500efi issues
07-21-2019, 06:41 AM
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500efi issues
ok experts, need some advice, 2001 Efi is running poor under load after 2800 rpm. Runs great up to 28 and free revs fine, it will also run fine for only a minute or so at higher rpm once on plane, then it falls flat, looses power and back fires. A complete tune up was just done, including all new distributor parts. Heads/valves/springs etc complete and all fine. Thoughts please!
07-21-2019, 08:34 AM
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monitor fuel pressure when running,could have a gas line collapsing.
07-21-2019, 09:28 AM
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Def do a pressure test first...should be 38-43 psi. We recently had issues and wish we started by checking fuel pressure. Might also have to replicate the issue to see if pressure is still there.
07-21-2019, 11:38 AM
#7
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fuel pressure test should be done at the start of every year and especially when anything has been done to the engine and or taken off on the fuel side. Scan the engine as well should be done once per year and logged to compare for years and years down the road to see if any of the parameters has changed. Kind of like a blood test every year persay.
And for the record PROPER fuel pressure spec for the HP 500 EFI is a very steady 39 psi at the correct idle rpms fully warmed engine and 41 psi at WOT very steady fuel pressure is needed. That is the factory OEM spec
Next is the injectors whether one thinks so or not - if it was a carb engine how many times would have the carb been clean and rebuilt on a 20 year old engine? Both are fuel delivery items both get get crap in them for a jist.
and proper ignition coil - also ohm out plug wires and look at the differences. Alot of cheap wire sets out in the market
And for the record PROPER fuel pressure spec for the HP 500 EFI is a very steady 39 psi at the correct idle rpms fully warmed engine and 41 psi at WOT very steady fuel pressure is needed. That is the factory OEM spec
Next is the injectors whether one thinks so or not - if it was a carb engine how many times would have the carb been clean and rebuilt on a 20 year old engine? Both are fuel delivery items both get get crap in them for a jist.
and proper ignition coil - also ohm out plug wires and look at the differences. Alot of cheap wire sets out in the market
Last edited by BUP; 07-21-2019 at 12:26 PM.
07-22-2019, 03:00 PM
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All great advice.
Backfire through the intake occurs from one of the following:
1. Incorrect spark event (ignition wires wrong or crossfire).
2. Extremely lean under load causing fuel to ignite in the intake tract.
3. Intake valve not sealed.
My experience has proven option number 3 to be the most likely culprit. Has a compression and/or leak-down test been done? How long has it been since the springs were done? 500 and 525 EFI engines need periodic spring maintenance. A lifter could also be an issue (had this problem on one of my MPI engines).
Backfire through the intake occurs from one of the following:
1. Incorrect spark event (ignition wires wrong or crossfire).
2. Extremely lean under load causing fuel to ignite in the intake tract.
3. Intake valve not sealed.
My experience has proven option number 3 to be the most likely culprit. Has a compression and/or leak-down test been done? How long has it been since the springs were done? 500 and 525 EFI engines need periodic spring maintenance. A lifter could also be an issue (had this problem on one of my MPI engines).
08-07-2019, 09:40 PM
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Unfortunately back at it. So...swapped the fuel pressure regulators (just to rule out), re-checked timing (dead on 8 deg base), fuel pressure readings are as follows...on the hose - 35lbs with ignition on, 39 lbs at idle & 33-39 at 2k (pretty erratic) on the lake it varies 20-41 lbs at 4K (very erratic) then it starves for fuel. Pretty obvious it needs a pump, so which one? Now by swapping the regulators it does seem to run a little better (still not right, but better) and when you give it a quick free rev it’ll stall as it comes back down, you all know the 500 efi will stay put at 1500 for a few seconds after a quick free rev. I’d assume this is the electric pump that’s bad, but just not positive.
08-07-2019, 10:28 PM
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Unfortunately back at it. So...swapped the fuel pressure regulators (just to rule out), re-checked timing (dead on 8 deg base), fuel pressure readings are as follows...on the hose - 35lbs with ignition on, 39 lbs at idle & 33-39 at 2k (pretty erratic) on the lake it varies 20-41 lbs at 4K (very erratic) then it starves for fuel. Pretty obvious it needs a pump, so which one? Now by swapping the regulators it does seem to run a little better (still not right, but better) and when you give it a quick free rev it’ll stall as it comes back down, you all know the 500 efi will stay put at 1500 for a few seconds after a quick free rev. I’d assume this is the electric pump that’s bad, but just not positive.
