502EFI Problem
04-13-2005, 09:55 AM
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502EFI Problem
I've posted here before on this problem but to date have no solution and it's now boating season once again. I have twin 1996 502EFI's ( with major HP500 mods ) that use the VST fuel system. I am familiar with the inherent VST screen problems and have eliminated that problem with the addition of two additional RACOR 10 Micron spin-on filters, after the standard Merc water seperator/filters and before the VST screens. I'm stating this just so everyone knows that the VST screen has systematically been eliminated as the culprit. I've also changed plugs, wires and distributor cap.
When cruising @ typical cruise RPM of 3500 RPM, I sometimes get a loss of approximately 300-400 RPM in one motor. It can come and go, but not usually something that just is off/on. I can sometimes cruise for an hour with no sign of loss at all and then all of a sudden it's there. Sometimes after I stop the motor and restart it's gone. Sometimes at or just off idle I can feel and hear the problem. When the "problem" is present, I can move the throttles forward from idle just a little and get a really missing, bad sounding sound from that motor. Like a major miss. And then sometimes it runs perfectly for a long time.
Any ideas out there ? Where to look ?
When cruising @ typical cruise RPM of 3500 RPM, I sometimes get a loss of approximately 300-400 RPM in one motor. It can come and go, but not usually something that just is off/on. I can sometimes cruise for an hour with no sign of loss at all and then all of a sudden it's there. Sometimes after I stop the motor and restart it's gone. Sometimes at or just off idle I can feel and hear the problem. When the "problem" is present, I can move the throttles forward from idle just a little and get a really missing, bad sounding sound from that motor. Like a major miss. And then sometimes it runs perfectly for a long time.
Any ideas out there ? Where to look ?
04-13-2005, 10:33 AM
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Re: 502EFI Problem
93 502 efi. vst system
hard to start a couple of times.
would suddenly lose power at various rpm's.
wait a few seconds and would start back up and run just fine for several hours.
finally would not start at all one day.
turned out to be the high volume fuel pump.
if i remember right the pump was around $500.00
hard to start a couple of times.
would suddenly lose power at various rpm's.
wait a few seconds and would start back up and run just fine for several hours.
finally would not start at all one day.
turned out to be the high volume fuel pump.
if i remember right the pump was around $500.00
04-13-2005, 10:49 AM
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Re: 502EFI Problem
Any trouble codes? Any change in fuel pressure when problem occurs? If it is a miss, identifying the probelm cylinder shoudn't be too difficult.
Dave
Dave
04-14-2005, 09:16 AM
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Re: 502EFI Problem
The problem shows no codes. We did have a fuel pressure gauge installed for testing and did experience the problem and saw no problem with fuel pressure. I believe it was around 31 pounds or so. We can't seem to isolate the problem to a single cylinder either.
Any more ideas ? Maybe we'll swap the VST systems complete and see it it follows. That would certainly isolate the problem.
Thanks for the ideas guys.
Any more ideas ? Maybe we'll swap the VST systems complete and see it it follows. That would certainly isolate the problem.
Thanks for the ideas guys.
