Intermittent hard to start

I have 2000 4.0 auto and it seems that about every other time i go to start it it just turns over. i have cranking, then turn the key again and it fires on the first turn. other times it fires right up....

I am not sure where to start on this, any ideas?

Try to zero in on as many specific facts as you can. These will help us help you diagnose the problem. For instance:
Does it matter if the engine is hot or cold?
Do you hear the fuel pump buzz when you turn the ignition on & it doesn't start?
etc.

My first guess is that your crankshaft position sensor is starting to die, but without more data, that is just a guess.

hot cold it does not matter.... i can start it at my house, drive for 2 hours shut it off try and start it and it will just crank and crank and crank

unhitched said:

hot cold it does not matter.... i can start it at my house, drive for 2 hours shut it off try and start it and it will just crank and crank and crank

Click to expand...

How long after you shut it off are you trying to restart it. It could be a heat soak issue but I can't remember if that's a 2001 problem only.

happens when cold as well, i just meant to say that it being warm does not make it easy to start, it is just about every other start

also if i stop cranking and crank again it will fire right up...

If it primarily happens with a COLD engine, suspect the check valve that is part of the fuel pump assembly; a very common failure on your vintage.

But you mentioned that it can happen with a cold or warm engine. I'd start with refreshing all electrical grounds.
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Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.

Check valve in the Fuel Pressure Regulator. It's located in the in-tank pump. Common problem on '97-'01 XJs. Try cycling the key a couple times to prime the fuel pump next time you start it. My money says it'll fire right up.

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. I specifically seek out Bosch fuel pumps as they are the best in the business. Stay away from Airtex, as IMHO, they have a bigtime reliability problem.

I've noticed that my '97 does this also, although probably not as often. If you turn the key on and wait a second or two before cranking will it start everytime. This is what I've resorted to doing.