Cold Idle stumble, idels well after warmed up

[greauxpete]

Serial number in signature.

I am experiencing a cold start idle issue in the last week.

On cold starts, the engine will idle rough for about 5 seconds and kill.

Then I restart the motor immediately after killing and it idles rough until temperatures reach about 120F on smartcraft tach and the idle is smooth and there are no further issues while warm.

The motor does this exactly everytime I start cold, but does not when it is warmed up even slightly. The motor runs through the full rpm range without issue (when warm).

*Note: I recently changed the spark plugs (6 hours), fuel filter (2 hours), and the belt (2 hours).
(Symptoms were present before fuel filter and belt change)

The thermostats come up to temperature of 120F- 127F (at idle) on smartcraft and I have verified "ballpark" temps using infrared temp gun on center of thermostat housings.

I run quickleen 1oz per 5 gallons, quickstor 1 oz per 5 gallons, and premix 150:1 premium plus oil in every tank.

I verified spark on each cylinder with inductive timing light.

I have also verified air and fuel pressures at idle, 5, 10, and 15 seconds after shutdown. Pressures are in spec.

See video of air/fuel pressure test here:



I recently had a water leak at the water pressure sensor compression fitting (fixed).

Any reccomendations on what could be causing this and further troubleshooting?

Thanks,

Steve

[Bob G.]

Were the symptoms present before the spark plugs were replaced?

[greauxpete]

No, pretty sure this started after
the old carboned up plugs were removed.
Defective plugs?

[SilverFox579]

Make sure plug wires are firmly seated and that you didn't disturb any injector connectors. If problem still exists remove plugs to inspect and verify proper gap.

[EuropeanAM]

Make sure plug wires are firmly seated and that you didn't disturb any injector connectors. If problem still exists remove plugs to inspect and verify proper gap.

+1... also inspect plugs for any lines that run even remotely LENGTHWISE in or on the porcelain that surrounds the electrode. ANY such line should be considered a crack- REPLACE the spark plug.

Make sure you are using IZFR5G spark plugs, gapped at .033".

[greauxpete]

10-4
I'll pull the plugs, label them, take pictures and report back.

[greauxpete]

Here are the plugs after 6 hours of run time:

20200717_010826.jpg

Replaced with NEW IZFR5G plugs gapped (gently with correct gapping tool and grabbing only the hex of the plug) at 0.033".
Still have a rough idle until it warms up then its smooth.

[Savage]

Yikes #2 and #3 have issues. Better retest coils and wires.

[SilverFox579]

Yikes #2 and #3 have issues. Better retest coils and wires.

^^^^

[greauxpete]

My testing on the coils is limited to the following:

1. I have confirmed spark only with a induictive timing light applied to each wire and confirmed a blinking light.
2. I have ohmed the coils out and compared results to the FSM specs. Although, i have heard they can still be "bad" even though they ohm out within spec.

Any other recommendations on testing/troubleshooting the coils?

Thanks for the help.

Steve

[EuropeanAM]

Any chance you can record a COLD start video like the one you did earlier?

Just a hunch... but I suspect you may have a pulse pump diaphragm leaking (pressures don't "look" like a tracker valve leak but that can be deceiving).

[greauxpete]

Here is a cold start video taken 5 minutes ago:



It starts with rough idle for a few seconds and kills, then it runs rough without killing on the second start and the the idle smooths out after the thermostat cycles. Repeats exact same behavior every cold start.

[greauxpete]

I tore into the pulse fuel pump, no obvious tears but it looks pretty ballooned /stretched out. Popped in a rebuild kit, but need to wait for the engine to cool off to retest.

See pics below:

20200717_143935.jpg

[Savage]

Hope you used a Genuine Mercury Marine Pulse Pump Kit Part# 857005A1. Aftermarket can cause problems.

[greauxpete]

Yes, I carry a genuine mercury pulse pump kit in my offshore spares box for occasions such as this.

Going to test it tonight.

I'm guessing if there was a pin hole in the diaphragm the motor may have been sucking extra fuel in through the pulse line causing my motor to run rich and fouling my plugs?

Thanks fellas..

[greauxpete]

After rebuilding fuel pump following the paper directions in the kit, the idle is still rough, but now I'm down on power, and it takes a while to get on plane (can not achieve 5500 rpms now)

[greauxpete]

I'm getting a new fuel pump kit and rebuilding the pulse pump, I must have assembled it incorrectly.

[greauxpete]

The pulse fuel pump rebuild solved the rough idle. Still need to check the #2 and 3 plugs for fouling after running it under load but the idle at cold start is smooth now.

The reason it was down on power was because "someone" left a coil wire unplugged..lmao..

I appreciate everyone's help.

[EuropeanAM]

[greauxpete]

After a trip offshore, I noticed a rough cold start idle.
So, I pulled the cowl and started inspecting while running on the muffs and found my pulse pump mounting bolts loose.
When I pushed the pulse pump against the block the engine idle speed sped up. The idle smoothed out as well, after retorquing to spec.

I'm positive I torqued these bolts to 55 in-lbs after remounting the rebuilt pulse pump. I made a 120 mile run offshore and back, and I guess they vibrated loose.

Question:

1. Should I be using loctite on the pulse pump mounting bolts?

2. Should I be concerned about a lean running issue on the last run offshore?

3. Should I rebuild the pulse pump?

Thanks,

Steve