Sorry, but another no start problem

96 xj, with auto transmission, we bought this Jeep not running. Previous owner said Jeep had run fine but needed a transmission so he put a used one in. After that Jeep would not start. I’ve read countless posts but none of them seem to be quite like this problem. Jeep cranks fine but has no fuel pump pressure, not even for the first few seconds. It has no check engine light when key is on or when cranking. No injector pulse, no power to CPS or cam sensor. CPS shows open when testing with ohm meter. We’ve replaced both relays, asd I believe and one other. I’m at a loss, could ignition switch be bad? Thanks for adding me to the group.

Is, or was the Check Engine Light ON ? Is the CEL dashboard bulb burnt out or removed ? Have you checked for stored CEL trouble codes or pending trouble codes ? Have you checked all the fuses in both the PDC under the hood and the fuse box inside ? Have you tested the fuel pump relay function, and jumpered the fuel pump relay socket to determine if the fuel pump will run ? Does the fuel pump have voltage when the relay socket is jumpered ?

The ignition switch might be faulty, but don't shotgun random new parts at an undiagnosed problem.

Always suspect the most recent repairs or modifications first when there is a problem. Confirm that the transmission is correctly installed and the all the engine and transmission wire harnesses and wire plugs are undamaged and correctly/firmly plugged in. A common transmission repair mistake is to pinch or otherwise damage the CPS during the install.

The most common reason for a cranking and not starting is the CPS, is the CPS a genuine Jeep part or a cheap Chinese clone part ? Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Cheap parts are cheap for a reason.

Unsure if check engine light bulb is good but when hooking up the scanner, it comes back “NO LINK”. All fuses good, if I jump fuel pump relay, pump fires up and I have 35psi fuel pressure. Ohmed CPS, comes back open, but no power going to it when cranking. Also no power going to cam sensor. Disconnected and cleaned all grounds. Put a ignition switch in, no luck.

Todd Hartman said:

Unsure if check engine light bulb is good but when hooking up the scanner, it comes back “NO LINK”. All fuses good, if I jump fuel pump relay, pump fires up and I have 35psi fuel pressure. Ohmed CPS, comes back open, but no power going to it when cranking. Also no power going to cam sensor. Disconnected and cleaned all grounds. Put a ignition switch in, no luck.

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Seems like he might have messed up the wiring. Almost as if its shorting out someplace. Did you check the wiring? Who knows how he took the trans out. Might have pulled the whole engine. It's hard to reach the torx bolts on the top of the bell housing with the engine in

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Update, checking voltage on pcm, we have 12 volts at pin 22, we have ground at pin 31 and 32 but we are not getting 5 volts out on pin 17 black connector and pin 31 white connector.

Todd Hartman said:

…. when hooking up the scanner, it comes back “NO LINK”.

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With this symptom I would suspect in this order: a faulty CPS, CPS wiring damage/issues, Transmission Control Unit (TCU) failure or wiring issues, another OBD engine sensor or O2 sensor with failure or wiring issues. I am not good with computer diagnostics, but if all OBD sensors test OK and their wiring tests OK and passes visual inspection one might suspect a faulty PCM.

Unplug the CPS and see if the check engine light comes back. If that doesn't work unplug both the CPS and the sync sensor. If that doesn't work unplug the TPS.

If something on the violet white wire circuit is shorted out it will shut down the 5volt power supply driver and the check engine light will not light with the key in the initial run position.

I've had shorted CPS on my 96 that tested good and was still shorting out. If the short is stopped (the right sensor unplugged) the Check engine light will/may come back on again, the link will/may be active and your five volt supply voltage will/may return to the violet white wire..

If the short is in your harness, a pinched wire, unplugging the sensors isn't going to help narrowing down the culprit.

Everything was unplugged when we purchased the Jeep, no check engine light and would not give us any codes. The one thing we didn’t do was check for 5 volts while everything was unplugged. We will do that next.

Another update, we replace the computer, right away our check engine light came back, fuel pump is working, we are getting 5.5 volts to CPS, and cam sensor, we didn’t have this before. Went ahead and changed out the CPS anyway just to rule it out. Still not getting any voltage to coil, we are getting a pulse when cranking out of the green wire going to the coil but no spark coming out of it. Any ideas?

Pulse on the green orange wire kind of throws me. Should be constant power, The coil has constant power with the key on, it triggers on the ground side through the computer.
Fuel pump primes when the key is turned to run, then shuts off until the computer gets a pulse signal from the CPS then turns the fuel pump full on and builds enough pressure for a start.
Test your 5 volts while cranking. Test for fuel pressure while cranking.
If the fuel pressure drops significantly while cranking and you are getting no spark, a sensor is likely bad. But don't discount a wiring issue.
I've ever had a bad cam position sensor, but have heard it will do the same thing as a bad CPS, won't let the ASD relay stay closed.
ASD relay provides power for the coil, alternator, injectors etc. You can test the orange green wire anyplace that is handy to see if you are getting battery voltage while cranking.
Just for giggles do an ohm test from your engine block to battery negative, just to eliminate a common ground fault issue.

Just for giggles test the coil.

Coil tests good, no 12 volt signal from no.7 pin on ecm.

The dark green orange wire is the *input* voltage (battery voltage) from the ASD relay to the coil. The black grey wire is the *output* which grounds through the computer or the trigger.

This is where I get lost, I thought that wire was supposed to be 12 volt hot, pin 7?

I still have no spark or injector pulse.

And I do have 5volts at map, CPS, tps and cam sensor and O2 sensors.

Now is the time for the scanner.

The speed sensor is also hooked up with the CPS, Cam position sensor etc.just info, unlikely to be an issue affecting the ASD relay.

Did you check the fuses? One of the 30 amp fuses supplies power to the ASD relay.

Best guess is you have a sensor issue (CPS or cam position sensor) or a sensor wiring issue. Remote possibility when the new tranny went in the flex plate/tone ring is the wrong year (96 specific). Is the wiring for the trans a plug/connector match or a splice job?

I am experiencing almost the exact same problems. I havent found the solution yet either.

so have you determined if you are not getting 12v+ to the Coil/ injectors? (take relay out jump the ASD relay), look for 12v+
Or you are getting 12v+ and the pcm is not grounding them?- its cranking but the PCM is not "trying" Start/ run. =Sensor problem.