Running rich

Caveman22

Caveman22

Active Member
Mar 6, 2020
225
Boat Info
310 Sundancer 1999
Engines
350 Mercruisers Blue Water, V drives
My 1999 350 mag runs runs very rich, especially on startup. I had the spark plugs out today while changing the exhaust manifold's and all the plugs were black with carbon. When I start it cold, it smokes and you could smell the fuel. Seems to get better when warming up. Any ideas what could cause this?
 
Either a sticking float valve in the carburetor and/or a misadjusted choke would be my first guess.
 
It's fuel injected. MPI
 
Check your fuel pressure, could be too high. Coolant temp sensor could be faulty.
 
techmitch said:
The IAC is not a sensor.
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I was being general in terminology rather than too technical. It's a common failing part that is within the control of the computer and its failure can cause those similar conditions due to its in-operation the various sensors will start getting weird reading and the computer then makes bad adjustments to a degree.
 
Hoplite808 said:
I was being general in terminology rather than too technical. It's a common failing part that is within the control of the computer and its failure can cause those similar conditions due to its in-operation the various sensors will start getting weird reading and the computer then makes bad adjustments to a degree.
Click to expand...
Um, no. Sorry.

Well, this is correct "It's a common failing part".
 
So I tested the coolant and map sensors on both engines. Very similar ohm readings cold. Then I ran a fuel pressure test on both engines. Starboard and Port psi is 28 - 30 psi when "primed". When port engine starts, the fuel pressure increases to approx. 50 psi. I did remove the vacuum line to the regulator and the pressure then goes up another 4-5 psi.
The starboard engine fuel pressure remains approx. 30 psi when running and also raises 4-5 psi with regulator vacuum hose disconnected. The port engine does have the little booster pump kit installed for the vapor lock problem I believe.

Anybody have any thoughts?
 
Would the fuel pressure regulator being bad cause the the pressure to go from 30PSI at prime up to 50 after about 30 seconds of running?
 
Looks like a real bear to pull out that cool fuel set up under the motor mount with twin 350s vdrive. Any helpful hints or shortcuts?
 
Caveman22 said:
Looks like a real bear to pull out that cool fuel set up under the motor mount with twin 350s vdrive. Any helpful hints or shortcuts?
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I just did mine last week but not on V-drives. The process to remove and replace isn’t terrible (1 hour and some of that was being gentle since I hadn’t done one before. LOL). However, unless you have a way to get back and under that engine… you’re gonna need a small person and some patience maybe.
 
I was thinking of removing the serp belt and alternator, slide it towards the rear, then up and out.
 
Starting Over said:
I just did mine last week but not on V-drives. The process to remove and replace isn’t terrible (1 hour and some of that was being gentle since I hadn’t done one before. LOL). However, unless you have a way to get back and under that engine… you’re gonna need a small person and some patience maybe.
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What symptoms did you have before replacing?
 
Does anyone have any problem with aftermarket fuel pressure regulators? 1/3 the cost of OEM!!
 
Caveman22 said:
Does anyone have any problem with aftermarket fuel pressure regulators? 1/3 the cost of OEM!!
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I used aftermarket pump.. Mercs are back ordered. And OEM regulator.. I read a lotta negatives on the regulator being non oem.. so for $180 or so.. sold.
 
Starting Over said:
I used aftermarket pump.. Mercs are back ordered. And OEM regulator.. I read a lotta negatives on the regulator being non oem.. so for $180 or so.. sold.
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I tried finding negative reviews for them, but didn't find any comments. Where did you find these? I've heard more bad about aftermarket fuel pumps.
 
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