Misfires above 2000 RPM.

1994 Jeep Grand Cherokee. 5.2 liter. Does not hold fuel pressure. Misfires above 2000 RPM.

'94 Grand Cherokee gets fuel pressure during the first

2 seconds. But loses that pressure almost immediately afterwards. Have replaced the fuel pump and the fuel pressure regulator. None of the fuel injectors appear to be leaking.

Where might the loss of fuel pressure occur?

The Grand Cherokee also misfires above 2000 RMP. This happens only with transmission in Park or Neutral, not in drive. It idles well and runs well up to 2000 RMP. At 2000 RMP and above get misfires as evidenced by roughness and high HC's. Misfiring is not isolated to just one cylinder.

Have replaced the crankshaft position sensor (which was bad). Have replaced the coil, the cap and the rotor. Inspected spark plugs and they look new. Checked spark plug wires and they are good.

What might cause misfires only above 2000 RMP and only in Park or Neutral?

Reply to
JimS
Loading thread data ...

JimS did pass the time by typing:

Just to make sure you know this, the pump only runs for a couple of seconds on startup to prime the system, then runs all the time as the engine is running.

You need a fuel pressure gauge on the rail. Pull off the vac line to the regulator and if the pressure jumps 4-6psi then the regulator is fine. I suspect the pump even if it is new.

That's basically it. Fuel pump check valve or fuel rail pressure regulator. It is possible you got a bad replacement pump. OEM or aftermarket? The aftermarket pumps are notorious for failing out of the box.

crossfire, there is a TSB out there for new wire routing on the 5.2 V8.

Reply to
DougW

Maybe that little screen in your gas tank that filters out crud from your gas is clogged? Rusty tank could cause this.

One idea, hope it helps.

Bill

Reply to
William Oliveri

Reply to
L.W.( ßill ) Hughes III

DougW did pass the time by typing:

Just a followup with a link

formatting link

Reply to
DougW

Sorry I have taken so long to respond. I had posted this for a friend who does not have Internet access. I gave him the results of the first responses. Then he did not get back to me for over week. (In the future I will be more judicial about posting for others, because I do not like leaving things hanging like this.)

DougW>It is possible you DougW>got a bad replacement pump. OEM or aftermarket?

The new pump was OEM. Same symptoms with both the old and the new pump.

Reply to
JimS

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.