Closed raw water intake -- no fuel pressure
 

I recently installed a fuel pressure gauge to monitor my electric fuel pump and it appears to be working fine -- the PSI fluctuated between 2 to 4.5 PSI while idling for about 20 minutes.

I shut off the raw water intake and opened a bypass intake which was immersed in a bucket of fresh water to flush out the salt water. I noticed the fuel pressure gauge stopped registering any pressure even though the engine was still running. I thought maybe it got stuck or the fuel pump turned off (I had the engine running for less than a minute so presumably there was sufficient gas in the carb bowl to continue operation.)

Out of curiosity, I repeated the steps -- opened up the raw intake, observed PSI readout within expected parameters, shut down the raw intake and started fresh water intake and observed the PSI readout drop to 0.

I'm not yet understanding the interplay between intake of two sources of water and the fuel pressure. Is this expected behavior, and if so -- why?

I've not had a fuel pressure gauge on this boat before so maybe jumping between pressure and no pressure based on engine needs is normal and I just happened to time things twice so that it looked like there was interplay? (I'm operating under the assumption that an electric fuel pump would provide consistent pressure and was surprised to see the needle jump between 2 and 4.5 actively, although I didn't see it drop to 0 during those times.)

Thanks and apologies for what is probably a stupid question/mis-timed set of observations but I'm trying to get a better understanding of how the systems work together.

I can't think of any link between water pressure and fuel pressure... So pretty curious to say the least. I will not make you the insult of asking if you fuel pressure gage is not a water pressure gage... :)

Absolutely stupid theory question: is your fuel pressure gage an electrical one with a sender, or just a local gage?

Hi Sea-
First... there are NO stupid questions here.
This is a classroom of discussions and we are all learning together. ;)

As an experiment, does the fuel pressure return to normal when you switch the water valve back over to raw (sea) water?

I can not think of a reason the changing the source of cooling water would have any relationship or effect on fuel pressure.

SeaHarliquin, has to be a coincidence. The pressure fluctuation has more to do with the "pumps" regulator. The pressure should stay steady and only fluctuate a tiny bit. If you are getting 4.5PSI you have a bit more pump than necessary and it should stay close to the 4.5 if it is operating properly.

By the look of the pump it just may be time to take a look at it or replace it.

The 4.5PSI is not a big deal at all just a bit much BUT the pressure should not vary so much so I think the internal regulator of the pump is becoming compromised. The fluctuations were probably just noticed when you changed to valves position as there is no connection between them.

Dave Neptune :cool:

Part II
 

Oops, also take a look at the OPSS if so equipped or add one if not. A faulty OPSS switch could cause a zero reading and then kick back on. Again a coincidence.

Dave Neptune :cool:

Loose wiring would have the same effect.

Try shaking the wiring while the engine is running and see if the PSI varies. Or run a wire from the battery to the fuel pump, bypassing the boat's wiring and the OPSS, and see what happens. This will tell if the fuel pump has a problem or if it is something before the fuel pump.

When troubleshooting a electrical device it is important to troubleshoot the device and the associated electrical circuit.

ex TRUE GRIT

Give me time, I may surprise you yet. :D

You've all given a lot of good information to process. I was cleaning up for the day so didn't pursue this further than that one test. Now that I know that's not normal, I'll play with it the next time I'm on the boat.

It's a local gauge. I do have an OPSS. The fuel pump does look a bit rough (I posted in another thread about it with pictures). I'll try replicating the experiment by monitoring the gauge for a longer period of time (given that I know it's supposed to stay relatively steady, it's fluctuations are now a red flag to me).

I'll jiggle wires, hoses, bypass switches, etc until I get more data to process and debug this. Thanks!

Rather than just jiggling, get a multimeter and monitor the voltage at the fuel pump when the pressure goes to zero.

I do have a multimeter. Where would I connect them on the pump? The positive terminal and anywhere on the case? What would I be looking for?

Thanks!

Correct. The positive terminal of the pump and the pump case.

You're looking to see if the voltage drops to zero when the fuel pressure goes to zero.

I am curious as to what would happen if you used salt water for the flush.
The fresh water may be a variable here.

Salt water tend to conduct and fresh tends not to conduct electricity.

Just a thought.

That was my “stupid theory”, would have been the sign of a really compromised engine ground. But it is a local gage, not electrical... so no crazy theory :)

Sea-
WHERE does the ground for the fuel pump come from?
I'd check both of those ground connections.
You may want to consider having a dedicated BUS BAR for your various ground terminations.
Same suggestion for any hot connections hanging on the battery. ;)

That's interesting -- thanks for the ideas re: the saltwater.

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.

What do you mean by "both of those ground connections"? Do you mean to check continuity between the pump to ground wire terminating on the engine block or is there another ground pathway I'm neglecting to consider?

Good call. The PO had hot wires running from the batteries to bus bars -- ditto for the grounds. There were a few exceptions in the engine compartment where ground wires were attached to the block itself (I think the exceptions were the coil and alternator) and since the pump used to be on the block without a ground going back to the ground bus bar, I figured grounding to the engine would be acceptable. I'll check the continuity but please do let me know if I've screwed something up or if any of you have recommendations on improving things other in general. Thanks!

http://www.moyermarineforum.com/foru...pictureid=2072

http://www.moyermarineforum.com/foru...pictureid=2073

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.

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.

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.

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

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

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.

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

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.

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

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. :confused: 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. :D I appreciate all the contributions, I've learned quite a bit.