Port engine popping problems

L

LadyLauraIV

New Member
Nov 7, 2021
24
ft pierce fl.
Boat Info
2002 340 Amberjack 8.1L Raymarine elect.
Engines
8.1L Mercruisers inboard
02 340 AJ 8.1 inboards. 393 hrs. we bought the boat from someone who neglected it.
during sea trial port engine would not get above 3000 rpm and popping thru intake.
indicating to me a lean backfire, the marina owners told me this boat hadnt been taken out in at least a year. it had 3/4 full tanks. i checked fuel pressure at idle and it gave me 36 psi.
so i changed both boost pump and hi pressure pump, coolers, regulators and fuel/water separators in the cf2 system on both motors (im sick that way) took it out and got better power but port side was firewalled at 3600 rpm with some occasional popping, but not as much. while starboard side was a little past halfway at 3600 rpm. we used as much of the old fuel as possible got down to around 1/4 tanks and filled up at our marina. then took it out and had a improvement in power but still popping and throttles still spread. we had very little issues until we turned around to go back, i powered up and got a ton of popping around 3400 rpm out of port motor. got back to the slip and put on the diacom system- no fault codes.
went to the test section and did a induced misfire test at 1600+/- 50rpm and #5 cyl showed no change. pulled plug an found porcelain was white on one side and dark on the other side. did compression test it was 172psi to 180 in all cyl with #5 being 180psi. replaced plug then tested injector pulse at idle no problem there. coil firing nice at idle.
i'm taking her out sat for a full load test with fuel pressure gauge and diacom setup. can anyone think of anything else that i might have missed? Thanks in advance for your input.
 
LadyLauraIV said:
02 340 AJ 8.1 inboards. 393 hrs. we bought the boat from someone who neglected it.
during sea trial port engine would not get above 3000 rpm and popping thru intake.
indicating to me a lean backfire, the marina owners told me this boat hadnt been taken out in at least a year. it had 3/4 full tanks. i checked fuel pressure at idle and it gave me 36 psi.
so i changed both boost pump and hi pressure pump, coolers, regulators and fuel/water separators in the cf2 system on both motors (im sick that way) took it out and got better power but port side was firewalled at 3600 rpm with some occasional popping, but not as much. while starboard side was a little past halfway at 3600 rpm. we used as much of the old fuel as possible got down to around 1/4 tanks and filled up at our marina. then took it out and had a improvement in power but still popping and throttles still spread. we had very little issues until we turned around to go back, i powered up and got a ton of popping around 3400 rpm out of port motor. got back to the slip and put on the diacom system- no fault codes.
went to the test section and did a induced misfire test at 1600+/- 50rpm and #5 cyl showed no change. pulled plug an found porcelain was white on one side and dark on the other side. did compression test it was 172psi to 180 in all cyl with #5 being 180psi. replaced plug then tested injector pulse at idle no problem there. coil firing nice at idle.
i'm taking her out sat for a full load test with fuel pressure gauge and diacom setup. can anyone think of anything else that i might have missed? Thanks in advance for your input.
Click to expand...
I would start with all new plugs and wires even if fuel pressure checks well. Could be fouled injectors also.
 
techmitch said:
I would start with all new plugs and wires even if fuel pressure checks well. Could be fouled injectors also.
Click to expand...
thanks Mitch i was pretty much headed in that direction the weird thing is i never got so much as a hiccup from the starboard side engine.
 
LadyLauraIV said:
thanks Mitch i was pretty much headed in that direction the weird thing is i never got so much as a hiccup from the starboard side engine.
Click to expand...
Do them both. Get yourself a good baseline since the boat is new to you.
Also with the way it's running, oil changes may be in order if they haven't been done recently or are now contaminated.
 
Start there and if that doesn't do it check your fuel pressure when your engine hits the wall. Is that a 3 or 4 bar fuel system.?
 
LadyLauraIV said:
actually i checked the spark advance and it was swinging from a high of 9 deg adv. to -15 deg
Click to expand...
A high of 9 degrees BTDC? Was that at idle? Make sure you're getting somewhere around 34 degrees BTDC when at cruise rpm. You have a great advantage in your troubleshooting regimen as there's a good running engine right next to it for comparison.
 
LadyLauraIV said:
actually i checked the spark advance and it was swinging from a high of 9 deg adv. to -15 deg
Click to expand...

I'd swap out some ignition parts from your running motor to the one having issues to find the problem.

Sounds like your a good DIY'er..... so while trying to trouble shoot don't toss to many new parts at it until you pin point the problem.
 
Little Ducky said:
I'd swap out some ignition parts from your running motor to the one having issues to find the problem.

Sounds like your a good DIY'er..... so while trying to trouble shoot don't toss to many new parts at it until you pin point the problem.
Click to expand...
i'm not a proponent of switching parts from one engine to another
techmitch said:
Do them both. Get yourself a good baseline since the boat is new to you.
Also with the way it's running, oil changes may be in order if they haven't been done recently or are now contaminated.
Click to expand...
lofs done twice since ive owned her (2 months)
 
Nater Potater said:
A high of 9 degrees BTDC? Was that at idle? Make sure you're getting somewhere around 34 degrees BTDC when at cruise rpm. You have a great advantage in your troubleshooting regimen as there's a good running engine right next to it for comparison.
Click to expand...
 
LadyLauraIV said:
it wasntconstant, that was just the peak advance at idle
Click to expand...
Understood, but you should be more interested in what the advance is doing in the rpm band where you're having trouble. That's why I suggested checking the timing up around 3000-3400 rpm. The reason you see the idle timing move around is due to the idle stabilization circuit that's written into the ignition control box.
 
Nater Potater said:
Understood, but you should be more interested in what the advance is doing in the rpm band where you're having trouble. That's why I suggested checking the timing up around 3000-3400 rpm. The reason you see the idle timing move around is due to the idle stabilization circuit that's written into the ignition control box.
Click to expand...
Where you learn this stuff? Seriously.
 
You must log in or register to reply here.

Forum statistics

Threads
113,119
Messages
1,426,565
Members
61,035
Latest member
Lukerney
Back
Top