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Spark Issue with drop in voltage

R

ROBSHAFER

New member
Hello all hope someone can help because this is weird and I've been chasing this issue for over a year.. I have a 1996 maxum with a 5.7 merc. The engine is new, (issues started after swap)the fuel pump, coil,  distributor and all the wiring is original. trying to fix this issue. new wires, plugs, cap,rotor, choke, alternator, battery . Cleaned tank pickup in line filters, checked anti siphon . What I have finally discovered. After running hard for half and hour or more, Something (electrical I think) gets hot and i get a back fire through carb. pop pop. Once it starts it gets worse and worse at any speed, until I'm force to run at idle speed with no issues. If i run at idle speed for an hour or so or sit with engine off for a good amount of time over half an hour. it runs better pops are less frequent. So heres where its weird. the last time this happened I was trying different ranges of speed to see if i could get it to run smooth faster then an idle. What I discovered is the second  I hit the tilt button it would back fire. So it appears something gets hot and a drop in voltage causes it to malfunction on demand instead of occasionally when its having trouble. IDEAS ??? I haven't checked loose connections, plugs, grounds, as electrical didn't dawn on me until the tilt thing. Thanks for the help​
 
It sounds like the tilt/trim is pulling so much current that it's likely screwing up your ignition system. The first thing to check is your battery cables. Disconnect, bend them back and forth, and if you hear a crackling sound, they are internally corroded and need to be replaced. Check the ends that connect to the battery lugs and selector switch for corrosion. Check the battery connections. They should be spotlessly clean and the terminals very tight with lock nuts installed. If you have a selector switch, bypass it temporarily. Use an auto jumper cable to connect battery ground directly to the engine chassis. Use the other auto jumper cable to jump from battery positive to where ever the main positive connector is on the engine. If that clears it up, isolate exactly where the problem is. Often times the contacts on the battery selector switch get corroded inside. If that is where the problem is, some of those selector switches can be disassembled and cleaned up. Other cannot and need to be replaced.
 
Thanks theres no selector switch. I can see the trim pulling current. But What do you think might be the issue that makes it do it without hitting the trim? Seems like something has to get hot and starts to fail?
 
Even without the T/T activated, you may be getting low current (amps) to the engine. It's most likely a grounding problem IMO. You may want to post this issue on the Merc I/O and inboard forum. Go to the top left of this page, click on "Forum Home" and scroll down to the Merc I/O and inboard forum and open a new post there.
 
chawk_man said:
Even without the T/T activated, you may be getting low current (amps) to the engine. It's most likely a grounding problem IMO. You may want to post this issue on the Merc I/O and inboard forum. Go to the top left of this page, click on "Forum Home" and scroll down to the Merc I/O and inboard forum and open a new post there.
Click to expand...

I get the issue after a long run, I just notice when it’s doing it randomly if I hit the trim it causes aback fire every time
 
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