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ICM, coil dis,? Back Firing issues

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<br><br>
 
"the engine is new...." can you fill in the blanks? did you get a brand new engine or did you get something like a reman long block and install that?

have you measured the voltage on the coil when the popping starts? sounds like a bad ground connection somewhere...the tilt button being activated shouldn't drag down the rest of the engine...
 
makomark said:
"the engine is new...." can you fill in the blanks? did you get a brand new engine or did you get something like a reman long block and install that?

have you measured the voltage on the coil when the popping starts? sounds like a bad ground connection somewhere...the tilt button being activated shouldn't drag down the rest of the engine...
Click to expand...


Its a brand new engine, exhaust mans and external stuff, pumps alt etc. were reused. The tilt button drops the voltage for a second, when I'm having the issues which occurs after running hard IE wide open or close to for a long period of time, it will cause a back fire every time its pushed. I haven't checked voltage. I only have the issue after a long high rpm run. If I park along the shore for an hour or so no issues. I haven't tried making it happen after parking as I need to get back to the dock usually and I don't push it.
 
makomark said:
"the engine is new...." can you fill in the blanks? did you get a brand new engine or did you get something like a reman long block and install that?<br>
<br>
have you measured the voltage on the coil when the popping starts? sounds like a bad ground connection somewhere...the tilt button being activated shouldn't drag down the rest of the engine...
Click to expand...
<br>

<br><br>Its a brand new engine, exhaust mans and external stuff, pumps alt etc. were reused. The tilt button drops the voltage for a second, when I'm having the issues which occurs after running hard IE wide open or close to for a long period of time, it will cause a back fire every time its pushed. I haven't checked voltage. I only have the issue after a long high rpm run. If I park along the shore for an hour or so no issues. I haven't tried making it happen after parking as I need to get back to the dock usually and I don't push it.
 
then maybe you have two issues vs just one.

Going lean after a long run is typically crud in the tank accumulating on the screen of the pickup tube...and you can clean them all day long and it will never make a difference....when the volume of fuel needed drops off, the crud falls back to the bottom of the tank.

The way i diagnose that one is a vacuum gauge in the suction line of the fuel pump. if you have a spin on filter, you c an use the normally present "extra" outlet fitting....the vacuum will increase with engine RPM and should be constant...if the vacuum keeps increasing at a fixed RPM, its due to an increasing restriction in the inlet....

And the popping typically indicates a lean mixture - continued running under load will cause you to repeat the engine replacement exercise...
 
makomark said:
then maybe you have two issues vs just one.

Going lean after a long run is typically crud in the tank accumulating on the screen of the pickup tube...and you can clean them all day long and it will never make a difference....when the volume of fuel needed drops off, the crud falls back to the bottom of the tank.

The way i diagnose that one is a vacuum gauge in the suction line of the fuel pump. if you have a spin on filter, you c an use the normally present "extra" outlet fitting....the vacuum will increase with engine RPM and should be constant...if the vacuum keeps increasing at a fixed RPM, its due to an increasing restriction in the inlet....

And the popping typically indicates a lean mixture - continued running under load will cause you to repeat the engine replacement exercise...
Click to expand...

When it starts acting up, and I hit the trim (drop in voltage) it back fires. Thats not a fuel issue i don't think?
 
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