looseconnection

Ok, more symptoms. poping thru intake. I spent a gread deal of time yesterday with the engine running and listening. Under no load engine runs up to higher rpm with out issue but I get a pop thru the intake once I advance throttle while in gear. Must have sun pad up to hear this. I am guessing fuel related now...I am going to check codes once more soon. I have replaced all the items considered maintenace items plus the sensors in the distributer-rotor, caps, plugs.

Motor only stumbles under load.... time to check fuel pressure, anit siphon, ect. I have checked for soft spots in fuel lines.

Could a map sensor be doing this? only under load?

Thanks,

LC

sprink58

LC...racking my head through fundamentals..."old school" logic points me towards ignition via spark lead cross over. Try running it in the dark to see if you have any arcs showing up.

I had an '88 'vette that did this...replaced the spark leads...problem went away.

keith2500hd

check 5 and 7 ign wires make sure in right order and that wires are seperated.

looseconnection

I will check 5 and 7 leads to verify no touch. Gonna go pull the anti siphon and check it, then see if any codes are up. Being that this issue is only when engine is under load what can a service shop do to simulate this while the boat is on the trailer?

sprink58

The only way to duplicate is in the water. I've seen guys down here do it tied to the dock but short of that it cannot be duplicated on the trailer.

looseconnection

Anti siphon valve free. Fule filter. Changed and old cut open. I blew backwrds thru there pickup and it wasnot clogged. Was considerable junk poured out of filer and in bottom of tank. Next is plug wire chaned. I have not done this yet. Routing is correct but isulation values unknown. Had to remove fuel water sep bracket filter was on too tight to remove in boat all the fuel lines were hand tight at best.... never leaked out but may leak in since its neg pressure side of pump..

4mulafastech

I had a fuel related issue with my '06 292. While not the exact symptoms you are describing, my starboard engine would periodically lose power and sometimes die for no apparent reason. Turns out the pick-up in the fuel tank was allowing air to get in the fuel stream, cavitate the electric pump and cause a lack of fuel pressure. Took me a while to finally figure out the plastic pick-up tube in the tank connected to the 90° fitting swelled and no longer had an air tight seal. Problem was defenitely worse when running lower fuel levels, which makes sense. Replaced both with welded stainless steel tubes and no problems since.

Expensive Date

I had a problem once I could not find. Had a tech that I know sit in the passenger seat with a laptop (merc. software) while I was running. Took about 3 minutes to find it it was a bad neutral safety switch the ECM thought the engine was in Neutral. I never would have found that.

Did you take a fuel pressure reading, do you have a gauge?

Expensive Date

Other possibilities, if running on a laptop is not an option.

Fuel pressure loss, if the 350s are like the 6.2s the have two fuel pumps. High and low pressure, you could have a bad high pressure pump, or regulator.

Fuel line tank, as stated in other post.

Crank trigger?

Bad plug wire

Bad ground to ignition system.

FIXX

iTrader: (2)

when efi engine are lacking fuel pressure they will pop through the intake like a mild backfire,,check youe fuel pressure,,also check your fuel pick up's at the tank,f they are a alumunum tubes you may hav a cracked one where it threads at the top of the fitting that screws into the tank..the replacement is a plastic tube so it can take the shock.