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350 Magnum, no spark on new motor

Old 09-04-2019, 08:58 AM
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Question 350 Magnum, no spark on new motor

Hi,
I am a brand new member here and I need some help with a 350 magnum, Multi Point Injection engine that I just put together. Serial number OMO28646. My issue here is that I cannot get any ignition spark .

I used to work as a mercruiser mechanic 30 years ago but now I work on trains and haven't kept up with technology. In other words I don't see how I can trouble shoot this ignition system the old way with a test light like I did going back 50 years...lol.

It is my understanding that the pulse signal goes thru the ECM. I don't think I am getting a signal and I don't know how to check to see if I am. When I pull the primary wires off of the coil, the negative side feeding the coil is HOT with the ignition hot wired but the positive side is not. The positive side is hot when the wires are hooked back up because the voltage is going thru the coil of course. When I crank the engine over both primary sides of the coil remain hot. I do not see any signs of a signal being sent to the coil.

I picked up this engine disassembled and put it back together with new heads and therefore have never heard it run. I am trying to start this thing on the floor and when I hot wire the harness plug the fuel pump comes on for 2 seconds, so I am told the ignition should be hot as well.

Thanks in advance for helping an old man with his old Pachanga!
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Old 09-04-2019, 03:31 PM
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Thanks for the serial number
Gen 1 cool fuel, EST distributor and MEFI 1 ECM

When cranking the motor you should see the tach come up around 300 rpm
Here is how the EST system is tested




Do you hear any beeps when the key is turned ON, or hear the fuel pump prime for couple seconds?
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Old 09-04-2019, 05:07 PM
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Hi,
Thank You so much for the reply!! I will check or replace the pick-up sensor this weekend. I think I have one on the shelf.

I do not hear a buzzer as I am trying to start this thing on the floor. I do however hear the fuel pump run for a few seconds and then it shuts off. I am told that if I hear the fuel pump run then I have the right wire on the harness connector for the ignition also???

The coil I have looks like the old ,round conventional style coil, but I did try another used coil today to no avail.
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Old 09-04-2019, 05:19 PM
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here is the ignition system you should have. if any of these parts are different then we can start to figure what is wrong.
https://www.mercruiserparts.com/bam/.../31745/2691/70
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Old 09-04-2019, 05:21 PM
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Post a pic of your motor, because you should have the EST with your serial number, but if it has the round coil, then somethings have changed
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Old 09-04-2019, 05:23 PM
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I hooked an ignition switch to these leads and pug it in to run on my engine stand
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Old 09-04-2019, 10:15 PM
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He has a Thunderbolt V ignition system with MEFI 3 ---- totally different ignition set than a EST that the older small blocks used.. In my best guess you have a bad Ignition sensor under the rotor or YOU NEED TO HAVE A GOOD GROUND TO IT. If its a 3 wire then you can jumper the ground wire from the sensor to the battery ground to see if you get spark. If its the old 2 wire GET RID of that and buy the OEM 3 wire and DO NOT BUY THESE ONLINE junk crap. If you need help which sensor to buy you can hit me up.

I will post a diagram of what you have the sensor and do not buy Sierra - Those darn thing after some cycles of heat and and warm engine can have a misfire I know I have changed a zillion of them.

Also there is many past SB s about the ignition sensor and some changes that parts / engine side sensors added.
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Old 09-04-2019, 10:18 PM
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Like I said T BOLT V -- OEM stock black side Mercruiser # 6 is the ign sensor I am talking about ---- the pic is the old sensor that is long gone. You want the 3 wire which has its own ground. ( black lead with big eyelet on it )

Distributor & Ignition Components for Mercruiser (350 Magnum Mpi Alpha / Bravo (Gen+) Engine) Engine

Last edited by BUP; 09-04-2019 at 10:22 PM.
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Old 09-04-2019, 10:25 PM
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MEFI 3

Electrical Components for Mercruiser (350 Magnum Mpi Alpha / Bravo (Gen+) Engine) Engine
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Old 09-06-2019, 10:58 AM
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Thanks for all of the reply's everyone!! I will get back on this motor Sunday with the new info I have gathered here and see if I can make some fire in the hole.

I did try to post a photo but it looks like I am not allowed to do so until after I make 10 posts as a new member.

I will replace the pick-up with the 3 wire version before I do anything and go from there.

have a nice weekend!!
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