99 Cherokee ignition issue
12-09-2012 | 11:01 PM
#1
Thread Starter
Newbie
Joined: May 2009
Posts: 14
Likes: 0
Model: Cherokee
99 Cherokee ignition issue
Hello
I have a 99 Cherokee sport with a 4.0. It has had a hard starting issue for the past few years and I would like to take cafe of it. So far I have changed the fuel pump, ign cap and rotor, coil, spark plug wires, distributor pick up, flywheel timing sensor, injectors, ecu, battery, O2 sensors, gutted the cat and installed a new ignition switch and throttle body switch. No change
I am thinking it is a ignition - wiring issue. It is getting plenty of fuel. When it does finally crank it acts like it is flooded and smells like it. I did put on a sparky tester on one of the plug wires and noticed the spark was week for the first 5 or so revolutions then the spark got hotter and it fires up. It is also easier to start on wet days, which is another reason I am thinking of wiring. The check engine light is not on, so that is no help. I have been unplugging the harness and cleaning the contacts and coating them with no ox but so far nothing has changed. I have also added extra grounds between the ecu, engine block and battery. Any one have any other ideas......
I have a 99 Cherokee sport with a 4.0. It has had a hard starting issue for the past few years and I would like to take cafe of it. So far I have changed the fuel pump, ign cap and rotor, coil, spark plug wires, distributor pick up, flywheel timing sensor, injectors, ecu, battery, O2 sensors, gutted the cat and installed a new ignition switch and throttle body switch. No change
I am thinking it is a ignition - wiring issue. It is getting plenty of fuel. When it does finally crank it acts like it is flooded and smells like it. I did put on a sparky tester on one of the plug wires and noticed the spark was week for the first 5 or so revolutions then the spark got hotter and it fires up. It is also easier to start on wet days, which is another reason I am thinking of wiring. The check engine light is not on, so that is no help. I have been unplugging the harness and cleaning the contacts and coating them with no ox but so far nothing has changed. I have also added extra grounds between the ecu, engine block and battery. Any one have any other ideas......
12-10-2012 | 12:35 AM
#2
CF Veteran
Joined: Jan 2011
Posts: 1,894
Likes: 4
From: Las Vegas
Year: 1999
Model: Cherokee
Engine: 4.0
The check valve is located on top of the gas tank and is part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When the check valve starts to fail, it reduces fuel pressure to a point where an extended crank 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) way to 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 a two more times
5. NOW crank the engine over
If the engine starts quickly and cleanly after performing this procedure, you may have the check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the bleed down and the 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 this symptom. Sounds strange but it definitely does happen. Have battery load tested if you have any questions; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.
Some troubleshooting tips for extended crank times:
Hook up fuel pressure gauge on the schrader valve on the fuel rail
Start engine and bring to normal operating temperature.
Observe test gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)
Shut engine off.
Pressure should not fall below 30 psi for five minutes.
If pressure falls below 30 psi, it must be determined if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking. An adaptor tool/hose included with the fuel pressure gauge can help you with this. Consult gauge manual for more information on this 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 - possibly the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.
You can limp a check valve problem along indefinitely if you wish as it doesn't mean the fuel pump itself is going bad. Normally, the check valve is replaced as an entire assembly as you have to drop the gas tank to access the assembly. Fuel pump assembly consists of fuel pump, regulator, check valve, filter. If you do replace the fuel pump assembly, purchase a high quality OEM style unit. Some cheap aftermarket assemblies don’t hold up and fail prematurely.
A good (and simple) way to 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 a two more times
5. NOW crank the engine over
If the engine starts quickly and cleanly after performing this procedure, you may have the check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the bleed down and the 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 this symptom. Sounds strange but it definitely does happen. Have battery load tested if you have any questions; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.
Some troubleshooting tips for extended crank times:
Hook up fuel pressure gauge on the schrader valve on the fuel rail
Start engine and bring to normal operating temperature.
Observe test gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)
Shut engine off.
Pressure should not fall below 30 psi for five minutes.
If pressure falls below 30 psi, it must be determined if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking. An adaptor tool/hose included with the fuel pressure gauge can help you with this. Consult gauge manual for more information on this 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 - possibly the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.
You can limp a check valve problem along indefinitely if you wish as it doesn't mean the fuel pump itself is going bad. Normally, the check valve is replaced as an entire assembly as you have to drop the gas tank to access the assembly. Fuel pump assembly consists of fuel pump, regulator, check valve, filter. If you do replace the fuel pump assembly, purchase a high quality OEM style unit. Some cheap aftermarket assemblies don’t hold up and fail prematurely.
12-10-2012 | 06:16 AM
#3
Thread Starter
Newbie
Joined: May 2009
Posts: 14
Likes: 0
Model: Cherokee
That was the first thing I checked about a year ago. Just to cancel the fuel system out, I installed a new fuel pump and injectors and it made no difference. You can turn the key to the on position multiple times to prime the pump and it still takes a bit to start. I will check the pressure again but I am still thinking it is electrical. Thanks for the FI info
12-10-2012 | 06:34 AM
#4
CF Veteran
Joined: Dec 2010
Posts: 1,700
Likes: 0
From: S.Jersey
Year: 1999
Model: Cherokee
Engine: 4.0
wow man. what a b1tch. I feel for ya.
I know you installed a new cpu. But perhaps you can try to take the plugs off of the cpu spray the plugs with contact cleaner. let them dry. then appy diaelectric grease to the pins on the cpu itself; kind of goop in there. then see what happens.
my 99 was having simiar issues. i cleaned all the grounds and bat terminals and it still did it. i did that with the cpu and it hasn't acted up in ayear. knock on wood.lol.
i know you put a new cpu in;but that does mean that moisture isnot still getting in there. thats why i say goop the greas in the cpu side ports.
hope this helps.
make sure you disconect the bat before just unpluging the cpu.
I know you installed a new cpu. But perhaps you can try to take the plugs off of the cpu spray the plugs with contact cleaner. let them dry. then appy diaelectric grease to the pins on the cpu itself; kind of goop in there. then see what happens.
my 99 was having simiar issues. i cleaned all the grounds and bat terminals and it still did it. i did that with the cpu and it hasn't acted up in ayear. knock on wood.lol.
i know you put a new cpu in;but that does mean that moisture isnot still getting in there. thats why i say goop the greas in the cpu side ports.
hope this helps.
make sure you disconect the bat before just unpluging the cpu.
Last edited by OEJ; 12-10-2012 at 06:38 AM.
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