Closed raw water intake -- no fuel pressure

[SeaHarlequin]

what is the ground connected to? A metal plate or a fiber panel? I would recommend to connect directly to the pump mounting bracket to make sure to have a good continuity

It's connected to a metal plate. IIRC I tested continuity between the connection on the plate and the pump but I don't recall if I tested continuity from the pump to the engine block. I agree with your suggestion that putting it directly to the pump's mounting bracket would be a better call -- I'll try to do that this weekend.

[ndutton]

Unless the machine screws for the pump mount and the ground wire are threaded into the metal plate, you should consider they are electrically attached to only the paint. Sheet metal screws don't count as electrical terminations either, must be tapped machine threads, preferably 32 TPI.
Moving the ground wire to the pump mounting ear may not make a difference in the current round of troubleshooting but it will certainly be a much better electrical connection.

[roadnsky]

I don't understand the question. The fuel pump was previously attached to the engine block itself and had no dedicated ground wire (presumably because of its mount points on the engine). When I relocated it to the bulkhead, I added a dedicated ground from the mounting platform to the engine block.

Sorry.
That IS what I meant.
Where is the ground for the pump coming from. (ie engine block)
Check that both of those connections are tight.

Here's a pic of my pump mounted on the bulkhead.

[SeaHarlequin]

Unless the machine screws for the pump mount and the ground wire are threaded into the metal plate, you should consider they are electrically attached to only the paint.

Yeah, I tapped the hole so they're threaded into the metal plate. At least I did that part correctly.

Sheet metal screws don't count as electrical terminations either, must be tapped machine threads, preferably 32 TPI.

Huh-oh. Thank you, I did not know that.

Moving the ground wire to the pump mounting ear ... will certainly be a much better electrical connection.

Yep, I'll just do that. I considered it but figured I'd make things easier on myself and just attach the ground to the plate which had easier access. Should've remembered the adage about if something's worth doing, it's worth doing well -- I'll move it.

[ndutton]

I'm not suggesting the way you did it will not provide a ground but rather advocating for good electrical practice.

[SeaHarlequin]

OK, I've tested for continuity between the pump and the engine block so ground is there. I still plan to fix that but need to go buy a bigger connector ring.

However, the engine continues to have issues. I could not start it up with the choke (it's a warm day ~70F) -- closing the choke and re-trying started the engine. It ran in idle for about 15 minutes and just as I was about to repeat the fresh water flush experiment, the engine died. I've tried to restart it several times but it won't restart at the moment.

I had a multimeter on between the pump and the block and it was registering voltage but it was jumping around -- is that normal? Should it be within a consistent range and if so, what range?

The pressure gauge was also all over the place which makes me think the issue with the pressure gauge dropping to 0 during fresh water flushing was a coincidence.

Does anyone have recommendations on the next debugging steps? Thanks in advance for any ideas.

[Peter]

Symptom summary

1) fuel pump voltage is erratic
2) fuel pressure is also erratic

Did you happen to notice what your oil pressure was doing during this episode?

Suggests to me that either you have:

1) erratic oil pressure that is causing the OPSS to cut in and out leading to erratic voltage and pressure
2) intermittently failing OPSS leading to erratic voltage and pressure
3) failing fuel pump

I think I would try bypassing the OPSS and seeing if it starts. If it does start, monitor the oil pressure carefully. If oil pressure is ok and fuel pump voltage/pressure is steady I would conclude OPSS is the problem.

If oil pressure is ok but fuel pressure is not steady, fuel pump likely problem.

If it does not start and there is fuel pressure then maybe not a fuel delivery issue. Check for spark.

If it starts and oil pressure is erratic that is a different kettle of fish.

Hope that helps,

Peter

[SeaHarlequin]

If it does not start and there is fuel pressure then maybe not a fuel delivery issue. Check for spark.

Thank you! That got it started.

I was getting a good spark from the coil lead so I initially dismissed the ignition system as a potential source of the problem. However, when I used an in-line spark checker on each spark plug, I found the 4th spark plug wasn't firing unless I jiggled the in-line spark checker just so. I was able to reliably get it started several times and duplicate the failed starts when removing the in-line checker and putting the lead back on the spark plug. I don't know how old these leads are and two of them do feel loose so I'll replace them.

Once the engine starts - oil and fuel pressure at consistent as are the multimeter readings. I have no theories, yet, as to why that wasn't the case last week. I'll keep investigating.

Anyhow, I started this thread because it appeared there was a connection between flushing with fresh water and the fuel pressure. I did think this was unlikely but wanted to get an education. Today, I repeated the experiment and verified that whatever the causes for the fuel pressure issues, it had nothing to do with the fresh water flush. I appreciate all the contributions, I've learned quite a bit.