Cold crank issue

Hi all...just picked this heep up a few weeks ago. 96 XJ, 4.0, 128k, stock motor tranny and tcase.

Has had a spot in the garage so it hasn't had any cold weather yet, gave the girl the garage last night so jeep sat in the driveway overnight. Ran fine, starts fine, until this morning. 35 degrees or so, frost on the windows, but not freakishly cold...cranks strong, tapped gas pedal after first handful of tries, sputtered for half a second and goes back to just a strong cranking. Sprayed ether into intake and it fired right up, ran fine, and restarted fine. That being said, until it happens again where would you all start? I understand if a part was broken, but it started and ran fine. Fuel pump? I can hear it prime when i turn the key to the accessory position. Any suggestions of what to tackle first would be appreciated.

If the engine starts with ether, you have identified a fuel delivery problem.

Troubleshooting with a fuel pressure gauge would be the best technique.

96 was a year of change for the fuel system if I remember right. Some have the "old" system where the fuel filter is along the frame rail on the drivers side and you can change it. Some have the "new" system where the filter is part of the fuel pump assembly, located inside the fuel tank.

Look along the frame rail on the drivers side. If there is a filter, change it and see if that helps. If there is no filter, than you have the new system and I'd recommend putting the fuel pressure gauge on a cold engine and see what you have for fuel pressure as you try to start it.

You can also try the "poor mans prime" to see if that helps. Turn the key to the ON position, you'll hear the fuel pump kick on. Turn the key OFF. Turn the key to the ON position again, effectively priming the engine twice. NOW try to start the engine. Does it start up using this technique? If it does, that means that you are losing fuel pressure as the engine sits, possibly due to a failing check valve in the fuel pump or sometimes a leaky fuel injector. Most often it's a check valve.

Depending on which system you have, the old system requires 31 psi to start the engine and the new system requires approximately 49 psi to start. So testing can be very helpful here. Many parts stores will rent you a fuel pressure gauge very inexpensively; call around for availability.

Good luck and keep us updated!

Excellent info, i agree with everything. I know it is the old system, and i have a fuel filter i will be replacing it with this weekend, along with other basic tune up parts just for peice of mind. Cap/Rotor, champion truck plugs, bosch wires.

I will try to the "poor man's prime" if I run into the problem again. So far it has only happened that one time. Cold weather coming in tomorrow night so i will experiment and leave it out of the garage into saturday morning so i don't have to rush like a mad man to get it started so i can get to work on time.

Thanks for the suggestions, I will post back with any progress or solution.

Ironically enough, the day you mentioned the "poor mans prime", it happened for the second time when trying to leave work....it was colder, dark out bc of daylight savings now, so temps were lower than usual. Cranked strong a couple times, so I applied your idea, cycling the key a couple of times, tried it and two cranks later it fired. Pissed off at that point i drove straight to the parts store, got the filter, and decided to do cap/rotor, plugs and wires, and swap my starter due to a "flat spot" sound developing on a pretty regular basis. This morning it was in the garage so there were no issues, but it feels cold out so i will update again when i leave it in my driveway overnight.

New question, what does the colder temps have to do with the fuel system not priming properly?

The moderate temp fluctuations may not have anything to do with your issue, more likely coincidental. Either way, it really doesn't change how you approach this problem.

If the new filter fixes your problem, you had a partially clogged filter that was struggling to create the proper pressure to the fuel rail.

If symptoms continue, I would go back to doing some basic fuel pressure testing with a gauge to see how quickly fuel pressure drops after you turn off the engine. If you have a relatively rapid drop, especially in the first 5 minutes or so, the primary suspect at this point is a leaky "check valve" on the fuel pump. But there are other things along the line as well like pressure regulator, injectors, etc. The factory service manual will have the exact procedure and specs for allowable fuel pressure drop AND how to truly isolate the root cause of fuel pressure drop. I'd recommend reading everything that the FSM has to say about this before digging in. Very helpful flowcharts and info. in the FSM.

Good luck and keep us updated!

Temp issues may have more to do than you realize. Computer looks at the ECT sensor first to develop starting fuel trims. On a cold morning it demands more fuel. The fuel system may be unable to meet the new, increased demand for fuel.

Update: With new fuel filter...the problem has not happened yet, however...temps here have been warmer than when the two occurances took place. Supposed to drop again tomorrow so i will update as needed, but as of now it seems like the fuel filter was causing or at least contributing to the issue.

New update: New plugs, wires, cap/rotor, new fuel filter, replaced ENTIRE fuel pump module which to my understanding on a 96 XJ should include check valve and pressure regulator?

Jeep STILL takes forever to start while sitting for hours in COLD temps. I have no problem trouble shooting, I even read posts about issues with the crankshaft position sensor, and leaky injectors....however the thing that is throwing me off is it is ONLY when the outside temps are below 45 degrees or so. I have confirmed this on a daily basis, as my jeep sits overnight in the garage, which doesn't dip below 50 degrees, 8 hours later it fires up on the first try. However, parked at work for 8 hours, only on days that temps drop below the mid 40's, it takes key cycles, and endless amounts of cranking, along with spraying ether into the throttle body. Once she fires, she runs and drives perfectly fine, and will restart an hour or two later even in cold temps. I'm bent....any more ideas anyone!????

Check ECT sensor. As stated before, it is the first thing the computer looks at to determine starting fuel trims. If it is biased, as in showing it is 75 when it is 45 it will not give the engine enough fuel. Cold temp=more fuel needed. It is a simple thermistor. Voltage in, voltage out is varied according to temp. There are many charts out there for matching voltage to temp.

Searched ect sensor and only found coolant temp sensor...what is ECT?

That is exactly what it is. Engine coolant temp.

That is interesting, and cheap, however I thought that only relays engine temp...not outside air, but i will add it to the list of parts to try. FML. Haha

Engine temp at startup is approximately ambient correct? Only takes a simple voltmeter to check. Check voltage to and check output voltage and compare to chart.

Good point. Will troubleshoot a few things this week and post back. Thanks again for all the suggestions.