1999 454 Mag MPI just quits - videos

370Dancer

370Dancer

Well-Known Member
Oct 2, 2006
2,489
Suncoast of Florida
Boat Info
1998 370 Sundancer
Engines
380hp MAG MPI Gen VI with V drives
Here's the latest in the saga of this Port Engine.
Videos in order, taken this morning.
https://share.icloud.com/photos/0jjO17nWxQuC4Q0YsGuR19uUA
https://share.icloud.com/photos/0WHMMm3mpsUo9JujX1BTwD7-A
https://share.icloud.com/photos/0YBi_DKBRh_Hjrao86FlhBf7w
https://share.icloud.com/photos/0tqRdct8gOpfwHKPlwkQ9BNag
https://share.icloud.com/photos/0Hwnr0uC61FWD15flTxAj_M6w port engine data after shutdown
https://share.icloud.com/photos/099GCF5IrraGrOMQK5H5kF5pg stbd engine data (no warmup)

Fuel circuit from the fuel tank:
existing 5/8" fuel line from tank pickup to Parker Skinner fuel shutoff (2011 replaced)
Tried shutoff in bypass and normal - no change
NEW 3/8" fuel line, heat shield wrapped from shut off solenoid to inline filter
NEW inline filter to low pressure fuel pump (August 2020)
NEW low pressure fuel pump (August 2020) to fuel/water sep filter
NEW (day before yesterday) fuel/water sep filter 1807844
NEW replacement fuel line from fuel / water sep to High pressure pump (June 2020)
Replacement high pressure fuel pump (June 2020) to fuel rail
Original fuel line from pump to fuel rail, new o-rings June 2020
NEW injectors (June 2020)
NEW replacement return fuel line from NEW (June 2020) OEM fuel pressure regulator (June 2020) to fuel / water sep
NEW IAC (June 2020)
NEW IAT sensor (August 2020)
Tried with cap off of fuel fill to eliminate vent - no change
100% monitoring of fuel pressure: no loss
The only difference I see is a bit more voltage on the TPS compared to the Starboard engine, which runs like a top, and goes to full rpms under load. ,43 v when I believe spec is .35 v at idle. But I see that on the STBD engine too.
Other:
NEW Ignition module (a few days ago) - suspect. will put the old one back on to see if there's a change
NEW plugs ( a few days ago) NGK BR6FS
NEW distributor module: (Sept 2020)
NEW wires, cap and rotor (April 2020)
Swap techniques:
swapped 2 relays from STBD engine: no change
swapped out ECM: no change
I am down to guessing the replacement high pressure fuel pump is failing after getting to some temperature, below 160.
Boat has sat since June due to other things. Put in a fresh set of plugs and the ignition coil to see if it would run up to plane. Right around 3000 RPM (struggling as usual), the engine just died. wouldn't start again until the next morning, and only for a few minutes, like you see on the video now, This is repeatable every day this week.
I didn't go to makeup before making the video.
 
Cliff,

I watched your videos which were quite helpful. I know how frustrating something like this is.
I had problems like yours on a client's MAG MPI a few years ago and on my on carb based port engine 3 years ago.

It would start and run with no problems at all. Then it would stop....sometimes it would restart and other times it wouldn't until the motor cooled down. I was at my wits end until I put an analog meter on the power 12 volt wire for the coil. Then it became clear that we were losing power on the coil wire. It is hard to see on a DVM but on an old analog volt meter the needle went to zero and then the engine quit.

To prove it....I ran a 12volt wire directly to the coil and voila....the engine ran perfectly....no more stopping or other bad behavior on the client's engine or my engine. Sometimes the connector gets loose (that was the MAG MPI issue) or corroded and the connection of the wire becomes problematic especially when it vibrates (when you throttle up).

Unfortunately....if running a jumper works.....you know what the problem is. Finding a wire is partially broken is another job all together. It is a serious pain to trace an intermittent connection.


I will also note the voltage on your port engine is slightly less than the starboard engine which may also indicate a bad/corroded connection.
 
Last edited:
Did you change the pickup coil in the distributor. I had one go bad but mine wouldn't start. Looks like you changed everything else. Can you swap the whole distributor with other engine?
 
370Dancer said:
Thank you for your insight and experience. I will chase that down at daylight. As pointed out, I changed the coil chasing the get on plane issue, and likely somehow introduced this one.
Click to expand...

I think you are right.....once you changed the coil....it worked for longer than it did in the video. It could be a connector or the plug. I'll bet a beer on it!:)

I'm not going to bet a case because you may be chasing a different gremlin after the coil wiring ......according to the schematic the wire that feeds the coil also goes to the fuel pump.
 
Last edited:
bone354 said:
Did you change the pickup coil in the distributor. I had one go bad but mine wouldn't start. Looks like you changed everything else. Can you swap the whole distributor with other engine?
Click to expand...
The pickup coil is about the only thing that hasn't been changed.Going back to the ignition coil first.
 
whatever is going on is getting worse. this morning idled for 2-3 minutes. While that was going on, I used a mechanic's stethoscope to listen to the high pressure fuel pump. It never stopped, and when the engine did, it of course ran for 2 seconds, and then shut off. Now the engine cranks but will not restart. That's different from yesterday.

