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500 efi not making top end power

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500 efi not making top end power

Old 10-12-2021, 10:26 PM
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Working one some customers stuff (in my head) i started thinking about some ign modules iut there where done run out if go go juicecearly. So, thought of here too and throw it against the walk.

Did your new distributors require you to install your old modules ? Prob not, but worth the question. .

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Old 10-13-2021, 05:01 AM
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Originally Posted by SB View Post
Working one some customers stuff (in my head) i started thinking about some ign modules iut there where done run out if go go juicecearly. So, thought of here too and throw it against the walk.

Did your new distributors require you to install your old modules ? Prob not, but worth the question. .
The modules were the reason behind the new distributors. They came with new merc modules. Both motors ran great, ran around 80 (around 5000 rpm)

not to say they canít go bad. Plan was to swap them.

When the originsl modules failed the engines would backfire, sputter - stall. Wasnít sure if causes top end issues.

Last edited by snowrunner; 10-13-2021 at 05:19 AM.
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Old 10-13-2021, 05:14 AM
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Originally Posted by 1MOSES1 View Post
Have you looked at plugs recently to see what they look like? Looks like itís burning oil. When you did top end, was the intake shield re-installed? Any grey smoke when you run?

does the engine break up at top end? Usually thatís an ignition or wire problem.
The pics are of the current plugs, have 4-5 run time on them - 1 hr of idling down a river.

The rebuild was complete build new pistons/rings and deck plate hone. Same story on the heads, completely hone thru, new seals.

Used maybe Ĺ qt of oil on either engine, no smoke.

Iím not clear on an intake shield though, what is it?
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Old 10-13-2021, 06:36 AM
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Originally Posted by snowrunner View Post
The pics are of the current plugs, have 4-5 run time on them - 1 hr of idling down a river.


I’m not clear on an intake shield though, what is it?
Heres story on 500 EFI oil shield, under intake there is a tin tray in lifter galley, IF left out when running a 500 efi intake it will get oil almost force fed into the PCV at wot and literally fog the intake and engine with oil. I highly doubt you have THAT problem. A guy brought a motor he built to my shop to dyno with shield missing, it literally ingested so much oil at wot it was rolling coal at wot and lost ring seal. Was blowing disptick out of the tube.
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Old 10-13-2021, 06:46 AM
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Asking about your plugs, did you tell me that motor flooded at one point with fuel and was hard to start? I have had motors on dyno that fueled up the plugs and were making say 600 hp and started making 480/520 being down a cylinder, would idle and run at part throttle OK but lay down at wot from 1 or 2 deep fouled plugs.
Ive also seen bad stock coils but not as often as you'd think. I built 2 454 MPIs, extensively worked intakes Bob M's cams and whipple 2.3 sidemounts. Dynoed both engines NA then blown. They both made about 560 NA, boosted first one made in high 700s, lowered boost and tuned it to like 725 hp. couldnt get motor two initially to make good power boosted, changed cold, immediately picked up to where motor one was, smashed bads coil a little so it wouldn't get used by accident and saved it to show customer. Ran perfect NA just couldn't burn fuel under boost
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Old 10-13-2021, 08:46 AM
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Originally Posted by articfriends View Post
Heres story on 500 EFI oil shield, under intake there is a tin tray in lifter galley, IF left out when running a 500 efi intake it will get oil almost force fed into the PCV at wot and literally fog the intake and engine with oil. I highly doubt you have THAT problem. A guy brought a motor he built to my shop to dyno with shield missing, it literally ingested so much oil at wot it was rolling coal at wot and lost ring seal. Was blowing disptick out of the tube.

ok, yes running the valley tray. Had to dimple it for the lifters.
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Old 10-13-2021, 08:49 AM
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Originally Posted by articfriends View Post
Asking about your plugs, did you tell me that motor flooded at one point with fuel and was hard to start? I have had motors on dyno that fueled up the plugs and were making say 600 hp and started making 480/520 being down a cylinder, would idle and run at part throttle OK but lay down at wot from 1 or 2 deep fouled plugs.
Ive also seen bad stock coils but not as often as you'd think. I built 2 454 MPIs, extensively worked intakes Bob M's cams and whipple 2.3 sidemounts. Dynoed both engines NA then blown. They both made about 560 NA, boosted first one made in high 700s, lowered boost and tuned it to like 725 hp. couldnt get motor two initially to make good power boosted, changed cold, immediately picked up to where motor one was, smashed bads coil a little so it wouldn't get used by accident and saved it to show customer. Ran perfect NA just couldn't burn fuel under boost
yes, first start of the year a leaky injector and wouldnít crank - that was a hydrolock. New plugs since, no damage was cyl 8.
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Old 10-18-2021, 11:58 AM
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Originally Posted by snowrunner View Post
Looking for input, have 2 rebuilds with 15 hrs. Both run great up to 4200, when the SB motor runs out of power snd RPM. The SB engine can drag it to 4400 or so.

New plugs, new injectors (Smitty Tuned on the water). Compression is 160-155. New distributors at rebuild. Wires are new 8 mm GM perf from Crate motor. 39 psi on rail under load. Timing at 8 deg. Moved rails from engine to engine

During tuning we didnít have any codes, no knock. The only ignition part not new is the coil, but this doesnít seem like a coil type issue.

Is there something I Ďm missing? Want to heck it out before its put away for winter.

regards.
So I have a pair of 572 with Edelbrock FI (ProFlow 4). I ahd a similar issue early in my tuning cycle. It seems the o2 sensor would stop working above 3500rpm, and the computer would go the table. Since the tune was still in learn mode, it would go very rich and cause the engine to simply loose power. If I stayed below 3500rpm, it would clear the issue. I know weird. Replaced th O2 and all was well. I will say that I do carry extra O2 sensors now. I dont get a lot of hours out of them before they start acting weird.

Of course, the PF-4 is NOT designed to be a marine solution.
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Old 10-18-2021, 05:50 PM
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Same issue with my 502 8.2 2011 seems to stop making power around 4100 rpm changed o2 sensors the boat has around 200 hours no burning oil starts right up no codes or misses sometimes when cold she burps one or twice going on plain but thatís it please any advice
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