377 mag mpi dts Hard start after the first time

[silver_power]

Hello,
I have twin engine boat with 2 x 377Mag Mpi Dts Axius. (S/N: 1A605669 & 1A605670)
The problem i have with the starboard engine is that it fires up ONLY the first time of the day. What ever attempt i try during ex. 10time period, it will not fire up and it will flood. It will not start, even with WOT. The only way to start, is to disconnect the power supply of fuel pump and start the engine. It will start at the second attempt without throttle at all.
The engine after it starts, runs perfectly. Something happens, only during cranking, and the engine floods
Checked till now:
1. Change spark plugs (the old were in very good condition and the combustion is very good, no oil, carbon etc)
2. Fuel pressure normally, 38-39psi@idle, 43psi with vacumm hose disconnected and 38-39spi during cranking
3. Voltage during cranking drops to 10.6V, 12.7V @StanD by
4. Change the fuel rail with the injectors from the port engine which starts perfectly without throttle
5. Change the ignition module and the common spark plug wire from the port engine
6. Pull out the temperature sensor and put a 390Ohm resistor so the engine see steady 72oC
7. Flame arrestor clean
8. Swapped the DTS throttle plate from the port engine
9. Fuel Filter new and the screen below them as well,
10. checked the water hose of the cool fuel module for blockage
11. Checked the FPR for destroyed diafragm and change it with new as it ruined during unistallation.
12. Check for faults with Diacom, all perfect (MAPT, etc) and no fault codes...

The next two things is to swap the distributor cap and all the spark plug cables with port's engine, but i am sure that this will be useless as if the cap-rotor -cables would be the problem, the engine would not started after unplugged the fuel pump, give a crank to clean and then connect it again.

Honestly i do not know what to check next........

Do you have any idea??

 

[alldodge]

Is a strange one, but with it flooding I would look closer at spark. Those flat distributor caps are known to look great but be bad. Many keep a spare on the boat because they can fail without warning

 

[silver_power]

I totally agree with you, but the fact that when it starts, runs perfect.......??
Would it run perfect if the cap had problem? I mean, with a weak spark, the engine would not run good during get the boat on plane of at 4000+rpm.....
Except if you have heard something similar......
At the other boat with 350mag mpi , having the same flat dizzy cap, when it failed, i had unsteady rpm during cruise. The rpm fluctuated about 300rpm, obviously because the spark jumped to wrong cylinder.......

 

[Scott Danforth]

check battery connections and other wiring to the starboard engine. if the voltage is low during cranking and is dropping, that would be bad connections somewhere

 

[silver_power]

I already checked them......nice grounds and the voltage during cranking does not drop below 10.5V.....the situation is not better even with starting at "BOTH" batteries.....
I alleady changed the starter with new, since the previous "died" because the lots o cranks!!
I believe and agree with you, that i am dealing with ignition issue.
Except dizzy cap and cables, is it possible the cam sensor cause the engine not to start? Is it easy to swap it from the port engine?
The fact that a twin engine boat gives you the ability to swap and test known well operational components, is very help full!

 

[alldodge]

Right now I of the opinion it's lack of spark, don't know if it's the cap or not only that they are known to have issues. I start with simple stuff than try other things. You have done many things and nothing works until it starts to work again.

Disabling the fuel system is just a coincidence, so what is keep spark from happening. The PCM looks for spark before fuel injectors are fired, it sees something enough to turn injectors on, but maybe not enough to get an actual spark. @muc

 

[Scott Danforth]

I already checked them......nice grounds and the voltage during cranking does not drop below 10.5V.....the situation is not better even with starting at "BOTH" batteries.....

these two sentences are a dichotomy.

if the voltage is dropping while cranking to 10.5 with one battery or two batteries, the issue is either the ground lug on the block or the power connection at the starter, or the ground and power at the cannon plug.

 

[silver_power]

Which is the sequence for the engine to start?...i mean, the pcm sees that engine started rotating from crank sensor and determine which cylinder is at top dead point...but it does not if it is at compression or exhaust stroke.so till now it has no fuel or spark....When the cam sensor synchronises give at pcm the signal and then engine fires the injectors and then the spark?
What happens at the meantime that engine see rpm but no signal from cam sensor?...is there possibility to fire the injectors even if it has not the cam signal?
If yes, then maybe the cam sensor if faulty and as it delays to give the signal to pcm, the engine is allready flooded due to extended cranking time.......

 

[alldodge]

The PCM must see at least 300 RPM, and ignition procedures will energize. Not sure about your motor and that's why I tried to get MUC into the conversation. Your distributor has a Cam sensor but I don't think it has a cable attached, and if no cable is attached then it just uses the crank sensor

The injectors are batched fired which means a few fire one or more times per revolution. The below pic is from a 555 ECM so not yours but just to provide an idea

 

[muc]

Yes, this engine uses and needs the cam sensor to run. Yes, you can swap them. No, I don't know if it's easy.
This engine has 8 injector drivers in the PCM, it fires the injectors in pairs.
I don't know if the CMP effects the injectors, I think it is just used for the ignition.
Are you using the Diacom recording function to check voltage drop during cranking? It is the most accurate because it measure voltage at the PCM (where it's important) not at the battery. With a PCM controlled engine voltage drop is very important. 10.5v is borderline bad with this engine. Especially if your getting the same reading with both batts selected. Red Flag!
The unplugging the fuel pump to get this restarted is very strange. Is this very repeatable? That you need to do this every time you try to start the engine warm?
I would use the Diacom to do a "wiggle test", use the record function KOEO and KOER.

