So i've been trying to figure out what's been going on with my discovery, Any time i reach a hill, The disco has a tough time maintaining speed, much less accelerating; and the gas mileage has dropped to about 11mpg from 15mpg in town driving. I changed the spark plugs, fuel filter, air filter, oil, and nothing changed. Then did an induction cleaning, and cleaned the throttle body, still nothing. I was talking to someone and they suggested MAF sensor or the fuel pressure regulator going bad, probably the fuel pressure regulator. Any thoughts from you guys?

1998 Discovery
138,000 miles

 

If you know someone with a tester, there's a port on the fuel rail to test fuel pressure. You could try cleaning the maf with CRC maf cleaner(wouldn't use anything else). People will say not to, it will ruin it,but thats on the D2's with a bosch maf. I've done mine and if you follow directions, works fine. 6 months and hasn't died yet. Plug wires?

 

Does it cold start OK, do you have any fault code numbers?

 

I replaced the plug wires about a year ago, It cold starts fine, no codes. We tested the MAF sensor, and it is working fine, I guess next i need to find a tester for the fuel pressure regulator.

 

Check your fuel PSI and then get back to us.
Could be your fuel pump or the regulator.
But with the drop in MPG it may be your O2's are going bad.

 

I'll try to find a tester tomorrow once i get into jacksonville.

 

Got in to jacksonville today, and my check engine light comes on, and starts flashing. Had it checked out and it was a bunch of misfires and the crankshaft position sensor. I've read a bunch of threads on here dealing with crankshaft position sensor, and my disco has a lot of the same symptoms. You think i should still have the fuel pressure tested, or just replace the crankshaft position sensor, see where it goes from there.

 

One reason I asked about your cold starts was because if it cold starts OK, there is a good chance it is not a fuel issue cause your pump is not bleeding down over night which can be the first indication of a failing pump.
Consider replacing the fuel filter and if still acting up, you may have a VSS failing, which is common and will cause what you are describing.

 

replaced the fuel filter when i did spark plugs, oil, air filter, induction cleaning, and throttle body cleaning on the 19th of december. will order the crankshaft position sensor, and if that doesn't do it, ill replace the VSS
Thanks

 

I am also betting on a failing VSS.
This is common on DI's, the part just wears out and then cuts the fuel injectors to slow you down.
The VSS is the speed limiter, if it thinks your going to fast it cuts the fuel supply.
The governed speed on a DI is 110mph.