502 mag mpi dies for unknown reason
 

I have a 99 502 mag mpi that will just shuts off after running. it has done this on multiple occasions. its happened at idle as well as when cruising. It will start right back up and go. It has done this on several occasions. Then after a few times it stops,. I have checked connections and don't see any loose or corroded.

Anyone else have this issue?

Eric

Electrical issues are very hard to find, and you have your work cut out.
It happens because of bad connections or failing part.

The MPI motor has a relays (main power and fuel pump) which if either one looses power will kill the motor. You have a kill switch which can also kill the motor. Connections to/from all components can get weak/loose/bad and if it breaks flow, the motor dies. The ignition switch can also do this

Start with connectors, remove, inspect and clean contacts. Move on to switches and relays and their contacts

In 1st bold, how long does it run continuously until it first shuts off ?

And second bold,How long until it ill restart ?

prob pick up coil and its rusty as hell causing it to get hot.

cap and rotor and ign coil how old is that. U prob need a FULL COMPLETE tune up along with a pick coil

other tests - what is your voltage showing when running and when the engine shuts off on its own ?

the cannon plug does that have great solid connection and very clean and tight with a hose clamp on it ?

battery connections good and clean and tight ?

Connections at the starter good clean and tight > Back side engines grounds the same ?

Alldodge/Camalot - I installed a new ignition switch this year, Kill switch I need to check and I have recently put new relays in for the ECU/Fuel pump.

SB- I don't even have to cycle the key when it dies. It will instantly restart and run. It happened to me three times yesterday. The fourth restart it ran for over an hour with no issues.

BUP - I recently installed a MSD blaster coil, Cap and rotor were new the beginning of this season, Voltage doesn't fluctuate at all (13 - 14V depending on load), cannon plug I recently checked. The batteries I rewired the beginning of the year with new marine grade 2 gauge wire, Blue sea systems ACR. I recently had a issue with my fuel pump circuit. Turned out to be a bad fuse block. I have rewired all the fuse blocks with new blue seas systems blocks.
all connections are secure.

Thanks for the inputs. I will probably try my backup coil to see if that could be the issue, check the kill switch for shorts and possibly replace the ignition switch. I will check all connections again as well.

When you fist turn the key to on position do you get a constant horn or no horn?

Chris

Yep we unplug the cannon plug and use a hand pick straight thru the middle to spread the male connectors open for better contact with the female side. Man that almost sounds X RATED.

blueabyss - yes when I first turn the key the horn is momentary then turns off.

30ftpanther/BUP - I did spread the male pins out before. I'll go back in there and clean it up really good then try it again.

Any chance it might be the distributor module?

My Formula has a timer on the alarm, so you have to leave the key on for a little bit before the timer ends and the horn will sound. Its good so you don't hear it when your starting, but bad usually won't know if its not working. Should say it use to turn on, but has not since repower, I still have to fix that

run the boat on a remote fuel supply tank with new fuel line attached and current fresh gas. just to eliminate all the boat side fuel systems. These kind of testing helps narrow down where the problem(s) are

BUP - mine is definitely an electrical issue. It has fresh gas in it as I have been filling the tanks for testing. I've been working with a tuner. I have the MEFI burn software. He sends me the file and I upload and try it.
The boat cutting out is recent. As mentioned earlier it starts right back up. No fuel starvation at all. Filters are all new this season. After it cut of the for the 3rd time, I restarted and ran at various rpms for over an hour without cutting off.

As a tech tip; even if not the problem I would take the msd coil out of the loop. These things are less reliable than, say, a 1986 Hyundai Excel.:(

Look up ratings of your exact coil (assuing #8226 ?) at Summit Racing and amazon,, many people had problems soon and some within days. remember, MSD no stands for "My Spark Dies."

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Typical module and coil issues show up hen hot, then okay for a little while when cool. Then get weak when hot and/or not allow restart until cools backdown. However, past dozen years or so, MSD anythings have caused normal and not not normal issues.

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Tell us more about your fuel pump and wiring issues before 'your fix."

did it ever do it before the coil change ? I had the same coils on a pair of carb engines and they would over heat the timing module to the point it was double firing @ 10* and 270*.......put the stock mercury coils on and they ran perfect, Id try the stock HEI mercury coil. BTY they are for sale cheap.......:D

SB/Baha Rooster/ F2 speedy - I have a stock coil for backup. I will try that first. Ignition module comes to mind as well. I might go ahead and replace that.

I have an Automotive 1000 marine pump. My only issue with that was the circuit. I found this by checking all the wires and it ended up being a bad connected from the blade connector to the fuse block.
I replaced the entire fuse block (blueseasystems) and no more issues. All are screw style vs blade connections. They are all secure.

I changed the ignition coil back to my stock coil last night. Had to change plugs as well. Ign module will be in Thursday so I will replace that as well.
I started and ran it for a few minutes in the driveway. All seems good. I won't know for sure until I water test it later this week.

Hey 99 the ign module is a good bet but if that does not fix it, give me a call. Too long of an explanation to post but easy 5 min diagnostic.

Chris

727-599-1941

Blueabyss - ok thanks!

Any updates to the post mines doing the same thing

ethanon1- nothing yet. Just changed back to my stock coil and changing the ignition module as well. Should have results this weekend.

Make sure you use real heat transfer compound (clear paste is not heat transfer compound - it is dielectric grease - it is a insulating compound..doh !) which is typically white or silver. If module comes with dielectric grease, most do thus why I an warning you like the last 1000 people - get real stuff like Arctic Silver (available at computer repair stores and Amazon and etc) and use very thin with razor or etc. Look it up online..will be vids on it.

The module isn't aftermarkt is it ? Must be same delco as you have or good fuking luck. :)

SB- thanks for the tip....I have a tube of dial electric grease. Im use to those from fords with TFI modules.

AND THAT IS JUST AS WRONG !

Parts stores and dealers have not known this for 30yrs ! That is around when the switchover happened and everyone copied each other,. It's like all the old counterman + engineers died or left across the nation on the same day !

Finally got the boat out...I ended up swapping coils to my factory gm, installing the new distributor module and replacing the cap and rotor while i was at it. Motor didn't die at all so it seems between at least two of those items between the coil ign module it fixed my issue.

I had a similar issue with my 454 mag mpi, it had codes for knock sensor, timing. I found the knock sensor was unplugged, i replaced the sensor and plugged it up knock code went away. Then had the ignition code to deal with, boat kept jumping timing. Replaced distributor and pick up coil and that code was gone. Boat was still shutting down under load only over 3k rpms. Had a mechanic bring a dummy dash in to eliminate all the gauges and switches up front. We isolated it to the motor. Checked all grounds and made sure main harness was not loose. Then we ran a fuel pressure test. My boat has an electric pump on the bottom that supplies the mechanical pump and then up to the VST tank. Initially i thought fuel system was good because vst tank was full of fuel. Found out the electric pump was heating up and locking up. Replaced with new holly electric pump and everything was perfect. Just relaying the steps I had to take to eliminate things to get to the root cause. Hope this can help.