After finally getting my Disco running after a month of no fuel/no spark, it is now behaving very strangely after only 3 days and is progressively getting worse!

Here are the symptoms:
When I go to start, it cranks for 5 seconds and then quietly fires up. My RPMs go to about 1500, then dips down to 600, sometimes stalling out completely, unless I hit the gas and save it.
When driving, my throttle response is delayed heavily, and I lose power very fast. I step on the pedal to accelerate, and my RPMs do go up to about 2000, but I seem to slow down, almost as if I’m going to completely lose power. Also when this occurs, there’s a strange clanking noise from the bottom of the engine. Then I slowly gain momentum. I struggle getting up to 40 mph.

The only causes I can think of for this would be a bad crankshaft sensor, leaking fuel injectors, or bad o2 sensors. Ugh!

 

What year is your truck? My 94 has a mechanical distributor and takes a few seconds to start. My 96 has an OBD 2 port with electronic timing and starts in a fraction of a second.

 

It’s a ‘97. Not pulling any OBD2 codes. Some of my spark plugs were pretty blackened and smelled like gas, so I changed them. I can tell I have leaky valve covers.
Still don’t understand why I’m having such a hard time starting now. It doesn’t really make a noticeable start noise, just kind of a “put-put-put” and dies.

 

Then you can read the Long Term Fuel Trim. What is the reading for each bank?

My mechanic says the normal range for a good motor is 0 to 5%. When I had a vacuum leak at the lower plenum to manifold, both of my LTFTs were over 11%. When, by mistake, I left the vacuum line to the fuel pressure regulator disconnected, LTFTs climbed to the max value 25% at idle, then dropped to normal values on the highway, with lousy power, bad gas milage, and lots of black at the tailpipe. The ECU tries to adjust fuel to compensate for all the extra air caused by a vacuum leak. After I fixed the leaks, LTFT went to -0.78%, and the rig runs great.

 

intake manifold gasket

 

SOLVED:
It was the hose coming directly from my fuel pump motor to the top of the fuel pump assembly (return line). The hose was cracked and developing leaks. It came in a kit to use with a Quantum brand fuel pump. Turns out their fuel pump motors as well as hoses are pretty much trash. Lesson's learne​​​​​​​d. Save​​​​​​​ yourse​​​​​​​lf the​​​​​​​ he​​​​​​​adache and buy an Airtex pump.

 

Congrats on the fix!