Mechanical fuel pump on a fuel injected 454ci?
 

I purchased a powerquest at the end of last season that needed work. I tore the motor down and had it gone through. Got it ready to fire up on Saturday and had no fuel pressure. Checked the fuel pump and had nothing. Put a new pump on yesterday and its trying to start, but sputtering. It is throwing a code for tps. Replaced tps this morning and still doing the same thing. I was told possible bad ecm? I am also being told that motor can't run on a mechanical pump? There was alot of hands on this motor I have a feeling before I purchased it. Any suggestions?

Two fuel pumps, one low pressure mechanical, one high pressure electric to run the fuel injection. What year, exact model engine would help.

It is a 1995 mark v magnum.

It can't run on just a mechanical pump, but as Prsmo10 stated, yours came with one low pressure mechanical, one high pressure electric to run the fuel injection. Looking at your year and model, the fuel from the mech. pump should go to a VST (Vapor Seperator Tank) tank. It has the high pressure fuel pump in it and a 2 wire connector to provide power. The power comes from a relay located behind the ECM box next to the VST, and I believe there is a fuse in that same area.

You need to verify there is a VST tank installed (see the thread below for a picture), verify the connector to the pump is connected, verify the Relay is connected and then verify power to all of it. Also the Ecm controls engagement of the relay when the key is turned on, and it only energizes for a few seconds when the key is turned on without the motor running.

http://www.offshoreonly.com/forums/g...t-exhaust.html

This should get you started in the right direction.

Do your self a favor and **** can the vst,s if thats what you have great for vapor locking do a search on here about vapor locking... Been there done that. Hard to get parts for... If you need one and that's the way you want to go I bought two spares.. May sell one pm me... Good luck..

I agree, if you don't have all the parts or connection the VST is not a good way to go. Merc quit using it. It was very prone to vapor lock and failure. I eliminated mine a few years ago along with the manual pump. Now i just run an aeromotive EFI pump.

Don't want to hijack this thread but 28 eliminator,, once you swapped to the aeromotive pump did problems
Go away.?. I think I'm going to do this winter,, I already ran return lines back to the tank. Just with
Twins,, it's gonna get costly with 2 pumps and 4 filters blabla.bla... Did you use the existing relay and power wire to your old vst or did you have to increase size?

Yes, the probelm is totally gone. It always fires right up no matter what. Do you still have problems with the return going to the tank? It was expensive, but then again when I blew a hole in the piston because the lift pump failed, I should have done it years earlier.
It takes bigger wire to feed the pump. I bought a dual relay kit and used the vst wires to enable them, not that I need the dual, but it would work really well for your application. That way the ECU runs it just like it does the stock pump.
http://www.jegs.com/i/Magnafuel/665/...FXRp7AodfUwAKQ

I also changed the fuel filter to the Ramco and then a smaller aeromotive filter after the pump.
http://www.ramcoperformance.com/flomax300M.htm

Thanks for the help guys I seem to have all the fuel system there, but think it has an ecu or harness issue too. I managed to pick up a known good harness, ecu, updated fuel setup, intake, injectors, rail, and fresh water cooling system if I want to put on as well. I tore it back down and ordered intake gaskets last night. Ill let you know how it goes. Hope to have it running this weekend. Making the push for the 4th still!