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#1
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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? |
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#2
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JimS did pass the time by typing:
> 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. 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. > Where might the loss of fuel pressure occur? 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. > The Grand Cherokee also misfires above 2000 RMP. This > happens only with transmission in Park or Neutral, not > in drive. > What might cause misfires only above 2000 RMP and only > in Park or Neutral? crossfire, there is a TSB out there for new wire routing on the 5.2 V8. -- -- DougW -- 93 ZJ 4.0 http://members.cox.net/wilsond HESCO Supercharger - 300W IASCA Stereo - Edelbrock IAS Shocks Gibson Exhaust - rear DCpower - custom gauge install - Stillen Rotors Banks Header - and BEER, in the fridge! |
#3
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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 "JimS" > wrote in message lkaboutautos.com... > 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? > > > |
#4
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May have something to do with your computer's rev limiter as free
wheeling it in neutral at high Revolution Per Minute would be destructive. God Bless America, ßill O|||||||O http://www.billhughes.com/ JimS wrote: > > 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? |
#5
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DougW did pass the time by typing:
Just a followup with a link > crossfire, there is a TSB out there for new wire routing > on the 5.2 V8. http://www.zjilla.com/pingtsb/18_48_98_v8.htm |
#6
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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. --- DougW>crossfire, there is a TSB out there for new wire routing DougW>on the 5.2 V8. DougW>http://www.zjilla.com/pingtsb/18_48_98_v8.htm I printed this TSB and gave it to him. Much later, he said that he had already checked the wire routing. --- The answer: He found another TSB about indexing the distributor. The distributor position was off and had to be turned. That stopped the misfires. As far as I know, the loss of fuel pressure is still present. But car runs fine anyway. --- Bill>Maybe that little screen in your gas tank that filters out crud from your Bill>gas is clogged? Maybe. I will mention this to him next time I talk to him. But I suspect this was checked when the fuel pump was changed. --- L.W.>May have something to do with your computer's rev limiter Sorry, the distributor got indexed before I had even read this comment. I did not check for more replies while waiting for a response to DougW's reply from him. Nevertheless, I personally find this comment interesting. I am a just a student with little real shop experience. I did not know PCM's had a rev limiter. I will look into it just to learn something. Jim S. |
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