Intermittent Backfire 4.3 EFI

[Watson27]

I’m new to this group. So forgive me if I accidentally leave out important information. Was referred to come here by a friend.
I own a 2001 Campion Allante with I/O 4.3 EFI mercruiser. This Backfiring issue just started happening on my last cottage trip. While under load it will intermittently backfire/lose power for a brief second then continue to running good. Idles fine. It gave me a couple issues starting. Had to give it some throtle but not every time starting. And it stalled on me while travelling at a very slow speed when I was about to load it back on the trailer. I obviously only use high test gas and the fuel filter was changed before winter storage last season. I am licensed vehicle technician but I don’t have much experience with marine. Thank you for reading and possible suggestions. Shaun.

 

[Scott Danforth]

First, welcome aboard

second get the factory mercruiser manual.

it will help us help you if you post a bit more about your engine. TBI or MPI? best if you post the serial numbers

until then you are getting generic answers

you are running lean. so start with the basics

• what is your fuel pressure and how does that compare to the correct factory manual specs?
• have you tested your anti-siphon valve?
• have you checked the contents of your fuel filter

 

[Watson27]

First, welcome aboard

second get the factory mercruiser manual.

it will help us help you if you post a bit more about your engine. TBI or MPI? best if you post the serial numbers

until then you are getting generic answers

you are running lean. so start with the basics

• what is your fuel pressure and how does that compare to the correct factory manual specs?
• have you tested your anti-siphon valve?
• have you checked the contents of your fuel filter

My engine serial number is GM1009586. I don’t have a fuel pressure gauge at the moment. I will check my fuel filter contents and repost. I don’t know how to test a anti syphon valve.

 

[Watson27]

First, welcome aboard

second get the factory mercruiser manual.

it will help us help you if you post a bit more about your engine. TBI or MPI? best if you post the serial numbers

until then you are getting generic answers

you are running lean. so start with the basics

• what is your fuel pressure and how does that compare to the correct factory manual specs?
• have you tested your anti-siphon valve?
• have you checked the contents of your fuel filter

Does the engine serial number determine if it’s TBI or MPI?

 

[QBhoy]

Hi. Firstly, lovely boat. Have a campion myself and run the owners group on the dreaded Face book. Only reason I’m on it.
anyway, at 2001, if the engine is original, I know it will be an efi and not a MPi. Was the only option apart from a carb then. I’d be almost sure you are having a crappy fuel problem. Running lean with water contamination. Take the filter off and pour it into a glass for an hour to settle. I’ll bet you have water at the bottom of it. Take the contents of the tank out and refill. New filter. You’ll be just fine after.

 

[Scott Danforth]

My engine serial number is GM1009586. I don’t have a fuel pressure gauge at the moment. I will check my fuel filter contents and repost. I don’t know how to test a anti syphon valve.

that is a GM casting number. the serial number is on a mercruiser tag riveted just above the starter. it should also be on top of your vanity cover covering the spark arrestor

 

[Watson27]

that is a GM casting number. the serial number is on a mercruiser tag riveted just above the starter. it should also be on top of your vanity cover covering the spark arrestor

I got that number from the vanity cover.

 

[Watson27]

Checked the anti-syphon valve, seems to be moving without sticking or catching. Going to check the fuel in the filter. Also notice the spark arrestor pretty clogged with debris. Will clean that out tomorrow with some brake cleans. I appreciate all the help so far. I’ll look for that serial number around the starter tomorrow too. Thanks Scott.

 

[Watson27]

Hi. Firstly, lovely boat. Have a campion myself and run the owners group on the dreaded Face book. Only reason I’m on it.
anyway, at 2001, if the engine is original, I know it will be an efi and not a MPi. Was the only option apart from a carb then. I’d be almost sure you are having a crappy fuel problem. Running lean with water contamination. Take the filter off and pour it into a glass for an hour to settle. I’ll bet you have water at the bottom of it. Take the contents of the tank out and refill. New filter. You’ll be just fine after.

Thanks for the advice. I’ll check the fuel in the am. My question is: wouldn’t the engine run consistently poor with water in the fuel?

 

[QBhoy]

Thanks for the advice. I’ll check the fuel in the am. My question is: wouldn’t the engine run consistently poor with water in the fuel?

Yes. That’s one of the potential symptoms

 

[Scott Danforth]

your serial number is 0M009586

4.3L EFI (GEN+) TBI GM 262 V-6 - 0L012009 THRU 0L618999

4.3L EFI (GEN+) TBI GM 262 V-6 - 0L012009 THRU 0L618999

www.mercruiserparts.com

 

[Watson27]

your serial number is 0M009586

4.3L EFI (GEN+) TBI GM 262 V-6 - 0L012009 THRU 0L618999

4.3L EFI (GEN+) TBI GM 262 V-6 - 0L012009 THRU 0L618999

www.mercruiserparts.com

Sorry my actual number is M009586

 

[Watson27]

Hi. Firstly, lovely boat. Have a campion myself and run the owners group on the dreaded Face book. Only reason I’m on it.
anyway, at 2001, if the engine is original, I know it will be an efi and not a MPi. Was the only option apart from a carb then. I’d be almost sure you are having a crappy fuel problem. Running lean with water contamination. Take the filter off and pour it into a glass for an hour to settle. I’ll bet you have water at the bottom of it. Take the contents of the tank out and refill. New filter. You’ll be just fine after.

Sorry have been working two jobs all summer. Haven’t been able to get to my boat till now. Just emptied my fuel filter contents into a glass jar and waiting the hour as suggested. My serial number is M009586. Will post a picture of the jar after an hour or so.

 

[Watson27]

So I’ve let the fuel filter solution settle and there is no separation of water at all. Is it possible the fuel pump is weak and needs to be replaced? Is the fuel pump for my engine located in the fuel tank or located on the engine itself? I do audibly hear my fuel pump when it gets power but it does sound very laboured if that makes sense.

 

[stang32]

there isa shrader valve on the fuel line you can test the pressure there, if you dont have a fuel gauge, you can rent one at autozone. make sure you have no leaks from the connections and have someone drive it while you monitoring the gauge. try to get it to backfire and note the pressure at that time,