Hunter369

Alright guys I’ve been investigating through suggestions found in older threads but nothing so far has worked so I believe it’s time to start my own. I have a 96 xj 4.0 sport

So, the issue I’m having is a long crank/ hard start by that I mean in order to start the vehicle I have to hold the pedal to the floor and crank for ~10 seconds and after it starts I have to hold the rpms at around 1500 for another 2-5 seconds when cold or it will sputter out. This problem is considerably worse when at op temp, roughly same crank time but seems more determined to die I have to hold the rpm’s much longer ~15 seconds maybe more. I’d also like to say that feathering the throttle doesn’t work it has to be to the floor.

I’ve gone through quite the journey trying to solve this issue I have replaced all spark plugs, wires, cap, rotor, and coil. Outside of spark I’ve replaced the fuel pump assembly, in-line filter, air filter and installed a fuel rail heat shield along with new injector o-rings all to no prevail. I then replaced the crank position sensor, that didn’t change anything so I reinstalled the old one and got the coil instead.

After this I did a compression test and was pleasantly surprised that all cylinders were ~125psi or more besides cylinder #1 which was just a little over 100 still not bad. During this test obviously I had to pull my new spark plugs (~2 weeks old) and they were carbon fouled. Also, it’s worth noting that before I changed the fuel pump assembly I did a fuel pressure test which showed ~20 psi while running. I have not redone this test since I replaced the pump assembly. Also, in regards to the fouled plugs, a generic search tells me that it’s either running rich or running too cold (there are other symptoms of course but these two seem likely to me) I know for sure the engine is running cold because someone installed a 160° coolant t-stat.

My next plan of action was to check and see if the darn thing is even in time properly however this seems like an incredible waste of time assuming that it most likely is in time since it runs fine.

I am very frustrated because it seems like the google algorithm is sending me down a rabbit hole on purpose at this point because I always search the same problem but it pulls up a different thread every time. That being said, the most recent thread I have read suggests a bad chassis ground or other ground which I will investigate later today but if anyone has any other ideas with all these fresh part in mind I’d be all ears and forever grateful.

Hunter369

Forgot to mention I have a little information supporting the bad ground idea because the transmission is incredibly slow to shift that being said I also had information seeming to support a heat soak condition so maybe I just have a bad transmission (on top of slow shifting if I floor it it seems to slip into neutral)

Hunter369

Update: I checked all the grounds they were indeed dirty so I cleaned them all off but it didn’t change anything(not sure about the transmission I didn’t go for a test drive). The braided ground wire seemed to be in good condition it wasn’t corroded just a little dirty lmk if you think perhaps replacing that with a proper wire would make a difference. Also, while I was doing that I noticed that someone has already added a non-stock ground wire from the battery terminal to the chassis. Please someone comment on this thread with suggestions I am stumped and almost out of things to replace on this jeep.

andjones

Someone has to break the news to you about the '96 XJ. It is a one year only for many parts including the PCM and the PCM has known issues. Having said that, don't go out and buy a PCM (if you can find one) before doing other tests. Do you have a Factory Service Manual (FSM) for the '96? If not find one. They can be downloaded cheap and possibly free.

Disconnect the battery first and have it load tested. Meanwhile I would check all of the connectors to the PCM for corrosion, especially the ground. Check wiring to the coil, throttle body and injectors for damaged wires or connectors. Then I would test the Throttle Position Sensor (TPS) per the FSM. The Idle Air Control (IAC) would be another item to test. Hopefully this will turn up the cause for your trouble. If everything checks out OK then a new PCM may be needed.

Don't go out and buy a bunch of parts and install them. Test and verify the original parts first. IF and ONLY IF they test bad replace them, one at a time then test to verify that it solves the problem. Replacement parts are flaky at best, so swapping in new parts can cause new issues or not resolve the current issue or fail prematurely.