt already (using the Seloc and GM manuals), I will hold off on the pricer one. But I think the ECM manual might help in my strange problem.

Also for what your about to do with the fuel system,
http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/gen3fuelmoduletesting.PDF

Yes it very well could be the crankshaft sensor or it could also be your rotor is not pointing at the correct timing mark on the HVS housing since you just installed it in your engine rebuild.

Just in case, try step 2 on Page 2 / 3 as well.
http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/gmefi-nostart.PDF

I don't think you're having this problem but just so that you are aware you may want to google and read (Paint inside mercruiser gen 3 cool fuel module) just to keep it in mind when looking things over.

Good luck.

Thanks for these links to the service bulletins as I will also check them out. I just landed overseas for some work related business, and it looks like Labor Day Weekend will be the soonest I can get to my boat, but if anyone has any suggestions or comments, I will be checking this forum to see if anyone can enlighten me more on my issue with possible solutions to my problem.

I also spoke with the Merc Tech Support guy about the Mercmonitor to help with the troubleshooting. He stated this is a great user tool, but other than showing you what codes are set and suggesting you call for service support, it doesn't really give you the details of any problem. He suggested a Rinda (spelling?) type tool where you can actually see data and information about what is really happening in my system.