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496 Mag conversion Problem

gcluett

New member
"I have a 1995 SR 290 that had

"I have a 1995 SR 290 that had a 454 installed. Bought a slightly used 2004 496Mag and installed it (after a few issues). I hooked the existing charging harness up for the key switch and accessory power functions. Then I bought a Systemview and Smartcraft guages and hooked up throught th 10Pin CAN harness. The engine starts but as soon as it warms up, the relays on the top of the ECM start clicking and the engine stumbles every 10 seconds. No fault codes, fule pressure is solid, no water or contaminates in fuel, voltage is 14.
Any Ideas??
George

Also - where the heck do you plug in the fuel sender???"
 
"The fuel(tank)sender

"The fuel(tank)sender is on a special"smart transom" harness that plugs in in top of motor next to the Data Link conection. they look the same. You may have a bad main power relay or a bad fuel pump relay,(you did say you had solid fuel presure) what PSI? the relays are cheap I'd replace them both and see if that doesn't help.
496's ,especialy the early ones, had sensor issues from mixed and loose grounds(most sensors use 5 volts and need a 5 volt groung through the ECM.
You also say no fault codes, Is that from a data link scan or the system view monitor? A data link scan with a laptop or DDT will give you freeze frame faults and fault sec. that may not show on a system view. ( no alarm)
hope this helps some."
 
"Thanks for the comments. I h

"Thanks for the comments. I have a transom harness hooked in and the pitot speedo is hooked up to it but I did not see a lead for the hookup to the fuel sender harness (which I also have)?
I have a systemview and we are trying to get a mechanic with a diagnostic tool on the boat to see what he can read. The wierd thing is the fun does not start until the engine warms up. Then all four relays start intermittent clicking and when the second one from the front actuates, that is when the engine stumbles. Beyond the start relay, I dont know what commands the others or why that would happen when the engine warms up??"
 
"Just a thought, does that SR

"Just a thought, does that SR have a special lead to the main power on the alt? or does the alt. have the factory (orange) main pwr lead?
I have seen some Issues from SR's custom charging system.

You may also want to use a test 10 pin harness, to isolate the boat harness from the engine harness. all the relays reacting at the same time is a concern because the ECM controls the relays. let me know what you find."
 
"I had a strange problem on a

"I had a strange problem on a 496HO a few years back where a high voltage leak (arc) under the PCM was disabling it for half a second, it would stumble and then recover, with the warning horn sounding when this would occur. It would happen very randomly, not on specific intervals.

I realize the sypmtoms are a bit different, but I would check for a plugwire or coil arcing to ground near the PCM.

I agree with allan on everything he has said, he seems to know his stuff, and has given some good advice."
 
"I am hearing that I should be

"I am hearing that I should be checking the ground connections and connectors. The thought is as the resistance drops in the temperature sensor, it starts to act as a ground. Ill be working that issue over the next few days."
 
"George:

Just a thought; th


"George:

Just a thought; there may be crud buildup on it. Remove the temp. sensor from the engine and clean the copper pellet with a fine 1200 grit abrasive and polish w/comet cleanser. Don't use any sealant to reinstall. You can test it with a light bulb and ohm meter to see how it changes in ohms. Put it in the freezer for 2 minutes first and test, then hold over a lamp."
 
"I don't think I would spe

"I don't think I would spend much time messing with the ECT sensor. I would check the ground connections.

If you are not aware already, the relays (should be only two) are always powered with 12+, and then the PCM completes the circuit by providing a ground, which engages the relay. A loss of the PCM ground will cause the relays to disengage, but should cause both to disengage, not one or the other.

A scan may help, and is always a part of diagnosing a problem on a computer controlled engine. However, what usually happens on a problem like this is the scan tool will lose connection when the main power relay disengages, making it very difficult to gain any useful information from it."
 
"I think Dave N. Is looking in

"I think Dave N. Is looking in the right direction. a Loose ground would act up in this manor, as the engine heats up the resistance in the circut would also go up and cause loss of connection.. Double check all your grounds , look at the grounds at the back of the engine. the smaller wires are the engine harness grounds.
Wiggle all the wires while it is acting up.

good luck"
 
This motor actually has 4 rela

This motor actually has 4 relays (see pic).They relays also are actuating randomly and rarely together. What is the best way to determine if the ground is good or bad (where do you take a measurement)?
George
 
"OK - I checked out the motor

"OK - I checked out the motor again, looked for loose grounds, everything checked out normal. I found what looked like a 10 gauge wire coming from the ECM harness and hooked to the port aft grounding stud on the back of the motor. The Battery ground is on the starboard stud so I ran a 10 guage jumper direct from the battery to the ECM harness ground and no improvement. The other item of note - when the engine stumbles and recovers the first time, the pitot speedo sensor goes to @ 10MPH and stays there. When you shutdown and re-start, same thing. It reads zero until the engine stumbles (from the relays flipping) then goes to @ 10 and stays there???
HELP!! I am out of ideas."
 
"George,
Your problem really


"George,
Your problem really sounds a lot like the high voltage leak/PCM disruption I mentioned in my first post in this thread.

It may start to happen when the engine is warm because the the fuel mixture is leaned out which increases the firing voltage at the plugs, which in turn increases the potential for a high voltage leak.

Check the connections of the plug wires at the coils and spark plugs, especially those very close to the PCM."
 
"More thoughts:

Don't j


"More thoughts:

Don't just "check" ground connections; remove, inspect, clean and reinstall. With that many relays chattering, have you checked for voltage drop? Alternator may have AC on the output from a diode that is intermittently shorting out arfter heating from the charging process. AC volts on the output should be less than 0.025 volts.

I have found poor connections at the computer. Remove the connector and use a magnifying glass to inspect the plugs; one or more of them that are wider than the rest can be suspect to being poor connections. Also inspect the board connections for the plugs for good contact; scratches from the plug connections should be evident and equal for all pins. Clean the board connections carefully w/a stiff (old) pencil eraser along the length of the surface and NOT across the length. Dark spots on the board indicates arcing.

A "TAP" test during failure mode on the computer may be necessary to detect poor solder joints on the boards. Use the plastic handle of a long slender SD.

Former Army Air Defense HAWK Radar/Missile Tech. NOT a Site Jockey; repaired individual electronic components to HV transmitters, recievers, etc."
 
"New Clue:I have a transom har

"New Clue:I have a transom harness plugged in for the pitot speedo connection. When I unplug the transom harness, the ignition switch will fire up the electrical and the fuel pump runs but when you turn to the start position, nothing happens (the start relay does not go). I am wondering if the ECM finds a ground through the transom harness and it is not enough once the engine warms up and the sensors start changing resistance??"
 
"New clue, the smart transom

"New clue, the smart transom harness connector looks the same as the data link connection. could the two be swaped. or transom harness be pluged into the wtrong connection?"
 
"The fuel(tank)sen

"The fuel(tank)sender is on a special"smart transom" harness that plugs in in top of motor next to the Data Link conection. they look the same."
from my first post.
 
"The transom harness might be

"The transom harness might be plugged in to the wrong socket but I would be surprized if the computer would get the pitot signal OK. In any case, what is curious is the engine wont crank wiht the harness off. We had this problem originally before we got the transom harness and had to jump the relay to get the engine to test fire.
Is there ANYWHERE that shows the proper locations and harnesses for connection of the smartcraft stuff (like a diagram)?? My transom harness does not have a connector labelled for the fuel sender so I still don't see how that connects and where. My systemlink documentation only shows from the engine up."
 
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