Port engine popping problems

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.
i am i just havent taken it out yet. sat. is the day
 
The reason you see the idle timing move around is due to the idle stabilization circuit that's written into the ignition control box.
This
Short version is that you have to either short two leads, or pull one to ground (depending on year/configuration) to disable that part of the circuitry before setting the timing. If not, the ignition will shift up and down in attempts to keep the idle speed at its prescribed value.
Long version; the idle stabilization circuit was put into wide-spread usage during the early 80's (don't quote me on that) as electronic engine controls began to come into their own. The advantage being that you could have a nice, slow idle, but would then pick up the timing when the car (automatic trans) was put into gear, keeping the engine from stalling. This was before IACs and fly-by-wire throttles came into play. The same can be thought of with our boats when engaging the prop.
I also have this option with the aftermarket electronic ignition I added to my antiquated Norton motorcycle. It really helps even things out between a cold, sluggish engine that doesn't want to idle, yet keeps it from revving too high once it comes up to temp.
 
@Nater Potater Isn't this engine distributorless and someone would actually have to know how to change the timing right? Or are you thinking something electrical is failing? Static and not running the system should be set up full advance; whatever that is (38 degrees BTDC) then in some of the older FI engines a connector disconnected and timed with a light at idle. Then when ignition is turned on the ECM sets the nominal start and idle timing once the engine does one or two start rotations (the ECM has to find where the crank and cam position is).
Popping through the intake plenum. TBI or MPI?
If TBI then clean the throttle body and send the injectors for cleaning and calibration.
If MPI there is likely an intake valve that is sticky. There is no fuel charge in the intake to do a lean backfire.
In any case a problem in the secondary part of the ignition system (plugs, wires, coils) would cause stumbling, rough running, and loss of power but doubt backfire through the intake unless there is some form of crossfire in the ignition. The timing would have to be way off to fire with the intake valves open.
Just my thoughts without knowing the fuel system on an 02 8.1...
 
Last edited:
ok, this is weird after closer inspection of the plugs, i found one with a tiny hairline fracture, so i changed them all.
also i happened to notice the bypass on the fuel shutoff valve was partially closed so i opened it all the way. took on sea trial and not one hiccup in 4hrs of running in different load ranges with different weights,full tank,full water 4 people, and so on. im leaning (no pun intended) towards a bad/sticky shutoff valve. if im not mistaken these are a electric version of the anti-siphon valves? Thanks to everyone for their input, i was pulling hair out and i dont have much.
 
Good find!

It could have been a combination of those things causing you grief. 8.1’s are known to go through plugs quicker than the small blocks.

Searching around here you’ll find others have cured issues with new plugs.
 
ok, this is weird after closer inspection of the plugs, i found one with a tiny hairline fracture, so i changed them all.
also i happened to notice the bypass on the fuel shutoff valve was partially closed so i opened it all the way. took on sea trial and not one hiccup in 4hrs of running in different load ranges with different weights,full tank,full water 4 people, and so on. im leaning (no pun intended) towards a bad/sticky shutoff valve. if im not mistaken these are a electric version of the anti-siphon valves? Thanks to everyone for their input, i was pulling hair out and i dont have much.
Were you able to reach WOT on both engines?
 

Forum statistics

Threads
112,950
Messages
1,422,863
Members
60,932
Latest member
juliediane
Back
Top