mercury 150 efi intermittnent fuel pump

[pancakes]

okay, i have tricky intermittent problem with a 2000 150 efi saltwater series. hoping someone can help!!!

The motor cold starts just fine and will run for half an hour or more. i can turn it off and let it sit for 10 minutes or so and it will start right up and continue to run, no prob. BUT, if i wait more than an hour to restart, it will not start. i've isolated the problem to the the primer fuel pump which is not coming on when cold unless it has sit for a few days. i've ruled out a kill switch problem by disconnecting the black/yellow wire. i've also checked all grounds and cannot find a problem there either.

Has anybody heard of or experienced the same?

my best guess is a fault inside the ECU that only shows itself once the motor is brought to operating temp and then allowed to cool causing some kind of motherboard thermal expansion/contraction.

the motor is probably not worthy of a ECU repair given it's age.

 

[alldodge]

Not an OB guy but if you don't mind, give me a bit more info

Does the motor have a Vapor Separation Tank (VST)?
Are you in a warm or hot climate?
Reason for asking is I'm wondering if it has something to do with vapor lock.

 

[pancakes]

it does have a VST tank and i'm in a warm climate.(miami)

 

[alldodge]

it does have a VST tank and i'm in a warm climate.(miami)

If you run it for a while so it gets good and warmed up, then after sitting it wont start, that leads me toward vapor lock (VL). The VST's are bad at this and the warmer the climate the worst it gets.

If this was an inboard or I/O I would suggest finding the fuel rail and the shrader valve (will have a cap) and press in on the valve and release the air which may have built up.

What may be happening if its VL, the fuel gets hot and boils, so air is what remains in the fuel rail. Once it cools down the fuel condensates and it will start again. There are fixes for I/O's but would need to thing and investigate this further if its VL on and OB

 

[pancakes]

would vapor lock cause the VST primer pump not to run? That is the symptom i'm getting after the motor cools.

 

[alldodge]

would vapor lock cause the VST primer pump not to run? That is the symptom i'm getting after the motor cools.

No, the pump runs but there is no pressure. If the pump is not running then look at connections. There will be at least 2 relays (main power and fuel pump) and these can be swapped. Have someone turn the key and feel for the relays to click. The main power should click and stay ON the fuel pump will turn ON then back OFF. When cranking the fuel pump relay will turn back ON

 

[Faztbullet]

There is no relays as fuel pump is controlled by ECU ground. You can disconnect the ground from pump and run to a relay that is turned on/off by the purple wire....or you can try a temp fix by smacking ECU right above the cast in letter with a rubber mallet, it reseats the fuel pump driver board.

 

[pancakes]

ah, nice idea, faztbullet. would you consider the purple wire relay jump a permenant fix? do you think the the VST pump would operate as normal, shutting off at correct internal PSI?

 

[Dukedog]

use a separate 12v (red) supply and a normal ground.. run tha 12v (red) supply from 12v batt. post on start solenoid thru tha relay to tha + on pump.. trigger/engage tha relay with tha with tha purple (key switched 12v) wire...pump will operate jus fine.. it never shuts down as long as tha motor is runnin' anytime..

fuel pump relay kit from summit 'bout 40 bucks....

do this and ya can leave tha "mallet" at home......