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Hard start when hot.

Old 07-10-2003, 06:24 AM
  #11  
J.V.IRONHANDS
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OK, thanks for all the tips, I tried leaving the hatch open, it does seem to help a little but it still hard to start. Next , I already removed fuel return line to seperator and ran it back to tank, recommended by engine builder to eliminate vapor lock. Fuel filter is clean, and using 92 octane, marina fuel so don't know how good it is, but never had problem before these motors. As far as fuel pressure goes, I did install gauges, and they do come up as soon as I turn key, than go to 0 until you turn key to start. This is for prime, while they're cranking to start they build up slowly because they're pumping after they start they stay at 41 lbs. I couldn't get the mefi1's programmed right after numerous tries so was advised to install FAST formally Speedpro. ecu's and the tech says I need to tweek the AFTERSTART circuit and this should eleminate problem. He called the problem HEATSOAKING. I will try this also. Anyone ever here of this?
 
Old 07-10-2003, 11:53 AM
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Before you start the motor move throttle off the idle position, as soon as motor starts then pull back to idle. See it that gets it to start quickly.

I think when a friend starts his efi motors the fuel pressure comes up as soon as he turns key on. Pressure stays up until motor starts. I will check next weekend when we are out.
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Old 07-10-2003, 04:07 PM
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J.V. Thats exactly what it's called, "Heatsoaking". I use to also run the blower for 5 min or so, AFTER shutting down. That also helped.
Your pump is running correctly. When you first turn the key on, the pump runs for about 5 sec. It stops because it doesn't get a signal that the engine is running. I also removed that plastic cover off the fuel/water separator, and the fuel pump to allow more air circulation around them. But the biggest thing I did was route the return FREE flowing to the tank... I havn't had that problem ever sence..

Here is the Dealer service Bulletin on your problem.

Mercruiser Vapor lock Bulletin
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Old 07-10-2003, 05:56 PM
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Originally posted by Kanookstr
Your pump is running correctly. When you first turn the key on, the pump runs for about 5 sec. It stops because it doesn't get a signal that the engine is running. ..
But shouldn.t the pressure stay up after the fuel pump runs for the first few seconds after turning the key on? If pressure goes down after pump shuts off before motor gets running there will not be enought pressure to inject fuel untll the motor sees oil pressure up, then the fuel pump will start again.
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Old 07-10-2003, 06:24 PM
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Originally posted by Turbojack
But shouldn.t the pressure stay up after the fuel pump runs for the first few seconds after turning the key on?
On my last 2 MPI engines I had a fuel pressure gauge, including this one.
The Pressure would go up when you first turn the key on, but if you are NOT cranking the engine. The fuel pump stops, and the pressure drops back down to "0". If you are cranking the engine, the pump gets a signal from the distributor or what ever it gets the signal from, and keeps pumping. The problem he is having is very common, and it's not the pump.
Theres a trick to fooling the ECU into thinking the engine is flooded, and this gets the engine to start without waiting for the Vapor lock to go away.

Put the throttle to WOT, (in neutral of course) then the TPS will tell (fool) the ECU that the injectors need purging, or what ever you want to call it.. The engine will crank over a few extra times and start right up with no waiting. Just be ready to lower the throttle so not to race the engine...

Last edited by Kanookstr; 07-10-2003 at 06:32 PM.
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Old 07-10-2003, 06:40 PM
  #16  
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I'll give it a try, thanks
 
Old 07-11-2003, 10:53 PM
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I use to have the 7.4 mpi in my challenger, no blower though. I made the mistake of putting in the 89 octane with 10% ethanol and it caused the boat to start hard especially after running for a while in hot humid weather. I had to pop the engine hatch and let it cool for a while before it would start again. Pain in the ass, especially when you are floating down the Missouri river @ 6-7 mph and it won't start! That was a night from hell. What ever you do don't use the 89 oct 10% ethanol... Good luck.

Todd
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