496 HO engine trouble - calling Ray@raylar
 

First boating weekend was the perfect nightmare for us....4 days off and best weather with temperatures in the 80s....eagerly awaiting the first test run of the newly installed 496 HO in our Baja 272 we slipped the boat to break the engine in before the poker run next week....BUT:
After having idled on the hose at home o.k, the engine stumbled after around 4 minutes of operation at idle. It seemed that not all cylinders were firing and one or more would suddenly catch and then die again a few revs later....We added some power and proceeded out of the harbour with approx. 1500 rpms and the problem seemed to be gone, motor ran smoother, but after returning to idle the problem ocurred again.
To make things worse when I tried to take her on plane it came out of the hole sluggishly, not at all the expected power rush from 425 horses, seemed more like 150, and vibrated unpleasantly. top rpm I could get was 3200 rpm with an 22" Bravo 1.......as if the engine was in some kind of limp home mode.......stopped to check all spark plugs and got extremely lean readings. Installed a different ECU borrowed from a friends boat...problems persisted, so the ECU can be ruled out.
Checked all cables to the sensors, checked the vacuum hoses from the fuel gallery to the manifold and the one routed up from the cool fuel system, no "easy" explanations could be found, everything is in place. Boating day was ruined, so we
took the boat out of the water to have it scanned with a diagnostic tool on Monday.
What could be my problem? Exhaust sensor failure, fuel pressure too low, stuck injectors? Seems like a fuel related problem to me, but that would not explain the idle problem.....Any ideas?
I want to gather as much info as possible before I go to the dealer again.....and please tell me were I can order the Rinda Scan Tool and where I can get an failure code book....with my old carbed engine I could almost fix everything on the lake, because it was EASY...but the 496 is a different animal, now one needs a computer to understand whats going down.....
Thanks very much for your thoughts, I need help quickly, I think you guys out there are a lot more experienced as my dealer.......

Re: 496 HO engine trouble - calling Ray@raylar
 

Just a thought, check to make sure all your battery and power connections are clean & tight. I've never witnessed any of these problems with mine but have heard that pour electrical connentions on these motor really play havic on them.. Since you just got the motor put in it could be something as simple as that, who knows. Check it out it may save your boating weekend, GOOD LUCK!!!

Re: 496 HO engine trouble - calling Ray@raylar
 

Is the audio alarm connected? I am sure you would have mentioned it, so I assume you are not hearing any alarms?

Check Rinda.com for scan tool ordering info. May not get anyone till Tuesday though.

Dave

Re: 496 HO engine trouble - calling Ray@raylar
 

Check the fuel pressure. Shadow on HB had similar problems although he was rich due to an error in setting the regulator.

Re: 496 HO engine trouble - calling Ray@raylar
 

I forgot to mention, that the alarm system is connected correctly and I had no alarm whatsoever......what I also did not mention is that the plugs had little white spots around the tips of the isolator.....I thought it to be burned condensation, because I can not imagine thet a new engine has defect head gaskets or is ingesting water...)..

Re: 496 HO engine trouble - calling Ray@raylar
 

Could you Possibly have water in the gas tank of the boat???

Re: 496 HO engine trouble - calling Ray@raylar
 

Preuni

Hard to say what the problem is from your condtions. I would also say that the Rinda techmate tool is a must for you. Make sure you order it with the #96004 adaptor for the Mercury PCM555. If you did not get any alarms it sounds like it may indeed be a fuel problem, water or dirt. Try changing the fuel water seperator. Does not sound like anything mechanical though. Good Luck, the Scan tool will eliminate a lot of possibilities.

Ray @ Raylar

Re: 496 HO engine trouble - calling Ray@raylar
 

check the water seperators

Re: 496 HO engine trouble - calling Ray@raylar
 

I have garnered from previous posts that "the hose" at idle is not a good idea because the pressure from the typical garden hose is much higher than the raw water pump pressure at idle. No water in the oil right?

Re: 496 HO engine trouble - calling Ray@raylar
 

OK, got that engine checked out with the diagnosis software at the dealer......no hard faults indicated only the normal stuff that turns up when you dont have the "smartass system" installed with that monitor that you can opt for when buying the engine.......So we thought it could only be a fuel related problem, maybe a bad pump or a bad regulator...or even dirt in the screen at the inlet of the boost pump or dirt in the screen of the tank.....took the boat out again with a pressure tester attached to the manifold to see what it does under load.
Surprise! Fuel pressure was spot on at 40 something psi and stable. But the engine behaved under load as if it was running on two cylinders only. It shuddered heavily and struggled to get the boat on plane...we broke the test up in order not to damage the motor and put the tester again on the motor.
NOW it was showing fault codes of both the crankshaft and the camshaft sensor!!!!!
It became quite obvious that the computer didnt know f**** when to ignite the mixture in each cylinder.....
Can it be true that both of these sensors go bad simultaneously? Or could the problem be generated by an error in the engine harness? Can I test the sensors by measuring the resistance before replacing them?
Any ideas welcome!

Re: 496 HO engine trouble - calling Ray@raylar
 

check the engine grounds coming from the engine harness to the ground studs on the bell housing.

Re: 496 HO engine trouble - calling Ray@raylar
 

as mentioned before check the fuel-water seperators, pull them and drain them into a clear container and check for water.

Re: 496 HO engine trouble - calling Ray@raylar
 

I agree with BBB, could be a fuel contamination issue.

It is not that unusual to find cam and crank faults in the fault code history even when both are fine. I am assuming these are not active faults which would trigger a steady audio alarm. Check the resistance according to specs below.

Camshaft Sensor - A to B 24.04 mohms and B to C 24.05 mohms

Crankshaft Sensor - A to B 23.2 mohms and B to C 23.21 mohms

What is the 5 volt sensor circuit doing when the problem occurs? Is it maintaining 4.9 to 5 volts?

I have also seen secondary voltage leaks near the ECM cause "phantom" problems on the 496. You have ignition coils directly below the ECM. The Electro Magnetic Interferance (EMI) from a 40,000 volt discharge (spark jumping to ground) within a few inches of the ECM will cause the engine to stumble. Sounds unlikely, but I learned that hard way that it can happen.

Dave

Re: 496 HO engine trouble - calling Ray@raylar
 

Thanks very much for the information so far!
Here is todays update:
- no water and no dirt in the water seperator....
- no dirt or debris on the screen of the inlet of the booster pump.....
- no fault codes when engine is at idle
- fault codes of cam and crankshaft sensor when under load, but these fault codes do not stay in the memory when engine is shut off and then is restarted
- all injectors tested ok
- fuel pressure stable at idle and under load, no fluctuation
- Batterie and ground connection of engine checked out ok twice...
- meassuring the resistance of the sensors produced strange readings..about 9 kohms

Ordered both crankshaft and camshaft sensors to replace the current ones. If that doesnt cure the problem I will tear this electronically overengineered piece of s*** out of my boat and put in something simple with a carb and a mechanical fuel pump! Any 540s on sale?


-

Re: 496 HO engine trouble - calling Ray@raylar
 

:eek: :eek: :eek:

Re: 496 HO engine trouble - calling Ray@raylar
 

I didnt read all these post but I had a similiar problem. I unplugged the knock sensor and WOW!!!! There was the problem and it ran like a spotted ape!!! I replaced the old one with a new one after that weekend and it was still fine. Bad Knock sensor!!!

-Shoe