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Fuel Pump on 454 MPI

J

johny74

Member
"I have a 454 MPI and for some

"I have a 454 MPI and for some reason the fuel pump won't kick on during start up or when she's running.

I manually checked the fuel pump and she runs fine no clogs, etc. I even switched the relay for the fuel pump, checked the connections, etc. As soon as I plug her in to the factory harness, boom nothing. No power coming from the factory harness either and no wires are cut or corroded. Out of ideas.....

This system has the Merc "Cool Fuel System" which personally I think stinks but hey what are you going do right?

Any ideas would greatly be appreciated, thanks!!!}"
 
Did you trace the fuel pump 12

Did you trace the fuel pump 12 vdc wire thru the loom until there is a bayonet connector? There have been a number of corroded connections at that point this summer.
 
"Hey Guy,

Yea, the two wir

"Hey Guy,

Yea, the two wires are gray and black and traced them back to the ECM harness. Inspected the main wire harness, etc. I know its something stupid I'm over looking. I swapped out the relay with the main power relay right next to it. Same part number. I even taught for a second it might be the ECM but I can keep her running on starter fluid and the if it was the ECM I don't think that she would stay running."
 
You can inspect both factory h

You can inspect both factory harness plugs carefully. What you are looking for is a pin darker in color than the others or a pin just not exactly the same as the others.

Are you sure the pump isn't dead? Does yours have a filter on the end that hasn't been changed? What year is it? Have you tested the oil pressure switch that provides 12 vdc for the pump?
 
"Oh yea I inspected harness ca

"Oh yea I inspected harness carefully for any corrosion or any possible cause. I jumped the pump myself personally and she works fine.
The engine only has about 3-6 hours on her. Old new stock deal if you know what I mean. She sat in the boat on land for about 5 yrs. Original owner past away as he was restoring her. The engine has to be 98-2000 I'm figuring because of the ECM connections from the front not the sides.
Oil pressure switch might be a culprit after start up no? When I turn the key, I get nothing. Not even the relay clicks for the fuel pump. Hmmm....
Guy you had an old post last night I found that gave me a few ideas for today. Going to check 86-87 for power on the relay then to do starter with the yellow/red wire for start up. Rings a bell yet?"
 
I sorta remember. Check the f

I sorta remember. Check the fuel pump fuse? I don't have your engine's wiring diagram but I believe it gets 12 vdc to the FP relay or directly to the fuel pump from the starter and then the oil pressure switch takes over sending power. I think the fuel pressure controls the on/off of the FP relay. Are you sure the ECM is turning on the injectors when you run the FP w/a jumper?
 
"Hey Guy,

Well yesterday I

"Hey Guy,

Well yesterday I checked out the relay socket for juice and I was getting two hot with ignition on and jumped the gray wire which goes directly to the fuel pump and it works. Fuse is ok btw. So I tried to start up the engine with the fuel pump jumped and it started up and died down. Almost like I had no ignition. AS I said she did start up but died right after. I'm not use to the MPI's. Does the injectors make some kind of noise when you turn the ignition?
If so, I didn't hear the injectors clicking either. "Oh Oh".
Possible ECM?"
 
"John -

hoped you jumped th

"John -

hoped you jumped the fuel pump to the fused lead and not the ECU relay driver. I doubt the driver lead will deliver enough current to keep the pump running. You didn't say will two were hot and you didn't say which year MPI so this is just going on what I have:

Grey is +12V to the fuel pump. Dark Green/White is the relay drive from the ECU. Pink/Black is the fused +12V feed for the pump. If you jump the Pink/Black to the Grey, the pump should run continously.

Does the warning horn sound when the key is turned on? If not, it could be the oil pressure switch is bad. This will keep the fuel pump from running after startup as the ECU will turn off the relay drive signal to release the relay."
 
"Hey Mark,

I jumped the fu

"Hey Mark,

I jumped the fuel pump relay socket "Grey wire" to the ignition 12+ on the starter so I can control it with the key. This was done for test purposes. I believe the engine is 98-2000. It would of been nice if they actually put the serial number sticker on the valve cover but God forbid if they made me life easy. The other sticker on the bell housing is too worn out to see and anything else I would have to pull the engine. Tight fit. I believe 98-2000 had the Delphi computer with the front harness rather than the side harness. "Correct me if I'm wrong". No warning horn goes off which you may have a good point. But when the key does go into ignition mode the fuel pump should at least kick on for a second to prime the start up?
These are the days I miss the old carb engines lol...."
 
