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Running rich 3000 RPM +

Old 06-08-2019, 09:51 AM
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Default Running rich 3000 RPM +

Hey guys I've been chasing a problem with my boat for the last few months with no luck. It won't get on plane or go over 3000 RPM on a Mercruiser 350 MAG MPI. At 3000 RPMs you can just smell the unburned fuel smell say at 75% throttle and going to 100% throttle only makes it worse the RPMs actually drop the more throttle you give and the engine start to sputter and can even get a back fire in the exhaust from the unignited fuel going off. From idle to 3000 RPM its smooth as silk.

Rinda TechMate Pro shows no codes and things like TPS show full 0-100% and match the throttle, the gear selector is showing it going from netural to drive so ECM doesn't think its stuck in idle, Guardian Mode is not on. Coolant temp was in the 150+ so I don't believe ECM thinks the engine is too cold and riching the mixture. The laundry list of things checked and replaced are low pressure fuel pump, high pressure fuel pump, new fuel pressure regulator, all screens checked and clean, new cap (NAPA Echlin), rotor (NAPA Echlin), wires, spark plugs (Sierra), ignition control module (coil), fuel sep filter, inline fuel filter, gear selector switch, crankshaft position sensor, map / mat sensor, iac vavle, iac filter, compression 165-175 across the board.

Pretty sure its ignition related but don't know where else to go. I am going to reduce the gap on the plugs to .035 from .060 today. I'm skeptical just that will allow the engine to go over 3000 RPM. I put a timing light on each wire and see a nice steady pulse at idle on each. I keep suspecting the wire order but as long as the cylinder 1 is front port side I've triple checked them and have them as follows.

Port Side Front
1
3
5
7
Starboard Side Front
2
4
6
8

Wires go to the numbers imprinted on the cap.
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Old 06-08-2019, 02:36 PM
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Does anyone have the Mercruiser Service Bulletin 2011-11R2 available? It details the HVS (crap crab cap distributor) "timing". Yes I know its not timing in the traditional sense but may expalin why low RPMs are fine but high RPMs are not.
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Old 06-08-2019, 02:40 PM
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Did this start out of no where , or after maintenance or a parts change.?
I think you have the Chevy distributor that has to be set dead on and doesnít adjust timing by turning it? Maybe wrong.
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Old 06-08-2019, 03:21 PM
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it was after a tune up plugs/wires/cap/rotor never been the same since. I have the crap crab distributor system from Chevy on this a real POS. I just lowered the gap from .060 to .035 per GM's new recommendion.
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Old 06-08-2019, 03:34 PM
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Was the distributor ever turned in the tuneup?
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Old 06-08-2019, 03:38 PM
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Change your title line to include Mercruiser 350 mpi. And some guys may check it out more with engine experience on yours.
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Old 06-08-2019, 03:44 PM
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There's a ton of posts on here about that POS set-up.
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Old 06-08-2019, 03:47 PM
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You are suspect of the firing order?
Check it by pulling all the plugs and set #1 cylinder to tdc on the compression stroke with a ratchet on the crank.
Once you have that, pull the Dist cap and see which wire it is pointing to. Follow the order from there. The order should be on the intake manifold .
If you have a wire or two misplaced then there’s the problem.
You know it’s in the plug wires Dist placement as that’s when the problem started.
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Old 06-08-2019, 06:06 PM
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well changing the gap from .060 down to .035 and now I got on plane for the first time in 2 months. Have an overheat fault but at least Guardian went off I like problems the computer can see and I can act on.
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Old 06-09-2019, 12:26 AM
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Originally Posted by toy4two View Post
Does anyone have the Mercruiser Service Bulletin 2011-11R2 available? It details the HVS (crap crab cap distributor) "timing". Yes I know its not timing in the traditional sense but may expalin why low RPMs are fine but high RPMs are not.
Brendanm posted some helpful info on this subject recently:

Distributor cap phasing adjustment

Are you using the specified spark plugs?

Do you think the fuel quality is good enough to not cause knock timing retard.

Do the tops of the risers ever get hot to your palm?

Last edited by TTaxi; 06-09-2019 at 12:34 AM.
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Old 06-09-2019, 05:19 AM
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There's a thread on this page right now about this..jeromy5 maybe?
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Old 06-09-2019, 03:57 PM
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Default HVS distributor indexing

i want to thank billstuart for the info on the crappy crab distributor caps in other threads I read. The gap reduction from GM to solve this on Chevy trucks really helps Mercruisers too.

i also think the HVS caps get a little bad rap... itís not just their inferior cross firing design inherent in running conductors in the cap so close to each other but a little know outside of Mercruiser of small block Mercruiser 350 MAG MPIs timing chains stretching causing the rotors to be out of alignment and causing cross fires.
Many are unaware of this and think ďit runs just fineĒ but they are missing out on high RPM performance since 20 hours in on their engines.

On the Merc internal tech bulletin service they acknowledge and provide a fix and a tool to use to find the sweet spot.

I donít have the bulletin but here is the video which goes beyond the service manual on how to fix these garbage caps:

i bought the premade HVS tool on eBay and you can too if you donít have access to the bulletin to build your own. Buy it. Set your HVS and sell it for the $50 it costs and your engine will thank you.

also I canít stress enough, as Bill has said stick to a cap and rotor from the same manufacturer and if not Mercury Quicksilver the NAPA Echlin cap and rotor are good and easy to find
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Old 06-09-2019, 04:05 PM
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Default Overheat

to finish off my boat, which is doing Guardian overheat and speed exceeded errors my online mechanic suggests in this order impeller then thermostat and lastly manifolds/risers. Exhaust flappers haven’t been high in his experience in these 350 MAG MPI Bravos but could be down the road.

if anyone needs an online mechanic because they can’t wait months like Orange County California is which has a fifty boat wait and less than ten mechanics try justanswer.com and a Marine Mechanic can guide you what to test and replace from experience saving you labor.

mechanics say there is a nationwide shortage of marine mechanics since the 2008 recession. Demands is through the roof in So Cal, rates are high, and wait times are months out for non hacks. Good profession to get into
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Old 06-09-2019, 04:27 PM
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I’m glad you are making progress, billnstuart and ttaxi are the ones to help you .
Missing flappers have been a problem for overheats that I’ve read,
but these guys will get you straight.
Just trying to help .
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Old 06-09-2019, 04:40 PM
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Originally Posted by toy4two View Post
i want to thank billstuart for the info on the crappy crab distributor caps in other threads I read. The gap reduction from GM to solve this on Chevy trucks really helps Mercruisers too.

i also think the HVS caps get a little bad rap... itís not just their inferior cross firing design inherent in running conductors in the cap so close to each other but a little know outside of Mercruiser of small block Mercruiser 350 MAG MPIs timing chains stretching causing the rotors to be out of alignment and causing cross fires.
Many are unaware of this and think ďit runs just fineĒ but they are missing out on high RPM performance since 20 hours in on their engines.

On the Merc internal tech bulletin service they acknowledge and provide a fix and a tool to use to find the sweet spot.

I donít have the bulletin but here is the video which goes beyond the service manual on how to fix these garbage caps:
https://youtu.be/oGoaZbY_7Gg

i bought the premade HVS tool on eBay and you can too if you donít have access to the bulletin to build your own. Buy it. Set your HVS and sell it for the $50 it costs and your engine will thank you.

also I canít stress enough, as Bill has said stick to a cap and rotor from the same manufacturer and if not Mercury Quicksilver the NAPA Echlin cap and rotor are good and easy to find
You're more than welcome!
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