"The Miracle" sat for a while, finally got it a new battery. While it ran mostly fine before, now it'll idle ok, run on the road for about 30 seconds, and then it gets to puttin'. No power up hills, no matter how slight. Doesn't change much no matter where the gas pedal is. It won't conk out totally but it runs like total garbage.

In the driveway it'll rev up and act normal, pretty much if I give it a little time to recover.

I can test the fuel pressure, but if its low, how do I know if its the pump or the regulator?

The pump primes fine on KOEO. I checked the TPS just in case but it is also fine.

 

The FPR(fuel pressure regulator) is on the engine and has a vacuum hose attached
Couple of things you can do with pressure gauge hooked up

The FPR has a spring valve set up, and its set for 43psi, approx., so at 44psi spring is pushed open and fuel flows back to the gas tank
The vacuum is used to maintain a 30-35psi pressure, i.e. at idle there is low fuel demand, and there is high vacuum, so vacuum pulls against the spring which pulls open FPR a bit, which lowers pressure down to 30-35psi from 43psi(no vacuum)
When throttle is opened, acceleration and high fuel demand, vacuum drops to 0 so spring holds FPR closed, so even though fuel use goes up pressure doesn't drop much

On startup and idle you should see 30-35psi
Unplug vacuum hose from FPR, and plug hose with finger or screw, and pressure should go up to 43psi(if gasoline comes out the vacuum port FPR is bad)

If pressure was lower than 30psi and doesn't go up with vacuum hose off it, then FPR may be bad, read below

If pressure goes up then FPR is probably OK, raise RPMs to about 2,500 and hold it high, if pressure starts to slowly drop then Fuel pump(or clogged fuel filter) is most likely the problem

The FPR has the Return fuel line attached to it, so you can use vise grips with some wider plates to pinch that return line closed, its nylon hose so you don't want to break/puncture it, it has 0psi pressure inside, so just needs a squeeze to close it
And if fuel pressure goes up above 30psi then you know FPR is not working as it should, its leaking fuel back into the tank

 

Thanks man, that is a solid method. I can't discount any variable here, this ranger was ready for the cannery when I got it.

 

YUP its the FPR. Getting 20psi at idle, pinched the return, and it shot up to 60.
Oh well. At least its not the fuel pump!
Thank you for the help!

 

Good work

Thanks for the update

 

well i installed the new FPR, it ran exactly the same. Wouldn't go up the hill. I messed around, checked some stuff.
Then I noticed that the vacuum port for the FPR was totally blocked.
I unblocked it and it ran 75% better, still a puttin a little but more gas makes it work better.
But now I am confused. If less vacuum = higher fuel pressure, the pressure should have been much higher, especially when the port was blocked, with either regulator. By law it should be running way worse with any vacuum, and yet its better.

Maybe I have a volume/flow issue and less of a pressure issue

 

Vacuum for the FPR is to stabilize pressure around 30-35psi

With no vacuum hooked up you should have 43psi pressure, thats the FPRs spring rating
So at idle, low fuel demand you should have 43psi
As you were driving the fuel use would go up, of course, so when you floor it pressure would drop to under 30psi depending on how long you hold the pedal down

Now the computer has to calculate OPEN TIME for each fuel injector based on RPM, throttle position and Air weight/flow data to get correct 14.7:1 ratio
And it has to do this in real time, every millisecond at any RPM, with feedback from O2 sensor
The amount of fuel that flows into the engine thru an injector changes, alot, based on the fuel pressure pushing that fuel in when injector opens
So having a reasonably stable fuel pressure is important.

With the vacuum assist, high vacuum at idle or cruising lowers the fuel pressure to under 35psi
When you accelerate vacuum drops quickly, so fuel pressure would go up, BUT.......fuel demand also goes up, injectors are opening longer so it only goes up a few psi, maybe 35psi

So computer has a stable fuel pressure to base its calculations on

Yes, could now be a volume issue, FPR was bad for sure from your testing
Hold engine at say 2,500rpms and see if pressure is slowly dropping, it shouldn't
Dirty fuel filter or "sock" in the tank can reduce flow, as can weak fuel pump
In a 1989 Ranger the "sock" in the tank can get pretty dirty over the 31 years

 

Yes I believe the something is rotten with the pump or filter. Rechecked the pressure, getting 20 at idle. Still goes up to 60 with the tube pinched. I couldn't get the pressure to drop from there under higher idle but when its driving the fuel use may increase dramatically. I don't have a long enough hose to reach out of the hood so I can see it while I drive around yet, but I am prepared for the bad news of having to change them. Fuel filter I'm not as worried about, I can change those in my sleep.

Seems a shame, I took a 180 mile round trip last year to deliver a lawnmower and it ran great, getting 21-22mpg the whole way. Everythings gotta break sometime I suppose.

 

News!
Not good news or bad, just news.
Replaced the fuel pump and fuel filter. The old pump had a 2013 date on it which sounds about right given what I have heard about its history. 2013 was its great first Resurrection after sitting for a very long time.
The problem is better but not gone. Its still puttin' up the hill but its not falling on its face like it was. Funny thing is, the fuel pressure reads exactly the same as it has, every time I have checked it. and yet it runs different, every time I make an improvement.
I guess I get to tear into the ignition system next. Since it sat so long the mice chewed up the wires real good on the EEC IV connector so the check engine light is snafu. What a fun project!

 

I found it this time, cylinder 3 spark plug wire was just "placed" upon the distributor, boot full of rust, arced itself useless.
I couldn't believe it.
Ah I'm a joke.