I tried searching no luck. My '99 4.0 has to crank over for what seems to me to be too long before it fires up. It runs great although only gets about 15 mpg. I was thinking new plugs and wires (don't know if or when they were replaced bought it recently with 160000 miles) or maybe fuel pump. Anyone had this problem? Thanks

 

Since it is new to you I would recommend doing a complete tune up with NGK copper spark plugs gaped at .035 and make sure that the dist cap has brass terminals not aluminum. Also make sure to change all of the fluid. As for the long start time. Try the poor mans prime. When you are going to start it turn the key on so you can hear the fuel pump priming then turn off the key. Repeat this 2 or 3 times. Then try starting it and see if it starts any faster. If so more then likely you have a bad anti-flow back check valve.

 

Thanks that sure helps Already changed all fluids to synthetic Local jeep shop thought cranking prob might be fuel filter Won't hurt to change that anyway Think I should change the spark plug wires? Runs like a bat out of .... so I'm thinking not.

 

^X2^ anti-flow back check valve is a common cause for your symptoms. Keep us posted. May help someone else someday~

 

You are welcome.
You really don't have a fuel filter. It's more like a screen and it is inside the fuel tank attached to the fuel pump assembly, Which means you will have to drop the tank to clean the screen.
If you don't know when the plug wires were changed last it would be a good idea to change them along with the other tune up items that way you know when everything was changed out.

 

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.

 

Outstanding info thanks I tried the poor man's routine and can't hear any priming going on. But I waited 3-4 secs turned it off and repeated a couple more times and it seemed to help.

 

Cool! At least you now know what is wrong with it. And as Mr. Walker said you can run it like it is in-defiantly. Also like he said if you do want to replace the valve replace the entire fuel pump assembly with only a Bosch or a Carter pump assembly and stay as far away as you can from the Airtex brand.