2000 Cherokee cranks but will not start ??
01-18-2014, 07:34 PM
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2000 Cherokee cranks but will not start ??
Need help ! The 2000 Cherokee 4.0L will crank over but won't start running till you prime it with a little gas in the throttle body, it will stay running on its own till you shut it down.we have checked fuel system,Relays and even replaced the PCM three time. The PCMs was flashed to the #s of the old PCM. need help with this one, its got us stumped.thanks.
01-18-2014, 07:49 PM
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Year: 1998
Model: Cherokee
Engine: 4.0L
Need help ! The 2000 Cherokee 4.0L will crank over but won't start running till you prime it with a little gas in the throttle body, it will stay running on its own till you shut it down.we have checked fuel system,Relays and even replaced the PCM three time. The PCMs was flashed to the #s of the old PCM. need help with this one, its got us stumped.thanks.
01-18-2014, 08:00 PM
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01-18-2014, 08:05 PM
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Year: 1999
Model: Cherokee
Engine: 4.0
How did you check the fuel system? For a 2000, you need 49 psi of fuel pressure to start the engine. Must be verified with a fuel pressure gauge. Watching a fuel pressure gauge when this occurs may yield important test data.
The fact that it starts with some gas indicates a fuel problem of some sort; not much doubt about that. It is possible that you are experiencing a serious (almost instantaneous) drop in fuel pressure as the engine sits.
Try the "poor mans prime" illustrated below and see if that helps. If it does, then you likely have a check valve problem on the fuel pump assembly.
---------------------------------------------------------------------------
The check valves (there are two of them; the primary one is on the fuel pressure regulator and a secondary one can be found on the fuel pump itself) are part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When a check valve starts to fail, it can reduce fuel pressure to a point where an extended cranking time is needed to start the engine. It is a very common failure. I experienced it on my 99 at around 75K.
A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”
1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over
If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.
Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.
Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.
*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood
*Start engine and bring to normal operating temperature.
*Observe fuel pressure gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)
*Shut engine off.
*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.
If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the
fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose normally included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, but here is basically how it works:
*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.
*If the pressure remains at 49 psi for an extended period of time then the problem is in the tank – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.
**Note. Where check valve is suspect, a quick loss of fuel pressure is often the fuel pressure regulator check valve and a slow loss of pressure is often the fuel pump check valve. But keep in mind that either or both check valves can be to blame.
You can limp a check valve problem along indefinitely if you like, as it doesn't mean the fuel pump itself is going to fail. Perform the “poor mans prime” before cranking to speed up your starts. However, if you have a check valve issue and want to resolve it, it is recommended that you replace the entire fuel pump assembly for two reasons. First, you have to drop the gas tank to access the assembly. Secondly, with two check valves, replacing just the fuel pressure regulator where one of the check valve resides may or may not resolve your problem; remember there are two check valves; the other check valve is part of the fuel pump.
The fuel pump assembly consists of fuel pump, fuel pressure regulator, fuel gauge sending unit, fuel gauge float, pickup filter and pigtail wiring harness. If you do replace the fuel pump assembly, purchase a high quality assembly. Know this….you do get what you pay for here. Some cheap aftermarket assemblies have been known to fail prematurely. I personally prefer Bosch fuel pumps as they manufacture the best fuel pump assemblies for the XJ. Carter is my second choice. Airtex is my least favorite choice and I will not recommend or install them. A search will show you why.
The fact that it starts with some gas indicates a fuel problem of some sort; not much doubt about that. It is possible that you are experiencing a serious (almost instantaneous) drop in fuel pressure as the engine sits.
Try the "poor mans prime" illustrated below and see if that helps. If it does, then you likely have a check valve problem on the fuel pump assembly.
---------------------------------------------------------------------------
The check valves (there are two of them; the primary one is on the fuel pressure regulator and a secondary one can be found on the fuel pump itself) are part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When a check valve starts to fail, it can reduce fuel pressure to a point where an extended cranking time is needed to start the engine. It is a very common failure. I experienced it on my 99 at around 75K.
A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”
1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over
If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.
Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.
Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.
*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood
*Start engine and bring to normal operating temperature.
*Observe fuel pressure gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)
*Shut engine off.
*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.
If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the
fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose normally included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, but here is basically how it works:
*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.
*If the pressure remains at 49 psi for an extended period of time then the problem is in the tank – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.
**Note. Where check valve is suspect, a quick loss of fuel pressure is often the fuel pressure regulator check valve and a slow loss of pressure is often the fuel pump check valve. But keep in mind that either or both check valves can be to blame.
You can limp a check valve problem along indefinitely if you like, as it doesn't mean the fuel pump itself is going to fail. Perform the “poor mans prime” before cranking to speed up your starts. However, if you have a check valve issue and want to resolve it, it is recommended that you replace the entire fuel pump assembly for two reasons. First, you have to drop the gas tank to access the assembly. Secondly, with two check valves, replacing just the fuel pressure regulator where one of the check valve resides may or may not resolve your problem; remember there are two check valves; the other check valve is part of the fuel pump.
The fuel pump assembly consists of fuel pump, fuel pressure regulator, fuel gauge sending unit, fuel gauge float, pickup filter and pigtail wiring harness. If you do replace the fuel pump assembly, purchase a high quality assembly. Know this….you do get what you pay for here. Some cheap aftermarket assemblies have been known to fail prematurely. I personally prefer Bosch fuel pumps as they manufacture the best fuel pump assemblies for the XJ. Carter is my second choice. Airtex is my least favorite choice and I will not recommend or install them. A search will show you why.
Last edited by tjwalker; 01-18-2014 at 08:14 PM.
