'96 Volvo Penta Ford 302 - Surging around 3000 rpms

rideus2003

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I originally thought it was the lower octane fuel (87) my wife put in the boat that caused it but 3 tanks of (93), new inline fuel filter, new fuel/water separator, and a can of SeaFoam and it still tends to surge around this RPM. Fluctuates about +200 rpm and then back down. It's not horrible and most people on boat don't notice but I do. Starts right up and runs good below and above the stated RPM above. Runs great at WOT.

Any suggestions where to go from here? I replaced the above parts as they were cheap and easy to change and most likely needed changed anyway.

I did notice the alternator belt was so loose you could turn the pulley while engine was off and tightened that, I realize that probably had nothing to due with the surging but a little FYI.
 

alldodge

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Most all surging is from fuel supply, what type is it, EFI, carb model
 

alldodge

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Assume TBI (Throttle body injection) and should also mention surging can also come from a vacuum leak.

With motor off, open the throttle some and then check throttle plates to see if they a loose (looking for play)

Check all rubber hoses and tubes which are attached to the throttle body or intake for cracks or loose fittings

Remove the MAP and IAC sensors to clean and inspect. Do not use chemicals on them, use soap and water or some WD-40. If gaskets are cracked, the gaskets will need to be replaced.

If that checks out, need to check fuel pressure at the TB
 

Scott Danforth

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I believe that the EFI is MPI for the 302
 

rideus2003

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I’ll check what I can - any hints as to where the MAP and IAC are located? Assuming around intake. Sure I can google it. I don’t have a means to test fuel pressure so may have to rely on mechanic. Picture shows it saying EFI - and the plastic cover over it states EFI. I’m not savvy of MPI/EFI difference. I can see the injectors however. Appreciate all the tips fellas.
 

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Scott Danforth

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rideus2003 if you post your complete motor model number with the complete alphabet soup behind it you can then look up your parts thru this link. https://www.iboats.com/shop/engine-parts click on the big orange "for OEM parts click here" and it will take you to www.volvopentastore.com. from there you pick your alphabet soup model out of the list and there are all sorts of exploded views.

for example it could be any of these motors:
photo300899.jpg
 

rideus2003

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rideus2003 if you post your complete motor model number with the complete alphabet soup behind it you can then look up your parts thru this link. https://www.iboats.com/shop/engine-parts click on the big orange "for OEM parts click here" and it will take you to www.volvopentastore.com. from there you pick your alphabet soup model out of the list and there are all sorts of exploded views.

for example it could be any of these motors:

Sorry - I do know my engine code it is 50FIPNCSCE - I assumed the FI after the 50 stood for "fuel injection"??. I've been to the link above quite a few times and appreciate the info on what I need to look for. Thanks again guys - appreciate it.
 

Scott Danforth

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nope - the alphabet soup actually means something

First two numbers is the engine size in liters
third character is the base engine manufactuer
the 4th character is the Power output. L is Limited (usually a carb) I is injected, S is superior, X is exceptional Xi is usually MPI
the 5th character is the steering. M for manual, P for power
the 6th and 7th character is the year range
the 8th is a service code (revision)


the 50 is for 5.0 liters
the F is for Ford - if it was a GM motor, that would be G
the I is for Injection
P is for power steering
NC is 1996-1997
S is the 19th iteration of the total mix
 

rideus2003

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Assume TBI (Throttle body injection) and should also mention surging can also come from a vacuum leak.

With motor off, open the throttle some and then check throttle plates to see if they a loose (looking for play)

Check all rubber hoses and tubes which are attached to the throttle body or intake for cracks or loose fittings

Remove the MAP and IAC sensors to clean and inspect. Do not use chemicals on them, use soap and water or some WD-40. If gaskets are cracked, the gaskets will need to be replaced.

If that checks out, need to check fuel pressure at the TB

Low Presure Pump - about 3 or 4lbs
High Pressure Pump - 34lbs

Both readings are while boat is running at idle.

Boat only has 320 hours - all hoses look good and not rotted to me. Should I remove/clean pressure regulator?

Cleaned MAP and IAC (didn't know if I could use an OHM reading to actually check?).
 

alldodge

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Looks like your pressures are in order at idle. If you could keep the pressure gauge on the HP side while its running to see if its varies

VP Fi and Gi fuel pressure.jpg
 

rideus2003

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Looks like your pressures are in order at idle. If you could keep the pressure gauge on the HP side while its running to see if its varies


Will do - I'll make sure I bring the gauge and my wife next time and she can check the reading....appreciate the great information.
 
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