Poor Idle & Stalling on 2001 Mercury 300X Motors!!

**Hydrogasm** · 01-26-2023, 12:05 PM

I have a pair of 2001 300X motors that only have 58 hours on them from new. I bought the boat back in 2017 with only 47 hours and have never been apart. I put new plugs and fuel filters and had all the injectors cleaned and flowed before I ran it because it hadn't been run for a couple of summers before I purchased it. I ran it for the summers of 2018 and 19 and it seemed to work fine. It did not get in the lake for the next two summers as I was re-rigging it and had a hard time getting the parts that I needed. I ran it last summer and both engines were harder to start especially cold and they would stall several times when shifting into gear. Once they were warmed up that seemed to improve. Sorry to ramble on it bit. I changed all the plugs and both fuel filters again but that didn't seem to make any difference. Any thoughts would be greatly appreciated as the boat is in the garage, so I can work on it over the winter.
Thanks
Gary

**Dave Strong** · 01-26-2023, 12:21 PM

With todays fuels could be injectors after sitting for 2 summers.

Dave

**Hydrogasm** · 01-26-2023, 12:27 PM

Originally Posted by Dave Strong

With todays fuels could be injectors after sitting for 2 summers.

Dave

Dave

I ran the engines dry of fuel when I winterized the motors but I do plan to send the injectors to be cleaned and flowed again over the winter though.

Thanks
Gary

**Dave Strong** · 01-26-2023, 01:31 PM

Originally Posted by Hydrogasm

Dave

I ran the engines dry of fuel when I winterized the motors but I do plan to send the injectors to be cleaned and flowed again over the winter though.

Thanks
Gary

Not a fan of running EFI dry, hard on pumps and injectors as use fuel to cool and lubricate.

Dave

**Jim Speros** · 01-26-2023, 03:44 PM

I agree with Dave on both posts.
Fuel sucks and needs a cleaner stabilizer,, pick your brand, used religiously every time you add fuel. Using ethanol free fuel is best and worth the money.
I think running an EFI dry of fuel is doing much more harm then good.

**cali kid** · 01-27-2023, 09:46 AM

Good advice above. I just want to say, that is one Wicked looking ride! Super jealous. Must fly.

**Hydrogasm** · 01-28-2023, 11:56 AM

Originally Posted by cali kid

Good advice above. I just want to say, that is one Wicked looking ride! Super jealous. Must fly.

cali kid
I am very happy with the boat and the best I have seen so far was 110mph on my Livorsi GPS speedo on a Sunday afternoon with a lot of boat activity on the lake. I am sure there is more there under the right conditions.
Thanks
Gary

**Hydrogasm** · 01-28-2023, 12:26 PM

Originally Posted by Jim Speros

I agree with Dave on both posts.
Fuel sucks and needs a cleaner stabilizer,, pick your brand, used religiously every time you add fuel. Using ethanol free fuel is best and worth the money.
I think running an EFI dry of fuel is doing much more harm then good.

Jim
I only use 91 Octane ethanol free fuel in my boats but that is good advice. Also I an wondering if the reeds might need to be replaced. I was thinking of installing Chris Carson reeds and crankcase stuffers. Any thoughts on that would be greatly appreciated.
Thanks
Gary

**kellytheaker** · 01-28-2023, 02:04 PM

I can only suggest a DDT read and see if issues are present . Pay attention to coils and see where the fuel percentage is at for a setting .

**Hydrogasm** · 01-28-2023, 02:15 PM

Originally Posted by kellytheaker

I can only suggest a DDT read and see if issues are present . Pay attention to coils and see where the fuel percentage is at for a setting .

kellytheaker

I have a Rinda Pro scan tool and I will definitely check it out to see if there are any faults.

Thanks
Gary

**kellytheaker** · 01-28-2023, 03:18 PM

yes sir i am aware of your pro scan tool , check the fuel percentage to see where its set at - you will have the capability of moving it plus several times or negative . Meaning rich or lean dependent of your sea level . I have never used the Rinda but Merc DDT allows the screen/Fuel settings as part of its capabilities .
Just be aware i had a conversation with Ted Gryguc/Mercury tech a while back- he stated watch for misfire on the coil packs - and replace coils as a set . This stuff is getting old at 20 years - mine was an 05 -280 .
Also as i mentioned check the fuel settings .
A TPS voltage check would be beneficial as well - just to ensure .
I found its always something basic
Hope this helps you forward

**Hydrogasm** · 02-12-2023, 04:18 PM

Originally Posted by kellytheaker

yes sir i am aware of your pro scan tool , check the fuel percentage to see where its set at - you will have the capability of moving it plus several times or negative . Meaning rich or lean dependent of your sea level . I have never used the Rinda but Merc DDT allows the screen/Fuel settings as part of its capabilities .
Just be aware i had a conversation with Ted Gryguc/Mercury tech a while back- he stated watch for misfire on the coil packs - and replace coils as a set . This stuff is getting old at 20 years - mine was an 05 -280 .
Also as i mentioned check the fuel settings .
A TPS voltage check would be beneficial as well - just to ensure .
I found its always something basic
Hope this helps you forward

kellytheaker
I pulled out my DMT-4000 meter and checked the coils. Here is what I came up with:

Starboard motor
Coil Driver 1
99.6 kohms red/black
9.96 kohms black/green
9.96 kohms black/green

Coil driver 2
104.3 kohms red/black
9.96 kohms black/green
9.96 kohms black/green

Coil driver 3
102.9 kohms red/black
9.94 kohms black/green
9.95 kohms black/green

Port Motor
Coil driver 1
92.2 kohms red/black
9.6 kohms black/green
9.5 kohms black/green

Coil driver 2
No readings

Coil driver 3
No readings

Mercury manual states:
85 kohms +/- 10% red/black
10 kohms +/- 10% black/green

Any thoughts would be greatly appreciated.
Thanks
Gary

**Hydrogasm** · 02-14-2023, 07:22 AM

Anyone have any thoughts on this? Let me know.
Thanks
Gary

**kellytheaker** · 02-14-2023, 11:37 AM

The Murcury DDT would show misfires and how often - an accumulation of misfires will lead you to believe plugs are possibly a problem but don't be fooled- misfires and an accumulation/ frequency can be coils and should be looked at closely .
The fuel setting on my 280 could be changed up or down - I suspect this is to offset your geographical location as far as sea level.

See if your fuel setting can be probed and changed OR at least know if it is set correctly for your location .
TPS setting should be checked if it is on your application . And check fuel lincage .
As far as coils not showing readings - I am uncertain but needs to be understood .
Some times a call to Mercury can be had and usually they ask your dealer number when a tech answers - be honest and usually they spend a few minutes and Or try and dealer close by that may offer some assistance on the issues since they may have similar occurrences.
All I know is the DDT showed misfires and it will take the driver out of the ECM . Simon Motorsports is the Guru on the ECM s in California .
These larger displacement motors will cover up a misfire due to their brut horsepower especially running a pair .
Hope this helps

**Hydrogasm** · 02-18-2023, 09:53 PM

Update!
I got my injectors back yesterday. The before and after tests the shop did on them show slight improvements in them. I am going to check my coils again to see if I can readings on the ones I didn't before. I checked the fault history and there were no misfire codes recorded.
Thanks
Gary