Fuel Pressure Question

[winstonwilliams]

I have a fuel injected 502 Mercruiser 8.2 and I cannot get it started... I hooked a pressure gauge up to it and turned the key (to turn on just the fuel pump) and only got 22 lbs of pressure. Is this correct? It seems low to me but I have never checked the fuel pressure when the engine is running well. I have been looking thru the manuals, but I cannot seem to find typical pressure.. Where can I find this info?

Thanks

Winston

 

[SR Tech]

Should be between 40-45psi at the fuel rail, with the key on or engine running. Typical pressure is about 43psi

Check your drop in fuel filter, if not clogged then proceed to the fuel pumps

 

[winstonwilliams]

Thanks for the help!

 

[winstonwilliams]

I got the engine running today, but the fuel pressure sits at 28 when the engine is running. There is also a knock coming from the engine that gets louder as the rpms increase. Do you guys think that there is a spark knock because the fuel pressure is so low?
Thanks
Winston

 

[fc3]

I don't think these engines run 45 psi on the rail, but my manuals are on the boat so I can't check. Where's the knock? Top end? Bottom end?

And fill our your profile. "adf" is cute, but there's a reason why those questions are asked.

 

[winstonwilliams]

The noise is coming from the top of the engine... almost like a valve or lifter knock, or even an exhaust leak... but I need to get a stethoscope and listen to find out exactly. Checked the oil level and it is fine and the oil pressure gauge on the dash says it is ok too. Checked all the cylinders and they all have spark. Checked the voltage going to the fuel pump and it is ok. The only thing that seems to be off is the fuel pressure. I wish I had checked the pressure on this engine before I had these problems so I would have a base line to compare the fuel pressure too. The engine did have a hard time starting when it was warm and it surged a bit in low RPMs

 

[Nehalennia]

Put the year of your boat in your profile too.

 

[fc3]

Hard to say without hearing it, but lifter doesn't sound out of the question. Pretty easy to change them, just need to remove the intake manifold.

 

[winstonwilliams]

I pulled the valve cover off and all the lifter looked ok..? I was thinking about buying a scan tool... Can anyone point me in the right direction? I am afraid to see how much it would be for the closest mechanic (30miles away) to come hook their scan tool up to my motor

Thanks for the help

Winston

 

[fc3]

Scan tool won't tell you anything in this case, I'll bet. The lifters ride on the camshaft in the valley of the block. You can't evaluate them without removing the intake manifold.

 

[winstonwilliams]

Does the 290 have a fuel filter in the tank or just the water sperarating fuel filter that is mounted to the block?

 

[SR Tech]

Yes my appologizes, that was off the top of my head and is a very common number. straight out out the mercruiser manual says you should have 34-38psi at the rail, engine not running, then about 3-7psi less at idle.

This 'knock' your hearing is probably denotation from lack of fuel or in terms "running lean"

There has to be a restriction in the line or fuel filter needs to be changed

Other possiblities are the fuel pressure regulator or the pump itself

 

[winstonwilliams]

I have some good news! I disconnected both fuel lines (the main and the return) from the fuel filter and put them into a remote gas tank. I turn on the fuel pump and the gage read the same. Which means the problem is not in my fuel filter or my gas tank. I went ahead and started the engine and the gage still read the same. I did notice that return line was pumping a lot of gas back into the bucket, so I went ahead and put my thumb over the return line and the pressure jumped way up.. To me this means that the engine has a bad fuel pressure regulator.. Is this correct?
I told you guys that I pinched the fuel pressure regulator line to see if the pressure jumped up. But I don’t think I understood exactly how the system worked. From looking at the picture I have attached the pressure regulator from the fuel rail (picture on the left) is connected to the fuel pressure regulator. This is the line that I pinched. From the attached drawing (on the right) I thought this line was the return to the fuel filter... but this is just a vacuum line that tells the fuel pressure regulator when to pull more fuel out of the fuel cooler? is this correct? I guess if there was a picture of how the fuel cooler worked I would have understood that I was pinching the wrong line.. Guess you live and you learn.
How do I know if the fuel pressure regulator (next to the fuel pump) is bad or the pressure regulator (on the fuel rail) is bad? because it seems like to me the pressure regulator is telling the fuel pressure regulator what to do..
Thanks for everyones help!
Winston