96XJ_MrFantastic

1996 XJ 4x4 with the 4.0. 146k miles. This is the first time I've had any issues with it starting. I hear the fuel pump kick on and prime, I wait 5-7 seconds, then go to start it and it will crank but only catch when I give it gas. I did get it to catch and keep running after giving it some gas. Idle seemed slightly rough at first but then went normal.

I know the CPSs on these love to go bad. I tested mine with a multimeter and there's no short at least. All fluids are good. New fuel filter. Has always run like a top until this morning. I'm hesitant to drive anywhere because of this issue.

Any ideas on what else to check?

EDIT: now it's starting up just fine. Is it possibly the fuel pump on its way out?

Garrett S.

Had it been sitting awhile when it did this or was the battery dead? I'v had them start like that if the battery is drained before.

PatHenry

It's certainly a possibility that the fuel pump is starting to go. Fuel pumps often die a slow death. I'd go over the grounds and connectors just to be sure, but it definitely sounds like the pump is starting to go.
I'd do a pressure test on it - best when it's acting up again - and see if it's got good pressure. Since you have a 96 there are 2 different possible pump setups - one has the pressure regulator on the rail, the other in the tank. From other folks on the forum it seems like the "in tank" style is more common. Pressure spec is 31psi for the old style (rail mounted pressure regulator) and 49psi +-5 for the newer IIRC. One concern is that the in-tank style pump assembly is unique to the 96 year. Folks have reported having trouble finding the part, but within the last month someone replaced theirs and didn't have any trouble finding a new one.
The part number was listed in that thread - you should be able to find it with a google or forum search.

PatHenry

Good call on this - definitely check the battery. The XJ is known to be picky about having a good battery and a battery is lot easier to replace than a fuel pump!

PatHenry

CPS's on the AUTOMATICS love to go bad. Over 3 manual Jeeps (700k+ 20+ year period) there were exactly 0 CPS failures. My theory is the manual tranny doesn't get as hot - but it's just speculation.

96XJ_MrFantastic

The battery was replaced last year. Jeep had been sitting for only 1 day. I have the in-tank style so I'll probably just end up replacing the pump and assembly if the problem reoccurs. I'm going to take it on a drive after doing a coolant flush so we shall see!

EZEARL

You ever serviced the throttle body and IAC?

PatHenry

It wouldn't hurt to check the battery anyway. That's what I would do if it were me since it's free and easy and it's certainly not unheard of for batteries to fail prematurely.

At least with the fuel pump you don't have to drop the whole tank to get at it in a 96. I dropped the tank twice in my last Jeep (TJ) and it was a whole lot of headache just to get access to the fuel pump.

jordan96xj

EZEARL is on the money. The IAC is the first suspect, way ahead of the fuel pump (unless a pressure test has been done and something unusual was observed).

If giving gas causes the 4.0 to start (or at least attempt to start) that is a marker for an IAC that is not opening properly on startup, which may in fact start working better once it warms up.

The other primary candidate is low voltage at startup. This can cause a strange rough and low idle where the motor dies if gas pedal is not depressed. Which can also be a down to the IAC not doing its job correctly because voltage is low and computer is confused. This condition will sometimes resolve after a few minutes of holding the throttle, as the battery/alternator start to catch up with the system's voltage demands.

96XJ_MrFantastic

Thank you for the responses! I'll be checking the IAC tomorrow for sure. However, it had no problems starting the rest of the day, even when cold.

On a side note, I had a coolant leak from a heater hose so I replaced both my heater hoses, deleted my HCV, replaced both my radiator hoses, and did a coolant flush. It ran great when I tested it once everything was done. No HCV also makes the engine bay look much cleaner!

jordan96xj

Based on everything you have posted, I would say you had a low voltage start. It can be hard to say after the fact why that happened, but that is what it sounds like.

BruceB

I had a similar situation on my Jeep. It ended up being the Coolant Temperature Sensor. With all the cooling system work you have done it may have affected the old sensor.

EZEARL

^^^
GOOD point. After needing to fix an IAC issue I got a code for the CTS. Didn't have one handy so I polished the end of mine. Code disappeared and it's still in use.