99 Mercruiser 5.7 Wont Start

[Georgearia]

Ok Guys, I’m new to the forum. I have a 99 Mercruiser 5.7 Carb Quadrajet, Thunderbolt 5 Bravo 2 Drive. Having issues get engine started. History, was running great. Died at dock one day. Would not start. Typically starts at turn of key. Assumed carb was fouled, so cleaned it, and ended up having it rebuilt thinking the issue was fuel related. Decided to cover all the bases while carb was being serviced. Changed Spark plugs and noticed #2 cyl wire arched to motor mount. Eureka, problem solve. Installed new set of wires, cap, rotor, and sensor module.

Installed Rebuilt carb, hard to start, rough idle until warm. Adjusted mixture and checked timing, Was running ok. Took boat out. Good idle, would not power up past 1500 rpm. Got boat back to house and know it wont start,, although it wants to...when it did a lot of soot out exhaust. Rough Idle again, until warm up. Today, no start up,, but wants to.

I bypassed oil shut down sensors, no start.
Fuel pump has power and runs
Ran Thunderbolt ignition test, all ok.
Checked fuel lines, about 3 seasons old...ok.
Electric Fuel pump tested , 9psi
Tried to start off remote fuel supply with another new fuel source, so fresh fuel in filter, No Start
Coil tested good, replaced it anyway.
Checked and cleaned engine grounds for good measure.

Noticed today that the Knock Sensor is all corroded, could that prevent the motor from starting?

Do the ECM codes need to be reset to start it? If so, how can I reset them?

Is there another sensor in the Guardian system that would prevent it from starting? Heat sensor?

Could the spark plug wire that fused to motor mount have shorted out the ECM or possible another sensor?

I”m out of ideas at this point, any ideas and direction is greatly appreciated. Thanks

 

[kenny nunez]

When the engine is turning over are you getting a spark from the spark plug wires? Is there also a spark from the coil wire?
A shorted rotor going to ground could be causing your problem. Check that the shift interrupter circuit is not engaged.

 

[QBhoy]

Hi don’t think this will have a guardian mode and perhaps only occasionally a age dependant knock sensor either ? Is it not a carb ?

could it be a sticking choke issue ?

 

[QBhoy]

When the engine is turning over are you getting a spark from the spark plug wires? Is there also a spark from the coil wire?
A shorted rotor going to ground could be causing your problem. Check that the shift interrupter circuit is not engaged.

Think it’s a bravo

 

[Georgearia]

Thanks for responses u all.

Getting spark all the way to plugs.... So I think we are good there. has New coil, new pick up sensor, cap and rotor, wires and spark plugs.

Choke is not sticking, pulls off when it starts to fire up. She just won't full run.... dies immediately.....

Bravo 2, so no shift interrupt switch.

The knock sensor is pretty rusted up, so I’m going to see if I can bypass that, see if it starts.

I wonder if the overheat sensor is shorted out although it has never over heated. Not sure how to test the sensor...

 

[Scott Danforth]

Does your distributor sensor have two wires, or the upgraded 3 wires (3rd wire is a ground)

 

[Georgearia]

It has three wires, you are correct 3rd is a ground which I did ground. The original module only had 2 wires.

 

[Triangleboater]

If it's getting healthy spark, I would move on to the fuel system.
Often, a rebuilt carb needs rebuilt again, something gets dislodged and clogs. I actually have the same issue. I rebuilt my quadrajet, guess what I have to do again. Yup.... Just part of it.

 

[Georgearia]

I agree, That’s next on the list I guess. I may send it back to the rebuild company and have them go over it.

Thanks.

 

[Bondo]

Ayuh,..... Welcome Aboard,....... That's not the original carb,..... by '99 Merc had gone to the Merc/ Weber AFB carb,....

'n yer fuel pressure is high,...... should be 4 to 6 psi,.....
9 psi might be pushin' fuel past the float/ needle valve, causin' a flooded condition,......
Are the spark plugs black, 'n sooty,..??

 

[Georgearia]

Yes the plugs are black n sooty... . I do have a pressure regulator inline to adjust the the pressure down to 4. I will double check the pressure with the regulator adjusted.

The carb number is 17080298. The original carb was in bd shape when I bought the boat. This is the rebuilt one I purchased in 2014, that I just had gotten back from carb guy. Boat ran great with it prior, although I now realize it's not the typical model for marine applications.

 

[Bondo]

although I now realize it's not the typical model for marine applications.

Ayuh,...... If it's not marine rated, it's an explosion hazard,.....