96 4.0L - Will only start with fluid

Hey guys...new here and just picked up my second XJ.
96 4.0L 177k

The jeep will crank and crank but not even try to fire over. However; it will start immediately if I give it a shot of starting fluid. After that it ran great. With key on, have fuel pressure to rail. Hand check at schrader valve. Checked fuel filter, replaced. Fuel amount at rail prior to start increased 3 fold. Still no start.

As a side note and maybe related: The jeep had been sitting for awhile prior to me owning it. Gas in tank is probably bad. I started it with starting fluid and ran for about an hour to burn all this gas out and the jeep just shut off. No sputter, just stopped. Same starting symptoms still exist. This drew my attention to the ASD relay. I'm not sure what role it could have in my starting issue if the thing runs good.

Another side note: I put a bottle of injector cleaner in the half tank when I got it to clean it out. Had hard starts when I got it. Replaced plugs/wires/distcap/rotor as routine maint.

If you use to much starting fluid your going to vapor lock the motor, thats what I have always been told anyways.

it is your fuel pump same thing happend to me and it ended up being the fuel pump

nevermind didn't read the full thing

Any useful advice? I plan to check the pressure at the rail pre-start, while running and pressure drop after it stops.

Anyone know the specs for this test?

Also, is there a pressure regulator inline anywhere? Only a checkvalve at the pump?

Started on fluid today, let it idle. It ran for about 45min or so and just stopped again. Same thing happening.

Stuck gauge on fuel rail. With key on...pressure jumps up to 49psi and then drops to 30psi in about 5 seconds, dropped to 20psi in 5 min. I thought if it was an injector then there had to be some fuel in one cylinder. I matted the gas to simulate flood condition and cranked to see if it would jump like it was firing. The damn thing started!

Running pressure was 46-50psi. Ran for 20 min. Pulled throttle up to 3k rpm for 10 seconds and let go. Engine shut off. Pressure dropped to 30 psi immediately and I heard a dripping noise coming from the engine. Pressure continued to drop to 20 psi and dripping noise stopped. Pressure held at 20 psi.

Can you say leaky injector? How can I troubleshoot to find out what injector is leaking other than pull the plugs and see which cylinder gas is in? I plan to do this in a second anyways but want to be 100% sure before I waste some money.

Any of the plugs look blacker than the others?

After the above, I pulled the plugs. One was blacker than all the others (they are new plugs). Consequently, I looked at my data from the compression test. This is the only cylider lower than the others (163psi: all others were 175psi). Tried a few more things that led to pulling the fuel rail to check for leaks.

Key on pressure jumps to 49psi. I checked all the injectors and none were leaking. I tried this several times. Fuel pressure still dropped. So...fuel pump. Put on a new pump and strainer. Drained all the old gas outta the tank to eliminate that option. Refilled with 5 gal 87 oct. Key on, bled the system kinda using the pressure gauge to get fuel up to pressure. Key on, 49 psi, only dropped to about 44psi with key on.

However, still won't run! This is killin me. May be a two fold problem. Fuel pump check valve was obviously part of it.

Well, shit just hit the fan. Can't even start it on fluid. With key on the coil does not have 12V. ASD relay tested good. Even swapped it out with another just to be sure. The PCM is not grounding it to pull in the relay coil.

Help.

Anybody have any suggestions!

ASD relay not pulling in when cranking. Pulls in breifly with key in On position but that is normal. No power to coil or injectors when cranking.

Replacing the crank position sensor tomorrow. Plugged the connector together and remove the insulation on the wiring harness at it so I could probe it. Tested middle plug to ground, good. Tested power source voltage with key on, 5 V. Tested power source while cranking ~5V. Tested signal wire while cranking, only mV. Seems like its not reading anything. I plan to clean and test it outside bellhousing with a magnet to see if I can get a reading from it. If so, I will reinstall and reposition. If that doesn't work then I'll put the new one in. Autozone $61 2yr warr.

TUrned out to be the crank sensor. For future testers... pull fuel rail... pull sensor but leave all hooked up. Turn key in on position. Stick a wrench or something up to the sensor. You should see the injectors fire once. Put volt meter up to middle terminal and the terminal that ISN"T the violet colored wire. Put meter on dash and watch the voltage as you crank. It should fluctuate 0v....5v... Or something similar. It really depends on the sampling rate of your meter. If not, replace it.

Fixed mine. I'm just glad I didn't shotgun it and waste a bunch of money.
Hope this all helps somebody.

Hey, thanks for all your helpful information, I am having the exact same problem, the engine will crank, but not start, the last three times I gave it some starting fluid and it would fire right up. Today it won't start even with the fluid. So I'm off to do some testing. I have already replaced the fuel filter and pump recently, so that shouldn't need replaced. Thanks for all the ideas, glad to see I may not be the only one with this problem. Any idea why it would start with use of starting fluid for a few times though?

Starting fluid is much more volatile and will respond to a weak spark. Once it gets turning over the weak CPS begins to finally pick up a signal and the computer takes it from there.

The cheap test for a CPS is to simply unplug it - to dump any residual voltage buildup or polarity, then reconnect and crank it up. Usually starts right up in an annoying display of working just fine - until you shut it off.

As explained for posterity - check the CPS before replacing pumps, especially if you get 30-49 pounds out of them. Three sensors can really mess with fuel injection, the TPS, MAP, and CPS. For a no start, they should be checked after cranking volts and fuel. They are part of the spark checking process.