Anthonyb

1996 sport 4.0

I have pretty much the same routine every day in my Jeep unless going on a trip.

leave for work at 0530 get home from work at 230 pm, repeat. We use my lady's car for any other driving because of the vastly better mileage.

So I'm not sure if this means anything or I am just paranoid, but in the am when I start it up it takes 2-3 seconds to fire counting in 1-1000 increments. Always cranks strong and has never not fired. When I leave from work 8 hours later, it fires almost immediately every time. What would cause it to crank longer in the morning and fire right away in the afternoon?

At work I park outside and at home, I park in a heated underground garage.

Xj88

Fuel Filter, or fuel pump. Maybe a dirty injector.

Xj88

Id start with replacing the fuel filter..they are cheap..and its easy to replace.

Anthonyb

ok, I did the filter about 2 years ago. Do you think I'd need to replace it that soon?

scottmphoto

Yeah, I'd replace the filter. Start there then once you rule that out, then if you still have the problem you can start to diagnose it from there.

Radi

Oh, the checkvalve back in the pump assembly is probably starting to fail, allowing the rail pressure to bleed off overnight. It isn't uncommon, nor does it hurt anything.
Turn the key to "ON", leave it there 5-10 seconds until the fuel pump stops running.
Turn key back to "OFF".
Repeat.
Now try starting. If it starts right up, that's the problem.

tjwalker

Agree with Radi on this one; a "checkvalve" issue on the fuel pump assembly is a primary suspect. Here is more on this issue.
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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 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 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.

Anthonyb

After this morning's experience I am convinced Radi is right as well. Just for s**ts and giggles and before reading this I turned the key to the "on" position before I started it this morning. I only did it once and for about two seconds, but as soon as I did that I didn't even get to my 2 count before the engine fired up. So I'm not going to worry about it too much unless it gets noticeably worse. Thanks for the help guys!

tjwalker

What you did is a quick and dirty confirmation that you are experiencing "fuel pressure drop" over time as the vehicle sits.

The extended crank time you have been experiencing is almost assuredly a failed checkvalve and that does NOT mean that the fuel pump itself is failing.

You can continue to perform the "poor mans prime" before starting. Many XJ owners are doing this. I'd recommend that you do so on "cold" starts to reduce starter wear and tear and to give you quicker starts.