2001 5.0L TBI Fuel Pump Question

[Chaparralbob]

Yet another fuel problem, but I haven't found the answer to this after considerable research...

My boat sat for 2 years as a result of heart surgery - no surprise, it wouldn't run this summer. I replaced the gas and fuel filters, and disassembled and cleaned the fuel injectors and pressure regulator. The engine now runs, but not well. It will crank occasionally, and then run for a short time. I can see gas squirting from the injectors while it runs, and it stops when I no longer see the gas squirting. It seems as though I am not getting enough fuel to the injectors.

I have run the pump directly into a fuel pressure gauge, and get about 30 lbs of pressure while the pump is running (for the short time the pump runs after turning on the ignition). Unfortunately, none of the local shops have the T fitting needed for the GM TBI - so that is why I have just measured the pressure directly. I hit the little bypass button on the pressure gauge, and it seems to flow clean gas, with no air bubbles, at a reasonably good rate into a little coffee can; again, while the pump is running. The pressure bleeds back down to near zero when the pump stops in several seconds. Several posts said something about checking the gas level in the fuel filter (spin-on filter and water separator), and it was full of gas, almost to the top.

The boat only has about 105 hours on it, and until recently, was well-maintained and trouble free.

Are these normal pressures? Is it normal for the pressure to bleed back down?

I am wondering if I might have done something to the pressure regulator when I put it back together?

I greatly appreciate any help with this - the budget just won't let me take this to the boat shop right now. Also, they are 4 weeks behind right now - it is their peak season!

Thanks!

 

[Bondo]

Re: 2001 5.0L TBI Fuel Pump Question

Several posts said something about checking the gas level in the fuel filter (spin-on filter and water separator), and it was full of gas, almost to the top.

Ayuh,... But was there any Water under the Gas,..??

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

Didn't find any water in the filter.

I went to some websites that talk about automotive versions of GM TBI, and they say that pressure regulator should hold about 12-15 pounds. It would seem that the pump has plenty of oomph at 30 pounds.

Seems like I need to rig a T fitting and see if the pressure regulator is not working.

I would still appreciate any suggestions!

Thanks!

 

[Don S]

Re: 2001 5.0L TBI Fuel Pump Question

Is this EFI engine Volvo or Mercruiser? they have different setups.
Forget automotive, it's completely different.
When you checked the filter for water, did you pour the contents of the filter into a clear container and check for sepertation?

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

I poured the gas slowly into an old coffee can, but did not have a clear container. I didn't see any water.

It is a Mercruiser.

Do you know the pressure that the pump should generate?

Also, what pressure should I see with a T connection so the the pressure regulator is in the loop?

It appears that the pump is delivering adequate fuel, but it isn't getting squirted out of the injectors. Even if I did have some water in the tank, wouldn't it still get squirted out the injector? I understand that the engine would run poorly, but it seems like there would still be something squirting out of the injectors.

Thanks for your response!

 

[Don S]

Re: 2001 5.0L TBI Fuel Pump Question

Do you have spark? If you don't have spark, there will not be a signal to the ECM to allow the injectors to fire.

Do you have a Merc SN for your engine? Being a 2001, it could be 2 different manuals and how they work.

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

The serial number is:

OM011189

It is an Alpha One outdrive, if that matters.

Thanks!

 

[Dshow]

Re: 2001 5.0L TBI Fuel Pump Question

I have a 2001 5.7L Merc with TBI. I believe the throttle body has a connection for a pressure gauge (although I have not tried it myself...). I believe the connection is between the fuel inlet line and the pressure sensor on the back of the throttle body. There is a black rubber cap there that looks like it's on a connection.

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

Thanks Dshow.

I'll have a look and see if I can find one.

 

[Tail_Gunner]

Re: 2001 5.0L TBI Fuel Pump Question

Do you have spark? If you don't have spark, there will not be a signal to the ECM to allow the injectors to fire.

Do you have a Merc SN for your engine? Being a 2001, it could be 2 different manuals and how they work.

As in mefi-3 or 555..Id bet his kill switch is the suspect. MEFI- does not have that inteligence..or does it..By the way i have acccecteped the mission..But i will be remapping the MEFI-3 prior to the cam just to see how much of a gain comes from such mod's...Later part of July.

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

Couldn't find a port on the gas line for this engine.

I did rig up something though. The pump goes right up to 30 pounds, just as it did when feeding directly to the pressure meter. It stops at 30 pounds, and when it has bled down to 20 pounds, it start up again. I would have expected the pressure to be lower when connected with a T fitting. Seems like the pressure regulator in the TBI would regulate to some lower pressure than the max that the pump can generate.

Does anyone know what the pressure should be between the pump and base of the TBI? That would help to put to rest this issue.

The injectors seem to fire occasionally, even though the engine is not turning. I saw a post somewhere about low battery voltage "scrambling" the ECU. I'll measure the battery and see if this might be the case. Either the battery voltage is an issue, or apparently the ECU isn't smart enough to know whether or not a spark is being generated. Or, maybe still something I'm ignorant about - don't know yet.

Once upon a time, I considered myself as a pretty fair back yard mechanic, but my estimation of my abilities has been going down in the last few days....

I really appreciate the help all of you have been giving.

Thanks!

 

[Dshow]

Re: 2001 5.0L TBI Fuel Pump Question

The fuel pressure connector I was talking about is located on the throttle body. If you look at this post, about half way down is a picture of my throttle body. The connection has a black cap on it that is right below the word "Firing..." on the intake manifold.

http://forums.iboats.com/showthread.php?t=256257

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

Thanks Seaman!

I remember seeing that cap!

I thought it was just a blocked vacuum line!

I went through a lot of grief that I didn't have to!

I still can't find info on what the fuel pressure should read! Even went to justanswer.com - no responses as of yet.

Thanks very much for your help!

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

Oops! I mean thanks "Dshow" - didn't read the handle correctly.

Again, thanks for your help!

 

[Dshow]

Re: 2001 5.0L TBI Fuel Pump Question

Hi Bob,
Took the cap off what I thought was a fuel pressure connection on my engine and it was not the threaded connector I was hoping for... It was just an open hose barb type fitting... so I don't think there is an easy way to read pressure there... I think your back to trying to find a 'T' fitting.... Sorry...

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

Dshow,

Thanks for taking a look!

Bob

 

[Chaparralbob]

Re: 2001 5.0L TBI Fuel Pump Question

Finally, a happy ending!

It ended up a 2 major problems:

1) The ignition sensor in the distributor was bad.

What I thought was a fuel problem was actually related to the engine warming up and the spark quitting. I had assumed that the fuel system just couldn't deliver a sufficient quantity to run the engine very long. It turns out that I had the "Rev A" version of the module; the one with the exposed circuit board. The mechanic at the local boat shop was very helpful with this diagnosis. He said that sine the module had been changed to the "potted" (encapsulated) version, he couldn't recall having to replace one.

After getting the engine to run well, I went to the lake for my one-week vacation at a rented house on the lake. The boat ran for one day and quit again!

2) Corrosion in the high-voltage tower of the ignition coil.

By pure chance, I noticed the spark arcing over from the high-voltage tower to one of the terminals on the ignition coil when one of my sons was cranking the engine for me. The high voltage wire pulled apart when I took it off! It was horribly corroded inside the tower. The story of chasing down a spark coil and wire set on 4th of July weekend is best left for another time! When I did manage to get what I needed, the boat ran fine for the balance of the week.

I would like to thank those who responded to my questions! I appreciate the help more than I can say!

Regards,

Chaparralbob