have to prime to start
05-06-2012, 12:36 AM
#1
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Year: 99
Model: Cherokee
Engine: 4L
have to prime to start
I almost always have to turn key on and prime fuel pump two-three times before starting or it has to crank forever to start. Been this way for months, now im sick of it. I have new plugs, previous owner had new fuel lines and pump put in and dist cap. Only line old and rusty is one on evap can.
Injectors?
Injectors?
05-06-2012, 01:13 AM
#3
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Model: Cherokee
There's an anti-drainback valve in the fuel pump, when it goes bad this is what happens.
Attach a fuel pressure gauge and see if it holds pressure after you turn off the key.
If you lose fuel pressure, repeat...only this time turn off the engine and immediately pinch off the fuel line to the tank. If it holds pressure this time, the problem is in the tank. If it still leaks down, it's injectors or related.
Assuming it's the valve, it's OK to drive that way provided the fuel pump is otherwise working fine, just a PITA to start.
Attach a fuel pressure gauge and see if it holds pressure after you turn off the key.
If you lose fuel pressure, repeat...only this time turn off the engine and immediately pinch off the fuel line to the tank. If it holds pressure this time, the problem is in the tank. If it still leaks down, it's injectors or related.
Assuming it's the valve, it's OK to drive that way provided the fuel pump is otherwise working fine, just a PITA to start.
05-06-2012, 06:25 AM
#4
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Year: 1999
Model: Cherokee
Engine: 4.0
The check valves (there are two of them; one on the fuel pressure regulator and another on the fuel pump) 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 a couple of seconds
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 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 one is on 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 unit; 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 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 a couple of seconds
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 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 one is on 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 unit; 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.
03-11-2016, 11:37 AM
#5
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Year: 2000
Model: Cherokee
Engine: 4.6 stroker Inline 6
The check valves (there are two of them; one on the fuel pressure regulator and another on the fuel pump) 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 a couple of seconds
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 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 one is on 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 unit; 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 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 a couple of seconds
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 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 one is on 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 unit; 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.
03-11-2016, 12:18 PM
#6
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Year: 1989 Limited
Model: Cherokee(XJ)
Engine: I-6 4.0L AMC Renix
If your jeep is renix they apparently are known for taking a little long I start. Like 2 or 3 rotations from what I've heard. But do what other guys said especially if it is longer than 2-3 rotations.
03-11-2016, 12:26 PM
#7
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Year: 2000
Model: Cherokee
Engine: 4.6 stroker Inline 6
Mine is a 2000, I just pulled pressure gauge off after leaving it on for an hour or so and it held 43-44psi the whole time, I'll try leaving it on over night and see what that does, I'm just curious if a leaky evap line could cause a slow pressure drop though,
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03-11-2016, 12:27 PM
#8
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Year: 1989 Limited
Model: Cherokee(XJ)
Engine: I-6 4.0L AMC Renix
Originally Posted by bassmaster86
Mine is a 2000, I just pulled pressure gauge off after leaving it on for an hour or so and it held 43-44psi the whole time, I'll try leaving it on over night and see what that does, I'm just curious if a leaky evaporate line could cause a slow pressure drop though,
11-27-2021, 07:51 PM
#10
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sorry to bring a thread back from the dead but this popped up when I searched my issue. I have replaced my whole pump assembly (bosch) and new bosch 4 hole injectors and I'm still getting the long crank after its been sitting, I noticed the line coming out of the tank to the evap canister is rusted very bad and I have an evap leak code, I am going to replace the line this weekend with some fuel rated hose but could this possibly be what is still causing my long crank issue?
I need to prime the car 3 times before turning key all the way to start and that makes it work most of the time.. sometimes it still just turns over and if I turn the key all the way back and forward again it usually starts right up..
would next step be to change fuel injectors and spark plugs? or should I order a MOPAR fuel pump and try that first?
car is nice and strong but almost at 200k and will be looking for something new some what soon.
11-28-2021, 10:48 AM
#11
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Year: 1989
Model: Comanche (MJ)
Engine: 4.0
(The Grand Cherokee forum is at https://www.cherokeeforum.com/f5/)
I would get a fuel pressure gauge and see what it's actually doing, and how fast the pressure drops when you turn it off. If it's dropping really fast after shutoff, you can clamp the rubber fuel line to the fuel rail to figure out if it's the check valve in the tank or a leaking injector.
I would get a fuel pressure gauge and see what it's actually doing, and how fast the pressure drops when you turn it off. If it's dropping really fast after shutoff, you can clamp the rubber fuel line to the fuel rail to figure out if it's the check valve in the tank or a leaking injector.
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