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    350 Mag Mpi hard to start when warm or hot

    Update 4: Boat booked in for a diagnostic test next Tuesday. I have checked grounds to other sensors all ok. However I did attach a vacuum gauge to the Inlet manifold & it is reading 12 Hg when it should be around 17-18 Hg so the map sensor is reading correctly. I will get them to compression...
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    350 Mag Mpi hard to start when warm or hot

    Thanks for reply. I had ground connection on my multimeter attached to the battery when i checked sensor 5v when it should probably have been on engine ground. I will recheck tomorrow.
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    350 Mag Mpi hard to start when warm or hot

    Thanks for reply. I will double check ect values in morning (night time here in Oz). As I increased the revs it seemed to progress to around 1.6v & stay there but I will check again.
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    350 Mag Mpi hard to start when warm or hot

    Thanks for reply. I did consider injectors at 1st but as the fuel rail was holding pressure I discounted that. Might rethink that now.
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    350 Mag Mpi hard to start when warm or hot

    Update 3: I can't get a diagnostic done for a couple of weeks. In the meantime I checked the map sensor signal voltage at idle & it was 2.6v when the ecm 555 manual specifies 1 - 2v. I put a new non oem map sensor on & that also reads 2.6v & when I open throttle it drops to 1.6v which is strange...
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    350 Mag Mpi hard to start when warm or hot

    Update 2: I tested the injector wiring with a noid tester light & that is OK so I am getting fuel. I tested for a spark with a timing light & that is good as I have a spark. What I have discovered is if I take the PCV valve hose off engine starts when warm/hot. This indicates I am not getting...
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    350 Mag Mpi hard to start when warm or hot

    Thanks for reply. Yes trying to find someone locally with diag tool. I have replaced iac & I think if the map sensor was faulty it would be playing up in other ways than the hot start issue. I have 12v at injector with ignition on. I will go up to boat again in the week & use a test lamp to see...
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    350 Mag Mpi hard to start when warm or hot

    Update: Replaced bad battery negative lead. Both batteries tested 100% health & charge. Motor cranks easily on either battery. Motor still not starting without throttle when hot. Sometimes it just catches & starts at a slow idle. What I have noticed is Motor will start if I put throttle to about...
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    350 Mag Mpi hard to start when warm or hot

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    350 Mag Mpi hard to start when warm or hot

    Yep apologies for that
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    350 Mag Mpi hard to start when warm or hot

    Not enough to crank motor. It was the last thing I tried before leaving the boat & although I thought I need to look at that too I hadn't associated it with the hot start issue mentioned in the other post. Thanks again for reply I will report back during the week.
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    350 Mag Mpi hard to start when warm or hot

    Thanks for reply I think you might be onto something as the batteries are fully charged & less than 2 years old both 780 cca. I should have mentioned in my original post that the engine would only crank & start with both batteries selected. If I select one battery it won't crank. Should be easy...
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    350 Mag Mpi hard to start when warm or hot

    Thanks for the replies guys that gives me something to try. Engine has a new iac muffler. My mechanic doesn't have diag tool i will find someone who has one. It will be a few days before I report back as boat is temporarily in a marina up the coast.
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    350 Mag Mpi hard to start when warm or hot

    350 Mag Mpi year 2006 serial No OW633284 approximately 400 hours. Problem: Engine starts fine when cold but won't start when warm/hot without opening throttle. If I put throttle to WOT & turn key it starts immediately. If I put throttle about 30 - 50% & turn key it cranks but doesn't start...
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    Quicksilver transom assembly replacement

    It's quite likely it's been replaced as mercruiser specify for it to replaced every 10 years. The tiller arm seal wears & if left unchecked leaks & corrodes. How I know is my last boat sank on its mooring because of it as it hadn't been picked up by the marine mechanic. Also just had one fitted...
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    350 mag mpi strange fuel pump relay problem

    The original FPR relay was bad I bench tested it. It appeared I had 2 faults the relay & a bad connection which would be unusual. Unless the spring contact in the relay base was faulty. If the fault remanifests itself I will post. Appreciate your response Alldodge.
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    350 mag mpi strange fuel pump relay problem

    Update. FPR relay although clicking when put in MPR base had internal fault & was not connecting MPR 30 & 87. This is where it gets strange. I connected wires & pins to the automotive relay allowing me to connect the pins to the harness socket. With ignition on the relay would only work if I...
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    350 mag mpi strange fuel pump relay problem

    Thanks for the replies. This YouTube video really helped With ignition on & multimeter leads in FPR socket 85 & 86 ecm switch side I get 12.5 v. Given I have power to 85 & 30, 86 grounds through ecm & relays are good I am pretty sure there is a contact fault with the relay base. I have...
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    350 mag mpi strange fuel pump relay problem

    Yes checked those thanks
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    350 mag mpi strange fuel pump relay problem

    Boat started from cold ok but after turning off for hour refused to restart. Fuel pump not coming on when ignition turned on. What I have found so far. 1. Both fuel pump & MPR relays audibly click when inserted into MPR socket with power on. 2. Both relays don't click when inserted into fuel...
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