91 4.0 backfire
09-02-2018, 05:04 PM
#1
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Model: Cherokee (XJ)
91 4.0 backfire
Hi everyone I am having a backfire though the throttle body only if quick stab the throttle. Runs fine otherwise.
new plugs,wiers,cap and rotor no codes 91 4.0
new plugs,wiers,cap and rotor no codes 91 4.0
09-02-2018, 06:31 PM
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Year: 1999
Model: Cherokee
Engine: 4.0
There are a few possibilities but I would start with testing fuel pressure. For a 91, you should have 31 psi at idle. Remove the vacuum line leading to the fuel pressure regulator and the fuel pressure should jump to about 39 psi. Many parts stores will rent you a fuel pressure gauge if you don't have access to one.
Good luck and keep us updated!
Good luck and keep us updated!
09-02-2018, 07:11 PM
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Year: 90,84
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Engine: 4.0,2.5
Howdy there TJ. Jerry, by chance has the distributor been out lately? (being off a tooth might do that)
Last edited by DFlintstone; 09-03-2018 at 07:58 PM.
09-02-2018, 07:53 PM
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There are a few possibilities but I would start with testing fuel pressure. For a 91, you should have 31 psi at idle. Remove the vacuum line leading to the fuel pressure regulator and the fuel pressure should jump to about 39 psi. Many parts stores will rent you a fuel pressure gauge if you don't have access to one.
Good luck and keep us updated!
Good luck and keep us updated!
09-03-2018, 06:03 PM
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Year: 1999
Model: Cherokee
Engine: 4.0
That is out of spec (too high). Should be closer to 31 psi. More is not better when it comes to fuel pressure.
Remove the vacuum line leading to the fuel pressure regulator and see if that changes the fuel pressure readings. Also inspect that vacuum line VERY closely; if there is any raw fuel in it you have a ruptured fuel pressure regulator and it must be replaced.
Remove the vacuum line leading to the fuel pressure regulator and see if that changes the fuel pressure readings. Also inspect that vacuum line VERY closely; if there is any raw fuel in it you have a ruptured fuel pressure regulator and it must be replaced.
Last edited by tjwalker; 09-03-2018 at 06:16 PM.
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