New v8 300proxs running problem

**Boozin909** · 07-03-2022, 06:13 PM

So I just got my new v8 300proxs. It has prob only 3 hours if that on it. I have not ran it wide open and nothing above 4200 rpm. So I have 2 gas tanks on my lake and one in front and one in the rear. I had no issues for prob 10 to 15 gal of gas. Then the motor started to buck or feel like a fuel flow issue so I switched tanks still the problem persisted. I could idle no problems get on plane get up to 3500 to 3700 and then it would start bucking again and then did that at lower and lower rpm to where I could only idle. So when I got back in I checked the manual gas tank selector that' was fine. So I checked hoses on each tank all the way to the fuel water separator on the motor nothing seems out of ordinary. After that went out ran it again no issue for prob 3 gallons keeping it at 3800 rpm or less. Once I tried to get above 4k it started bucking mildly at first then got worse and continued to do it at lower rpms until idle again. I thought maybe a hose was loose but they all were tight. Then I thought fuel filter/water separator may have got junk in it from running tank low but that seemed fine blowing through it and I just had my tanks pumped and cleaned. I also have been redoing the whole boat so whole new re wire of the boat, new fuel lines new lithium batteries trolling motor ect rigged by boattronics in jacksonville. If anybody has any idea on all ears
Thanks for any help

**Jim Speros** · 07-03-2022, 06:27 PM

No engine alarms? Are tank vents clear? Can you run on a remote tank? Can you feel the primer bulb while running? Are volts stable at 14 Volts?

**Boozin909** · 07-03-2022, 08:12 PM

Originally Posted by Jim Speros

No engine alarms? Are tank vents clear? Can you run on a remote tank? Can you feel the primer bulb while running? Are volts stable at 14 Volts?

No faults or engine alarms vents seem clear blowing into lines. When boattronics ran new gas lines they didn't install primer bulb so I was going to put one on and try that next.

**RSWORDS** · 07-25-2022, 08:20 PM

Originally Posted by Boozin909

No faults or engine alarms vents seem clear blowing into lines. When boattronics ran new gas lines they didn't install primer bulb so I was going to put one on and try that next.

Don't add a bulb.

Check the fuel restrictions. You can watch the fuel trim.with G3

**Pulsare2400** · 07-25-2022, 09:02 PM

I have a 300R and it did something similar but at higher rpm and it just kept getting worse. Finally, Don Weed at European Marine found the issue quickly and corrected it. A faulty fuel injection wire harness on #7 cylinder caused a large misfire that resulted in the engine going very rich and back to lean. The wire harness was repaired, and the plug wires all changed under warranty and 50 hours later still performing well.

**WaterZebra** · 07-26-2022, 08:10 PM

Originally Posted by Boozin909

So I just got my new v8 300proxs. It has prob only 3 hours if that on it. I have not ran it wide open and nothing above 4200 rpm. So I have 2 gas tanks on my lake and one in front and one in the rear. I had no issues for prob 10 to 15 gal of gas. Then the motor started to buck or feel like a fuel flow issue so I switched tanks still the problem persisted. I could idle no problems get on plane get up to 3500 to 3700 and then it would start bucking again and then did that at lower and lower rpm to where I could only idle. So when I got back in I checked the manual gas tank selector that' was fine. So I checked hoses on each tank all the way to the fuel water separator on the motor nothing seems out of ordinary. After that went out ran it again no issue for prob 3 gallons keeping it at 3800 rpm or less. Once I tried to get above 4k it started bucking mildly at first then got worse and continued to do it at lower rpms until idle again. I thought maybe a hose was loose but they all were tight. Then I thought fuel filter/water separator may have got junk in it from running tank low but that seemed fine blowing through it and I just had my tanks pumped and cleaned. I also have been redoing the whole boat so whole new re wire of the boat, new fuel lines new lithium batteries trolling motor ect rigged by boattronics in jacksonville. If anybody has any idea on all ears
Thanks for any help

If you didn't install a new wiring harness with your V8 ProXS, you should do that. Also, you need a dedicated clean power circuit from the primary battery to the ECU.
Your ECU should be spitting out error codes to easily diagnose the problem. Change EVERY fuel filter you've got and run fuel directly to the engine from a pristinely clean small tank so you can isolate one problem at a time. Again, your ECU should be telling you what's failing. Your dealer's laptop should tell you what the problem is in 5 minutes. Having your tanks "cleaned" maybe causing more fuel debris problems than you think.

