Lethbridge_XJ

Lately i have noticed that when the weather is warmer and my 98 xj has sat for awhile it takes forever to fire while starting. It cranks for a good 15 seconds then finally fires. Any help with this issue is much appreciated!

maximan1

Make sure that the ground strap from the back of your head to the firewall is in good shape. Connect a jumper cable from one bolt to the other, and see if that helps. I've heard that when that cable goes bad, the computer has a hard time reading and it takes longer for it to start, I'm assuming because the computer tries to default to a richer mixture. I don't have a lot of experience with Jeeps yet, this is just stuff I've read from this site and my previous experience with aircooled Volkswagens.

Lethbridge_XJ

Thanks, I will have to give that a try

944.0

Try cycling the fuel pump a couple of times. Just turn the key to the run position and wait for the pump to shut off. Do it twice and then start it.

tjwalker

A high likelihood that you have a "check valve" issue in the fuel pump assembly. Here's more on that.
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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.

Lethbridge_XJ

Thanks for the in depth reply!

TSea99XJ

I just got done dealing with a very similar issue myself, here were my findings.

After posts and replies on the forum, I replaced the usual suspects, the Crank Position Sensor, and the Ignition Coil, both to no avail. Testing showed fuel and spark were both good, and to prevent just throwing more money at it, I brought it into a shop to be looked at.

Their findings were corroded Cap and Rotor for the distributor, and since replacing them, I've had no crank/no start issues.

The only reason I didn't replace them myself before bringing it to the shop was the dealer I purchased it from stated that the Cap/Rotor/Plugs/Wires had all just been replaced.