8.1 fuel pumps running after fuel rail pressurised

juggernaut1

juggernaut1

Well-Known Member
Apr 19, 2015
1,152
Perth, Western Australia
Boat Info
Boatless - sold Searay 38 Sundancer
Engines
8.1’s
Fella's

Wondering if you can shed some light on a possible issue.

Firstly can anyone confirm the 2006 year 8.1's fuel pumps should shut down after the rail is pressurised? That is when the ignition switches are armed but before starting the motors, should the pumps run only long enough to pressurise the fuel rail and then stop running. I can hear a pump(s) continue to run although I don't know if its the high or low pressure pump or both.

On the basis they should be stop running does anyone have any ideas why they might still be running and where should I start investigating.

Some background info:

They have always in the manner described above since I owned the boat (approx 18 months ago). I had the boat surveyed and no issue was mentioned at this time.
I had one of the cool fuel modules replaced a couple of months after acquiring the boat due to corrosion and at the same time I had the exhaust manifolds changed. Again no issue was mentioned at this time.
Both motors run the fuel pumps in the same manner.
Only used 95 RON fuel with no ethanol.
Swapped out fuel pump relays and no change.
Motors run flawlessly

Motors unseen the Mercruiser tech is suggesting cool fuel modules or PCM's......and I'm getting nervous.

Thoughts before I decide the let the Mercruiser tech investigate further?

Edit:

This 2004 service bulletin (at the "Electrical" heading) suggests the relay only remains active for 2 - 3 seconds whilst the key is in the run position.

http://clubsearay.com/showthread.ph...mpete-with-pictures?highlight=gen+fuel+filter
 
Last edited:
When switching the ignition on my fuel pumps only run for 2-3 seconds.
 
This is happening with both engines? Seems odd that both would malfunction at the same time.. Are you sure your hearing the fuel pumps?
 
If the boat runs well and there are no other issues, I can't imagine where all that extra fuel is going. Does You should hear the same thing as you do when you start your car (assuming it's fuel injected). Couple of seconds and then nothing. Very odd. As Vince asked, are you absolutely sure it's the fuel pump that's running?
 
I believe the oil pressure is the permissive for the fuel pump. The ECU initializes the pump for a few seconds to put pressure on the rail to allow the engine to start. Once oil pressure is met, the pump turns back on for continuous operation. If you are certain it is the pump (easily unplugged to verify), maybe look at your oil presure sensors, but it would be odd both are bad.
 
Thanks for the responses.

The running fuel pumps was picked up by the Mercruiser tech last year when he was diagnosing a transmission noise which I eventually discovered to be a faulty spark plug wire. I have verified it's the fuel pumps by pulling the relays and the pumps can no longer be heard. I did this test at the time I temporarily swapped in the new relays.

Yes I also find it odd that both motors are plagued with this same issue, hence why I thought it was a normal condition until mentioned by the Mercruiser tech last year.

Thanks Paul on the heads up re the oil pressure sensors.

I wonder if something occurred when I had the exhaust manifolds changed as this is the only thing that could explain why this condition is present on both motors. However I'm certain the problem has always existed.

If I test fuel rail pressure should I see an elevated pressure reading?
 
Last edited:
Probably won't be an elevated pressure because that is regulated. Really odd.
i would call Merc tech support and discuss it with them. Have your serial number ready and they are typically super helpful.
 
What is your pressure at the rail, key on not running ?

Does it stop when you disconnect the oil pressure switch ?
 
I'm having the same issue with my starboard engine, it won't stop priming. Juggernaut1 did you get anything from tech support? I'm chasing a ghost.
 
I haven't contacted tech support as yet but have booked the merc tech to take a look at it next Thursday. Apparently he has seen a few boats in recent times with the same problem. He's also doing my raw water pump impellers at the same time as this is not a job I wanted to do - so killing two birds with the same stone.

Will let you know the outcome.
 
Just chiming back in with a progress report.

Background: When I previously changed the fuel pump relay I only changed it on the starboard side motor - no joy - so I didn't bother with changing the port motor fuel pump relay.

With the tech on board he changed the port side motor fuel pump relay first and that seemed to fix the problem. He then changed out the old starboard side fuel pump relay for another new relay and no joy - still kept running. Just for fun......he then swapped out the new relay from the port side motor into the starboard side motor and vica versa that "seemed" to fix the problem on both motors - interesting - but it was difficult to explain why the starboard side preferred the ex port side relay!!

Cautiously thinking the problem was fixed on the starboard motor, the tech went about changing the raw water pump impellors - glad I pick my battles and didn't do this job - I don't have the dexterity in my body.

So I go to start the motors up to check for leaks etc after changing the impellors. The port side still good as the relay shuts the fuel pumps off after 2 -3 seconds. However, the starboard side fuel pump has gone back to its previous bad behaviour and continues to continuously run again. At this stage we had run out of time and the tech will return to attempt to diagnose the issue further.

Stay tuned.
 
Last edited:
So in my 320 it ended up self fixing, I was poking around and am guessing there is a bad connection somewhere. If you haven't check your wires.
 
Just chiming back in again.

In the lead up til today both pumps continuously run again.

The merc tech took an old but spare pcm 555 and swapped it over for the original.....and magically the fuel pumps stop running after 2-3 seconds. It would appear to be the pcm causing the issues on both motors as it seems to be some sort of timer that's failed. And this would seemingly to be a common problem if the whipple supercharger site is anything to go by.

https://whipplesuperchargers.com/index.php?dispatch=products.view&product_id=73

Looks like I'm up for a pair of pcm 555's. There goes the funds I had earmarked for new props.
 
Why not let Whipple reprogram? Have them tweaked at the same time.
 
paulswagelock said:
Why not let Whipple reprogram? Have them tweaked at the same time.
Click to expand...

Certainly an idea - my only concern is that its money down the drain if some other problems are festering in the original PCM's to raise there head down the track - any money saved now could be clawed back in the future.
 
Chiming back in again. Whipple superchargers was able to fix the PCM and was happy with the turnaround time. I did make enquiries about retuning the PCMs but decided not to as I couldn't be confident I would have the necessary octane in our fuel when sitting in the tanks over time.
 
You must log in or register to reply here.

Forum statistics

Threads
113,118
Messages
1,426,555
Members
61,035
Latest member
Lukerney
Back
Top