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2002 496 Mag Fuel Injectors not firing

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2002 496 Mag Fuel Injectors not firing

Old 06-09-2021, 08:33 PM
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Default 2002 496 Mag Fuel Injectors not firing

Hello Again,
I am stumped on end of a two year project. I posted earlier about the Cam position sensor. Got the wiring and the conversion looks wired correctly.

I have what was a 2002 496 Mag 375 hp engine (serial#OM084202). Purchased a new short block from a member on this site (thank you). Rebuilt the heads, put new injectors, coil packs, alternator, starter, raw water pump, fresh water pump, IAC, TPS, Risers, Manifolds, and more. Having read on the forums about the issue with the Cam position sensor being NLA and the conversion required. I decided that while the new engine was out of the boat, convert to the 2004+ cam position sensor and all that entailed. I used information from here and the link provided (Vortec 8100 8.1L Chevy GM Camshaft Position Sensor Guide - 496cid Cam Gear Sensors - Raylar Engineering)

After putting all the fluids and charging the batteries, the boat will crank but not start. It does start if you spray starter fluid down the throat. I had a marine mechanic come out. He was only able to get it to start and idle by spraying gas down the throat. He stated that the PCM was bad. The PCM thinks it is sending signal to the injectors but the injectors are not receiving signal. He said oil and fuel pressure look good. Since the PCM had been pulled and refurbished two years ago and was still under warranty, I pulled it and sent it in. Last Friday the tech called while running diagnostics on the PCM. He found no issues. He even ran a pin test on it. The PCM is firing the injectors as expected.
I finally received the PCM today and installed it. I pulled the pig tail from the Cam Postion Sensor and the wiring looks correct (compared to what the tech told me and the picture from this forum). So now I am stumped. Why am I not getting fuel? Why are the injectors not firing?
Where to start looking now. If this boat will start, I can take it out and enjoy the summer!

Any suggestions are welcome. (Sinking the boat is NOT an option) I am calling the mechanic back out, but am not confident he will take the time to truly troubleshoot the issue after wasting two weeks pulling the PCM sending it out to be tested and finding no issue with it.
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Old 06-09-2021, 08:41 PM
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So, proper fuel psi is getting to injectors but injectors arenít going clicky clicky (have you felt or listened) when cranking ?
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Old 06-09-2021, 10:38 PM
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verify that you have cranking rpm
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Old 06-09-2021, 10:54 PM
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DOes the engine still do this ?
496 Mag - New Engine Starts will not run

Do these engines cut fuel pump if oil psi sender goes to/near 0 like other fuel injected engines ? I canít remembet.
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Old 06-10-2021, 04:25 AM
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Get a noid light and put in injector harness to check signal.
Typically injectors have constant 12v with key on and ECM controls ground.
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Old 06-10-2021, 08:46 AM
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Originally Posted by liberator221 View Post
Get a noid light and put in injector harness to check signal.
Typically injectors have constant 12v with key on and ECM controls ground.

I also have a 2002 496 and from Mercury PCM #33 manual the injectors are feed fused 12v with pink/white and pink wires to each injector bank. I would check with voltmeter at each bank while cranking.
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Old 06-10-2021, 07:40 PM
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I will be checking that this weekend...thank you for giving me some things to check. I will report back with what I find.
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Old 06-10-2021, 07:41 PM
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correct...no clickety click
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