All right gurus, I have a 1990 YJ that I swapped out the 2.5 for a 4.0 out of a 1996 XJ. I have an AX15 transmission.
I have a starting problem, that I have been unable to diagnose.
My motor was running good until this morning. I went to move it and all it does is crank. I had an issue with it taking extra long cranks to start it if the motor was hot. It would also run rough after the long crank.
Looking into it, the first thing that I noticed was that the fuel pump would prime when the key was turned to "Run." But when cranking it was not running. Back when it was running, the pump would run for three seconds after you stopped cranking (In the event that it did not start).
The first thing that I tested was the Crankshaft Sensor. It tested bad, so I went ahead and put a new one on. I thought this would fix the problem, but it didn't.
I am a one man show right now, so the only way that I could think of for checking spark was spraying starter fluid in her and see if she fires. No go.
From what I am reading online, everything is pointing to the Crankshaft sensor, but I already replaced it. I unplugged it and checked for corrosion. The engine harness side has some corrosion in it, so I used a paper clip to clean it up the best I could. Open to suggestions for cleaning this.
Right now, I am beating my head against the wall trying to get this thing running. I know that the ASD relay is activating when the key is turned on, but the computer is not telling the motor to run during the cranking process.
Other things I have checked.
Swapped relays around, just to make sure.
Unplugged O2 sensors in case they were shorted out.
unplugged all sensors to check for corrosion.
Checked the grounds that I could find.
Unhooked the battery reset the PCM.
I am hoping I can get some ideas on what to do next. Seems like all the threads I have found, the fuel pump doesn't prime, but mine does.
Not 100% sure but I think that I read that there is also a Cam position sensor besides the the crank sensor that can cause similar issues, but somebody with the 4.0 would have to speak up. IIRC the cam sensor is by the dizzy.
Do you have the diagnostic light hooked up to read codes? if not the you can read the codes by hooking a 12Vdc light to battery and ground to pin 32 of the ecu. You are throwing parts at something that could be the bad cap in the ecu issue. Hook up the test light and look for the codes first.
Okay, here are the codes that I got and descriptions according to Chiltons.
12 - Memory to controller has been cleared within 50-100 engine starts
42 - Fuel pump or no ASD relay voltage sense at controller
44 - Battery temperature voltage - problem exists in the PCM battery temperature circuit or there is an open or short in the engine coolant temperature circuit.
24 - TPS voltage high or low
22 - Coolant voltage low - coolant temperature sensor input below the minimum acceptable voltage/Coolant voltage high - coolant temperature sensor input above the maximun acceptable voltage
23 - Air charge or throttle body temperature voltage high/low - charge air temperature sensor input is above or below the acceptable voltage limits
31 - Purge solenoid circuit - open or short detected in the purge solenoid circuit
55 - End of Message
The codes will not pop until the engine cycles and the ecu runs the diagnostics on them. I think you need to check the ECU ground and the sensor grounds. When you read the voltages while troubleshooting, make sure you refrence to the same ground the sensor or module uses. Check resistance for the ground refrence for for both.
I found out that I did not have ground to the sensors. I checked continuity between the sensor connectors and the PCM connector. All were good. I then checked the "Sensor Ground" pin on the PCM itself and it is not grounded with the key on or off. I checked the two ground wires on the PCM connector and they are both grounded. I went through and cleaned up the grounds and I am stumped now. It is sounding like I might have a bad PCM. I just dont want to throw parts at this thing.