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2006 Mercruiser 6.2L MPI BravoHot start Issue

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Randyh222

New member
Hello,
I have an ongoing problem with my MCM MX 6.2 MPI. It starts perfectly cold, then runs perfectly but when shut off it does not fire back up. It will turn over and get a couple cylinders to pop but will not fire up. If I give it nearly full throttle, it will fire but after a lot of turning over and just barely make it. If it gets close to firing and I stop, it flat out will not start unless I wait an hour or so. One thing I have noticed is that if I run it, then put the boat on the trailer, take it home and fire it up about 30 minutes later on a hose, it will fire up normally even though given the same circumstances with the boat staying in the water it would not have. This issue has stumped the mechanic that works on it. So far the following has been done to the motor: Replaced entire fuel pump assembly- which by the way does not warm up when running. The injectors have been cleaned up and are up to spec. The Idle air control valve has been replaced. The throttle body has been replaced. The Mapt sensor has been replaced. The Crank position sensor has been replaced, the fuel regulator has been replaced and lastly the throttle position sensor has been replaced. Quite frankly I am running out of money and Ideas to toss at the motor. Does any body have any guesses as to what else could cause this hot start issue or any test that I can preform to check?
Thank you,
Randy
 
Thank you for the reply. Will give it a shot next time I have a chance to put it in the water, probably next weekend and check back to you. What exactly will that test? Vaporlock?
 
The Fuel Module kit ([FONT=&quot]8M0047215)[/FONT] was replaced so I am pretty sure that the cooler is part of that. I will talk to the mechanic that replaced it to make sure though and get back to you later today.
Thank you for your help!
 
The reason that the Fuel Module kit was replaced was an engineering defect by Mercuriser where the paint on the inside of something in the kit got dissolved from the fuel and ran paint chips through the system. In theory every thing has since been cleaned up, including the injectors, but my question is, other than causing leaky/clogged injectors, are there any sensors or anything that the paint chips could have messed up and cause a hot start issue? The injectors read within spec as far a leaking.
 
Randyh222 said:
The reason that the Fuel Module kit was replaced was an engineering defect by Mercuriser where the paint on the inside of something in the kit got dissolved from the fuel and ran paint chips through the system. In theory every thing has since been cleaned up, including the injectors, but my question is, other than causing leaky/clogged injectors, are there any sensors or anything that the paint chips could have messed up and cause a hot start issue? The injectors read within spec as far a leaking.
Click to expand...

The paint will clog your injectors, that is all. No sensors to harm.
 
Thanks for that piece of mind. I got a chance to talk to the Mechanic that installed the fuel module kit and the Fuel cooler was indeed part of it. Now waiting for an opportunity to take the boat out and give the fuel purge test a shot.
 
First off, sorry for the delay. Just finally got a chance to do some tests on the boat. I took the boat out today with the intention of testing three things: Vaporlock, Voltage check for battery and starter and lastly just wanted to get a better idea on how much back pressure affects the condition.

Started up the boat right at the dock shortly after putting it in the water while checking voltage. The boat fired up normally and voltage read within spec. I then waited for the motor to get up to running temp with out ever coming off idle. Once warm I shut off motor, purged the fuel pressure and tried firing motor back up, once again with voltage check. Voltage was fine, however motor would not start with or without throttle. Durring these tests I had a fuel pressure gauge hooked up the whole time and it got up to 42lbs when cranking however while it was running was at 38lbs. Interestingly when the motor shut off it would immediately come down to 34lbs but slowly(over a few minutes) build back up to 40lbs when it was shut off. Now here is where things get a little more interesting. After the motor did not fire in the water, I quickly put the boat back on the trailer and hooked it up to a hose(within 5 minutes of it not starting in the water) and it fired up with throttle. After that it easily starts, even with out throttle while hooked up to a hose and not in the water. After this I tried putting the boat back in the water (With in five minutes of everything working fine out of the water) and it would not start in the water with or with out throttle. Once again the boat was brought out of the water where it started up with throttle on the hose.

Does anyone have any Idea as to how back pressure can make a motor not fire once warm? For reference, the exhaust flappers were just replaced.
 
OK, It has nothing to do with the back pressure. Your fuel pressure is good.
It seems like you are losing 5.v reference power.
Do you have a DVOM?
Take your digital volt/ohm meter, disconnect the three wire plug on the Throttle position sensor. One wire is ground, one wire is 5 volts and one wire is for reference. I want you to check these wires so you understand what I am explaining. Now restart the engine while the boat is in the water, recreate the no start condition and when it happens you want to make sure you still have 5 volts. If the 5Volt system goes down the engine will not start. All three wire sensors are on the 5 volt system.

If your engine has a transom harness plugged into it, make sure it is not hanging down in the bilge water. (engines came from merc with this harness and it may not be in use) You can find this harness on the back of the engine by the HVS (distributor) it will be marked "Transom Harness"

Early engines had one 5 volt reference system and if it went down the engines would not start. Later engines had two 5 volt systems to combat this problem.
If you find that the 5 volt system is down, disconnect all 3 wire sensors one by one until the voltage comes back.

The water pressure sensor is usually suspect.
Easier to explain on the phone.
9086464626
 
Thank you for the good explanation of the 5 volt test.
I have a couple questions though, what is a good time for me to call you? Also, you are on the East coast right?
 
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