**obrien** · 07-26-2022, 09:21 PM

Originally Posted by WaterZebra

If you didn't install a new wiring harness with your V8 ProXS, you should do that. Also, you need a dedicated clean power circuit from the primary battery to the ECU.
Your ECU should be spitting out error codes to easily diagnose the problem. Change EVERY fuel filter you've got and run fuel directly to the engine from a pristinely clean small tank so you can isolate one problem at a time. Again, your ECU should be telling you what's failing. Your dealer's laptop should tell you what the problem is in 5 minutes. Having your tanks "cleaned" maybe causing more fuel debris problems than you think.

just because there is a run issue does not mean the computer is going to give him a fault code. If there is no alarm, there will be no stored codes. With this being a brand new engine, he should take it back to the dealer that installed it and have them diagnose it. I would expect the clean power was installed as the engine would not run without it, but all connections should be checked as well
Also, as it was stated before in this post, do not install a primer bulb

**Pulsare2400** · 07-27-2022, 10:03 AM

My 300R did not store any codes when we had the faulty injector wire harness on #7, and as mentioned above, no alarm went off either. Just ran very poorly.

**Capt j** · 07-27-2022, 10:37 AM

Also for break in, you're supposed to run WOT for 1 minute every 2 minutes for the first 2 hours to seat the rings varying rpms otherwise and staying under 4500. Then hours 2-10, vary rpms staying under 4500, and then wot no more than 5 minutes at a time. Once you get this resolved I would do the proper break in ASAP.

**WaterZebra** · 07-28-2022, 07:33 PM

Originally Posted by Boozin909

So I just got my new v8 300proxs. It has prob only 3 hours if that on it. I have not ran it wide open and nothing above 4200 rpm. So I have 2 gas tanks on my lake and one in front and one in the rear. I had no issues for prob 10 to 15 gal of gas. Then the motor started to buck or feel like a fuel flow issue so I switched tanks still the problem persisted. I could idle no problems get on plane get up to 3500 to 3700 and then it would start bucking again and then did that at lower and lower rpm to where I could only idle. So when I got back in I checked the manual gas tank selector that' was fine. So I checked hoses on each tank all the way to the fuel water separator on the motor nothing seems out of ordinary. After that went out ran it again no issue for prob 3 gallons keeping it at 3800 rpm or less. Once I tried to get above 4k it started bucking mildly at first then got worse and continued to do it at lower rpms until idle again. I thought maybe a hose was loose but they all were tight. Then I thought fuel filter/water separator may have got junk in it from running tank low but that seemed fine blowing through it and I just had my tanks pumped and cleaned. I also have been redoing the whole boat so whole new re wire of the boat, new fuel lines new lithium batteries trolling motor ect rigged by boattronics in jacksonville. If anybody has any idea on all ears
Thanks for any help

It appears that BoatTronics specializes in electrical stuff. So who did your 300ProXS installation?

**Instigator** · 07-28-2022, 07:43 PM

Man I wish I had a pair of these!

**Capt j** · 07-28-2022, 08:50 PM

Wait, do you have a lithium starting battery????? Is it a Dakota that is rated as a dual purpose battery, or just a lithium battery? I'm willing to bet it's the BMS shutting the battery off and on.......put an AGM battery in and see what it does.

**WaterZebra** · 07-29-2022, 08:21 AM

Originally Posted by Capt j

Wait, do you have a lithium starting battery????? Is it a Dakota that is rated as a dual purpose battery, or just a lithium battery? I'm willing to bet it's the BMS shutting the battery off and on.......put an AGM battery in and see what it does.

Lithium batteries (at this point in time) are a bad investment for marine power. AGM is a solid dependable choice and could eliminate the BMS gremlin. As I said before, make sure your ProXS has a CLEAN POWER CIRCUIT to the ECU.

**half fast** · 07-29-2022, 08:59 PM

We have seen some of the V6 and V8 mercs fail the hi psi fuel pump very early on . It’s officially called a fuel module . Sounds like yours may be bad . Hf…

**kellytheaker** · 07-30-2022, 03:02 PM

Interesting point on the hi pressure fuel pumps - is this a sitting long periods . Stuck pumps -
When I purchased an opti - 200xs - I had heard mention of it - his remedy was run pump backwards momentarily - it worked and has run the Merc fuel conditioner since .
So I'm not sure on what fuel pump frequency your seeing - can you expand the issue .