4.0 starting issue
 

I have a 1996 Jeep Cherokee with the 4.0 engine it is my daily driver. The problem is when I try to start it, most of the time it will start on the first crank but it takes anywhere from 5-10 seconds to start and it’s bad enough that I feel like it’s putting unnecessary wear and tear on the starter. I had the fuel pump replaced at a shop recently and I replaced the spark plugs myself. Those are the only things I have done to the engine. Any help or input would be appreciated as I cannot figure out what the problem is. Also it has 140,000 miles

Check the condition of your battery.

I'd start by putting a pressure gauge on the fuel rail and see if it's leaking down while it sits. Do you have spark while initially cranking? Is it cranking nice and strong, or are the battery cables dirty or rotten?

A good (and very 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 even though you said you replaced the fuel pump as fuel pump quality varies widely. What brand fuel pump did you install?

**If your engine 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.

**Leakdown pressure testing using a gauge as lawsoncl mentioned can be very helpful in diagnosing an engine that is symptomatic as you mentioned but starts quickly using "the poor mans prime".

**Also as mentioned by NM-XJ, be aware that a bad battery can give you starting symptoms as well. And yes, you CAN have a battery strong enough to turn the engine over well but marginal enough to give you starting problems as your XJ does NOT like low available battery voltage! Have your battery load tested which any parts store will do for you for free. Be sure battery connections and posts are CLEAN.

Good luck! Job #1 for you is to run "poor mans prime" test and report back what you find and we can go from there.......

So I have done the poor mans prime already and it starts right up how it should when I do that sometimes it is a smooth start and other times it’s pretty rough and shakes the steering column so it could be a leaky fuel injector I will definitely look into checking the fuel pressure and I don’t know that brand of fuel pump put in. Thanks for the input

And I have the battery is in good condition and the connection is good too. It also has spark while starting.

'96 is a "one off " year for fuel pumps, in that the pump, regulator and sender all integrated into one unit..expensive and hard to find

However you can replace both the pump and regulator seperately

I am about 90% certain they are both the same as a '95 and earlier, (not the 97 and later), but check pics on Google etc

I replaced just the pump on one of my '96