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-   -   454 mag mpi lack of power? Idles and revs fine, no miss (https://www.offshoreonly.com/forums/general-q/326074-454-mag-mpi-lack-power-idles-revs-fine-no-miss.html)

johnny b good 05-11-2015 07:14 AM

It wouldn't hurt to check your anti-siphon valve in the fuel tank for blockage/function.

nailit 05-16-2015 01:32 PM

4 Attachment(s)
Update: fuel filters replaced, P had something in it. looked like flakes from ethanol but I only use non ethanol.
also both caps and rotors have corrosion. Thinking I have found the issue with the fuel filter and corrosion even though corrosion was on both. I had the wrong rotor and cap, so I had to order the correct ones.

[ATTACH=CONFIG]541125[/ATTACH][ATTACH=CONFIG]541126[/ATTACH]

Look in the lil holes, you can see some flakes.

oh, and rotors looked different??

The P looked older?? the S looks like the diagram, So dont know if they even changed the rotor when they replaced the engine or just a different kind? Has only 1 contact and the S has 2?

[ATTACH=CONFIG]541128[/ATTACH][ATTACH=CONFIG]541127[/ATTACH]

Griff 05-17-2015 01:37 AM

Yeah that dist cap is smoked. I'm surprised it ran as good as it did.

nailit 05-17-2015 01:55 PM


Originally Posted by Griff (Post 4305315)
Yeah that dist cap is smoked. I'm surprised it ran as good as it did.

yep, hoping btw that and the fuel filter, it solves my issue. THe S cap had a lil corrosion too, so we will see next weekend when I get rest of parts in and installed.

BUP 05-17-2015 03:28 PM

You better take a hard look at the fuel filters mounting pads under sides, all fitting , fitting plugs , barbs within the mounting pad etc...- It might surprise you how much crap and or aluminum oxide corrosion is under side of the mounting pads. I have reported this up here a couple of times.

Proper fuel system and gas tank lay up / winterization is very important nowadays no matter what fuel is used. E 10 or not - the fuels today really do not have the lubricity of years past anymore plus E 10 causes a lot of aluminum oxide corrosion problems within the fuel systems and even internally of the carbs. I understand you have a MPI set up as this post was a generalization for whomever on top of.

Aluminum oxide corrosion is a or can be huge problems for the fuel injectors and or at the very least for there internal basket filters. FYI

nailit 05-17-2015 04:15 PM

1 Attachment(s)

Originally Posted by BUP (Post 4305475)
You better take a hard look at the fuel filters mounting pads under sides, all fitting , fitting plugs , barbs within the mounting pad etc...- It might surprise you how much crap and or aluminum oxide corrosion is under side of the mounting pads. I have reported this up here a couple of times.

Proper fuel system and gas tank lay up / winterization is very important nowadays no matter what fuel is used. E 10 or not - the fuels today really do not have the lubricity of years past anymore plus E 10 causes a lot of aluminum oxide corrosion problems within the fuel systems and even internally of the carbs. I understand you have a MPI set up as this post was a generalization for whomever on top of.

Aluminum oxide corrosion is a or can be huge problems for the fuel injectors and or at the very least for there internal basket filters. FYI

I actually took a pic underneath to check it out after I found the lil flakes in the filter. Not sure what they are as I do NOT use ethonal. The other good thing is we dont have much layup, usually only a few months 3-4 when she isnt in use and I put 100 gal of fresh fuel in Feb cause of fuel prices :-) (saved $100)

[ATTACH=CONFIG]541171[/ATTACH]

The underside of fuel filter pad looks pretty good.
Question: Which way does fuel flow?? Does in come in through the big screw on fitting or does it go back up through there??

BUP 05-17-2015 04:44 PM

The center hole of the filter and center adaptor fitting on the mount is the exit. This it is the same for oil filters to.

Fuel enters from the outside smaller holes thru then passes thru the internal media into the center of the filter and exits outs out of that center cavity hole. The exact same for oil filters - why this way.

2 main reasons are, it offers more filtration coverage area and improved flow volume.

U need to look straight up the center adaptor - way up internally to tell things as well. Your sealing surface that the filter O-ring seals against sure looks to be Aluminum oxide to me A COMMON PROBLEM to. This can cause a poor seal of the o-ring that can cause slight fuel leaks seeping and or air entering into the fuel flow - hence if too much air can cause lean conditions. Just saying.

nailit 05-17-2015 06:21 PM


Originally Posted by BUP (Post 4305494)
The center hole of the filter and center adaptor fitting on the mount is the exit. This it is the same for oil filters to.

Fuel enters from the outside smaller holes thru then passes thru the internal media into the center of the filter and exits outs out of that center cavity hole. The exact same for oil filters - why this way.

2 main reasons are, it offers more filtration coverage area and improved flow volume.

U need to look straight up the center adaptor - way up internally to tell things as well. Your sealing surface that the filter O-ring seals against sure looks to be Aluminum oxide to me A COMMON PROBLEM to. This can cause a poor seal of the o-ring that can cause slight fuel leaks seeping and or air entering into the fuel flow - hence if too much air can cause lean conditions. Just saying.

sounds good, thats what I was hoping, so the flakes I saw were in the smaller holes. So I should be good, I may put some seafoam in the filter to run through the system for good measure. The rim on the fuel filter was smooth to the touch when i ran my finger around it.

nailit 05-23-2015 06:52 PM

UPDATE: still lack of throttle reponse.

I changed plugs, cap, rotor, fuel filter that had crap in it... Actually funny, at first it was running real bad! Then after being stumped for a while, I went get some new plugs... then found 2 wires swapped, (I guess when I changed cap?!)

Took for a run today, runs good, idles fine, but still doesnt have the throttle response of the S motor!! Thinking of pulling manifold and pulling injectors to see if they have trash.. oh, but first I need to spray wd40 to see if I have any vacuum leaks..

Any other ideas??

sutphen 30 05-24-2015 07:50 AM


Originally Posted by nailit (Post 4307923)
Any other ideas??

send out the injectors and hope they can be cleaned.if not,you'll be replacing some if not all.


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