Swapped the ignition coil with STBD, no start.
swapped the distributor module with a spare. No start
swapped the wire harness from the ignition module to the distributor module. no start
Pulled a spark plug (#7) not wet

So, either my pump is running, but not moving fuel (however pressure stays at 40-45 psi)
or I am losing spark. Off to Harbor Freight for the cheapo spark tool, I've not done this before, but can't I put this between the ignition coil and the distributor cap to see all 8 pulses, or do I have to put it at the spark plug?
 
I assume that I have to pull the distributor, and take it apart to replace the pickup coil? That's what it looks like. No easy access from the top?
Wish I had a spare distro laying around.
I also tried disconnecting the MAP to get the ECM to use its internal value. No start.
 
Be careful with the clip that holds it on, new ones don't come with 1. This should be easy enough to diagnose with a no start condition
 
The problem sure seems electrical. The HF spark tester is in line..... meaning it goes between an individual spark plug wire and a spark plug. It is a helpful tool but all it really tells you is if you have a spark or not.

My bet is that you don't. I believe you have a Thunderbolt V distributor......this is the test sequence:

https://f01.justanswer.com/schembrinoel/0d171f02-5abb-4e5b-875f-9e7fb0c3b44a_17B4R2.pdf

When you test for 12v move the wires around to see if a wire is broken or a terminal is loose.
 
What's different today, is that the engine ran this morning for a couple of minutes before stopping like previous days, but today, no restart. I am throwing a code 34, which is the MAP sensor, but I had disconnected it this morning to see if it would start with an internal value, and that probably set it. I'll clear that in the am, and see if it starts in the morning. At this point, I am thinking whatever my intermittent issue was, has gone hard. good. Here's what I don't know. If I have pressure in the fuel rail, solid 40-45psi, could that just be air, or would that read differently, like zero? I swapped the ignition coil with the original from the STBD engine. that engine runs fine with the new replacement, and this one still doesn't start, so I'm ruling it out for now. I probed the harness going into the coil, and voltage is there. I ohmed the pickup coil in the distributor and got a .85 on the 20K ohm scale. I'll measure the STBD in the morning to see if that is way high.
This is the HEI ignition. Gen VI MEFI-3 with a 4B replacement on it (and the adapter harness), When I swapped out the ECM yesterday, I removed the adapter harness and plugged in a MEFI-3 I had from the previous set of engines. Not a perfect test, but no symptom changed.
It's dark now, so I'm going down to see if I'm getting spark on that engine.
 
No spark. splains a lot, but why, not so much. Focus, grasshopper.
I have read all 1027 pages of the service manual at least 4 times, albeit for different reasons. One more time?
measuring the resistance of the STBD coil after I recover from not so daylight savings time.
Gawd, I love boats.
 
Check the physical plugs on the various harnesses, coils, etc. Quite possible the male/female pins are not making contact somewhere.
 
It's a hair pullin day for sure.
I have been all over everything from the system relay to the HP fuel pump. Things seem right, but clearly are not. Daylight will bring more info.
 
scoflaw said:
Be careful with the clip that holds it on, new ones don't come with 1. This should be easy enough to diagnose with a no start condition
Click to expand...
"should be"
Let me know when you are South. I could keep you busy for a minute.
 
And, in case you guys are still awake,
if I move the distro from the STBD to the PORT, I would need to make reference marks where the rotor is.
Mark the STBD, pull the distro, and not move the STBD engine until all is done.
Mark the port rotor point, pull the port distro, and then insert the starboard distro so it lines up with where the port one was.
try as I may to start the port engine. regardless of results, mark the port rotor where it points when done
replace starboard distro to the starboard engine, pointing as per mark
replace the port distro to the port engine, pointing as per mark
check/adjust timing on both.
 
370Dancer said:
No spark. splains a lot, but why, not so much. Focus, grasshopper.
I have read all 1027 pages of the service manual at least 4 times, albeit for different reasons. One more time?
Click to expand...

I know it frustrating but you have to run through the test procedure I cited earlier. While you do it you have to push and pull on the wires to ensure you don't have a broken wire or connector. I would not swap the distributors at this point.
 
If you have the EST diz, you can buy that pickup coil at an auto parts store for around $30. !988 camaro, same everything.
 
scoflaw said:
If you have the EST diz, you can buy that pickup coil at an auto parts store for around $30. !988 camaro, same everything.
Click to expand...
Sierra is 28 bucks, so no fear.
swapped distro with module, rotor and pickup coil intact. No change.
nothing went back in as advertised, so I wound up having to find TDC, setting the distro per #1, and then adjusting for 8 deg BTC. Starboard back to its usual self, port still hosed.
John, I think you are righter at the moment about harness and connectors. spraying them, but that's probably not enough.
I'm not a dummy, but I am feeling like one today......
 
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