"Guy,

I actually did order

"Guy,

I actually did order a new pressure regulator because the tip that connects to the vacuum hose was rotted off. With out the vacuum hose connect it should still idle at least no?"
 
"The pump should turn on for a

"The pump should turn on for a short period of time with the key turned on. Put a meter on teh dark green lead and watch it when the key goes on. If it never 'turns on' when the switch goes to run, the pump won't run that 'prime' cycle.

It should run with the regulator hose pulled.

this link should help, if you want more details:
http://www.boatfix.com/merc/Servmanl/16/16C5R2.PDF
(thanks for the link goes to BT Doctur)"
 
"After messing with it all day

"After messing with it all day again, still nothing on the fuel pump. I can't figure this out and its driving me crazy. On the relay I have power to the green with a white line, the other two lines are hot. The only thing is not getting power is the gray wire going to the pump. "The pump works when I jump the gray wire". I also switched the relay from the main power relay. She starts for a second then dies out but the pump never attempts to turn on. Am I missing something or am I going crazy?

I tried running the pump on a jumper while trying to start the engine and still won't stay running. She starts but dies down right after. Engine still has no real hours on her. Maybe 40-50 hours give or take. The engine did sit for a few years before this and yes I did change the water/fuel separator and hooked up the fuel line to a portable tank. So I know I have fresh gas in the system."
 
"Hey Mark,

No I didn'

"Hey Mark,

No I didn't nor do I have the tool to do it. My main goal right now is to get the pump running the right way without jumping it."
 
Is the grey wire open? Did yo

Is the grey wire open? Did you ohm it? Perhaps it's time to open the wire loom and look for the problem.
 
"John:

I've re-read thi

"John:

I've re-read this a few times and am getting confused, too.

when you supply +12V to the grey wire, does the pump run continuously? (I think I've read Y & N.)

Did you check for +12V at the relay coil, when the key goes to ON? if so, light on, for how long?

Did you verify a good ground for the pump and the relay coil?

Have you checked the oil pressure switch - not sender- for proper function?"
 
"Hey Mark,

+12v to gre

"Hey Mark,

+12v to grey wire pumps runs continuously.
+12v to rely coil with key on I three out of four wires hot "+12v".
Pump has a good ground, never had a problem when I jump it from the relay coil.
Oil pressure switch I did not check. Sending unit I checked, with +12v coming out of the wire.
Oil switch I did not check nor locate. I figured this would be an issue if I had a problem while running.

Guy, no I did not do an ohm test on the grey wire.
I even swapped out another relay today and still nothing."
 
"John:

you may wanna hold o

"John:

you may wanna hold off on the oil switch....I read thru the MPI fuel delivery section of Manual 16 and found this little nugget in the text:

If the ECM does not receive ignition reference pulses (engine cranking or running), it shuts OFF the fuel pump relay, causing the fuel pump to stop.

So, if you have the relay installed and turn the key to on, the pump will 'prime' the rails, you start it up and then it dies.....sounds like the loss of the reference signal.

I bet if you poke around on that site (link above) you can find the rest of the manual which I'm sure will define where that reference signal comes from (I suspect the distributor). Maybe somebody else can provide the direct link for hte whole manual"
 
"We'll it looks like I&#39

"We'll it looks like I'm shooting for the ECM. After doing some research, it all points to the computer. The engine it self has no hours on her. But she was left outside for a few years. The reason I'm thinking its the ECM is two of the following:

When I turn the key I do not hear the injectors clicking which I think I should for a second or two.

Second I get no reference signal for the fuel pump. Even after I jump her from the relay socket she won't start up.

Last which confuses the crap out of me is she will turn over and start up and run if I feed her starting fluid in the throttle body. What the confusing part about this more is if the ECM was bad wouldn't that prevent the engine from also starting???

Last question, is there a way for someone to check the ECM? Before I go for a new one I would like to be 100% sure. Does Anyone have a 98-2000 454 7.4L MPI in the NY city? lol
Mark and Guy, thanks for all the help. Again I miss my carb engines for this one reason...... Anyone wanna trade for an MPI? Heh.

John"
 
"John:

You won't hear t

"John:

You won't hear the injectors with the key turned ON though you should hear the fuel pump for a couple seconds.

Sounds like you have spark as the engine runs with the fluid...that means the distributor reference signal is present.

When you had the fuel pump relay out, do you think you may have jumpered the relay drive from the ECU directly to the fuel pump +12V? That may have taken out the output driver in the ECU.

As an alternative to replacing the ECU, you could rewire the fuel pump control so it bypasses the ECU, but still uses an oil pressure switch for control...i think it would save you a few bucks and get you running again."
 
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