1994 Volvo 5.7 TBI fuel pressure issue

[natecollins]

Hi,

I am working on a 1994 Volvo 5.7 Liter throttle body injection engine on a 26' Regal cuddy cabin. It was sitting up for about 2 years before I started working on it.

I performed the following repairs then:

Removed old fuel & added 20 gallons of new fuel.
Changed engine oil
replaced spark plugs
changed water pump impeller.

I got the boat running, but noticed that it seemed to be starving for fuel during the first lake test

I then performed the following repairs:

Replaced fuel filter
Replaced fuel injector screens and surrounding gaskets.
Replaced the low pressure fuel pump (the old one was not turning on).

I put the water on the lake today. It idled fine about 600 rpm. The boat also shifted and drove fine at low speeds. The boat got up to about 12-15 mph @ 2500 rpm, but could not get on plane. I put a fuel pressure tester on the schrader valve on the line going to the throttle body. When the motor got up to about 2500 rpm, the fuel pressure started to drop off and when down to 0 psi and then rpms would drop off.

When I turn the key on the pressure rises to 12-13 psi, but then slowly drops back to almost zero. My manual said that this particular motor has a pressure bleed-system, so I would assume that is normal. While running at idle the pressure maintains around 12-13 psi.

I brought the boat back over to my shop and hooked up a remote gas tank just before the fuel filter and then ran the motor again on a water hose. When I reved the motor it again lost fuel pressure. I placed my hand on both the high pressure and low pressure fuel pumps to see if they are running when the key turns on. They both feel like they are running.

Please help.

Thanks,
Nate

 

[JustJason]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

is there a vst on the motor???? make sure there's fuel in the vst itself.
run it at idle and crimp off the vac line that goes to the fuel pressure regulator... make sure the pressure goes up. if it doesn't then you more than likely have a bad regulator.

 

[natecollins]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

The way this appears to be set up as follows:

low pressure fuel pump at front of motor.
steel line to high pressure high pressure fuel pump at rear of motor. This tank has a mechanical float. The high pressure fuel pump is attached to the top of the fuel pump tank.
Another steel line goes from the discharge end of the h.p. pump to the throttle body.
A return line goes from the throttle body back to the h.p. pump fuel tank.

If I do this test do you want me to remove this last line at the h.p. fuel tank end or at throttle body. All lines are steel w/ brass fittings so it may be a little hard to manuever and I am unable to crimp them. Also, what rpm should I do this at?

I had the fuel pressure regulator diaphragm out when I serviced the injectors. It did not look bad, but you never know.

Thanks,
Nate

 

[Don S]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

It may not be the engines fuel systems problem.
Try this test and see how your boats fuel system checks out.
A shortcut for the test would be to run the boat on a remote fuel tank (ie 6Gal outboard tank) plumbed into the engines fuel filter.

http://forums.iboats.com/showthread.php?t=167561

 

[natecollins]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

Hi Don S,

Thanks for the help, but I mentioned in my first post that I tried a remote fuel tank after taking the boat out of the lake. It did not help. Thanks.

 

[Don S]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

Hmmmm, so you did. Guess I stopped reading before the end of the post. I really got to stop doing that.
Anyway. You said you had 12-13 psi on the hi pressure side, what did you have on the low pressure pump when the problem occurs? I know it's a new pump, but is it working properly?

 

[180shabah]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

I brought the boat back over to my shop and hooked up a remote gas tank just before the fuel filter and then ran the motor again on a water hose. When I reved the motor it again lost fuel pressure.

It lost fuel pressure on the remote tank as well

 

[Don S]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

I brought the boat back over to my shop and hooked up a remote gas tank just before the fuel filter and then ran the motor again on a water hose. When I reved the motor it again lost fuel pressure.

It lost fuel pressure on the remote tank as well

Was that a question or a statement.
If it was a Statement, Like I said, in the previous reply, I didn't read that last paragraph.
If it was a Question, then YES, he lost pressure when reving the engine on a remote tank. Or at least that is what he said.

 

[JustJason]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

well..... there's not much to it when you think about it. the low pressure pumps job is to fill the vst and thats it. is the vst filling all the way?
the high pressure pumps job is to create more than enough fuel pressure to run the boat at wot. the pressure regulators job is to maintain correct pressure at idle and wot.
so....
1. your either running out of fuel and the vst is running dry. (look downstream)
2. the high pressure pump... although is turning on, may not be making enough pressure. this may be a clogged inlet screen. a clogged fuel filter in the vst if it has one. or a motor that's gummed up and not spinning the correct rpms. (put your meter inline on a test line and measure the current of the motor, its usually not more than 3 or 4 amps, although i can not give you a VP spec)
3. the regulator.... is not regulatin!!!!
4.... just for giggles go hook up your fuel pressure gauge to your car or borrow another one to make sure your gauge isn't fubared and sending you on a wild goose chase.

 

[dcg9381]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

High pressure side of a TBI should be around ~15psi - I know that doesn't solve your problem, but this is different than a carb'd setup and different than a MPI setup.

 

[natecollins]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

Hi,

I think I found what it was.

I opened up the h.p. fuel tank and took off the h.p fuel pump. The inlet screen of the fuel pump was clogged up with about 1/4" of crud. Also the h.p. fuel tank was filled with bad gas and trash. I will try to run it again soon.

 

[newport dave]

Re: 1994 Volvo 5.7 TBI fuel pressure issue

Just fyi, I am working in the exact same fuel system setup on a pair 5.0GLi's. Like Nate, I found a bunch of crap in the VST and clogged high pressure pump screens.

I also found the fuel cooling hoses, fittings and cooling chamber on the VST's completely blocked with salt. I cleaned out the VST's and discovered both had multiple very smalll leaks in the bottem of the VST that allowed a small amount of seawater to enter the tank.

Word to the wise, if you have this fuel system, periodically clean/flush the fuel cooling systems and carefully inspect the VST's for leaks.

Dave