500 efi not making top end power
 

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 didn’t have any codes, no knock. The only ignition part not new is the coil, but this doesn’t seem like a coil type issue.

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

regards.

New cams degreed in ?
New valvesorings just out in or did someone do all the actual trsting and measurements ?
Exhaust have mufflers ?

In boat tuning with wideband ? Assuming yes but checking
wot verified ? Assuming yes but checking

Tyler Crocket built the heads.
no mufflers, Hardin Manifolds
wideband
boat ran 78 after new distributors last year ( ign modules were junk). Running around 70 now.

The issue started before injectors, changed them all after one stuck open.

i rarely run full out, so not clear when it started

After providing a "scaled" tune for the 48 lb injectors I provided and hearing boat doesnt "pull" on top, snowrunner verified timing, fuel pressure, changed filters, etc. Still having the issue, I became concerned the scaled tune may just simply be too rich and the port motor which isnt pulling as well as the stbd motor may possibly be loaded harder than the stbd and running in a higher map setting, possibly getting into the 10s in afrs or something. I DID flow these new injectors against some good stock ones and used that data to scale the tune, Sooo, I offered to come down and scan/tune boat with AFR meters on water. I found the light throttle 50, 60, 70 map areas under 2200 were in low 11s and tps accell was still too rich, rescaled these to clean it up BUT the afrs in midrange and wot are pretty much where they belong in low to mid 12s. I did some touch up work to those areas and pushed some more timing in mid range with no sign of KR.
So, the wot AFRs are in 11.9 to 12.4 area, its got as much timing as Id dare to put in with 87 octane, NO KR, tps, ect, iat, look fine. The ONLY anomaly I DID see is the lower rpming motor is running in general in a slightly higher map cell and running .3 to .4/.5 richer than "good" motor, of course if its got a problem thats exactly what it will do. Not uncommon too though to see one motor in a twin at 12. and one at 12,4 at wot. On my dyno going from 11.8 to 12.2 to 12.5 barely changes power a measurable amount, to NOT rpm from tune, it would have to be burn down lean or pig rich, I was HOPING it was signifigantly off and some clean up would fix it but unfortunately NOT, injectors been swapped from side to side with no changes also.
Snowrunner, what valve springs are on your heads?

Engine hydrolock ?

Thx Smitty!

Running Isky springs, crane rockers, Johnson 2126BBRB lifters. Stock 500 EFI For everything else.
https://cimg4.ibsrv.net/gimg/www.off...eccba9c7b.jpeg
https://cimg5.ibsrv.net/gimg/www.off...708b4c7b3.jpeg

No Hydrolock.

Compression good all cylinders within 5 psi.

cut filter, no debris. May be able to bend a rod, but should make noise or cause debris.

Those plugs are pretty black BUT motor was idling and running fairly rich down low so the color is deceiving. IF you had new plugs in and were driving it today, they would be much cleaner overall. At one point you changed them and made no difference, correct?

I changed them after the original injector failed, then again after the new injectors.

Made a difference after the stock injector failure, though changing them after new injectors but really didn’t change anything. They look the same now as the set that came out when the injectors went installed.

I keep leaning toward a SP wire with a weak connection or resistance issue issue a peak power and full load? Looking at the wires, these were not new with the rebuild - but have max of 75 hrs and were from my 502 MPI.

Have you looked at plugs recently to see what they look like? Looks like it’s 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 that’s an ignition or wire problem.

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 can’t go bad. Plan was to swap them.

When the originsl modules failed the engines would backfire, sputter - stall. Wasn’t sure if causes top end issues.

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 ½ qt of oil on either engine, no smoke.

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.

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

ok, yes running the valley tray. Had to dimple it for the lifters.

yes, first start of the year a leaky injector and wouldn’t crank - that was a hydrolock. New plugs since, no damage was cyl 8.

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.

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 that’s it please any advice

have you squeezed all the power out of your proflow 4' there is? I've done some rxtensive testing with tb mods, cone filters, air entry eyc and saw big gains on flowbench and dyno

I was responding to Snowrunner about his 500EFI issues.

However, I will always listen to any feedback on the PF-4 system. My main concern is O2 sensor failure rates. I get about 8-10 hours before they fail. I am sure it is moisture in the exhaust post shutdown. I have the sensor in the dry part of the system, but 18 inches after the sensor is the water dump. Dry pipes are an option, but would have to build a very custom one-off as I have side exhaust. Thru transom is not an option.

Also, the engines were dyno'd extensively before installation, so Im pretty sure Ive got 80-90% tune dialed in. Most of my tune issues left are now on idle issues, and hot start issues. Which I think is related to the moisture in the exhaust, messing with the O2 sensors. I placed the bungs just above the elbow flange (about 2 inches down pipe). the goal was to be at least 18 inches from the water dumps. All the pipes are flowing down from the elbow, and into the internal mufflers. But I bet that just holds the wet in the pipe and takes out my sensors.

