1996 mercury 150efi help

[BronsenHand]

Been having an issue with a surge I have bench tested the stator, trigger, and installed backup new switch boxes checked all the coils new plug wires a month ago new reeds a month ago spark plugs are new. These symptoms have been slowly getting worse for a couple of months to the point I’m worried about hurting the engine.

I’m just lost it got a new 2nd hand ecu supposedly rebuilt by cdi last year as well as stator and trigger boxes it had an electrical meltdown.

Now this year it started with a decel surge then when you hold it at anything less than full throttle it surges bad. Going to run a fuel pressure test tomorrow. Would love some more ideas those.

I have tried unplugging 2 spark plugs at a time but engine still surges with no load.

 

[Miles2000]

That part throttle surge with no load points me at the TPS before the ignition. Sounds like you already covered the stator, trigger and both switch boxes.

Key on, engine off. Backprobe the TPS and roll the throttle slow from idle to WOT by hand. Voltage should climb smooth with no jump and no dead spot. I have seen them wear right where you cruise... and then the ECU is chasing a throttle position that isn't there any more.

Put the gauge on the rail schrader and watch it while it surges, not just at idle. If pressure drops when it starts hunting, it's the high pressure pump or a plugged screen in the VST. If it holds dead steady, I'd stop looking at the fuel side.

That meltdown history bothers me too. Clean the block ground and the ECU ground, and pull the ECU plug to look for green pins. A stator can bench test fine cold and fall on its face hot, so if this only shows up after 20 minutes that's where I'd go next.

Does it do it in neutral on muffs the same as in the water? Does the rpm really swing or is it just the sound? Post up the fuel pressure numbers tomorrow. Thanks.