How to tell if efi fuel pressure regulator is bad

[redpickle]

How can I check if my fuel pressure regulator is bad on my 87 2.4 bp efi. I have had a problem where the motor acts like it is running out of fuel and loses power. I have a fuel pressure regulator and it stays rock solid at 39lbs. But I know the 39lbs is the pressure before the regulator not after it.

[bigbluechevy454]

Sounds like your ecu of tpi if you have that system may be failing

[redpickle]

The ecu and tpi was my first thought. The motor would act as if it could not read where the thottle position was It worked fine at idle and full throttle but confused in between. So I bought a used tpi. With the tpi replaced the ecu seemed to read the throttle position fine but it would not idle correctly. So I said screw it and bought a brucato acu. Still ran exactly like before it would not hold a idle. I increased the low end timing to get it to idle and it would idle for a minute or so and then cut off like it was running out of fuel. The last time I had it out I had to limp it back home. It would crank and idle and when I went to take off it felt kind of weak and as soon as the boat would start to plain it would cut off still with full fuel pressure. This is what makes we wonder if is the fuel pressure regulator is bad. I did later find out one of my coils was bad after doing a coil and stator test.

[h2oskiier30]

The pressure after the regulator doesn't matter...that's just the return to the tank. Your injectors are on the pressure side of the regulator. If you have a gauge and it stays solid at 39 lbs, the problem is not your regulator.

[redpickle]

Man that brings me back to square one again if the regulator is not bad. The stator and coils have been checked, injectors cleaned and flow matched and the brucato acu eliminated most of the other electronics. My problem is I don't have a good mechanic local to help diagnose it further either.

[bigbluechevy454]

Water on the plugs maybe a crank exhaust divider plate

[Dave Strong]

Man that brings me back to square one again if the regulator is not bad. The stator and coils have been checked, injectors cleaned and flow matched and the brucato acu eliminated most of the other electronics. My problem is I don't have a good mechanic local to help diagnose it further either.

Time to buy some tools and a Merc manual.

Dave

[redpickle]

After digging thru a few threads it seems the fuel pessure should not vary much from 39lbs. I kind of assumed the pressure could vary a few pounds + or - and be fine but from what I recently read as little as a 3 pound change could make a difference. What is a acceptable range from 39lbs? I have noticed my fuel pressure over and under 39lbs but did not pay close attention to the number as long as it was close because I was looking for a bigger swing in pressure. I have seen automotive applications fall as much as 10 pounds at wide open throttle but of course we are not talking about a car.

[Tony Brucato]

Your pressure should remain at 39 PSI with the motor not running. At idle RPM it may drop down to 34 PSI because of the manifold vacuum effect on the pressure regulator.
At high RPM and wide open throttle you should be seeing very close to 39 PSI on the gage.
If the pressure drops off much at high RPM, it's likely that your pump can't keep up the fuel pressure at that high volume.
Make sure the pump is wired on a dedicated circuit, either through a switch, or through a relay. Do not wire the pump from the purple accesory wire. it can't suppy enough current to do the job.

[CharlieB53]

Running out of power at speed can be either a failing fuel supply, or a failing ignition.

Tony already pointed out the check the fuel pump carefully, failing pressure at speed can melt youor motor, so check it thoroughly.

Failing ignition at speed can be caused by poor coil grounds, or aged and corroded trigger wires failing to carry the voltage demanded of load at speed. Clean all coil grounds bright and tight, if possible paint over each once assembled with liquid tape to seal out moisture making your work last much longer. DVA test the triggers, during testing it is always a good idea to disconnect the throttle cable and move the throttle arm from idle to WOT and back slowly while watching for any change in DVA output, indicating a failing or broken yet abutted wire.

[blackcloud]

Sounds like trigger bad to me.

[pyro]

+1 what Tony said.

Check the vacuum hose fittings on the intake and make sure they're not clogged with gummy residue.

[sixpac]

fuel pressure should stay at 39 psi at all times +/- 1 or 2 psi, pump has to maintain pressure and volume, ive seen pumps with good pressure that could not maintain volume when at speed, if in dout replace with a new pump that's rated for the engine.

[Dave Strong]

What Tony said I have found at a high vac at idle the press will be less than 39, if you have less than 39 at idle you can pull the vac line off the regulator and if the pressure increases the regulator should be OK.


Dave

[cptunnel]

i used to have a very similar problem with same motor, found a clogged fuel filter. check that too!