I tune alot of boats on the water using WB02 sensors, have you installed these directional innovate HBX-1 extenders? They are directional, they protect the tip from reversion but in my testing on water and on my dyno they absolutely did not change 02 readings, slow down response etc. I tuned a 322 baja with lightning headers, thing went thru 02 sensors in record time, these made them last night and day longer.
does your prfolow 4 look like a open plenum intake with 4 bbl TB on top or like a tunnel ram with a monoblade on front, the proflow 4 XT is one I was referring to making signifigant gains with (front mounted tb), Smitty
https://www.ebay.com/itm/27498899266...iABEgLQBfD_BwE

So this heat sink looking bung does that thread into the exhaust manifold and then the o2 sensor threads into that?

I use the 4150 throttle plate style, and a large K&N marine 5" tall air cleaner/arrestor. The XT was tested on my motors and gains were slight at best. I think with a bigger cam motor, these would make more power. I have big cubes but mild cam for low and mid-range torque, so the XT was not any better at these lower RPMs. I almost put them on because they are also pretty cool looking!

I like the bung extension. I think I will look at these as a possible solution. many thanks!

-jeff

yup, sounds similar.

Mine is hibernating in storage for the winter, will be a spring project now.

let me know if you find anything

Yes, and its directional, I have shimmed them with spark plug gaskets, filing brass washer comes with it, etc, they work, Smitty

Yeah whole different setup than the proflow4 XT's ive been modding/using, they are a mini tunnel ram with monoblade tb, they work very good, great hp on top once modded, unfortunately, not at all like a proflow 4 so my results are irrelevant to yours, Smitty

Will do last night I changed the throttle positioning sensor and another sensor on top of the manifold parts changing try to chase this issue and in the spring I’ll change fuel filter I swear i am moments away from pulling this set up out and building a dart block set up with an EFI carburetor and calling it a day I just can’t handle no tuning and no modding of this motor mercruiser has a cease and desist order on tuning for all catalyst engines tell me your thoughts if you don’t mind.

Hey if i had to start over, that is the route I would go also. 16 is too many injectors to go wrong in my opinion. Only reason i am staying put with Mefi3 MPI is I've already bought 16 new OEM injectors 3 years ago and so far, plugs look real even. But one goes off and you can lose a motor quick. Not the way to go. I like your idea.

I presume you have the cat converter? That was the most ignorant thing - adding those. So much money and takes up valuable room, and adds weight. For what - to REDUCE emissions. Over a whole season I bet on a boat that DIFFERENCE in emmisions would be about what an 18 wheeler puts out in probably one minute. Follow..... the ..... money I always say. . Not what was is the smart thing to do, or the right thing to do..

Well that's been the unspoken standard at the OEM level forever. The OEM's have been trying to thwart tuning forever.
But with you saying that, is it hearsay or have you seen something in print from Mercruiser?

Are you having troubles with O2 sensors surviving in an OEM catalyst situation?

Thank you for the interest, actually I had a couple o2 sensor codes so I replaced them all and they seem to be working fine now however, I was in the process of trying to eliminate the o2s purchasing that o2 eliminator box as well as exhaust manifolds to remove the cats and everywhere I was reading they said to call whipple they can do some custom tuning to the ecu or there was one other guy to build tunes as well. So I figured If I could do the exhaust manifold maybe a set of heads, larger injectors, cam etc however when I spoke to the rep at whipple he told me Mercruiser slapped them with a law suite and until they work out this issue they are no longer capable to do any tunes nor will anybody else on these black model engines without getting themselves in trouble as well. basically they were making as much power as the 525 with exhaust, new throttle body, and a cam so i'm thinking they were taking $$$$ out of Mercruisers pocket not to sure. But sucks for our stock engine weekender.

They use the same computer module, and Edlebrock suggested I could upgrade the intake to the XT if I wanted to. they are wicked cool looking too!

jdr

Ordered a pair of the bung extensions. Ill let you know how they work out. May not know until next year as Im replacing my Bravo 3s with Arnesons. Rooster tails for next year!

So I got the bungs today! man these are not junk, but really well made. they indicate their use as being for high temp usage such as turbos, and other power adders. Bbut it makes sense given the design tht these would work really well in keeping water from getting to the sensor.

More to come as I test!

What brand/model did you get.
I need to look into some. Figure how to put on some fairly new Eddie Marine elbows that dont have a bung.

THESE are what you want, I was tuning a twin with lightning headers, was only thing that would make o2s last more than minutes. I tried them on my dyno and in boats, there was no diff on dyno in afrs or response time, directional, they keep water off o2s great! not cheap but well worth it
https://www.ebay.com/itm/27498899266...iABEgLQBfD_BwE

I had a local guy weld the bungs in. Not cheap, but I could not find an adapter for my NoS Smooth side Gils headers. Hardin does have some good options here though:
https://www.hardin-marine.com/c-391-o2-sensors.aspx
-jeff

I’m just going to keep this as the shortest post so far I feel. If I had Smitty tune it and I had issues, I’d reach out to him and resolve the issue as he’s a very sought after tuner and customer service is second to none before I blew his name out as working on it then looking for internet ideas. Just a thought.

Chad, tune wise, on the water the afrs were pretty close to target, we dialed them in even better. So both motors have right timing, afr's, fuel press etc yet one pulls much less rpms and lags behind the other one hence OP "snorunners" post. He has also swapped all the efi components from one motor to other with same motor still not pulling rpm. At this point Im confident its NOT in the tune or injectors I provided, If it was up to me, that motor would be out of the boat and getting dissected or dynoed, smitty

I didn't read this whole thread but has the OP swapped props?