 

[silver_power]

Yes, this engine uses and needs the cam sensor to run. Yes, you can swap them. No, I don't know if it's easy.
This engine has 8 injector drivers in the PCM, it fires the injectors in pairs.
I don't know if the CMP effects the injectors, I think it is just used for the ignition.
Are you using the Diacom recording function to check voltage drop during cranking? It is the most accurate because it measure voltage at the PCM (where it's important) not at the battery. With a PCM controlled engine voltage drop is very important. 10.5v is borderline bad with this engine. Especially if your getting the same reading with both batts selected. Red Flag!
The unplugging the fuel pump to get this restarted is very strange. Is this very repeatable? That you need to do this every time you try to start the engine warm?
I would use the Diacom to do a "wiggle test", use the record function KOEO and KOER.

Yes, i need to unplug the fuel pump every time i try to restart engine, especially warm.
I like the idea of the wiggle test using recording at diacom.....i will do it!

 

[silver_power]

Well, today i changed the dizzy cap and the rotor......the dizzy cap had obvious corossion at the contacts inside......engine starts more easy now....meaning that if i start it with "throtle only" mode , it will start al the times. But without throttle it will not start after about 5mins......the cam sensor was difficult to change it today, eventhough i had a new one with me, as i had to pull out the distributor.....
Next thing and the only lasts, are the cables......

 

[alldodge]

engine starts more easy now....meaning that if i start it with "throtle only" mode , it will start al the times. But without throttle it will not start after about 5mins.
Next thing and the only lasts, are the cables......

Don't see anyway it can be the cables, the TB is closed at idle and the IAC regulates the air intake during starting and idle. It starts with giving it a bit of throttle but not without, it has to be something there

 

[ejnichol]

Try unpluging the iac, removing it and gently depressing the plunger back towards the body. Reinstall iac and without plugging it in, try starting it and see what happens.

 

[Fun Times]

I have twin engine boat with 2 x 377Mag Mpi Dts Axius. (S/N: 1A605669 & 1A605670)

Just a quick note that since this engine has DTS (Digital Throttle and Shift) would indicate this design throttle body doesn't utilize an IAC valve but does remind me of a recent story of a good friend diagnosing a hard to no stater condition on a work automotive type van that uses a fly by wire type throttle body that the internal motor wasn't working properly and he mostly found it by both feel and sound as it wasn't throwing a check engine fault code....

He could tell the T/B motor was skipping like a gear would slip.... Put a new throttle body on and all was good...Maybe inspect and try swapping your throttle bodies around there @silver_power.
https://www.mercruiserparts.com/bam/subassemblydetail/51444886/28194562

Genuine Mercury Marine parts, large inventory, fast shipping. 377 MAG MPI BRAVO 1A300000 THRU 1A611927

377 MAG MPI BRAVO 1A300000 THRU 1A611927

www.mercruiserparts.com

 

[Mc Tool]

I dont really know anything about these set up but from a diagnostic point of view .... Im assuming you are testing battery voltage during cranking at the battery @ 10.5v , if so that does not necessarily mean that all the components are getting that 10.5v . If there is a bad connection that plays up after some time ( after it warms up a bit , maybe due to the resistance of the bad connection itself ) If you have a volt drop of a couple of volts the affected component may well continue to work at 10v until you stop the motor , but when you try to start you have the cranking voltage dropping to 10.5v plus the now affected bad connection which would further drop the voltage to around 8v ( for example ) during cranking ..... some electrical stuff wont like that .
I would either do a volt drop test on the components of a hot motor or test voltage on individual components during cranking on a hot motor .
Its possible that when you disconnect the power supply to the fuel pump you are inadvertently disturbing the bad connection by moving the wiring harness ......sometimes thats all it takes .

 

[silver_power]

Just a quick note that since this engine has DTS (Digital Throttle and Shift) would indicate this design throttle body doesn't utilize an IAC valve but does remind me of a recent story of a good friend diagnosing a hard to no stater condition on a work automotive type van that uses a fly by wire type throttle body that the internal motor wasn't working properly and he mostly found it by both feel and sound as it wasn't throwing a check engine fault code....

He could tell the T/B motor was skipping like a gear would slip.... Put a new throttle body on and all was good...Maybe inspect and try swapping your throttle bodies around there @silver_power.
https://www.mercruiserparts.com/bam/subassemblydetail/51444886/28194562

Genuine Mercury Marine parts, large inventory, fast shipping. 377 MAG MPI BRAVO 1A300000 THRU 1A611927

377 MAG MPI BRAVO 1A300000 THRU 1A611927

www.mercruiserparts.com

Unfortunately i allready checked it by using the TB of port engine......nothing different....