My 97 XJ with the 4.0 is getting hard to start. I have a new fuel pump so it's not the pressure. It turns over for a good 5 seconds before it starts and when it starts it idles rough until I get going.

I'm thinking fuel injectors. Anyone else have this problem? Anything else I could be missing?

 

Did you have this symptom both before AND after replacing the fuel pump? My point is that just because something is newer, doesn't exclude it as a possibility. Newer stuff fails all the time and fuel pumps are high up in that category. What brand fuel pump is it?

Best to put a fuel pressure gauge on it and use that gauge to troubleshoot if you have 1) pressure leakdown and 2), if you have proper fuel pressure while running, which for your 97 would be 49 psi, plus or minus 5 psi.

More on testing fuel pumps below, but testing is the only way to rule out a fuel issue. Good luck!
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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 Google search will show you why.

 

^^^^^ but if that isn't it, trying clean the throttle body and all of the sensors with the correct cleaner. also try running fuel system cleaner.

 

Could a leak in the vacuum system also be a reason for starting trouble? For example, the hoses going into the top of the valve cover might not be sealed fully where it connects to the base of the VC, which will cause a pressure leak. There are YouTube videos on how to find a vacuum leak and the two methods I've seen are using a long rubber hose as a stethoscope, and the other spraying carburetor cleaner to check for leaks because it could bog the engine down or even stall it when you spray where the leak is however it sounds very dangerous and I would just use the hose method. I haven't done these things myself but I just wanted to share what I have found because I have a the same issue with my XJ but I just do the poor mans prime for now.

 

Mine was hard to start when i bought it. My fix was replacing the battery, cleaning the grounds along with the starter which was covered in dirt and oil. Started just fine after that.

 

Is there a way to put a check valve in line somewhere?

 

Colin, I'm working on the exact same issue myself with a '99 4.0. I put in a new (Bosch) fuel module and it started fine for two or three days. Now it is back to this hard starting. When it warms up it runs strong Did all manners of things to sort it out including all the advice given to you. Let's keep plugging away at one, one of us is bound to find something.

 

I recently had this problem with my 99. It would even stall on occasion until it warmed up. I cleaned the **** out of the throttle body. I used an entire can of throttle body cleaner and used a brass brush to scrub off some build up. It starts right up now and idles and accelerates smoother. Cheap fix for sure, under $5.

 

I will have another go at it. I had it off and cleaned it once, also replaced the IAC valve. Thanks for the input.

 

Hard starting, crank sensor and CAM sensor (mopar calls it the distributor switchplate)
Use mopar ONLY on these or regret it. Magnets are stronger on a 200k mile OE sensor than they are on a brand new dontalast sensor. Trust me just went through this in the spring, 2 brand new cam sensors went bad, ended up getting one from a junkyard and bingo. Actually put my original one back in that was broken for a while and that worked too.

 

Subbed thanks for the info.