Follow up to my earlier post "whats wrong with my 455?"

[dgie]

This is the original post:
I took my boat out today and the engine runs fine up to 3800 rpms then starts to pop and cutting out. I changed out the distributor cap, rotor, and points. I am running a Mallory single point distributor. I checked the timing with a timing light and it within specs. I made sure it was advancing via timing light and all looked well. Now for the fuel system I am running a Holley Red electric pump. I am running a Holley 750 Marine carb. I pulling fuel from side tanks and running through a fuel/water separator and an electric fuel selector valve from a Chevy pickup. I am running 5/16" line for the fuel system. The exhaust headers are black inside and on tips at the end of the day. Anyone have any Ideas on this one??
Here is the follow up:
I changed out the fuel lines to 3/8" from 5/16". I added the fuel pressure gauge just before carbarator. I took the boat out and I noticed I was getting 5 psi up to 3200 rpms and then it would start to fall to 3 psi then at around 3800 rpms it would start to fluctuate like crazy. I found that the pump (Holley Red) is only getting 10.6 volts. Am I running too low voltage to the pump and how does this effect my pressure at higher rpms?

[victorfb]

who set up the carb? id look at the floats. and not just float level. pull the bowls and see if the needles are still hooked on the float clips, check the needles and if they seeting properly. and definatly set the float levels right. it makes a differance you wouldnt believe. i would think that even with 3 pounds it should still be fine.
did you check that cam? valves? ?????

[Rexone]

Yes reduced voltage will affect pump operation, but you may also have a fuel pump problem beyond that. Fix these things before you run it hard again or you are risking leaning out the motor and burning it down. Popping from lack of fuel is not a good thing.
Find out where your voltage drop is occuring and correct it. Then run it again watching the gauge. Do not run it hard if you see that pressure drop again. If you have full voltage to the pump and the pressure still drops fix or replace the pump. Assuming you are running an alternator and it's working you should have around 13-13.5 volts at rpm. If you don't, fix that problem first.
:)

[dgie]

not yet, I got antsy and wanted to get it on the lake. I am fighting with rain all the time out here in Texas. I had the neighbor (race car driver) check the float levels. they were fine. I am suspecting the fluctuation in the fuel pressure being linked to not enough voltage applied to the fuel pump. I do not know what the range of voltage that can be applied to the pump to make it operate correctly. Is it 12 volts and thats it? Holley does not post it.

[dgie]

Mike, how would I know if I have already done damage to the engine. I am taking the alternator in tomorrow and get it checked. It should put out at least 13 volts, correct?

[victorfb]

definatly take REX's advise. and i would still check those floats and needles. they may have come off the clips. float comes down but needle sticks for a bit then drops to the float. you can try going through the check hole (first pushing the needle into the seet all the way) and then holding down the float with something , just be careful not to damage the float. run the pump with the motor off and see if the fuel comes out the check hole. its not a very good way of doing it, but im betting you just dont want to take them bowls off.

[Rexone]

dgie:
Mike, how would I know if I have already done damage to the engine. I am taking the alternator in tomorrow and get it checked. It should put out at least 13 volts, correct? That's correct. A fully charged 12V battery will read about 12.5 at rest. With the alternator charging correctly you will see between 13-14 volts normally. Usually around 13.5 or so. Anything under 12 is an indicator your alternator isn't charging.
If it's still running good you probably haven't hurt it yet. Pull the plugs and take a look at the electrodes. If any are partially burned off you're definately on the edge. I'm guessing you ran it until it popped and then backed off and crusied and probably didn't cause damage.
Definately get the voltage up and then check the fuel pressure closely again before running it hard. Don't just assume it will be fine. By what you've said I suspect the low voltage is at least part of your problem and possibly all of it.
Also, with some ignition systems, if you get down around 10 volts they will misfire, and some will not even run. That also could be the source of the popping. :)

[victorfb]

especially if your running points. great advise from mike. Thanks mike.

[dgie]

Thanks yall, this will give me some things to check tomorrow, if it stops raining. I may hit yall up for more info if this does not fix it.
thanks again,
Darren

[victorfb]

good luck darren. i hope you get that thing going good.

[Rexone]

your welcome good luck.
btw if that alt tests good, you have something in your wiring causing that voltage drop and will need to find it and fix it. Battery cables, tight ground on an unpainted engine surface etc are good places to start with. You have to get the voltage up to normal as a first step. :)
[ June 11, 2003, 12:57 AM: Message edited by: Rexone ]

[dgie]

I hope so too, one last question for the night if damage did occure what would it be to the engine?

[Rexone]

dgie:
I hope so too, one last question for the night if damage did occure what would it be to the engine? could have a burned piston or a tuliped valve, something of that nature, from the excessive heat caused by running too lean.
One step at a time and don't jump to conclusions. Could be the ignition popped from the low voltage before the fuel pressure completely went away in which case you're probably fine.

[dgie]

Sounds good, I will hope for the best, thanks again Mike and Vic
Darren

[Taylor LP]

Ok, just a thought here.
If the alt checks out ok, how is the pump wired in? I've seen a lot of people hook the pump up to the ballast resistor and make the connection on the output side. This could account for the low voltage. So could a lot of other things, but let us know how the pump is wired, from the power source to the pump.

[Rexone]

Taylor LP:
Ok, just a thought here.
If the alt checks out ok, how is the pump wired in? I've seen a lot of people hook the pump up to the ballast resistor and make the connection on the output side. This could account for the low voltage. So could a lot of other things, but let us know how the pump is wired, from the power source to the pump. Good point.
Also a long run from the dash on a switch of some kind with small wire could account for it. (no idea if that's the case).
Was that voltage reading checked at the pump or at the battery?

[572Daytona]

I had a similar problem with my Tahiti that was caused by sediment in the fuel tanks. I put on a clear in line fuel filter and what I observed was that at low rpm the sediment would lay around at the bottom of the filter and it would run fine but at higher rpm the sediment would pretty much completely cover the filter element blocking the fuel flow, if I let off the gas the stuff would fall back to the bottom of the filter and life would be fine again. No matter how many times I cleaned out the filter, I would keep getting more crap from the tanks.

[Omega21]

I agree with Taylor. It sounds like the pump is hooked up to the coil power on the wrong side of the ballast resistor. If your alt is working, you should be able to find a circuit that reads 13.5 volts or so with the key on and engine running. Without the engine running it should be at 12 or 12.5.
Todd