90HP Mercury 4Stroke EFI Stalling at Idle and Surging

[allnencore]

Hello Boaters

I have 2019 90Hp Mercury 4stroke EFI its also a command thrust. Serial # 2B566524

Let me start by saying I have read some great in-depth responses on this board so thank in advance for any input.

Well out of the gate I think I have 2 separate problems just based on what I am seeing but we will see.

Issue #1 Engine refuses to idle without stalling. Even upon initial startup or at least within 30 seconds there of. And then stalls. After warm it wont stay running at idle out of gear or just in gear without throttle up.

Issue #2 I can be driving the boat like yesterday a full hour into a trip running 4000 rpms and it randomly started to surge. Oddly, I watched the tachometer while this was happening it never moved. Stopped for 15 minutes to take a swim and headed back to the marina for 1 hour at 4000 rpms and no surging on the way back.

Work I have done thus far to try to fix these problems.

New IAC valve
New ECM
New Plugs
Drained fuel and started new with fresh fuel
New Fuel Filter

Also when I hooked it to the scanner there were no error codes - full disclosure the scanner was a recent purchase and I know very little about how to use it but in the "read codes" feature there were none available.

So as you can see Iv tried a few things to no success.

OK gang fire away! And Thanks.

 

[dingbat]

A surging EFI fuel delivery problem.
Why did you change all those parts?

What is the fuel pressure on rail before startup?

Have you monitored fuel pressure while running?

 

[Scott2020]

A surging EFI fuel delivery problem.
Why did you change all those parts?

What is the fuel pressure on rail before startup?

Have you monitored fuel pressure while running?

DB, how is this done? I have VesselView on a 2013 90 EFI 4Stroke, but was disappointed to not find a parameter for fuel pressure. No sensor I assume.

 

[dingbat]

DB, how is this done? I have VesselView on a 2013 90 EFI 4Stroke, but was disappointed to not find a parameter for fuel pressure. No sensor I assume.

Pressure and flow sensors are notoriously inaccurate and failure prone. Besides, fuel pumps work until they don’t.

The display would say 45 lbs. day in and day out until the time it said 12 lbs. and the boat starts surging and acting like it’s running out of fuel…lol

You either buy the Mercury diagnostics package ($$$) or you put a fuel pressure gauge on the rail. Typically has a port to plug in. Would need to monitor pressure while it’s was acting up to confirm.