350 mag mpi issues

QBhoy

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so guys it’s now about time for me to deal with my friends engine issues. I’m decent enough with my own current and precious engines. Mpi 5.0 and all variants of GM engines before that in carb form. This 350 mpi with Bravo 3 is a new challenge.

First issue (previously touched on last year)
the engine snapped its belt and creeped towards the upper end of the temp range and just over at about 180/190 and was noticed almost instantly. He shut it down and was towed in. Fitted the new belt. All was well for 10 mins then it started to overheat at slow rpm. Bring the revs up and it would settle down. Naturally I thought it must be the impeller on the front of engine...later asking myself why this would suddenly go bad if it wasn’t ran dry. It surely just stopped turning when the belt snapped ? Any thoughts on this ? Perhaps the belt snapped for a reason ??

secondly and perhaps a complex issue.
The boat was bought on a sold as seen basis. It had had a new full distributor gear fitted 2 years previously and sat ashore un tested until he bought it.
I took the boat out on the lake and it wouldn’t even near get on plane. Popping and banging and missing.
I loosened the retaining on the diz assembly and turned it a few mm. Literally about 2/3mm until it ran much better. (I know, I know. These engines are timing set by ecu and the diz needs only be within the setting lines, but it improved it 90%). The boat now takes off like a rocket and sees max rpm at 5000 and a healthy 50mph gps. Only thing is that at about 2700 rpm and right where the cruising rpm is. It still takes a wee pop and a miss occasionally.
So. We try to replace the diz cap after knowing that these are easily bad. The oem cap would not fit the assembly quite perfect. Literally a mm off getting it down in place enough to tighten the two torx screws. The cap fitted is blue...any I’ve seen are black. Is it possible the seller fitted the wrong assembly perhaps from a similar GM engine but not the same ?

Other thinking is around this cool fuel paint issue and fuel regulators.

What say you all ? Thanks.
 

Fun Times

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Thinking maybe (since the engine got hot again at low RPM) the belt broke due to a bad impeller bearing / shaft assembly within the impeller pump housing assembly....Try taking the belt off and wiggle and pull/push the pulley to see if the shaft assembly is loose fitting, etc...Should be tight.
https://www.mercruiserparts.com/bam/subassembly/31749/11652/270

Maybe the distributor was a summit racing purchase as seen here, https://www.summitracing.com/oh/parts/sum-850098/overview/

^ Read some of the Q & A's within the link too. The line up marks are possibly still out of adjustment as they are critical...Plus an uneven fitting (screwed down) cap and or rotor would make it miss at odd RPM's....That was recently posted on a boating forum someplace to be an issue I saw.

Or another blue cap here too, https://bpi.ebasicpower.com/shop/me...trical-system/electronic-ignition-kits-for-gm

From the summit site it looks like "Davis Unified Ignition" Vortec D.U.I. Distributors has their own design cap and rotor that may be why the fit isn't working so good for you if fitted with such.

Also I'd question the HVS designed marine vs automotive distributors for spark safety.....:redesigned vent screen to allow better air circulation inside the cap to prevent the accumulation of moisture...,
V6 and V8 GMEFI with No Start, Engine Miss-Fire or Engine Shut-off Conditions:
https://manualzz.com/doc/23430314/service-bulletin---marinemechanic.com

What year is the boat?
 

alldodge

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new full distributor gear fitted 2 years previously and sat ashore un tested

Literally about 2/3mm until it ran much better

There is an adjustment procedure for for these motors exactly as you did it. Also another which used a 9V bat and LED. In any case, moving the dist a very small amount one way or the other is the correct method for adjustment
 

QBhoy

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Thank you to both of you guys.

Fun times. Great info there. Yeah the cap is identical looking to that one. The oem and also an aftermarket replacement black cap just didn’t fit on the installed ones base properly. He even cracked one whilst tightening it down.
It’s a 2003 engine.
Going to get an oem diz complete unit and see how she goes. If not, I’ll be looking at the cool fuel for paint and also the fuel regulator too.

All dodge, on the adjustment, I’ll have a closer look at this. Although I only moved it a few mm to get it running to a useable state, it seemed as if it was already turned fairly far round. A few mm more sees the HT leads on the port side hard up against a bracket. Looking at my own boat for reference earlier, suggests it’s maybe a good few degrees further round. Any other position other than where it is...the engine won’t run properly or at all. That’s what’s making me question the suitability of the part and/or something else.

Thanks again guys.
 

Fun Times

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Happy to try and help a fellow member out where I can.:)
Being an 2003 engine year...Any word from past owner why a new distributor assembly was installed?

2003 was a rough year for the 3 ignition components as indicated within that service bulletin I posted to certain engine/drive combo models....Maybe they found moisture under the cap plus found the service bulletin and went for a change out to aftermarket?.Or maybe something else as you mentioned a distributor gear....Did the distributor gear fail somewhere along the line?
 

QBhoy

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Fun times.

The boat came to the lake a lake a few years precious and was from the sea originally. I knew the last owner too. When it came from the sea to the loch (fresh water lake) it had a number of issues to throw at the last owner. The usual manifolds and risers. Also had the transom shield replaced and a few other things. Probably not all sea water related, but just had maybe one or two more issues than it should have had.
Anyway. It had a lot of money spent on it...then it was eventually traded into the local dealer for a newer and larger doral cruiser. The day it was traded in...it apparently had running issues to be assumed distributor related. The local dealer is pretty knowledgable for the most part, but a specialist in all things mastercraft, Malibu, nautique etc. Usually powered with similar but not identical engines. Like PCM and ford even. That’s what led my thinking about perhaps not being the right diz unit. But as you pointed out. You can get the blue cap and ally unit for the 350 mpi in aftermarket.
Long story short. As decent a boat as it is to most (maxum 2400 SCR, not my cup of tea), it was about the least valuable in the dealers stock. So say at the back of the yard without much attention. Then my friend makes a cheeky offer and the story leads on from there.
 

QBhoy

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Update on the overheating.
was at the boat today with my vessel view plugged in. Ran the engine on the hose. Temp creeped up after fitting new t stat (160). Got to nearly 180 and shut it down. Risers hot.
Ran again and cracked open the plugs on the big circ pump, along with t stat vent plug. Big spurts of air and then a full flow. All good now and sitting steady at idle at 158-160 on vessel view and about 175 on gauge on dash.
 
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