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?

Re: Misfires above 2000 RPM.
 

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!

Re: Misfires above 2000 RPM.
 

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!

Re: Misfires above 2000 RPM.
 

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!

Re: Misfires above 2000 RPM.
 

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" <jims_89@yahoo.com> wrote in message
news:ce14122b9fa1555e7fef9216ab81906f@localhost.ta 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?
>
>
>

Re: Misfires above 2000 RPM.
 

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" <jims_89@yahoo.com> wrote in message
news:ce14122b9fa1555e7fef9216ab81906f@localhost.ta 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?
>
>
>

Re: Misfires above 2000 RPM.
 

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" <jims_89@yahoo.com> wrote in message
news:ce14122b9fa1555e7fef9216ab81906f@localhost.ta 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?
>
>
>

Re: Misfires above 2000 RPM.
 

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
mailto:-------------------- http://www.----------.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?

Re: Misfires above 2000 RPM.
 

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
mailto:-------------------- http://www.----------.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?

Re: Misfires above 2000 RPM.
 

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
mailto:-------------------- http://www.----------.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?