01-19-2014, 01:08 PM
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How did you check the fuel system? For a 2000, you need 49 psi of fuel pressure to start the engine. Must be verified with a fuel pressure gauge. Watching a fuel pressure gauge when this occurs may yield important test data.
The fact that it starts with some gas indicates a fuel problem of some sort; not much doubt about that. It is possible that you are experiencing a serious (almost instantaneous) drop in fuel pressure as the engine sits.
Try the "poor mans prime" illustrated below and see if that helps. If it does, then you likely have a check valve problem on the fuel pump assembly.
---------------------------------------------------------------------------
The check valves (there are two of them; the primary one is on the fuel pressure regulator and a secondary one can be found on the fuel pump itself) are part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When a check valve starts to fail, it can reduce fuel pressure to a point where an extended cranking time is needed to start the engine. It is a very common failure. I experienced it on my 99 at around 75K.
A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”
1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over
If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.
Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.
Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.
*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood
*Start engine and bring to normal operating temperature.
*Observe fuel pressure gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)
*Shut engine off.
*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.
If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the
fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose normally included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, but here is basically how it works:
*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.
*If the pressure remains at 49 psi for an extended period of time then the problem is in the tank – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.
**Note. Where check valve is suspect, a quick loss of fuel pressure is often the fuel pressure regulator check valve and a slow loss of pressure is often the fuel pump check valve. But keep in mind that either or both check valves can be to blame.
You can limp a check valve problem along indefinitely if you like, as it doesn't mean the fuel pump itself is going to fail. Perform the “poor mans prime” before cranking to speed up your starts. However, if you have a check valve issue and want to resolve it, it is recommended that you replace the entire fuel pump assembly for two reasons. First, you have to drop the gas tank to access the assembly. Secondly, with two check valves, replacing just the fuel pressure regulator where one of the check valve resides may or may not resolve your problem; remember there are two check valves; the other check valve is part of the fuel pump.
The fuel pump assembly consists of fuel pump, fuel pressure regulator, fuel gauge sending unit, fuel gauge float, pickup filter and pigtail wiring harness. If you do replace the fuel pump assembly, purchase a high quality assembly. Know this….you do get what you pay for here. Some cheap aftermarket assemblies have been known to fail prematurely. I personally prefer Bosch fuel pumps as they manufacture the best fuel pump assemblies for the XJ. Carter is my second choice. Airtex is my least favorite choice and I will not recommend or install them. A search will show you why.
The fact that it starts with some gas indicates a fuel problem of some sort; not much doubt about that. It is possible that you are experiencing a serious (almost instantaneous) drop in fuel pressure as the engine sits.
Try the "poor mans prime" illustrated below and see if that helps. If it does, then you likely have a check valve problem on the fuel pump assembly.
---------------------------------------------------------------------------
The check valves (there are two of them; the primary one is on the fuel pressure regulator and a secondary one can be found on the fuel pump itself) are part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When a check valve starts to fail, it can reduce fuel pressure to a point where an extended cranking time is needed to start the engine. It is a very common failure. I experienced it on my 99 at around 75K.
A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”
1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over
If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.
Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.
Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.
*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood
*Start engine and bring to normal operating temperature.
*Observe fuel pressure gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)
*Shut engine off.
*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.
If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the
fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose normally included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, but here is basically how it works:
*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.
*If the pressure remains at 49 psi for an extended period of time then the problem is in the tank – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.
**Note. Where check valve is suspect, a quick loss of fuel pressure is often the fuel pressure regulator check valve and a slow loss of pressure is often the fuel pump check valve. But keep in mind that either or both check valves can be to blame.
You can limp a check valve problem along indefinitely if you like, as it doesn't mean the fuel pump itself is going to fail. Perform the “poor mans prime” before cranking to speed up your starts. However, if you have a check valve issue and want to resolve it, it is recommended that you replace the entire fuel pump assembly for two reasons. First, you have to drop the gas tank to access the assembly. Secondly, with two check valves, replacing just the fuel pressure regulator where one of the check valve resides may or may not resolve your problem; remember there are two check valves; the other check valve is part of the fuel pump.
The fuel pump assembly consists of fuel pump, fuel pressure regulator, fuel gauge sending unit, fuel gauge float, pickup filter and pigtail wiring harness. If you do replace the fuel pump assembly, purchase a high quality assembly. Know this….you do get what you pay for here. Some cheap aftermarket assemblies have been known to fail prematurely. I personally prefer Bosch fuel pumps as they manufacture the best fuel pump assemblies for the XJ. Carter is my second choice. Airtex is my least favorite choice and I will not recommend or install them. A search will show you why.
01-19-2014, 05:26 PM
#6
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Year: 1999
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You didn't answer exactly how you verified the fuel system. If you just tested fuel pressure with the engine running, that isn't enough.
You need to have a fuel pressure gauge installed and do both a static and dynamic test. Meaning you need to see what the fuel pressure does when you turn the engine off and what it is as you try to start it as well as what the fuel pressure is while the engine is running.
The devil is definitely in the details. Having to manually prime an engine to start it still points directly at a fuel system problem of some sort. And some serious and in depth testing with a fuel pressure gauge will likely lead you to the root cause.
You need to have a fuel pressure gauge installed and do both a static and dynamic test. Meaning you need to see what the fuel pressure does when you turn the engine off and what it is as you try to start it as well as what the fuel pressure is while the engine is running.
The devil is definitely in the details. Having to manually prime an engine to start it still points directly at a fuel system problem of some sort. And some serious and in depth testing with a fuel pressure gauge will likely lead you to the root cause.
Last edited by tjwalker; 01-19-2014 at 05:30 PM.
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