502 MPI won't rev
07-22-2017, 08:57 PM
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502 MPI won't rev
Hi folks. I have a 41 PC with twin 502's (MPI). My starboard engine won't rev above 3600rpm and I can't figure out why. Despite being at full throttle, it will only rev to 3600. It has new distributor, new ignition module, new plugs, new plug wires, almost new fuel pump. I plan to change the plugs again tomorrow as they are showing that they are wet. What should I try next? My plan is to change the plugs + fuel filter. Thanks!
07-22-2017, 11:05 PM
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Hook a fuel pressure gauge to schraeder valve on efi rail, just had customer w same problem, only had 28 to 30 psi, bad regulator, should be 38 to 43 psi, Smitty
07-23-2017, 12:45 AM
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and if --- the fuel pressure is NOT being the issue - I would scan the engines and compare parameters between the 2 and the reading of rpms of the engine not reaching correct WOT rpm levels from the engine scan as well.. Check the tach to make sure its accurate .If no scan tool on hand -- Maybe swap tachs or a digital remote tach or timing lite display of rpms. Then prob compression testing and spark plug reading
Next if nothing stands out - I would switch the drives and see what happens there. Check the props as well - especially rebuilt ones by sub par prop shops. I prob see about 2 or 3 twin engine apps with one side different gear ratio per year and about 10 times per year with mixed match and or poorly rebuilt props on twin engine apps. .
Next if nothing stands out - I would switch the drives and see what happens there. Check the props as well - especially rebuilt ones by sub par prop shops. I prob see about 2 or 3 twin engine apps with one side different gear ratio per year and about 10 times per year with mixed match and or poorly rebuilt props on twin engine apps. .
Last edited by BUP; 07-23-2017 at 12:47 AM.
07-23-2017, 07:27 AM
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and if --- the fuel pressure is NOT being the issue - I would scan the engines and compare parameters between the 2 and the reading of rpms of the engine not reaching correct WOT rpm levels from the engine scan as well.. Check the tach to make sure its accurate .If no scan tool on hand -- Maybe swap tachs or a digital remote tach or timing lite display of rpms. Then prob compression testing and spark plug reading
Next if nothing stands out - I would switch the drives and see what happens there. Check the props as well - especially rebuilt ones by sub par prop shops. I prob see about 2 or 3 twin engine apps with one side different gear ratio per year and about 10 times per year with mixed match and or poorly rebuilt props on twin engine apps. .
Next if nothing stands out - I would switch the drives and see what happens there. Check the props as well - especially rebuilt ones by sub par prop shops. I prob see about 2 or 3 twin engine apps with one side different gear ratio per year and about 10 times per year with mixed match and or poorly rebuilt props on twin engine apps. .
07-25-2017, 08:05 PM
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Figured it out. Had a fubar plug wire. While there I changed plugs, plug wires, distributor cap/rotor, ignition module, fuel filter. She's running perfect now! Thanks!
07-25-2017, 08:10 PM
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Cool ! But I thought you just did all that and more ?
07-25-2017, 08:12 PM
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07-25-2017, 08:31 PM
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Hi folks. I have a 41 PC with twin 502's (MPI). My starboard engine won't rev above 3600rpm and I can't figure out why. Despite being at full throttle, it will only rev to 3600. It has new distributor, new ignition module, new plugs, new plug wires, almost new fuel pump. I plan to change the plugs again tomorrow as they are showing that they are wet. What should I try next? My plan is to change the plugs + fuel filter. Thanks!
Just pointing out, to help us help you diagnose, info told to us needs to be accurate as possible.
That said, and again, cool to here you are all set. Good job.
07-25-2017, 08:33 PM
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Yep, understand. I used to drag race and built my own car --- so i understand. It was my intent to INSTALL every single part. However, time would not allow. Therefore, I wasn't trying to mislead anyone. I had every single intention of installing all those parts LOL.
