Carbed 5.0L stalls at idle. Oil pressure safety switch? How to replace? - Page 2 - Maxum Boat Owners Club

ss3964spd · 10-02-2013, 01:42 PM

I don't know that you even need to crimp anything for this test. The voltage/amperage you're working with is very low so you really just need to get the jumper to stay put long enough to see if the engine will start and idle normally. Twist the wires on, jam them in, hold them with tape, have Mrs. Max hold them with her fingers, etc. Just ensure no bare wire touches anything metal on the engine itself.

While you're preparing for this test also remove the flame arrestor and, with the engine stone cold, make sure the choke is closed. When the engine is up to operating temp make sure the choke is completely open.

mmwjr · 10-02-2013, 04:56 PM

SS396, since the lugs on the harness are insulate to prevent short to block you can't very easly jam them together without risk of damage. Probably the least one could do is use a piece of wire with each end striper and jam into harness lugs without crimping proper mating blades on. This wire is conducting 12V and a few amp that the fuel pump draws.

I prefer to do things saftely so not to damage anything else nor introduce a potential false (intermittent) isue when trying to troubleshoot. But that's just me.

Maxumillion · 10-02-2013, 10:36 PM

That's always my intention, but not always the outcome... (Think, Tim the Tool-man Taylor, only in the bilge!)
Thanks for the advice-

Nehalennia · 10-02-2013, 11:01 PM

My guess is that if it's a 5L EFI that it's the IAC. This is a common part to fail on the Merc engines. The IAC(Idle air control) valve is easy to replace right at the carbs throttle body.

mmwjr · 10-02-2013, 11:59 PM

Max does that make me Wilson (giving advise over the fence that gets mis-translated) oh dear I don't want to hear the results.

Hope no trips to the hospital.

mmwjr · 10-03-2013, 12:03 AM

Todd I would agree the issue sounds like a IAC but Max has stated not EFI but carb with choke. 5.0L it my knowlwdge is 5.0 with 2bbl carb. EFI whether throttlebody or ports uses different engine names.

ss3964spd · 10-03-2013, 02:14 PM

Those two wires are probably tripping a relay and not the pump itself, so very low amperge. But I do hear ya Mike, better safe than sorry.

This test is certainly quick and cheap, so worth a shot. The switch needs X PSI to close, either 6 or 10, which may not be achieved during cranking (unless there is a lot of cranking) so I believe there is a OP switch bypass in the curcuit, probably at the starter solenoid. I don't think the engine itself is suffering from low oil pressure since Max hasn't mentioned anything about hearing an alarm.

If the engine does have a carb, and an electric pump, and a mechanical pump I'm struggling to understand how he could get it started at all if the pump isn't working. The carb's fuel bowl would have to get filled to get the engine started, and then it would probably run normally for 15 to 30 seconds until the fuel in the carb bowl ran out. Given that he can start it, and it'll run at 2K, it sounds like the carb maybe dumping too much fuel due to a bad, or mis-adjusted float, or a bad float needle/seat, or too much fuel pressure. Outside chance of a vacume leak but it would have to massive and would be audible I think.

But until we hear back from Max we're just guessing.

mmwjr · 10-03-2013, 04:38 PM

From the wiring diagrams I have looked at electric fuel pump on carb engines is directly powered by the OP switch. EFI models have a relay.

Yes the starter solenoid bypassess the OP switch when cranking so the pump runs then get power from the OP switch when the key is in the run position.

Yep Max needs to dive in and provide feedback on what he finds out to take this any further.

Maxumillion · 10-30-2013, 05:16 PM

Update from the yard: After way too long of a wait from the marina they finally had their more experienced mechanic check the carb & found a "broken spring" on the butterfly/choke which seems to be causing the non-idle cond. So i'm just waiting (again) for them to install part on order to make sure this is the real fix.. The first mech said the butterfly was stuck & he freed it up & I was billed 100 bucks, since credited back for the non-fix.. Either he missed the spring issue orig or it broke when he freed it up & there still may be another issue, so we'll see & provide the solution when she's purring again... Thanks to all for your suggestions & support this far! It's been a bummer season between this & having to deal with a seized gimbal bearing in the opposite drive upon the yard's springtime shakedown cruise. They break my boat & then I have to wait all season for 2 fixes & prod them all the way for any service whatsoever. Looking forward to a better season in 2014

mmwjr · 10-30-2013, 05:34 PM

Max, hope this is the final fix and next year is flawless.

"spring" is this the electric choke? coiled bi-metal element in round housing on the side of the carb that has two wires one is ground on a screw and other is hot on center terminal?

Maxumillion · 10-30-2013, 08:46 PM

Thanks Mike, hope so too... As far as any other name it goes by, you got me.. They just said it was a spring that was broken which controls the butterfly which I assume is the same as the choke (?)

mmwjr · 10-31-2013, 12:12 AM

Yep choke plate is sometimes refered to as butterfly. In the base of the carb are the throttle plates which control the amount of air the carb allows into the engine and is controlled by the throttle cable.

The choke element is a coiled bi-metal spring that heats up and unwinds a bit. It is connected to a rod that then open the choke plate. The choke plate should also be free so that when the throttle plate opens wide the engine vacumn will actaully cause the choke plate to open even if the spring has not yet fully heated up.

Maxumillion · 06-04-2014, 01:59 PM

6/2014 Update: A Brewer Shipyard mech finally "adjusted" the carb for a 2nd time, idles but the idle was set to 1,000 rpm in error based on what I've read which should be @ 650 like its twin. How they thought it was ok to have so out of synch is beyond me, but par for their course this far.. So I lowered idle, but problems still exist that Brewer claims was fine when tested:
Problems are as follows:
1) hard start req'ring rpms above 2K until fully warmed or stalls repeatedly
2) bogs down & wants to stall when throttled up slowly or quickly in either neutral or in gear. Hear air/sucking sound as it bogs.
3) when throttle is pulled back as it is bogging to prevent stall, the rpms then jump way up to where the throttle was just prior even tho its back to idle position.
4) upper rpm range is totally fine & runs strong thru 3K's
Anyone have this issue or know of an easy fix, ie fuel/air mix etc??