This Jeep is driving me nuts! All of the mods have been on the Jeep for years and this issue started when the battery started failing. It would crank but would not start because the battery voltage would drop low enough that the fuel pump relay would not engage. The battery was replaced (it would not hold a full charge) with an Exide 1000cca battery (cannot have too big of a battery!). If it sits overnight, it will not start on the first crank even if you wait to see that the check engine light displays immediately when the key is turned on (as it should), however the fuel pump does not spin until after you try to start it and the key has been turned off, then back on again (occasionally multiple times). Then the pump spins and pressures the system and then will start and run just fine. Once started, it will restart and run just fine until it sits overnight.
Things I've checked, or tried: cleaned and re-tightened battery cable connections, checked all engine bay ground connections and disabled the security system. All relays check out okay. All fuses check out okay. The fuel pump was replaced several years ago with an oem unit. The fuel pressure checks out to factory specs and the pressure regulator checks out okay as well. The only codes displayed are 12 and 55. Any other ideas or suggestions? Help!
Make sure that the check engine lites up immediatly after you turn the key on.
If it takes a few seconds then your computer may not be waking up.
My 95 did this and it progressivly got worse.
At first I would have to cycle the key or wait 10 seconds or so before the lite would illuminate and the Jeep would start.
After a few weeks it got to be up to 10 minutes before the check engine lite would come on and fire right up.
Changed PCM runs like new.
Totally unrelated to the PCM issue , but do you have the correct Champion plugs in the engine?
The check engine light displays immediately when the key is turned on (as it should). I thought that this was the problem that indicated the PCM. The only issue seems to be the fuel pump not engaging during the initial start cycle. Sorry, I do not recall the brand of spark plug, it's been a couple of years (approximately 10k ago).
Only one capacitor tested bad, but since it was so much trouble to replace I decided to replace all three. They were $1.39 each here in Oregon, so not an expensive thing money wise. Just frustrating that it did not fix it. Willing to listen to any other ideas!
On second thought, if it were the injectors wouldn't it fail the fuel pressure leak down test that is in the factory repair manual? This one passed, consequently I feel even more confused.
Broke down and ponied up for reman injectors with the 4 pintle. (hope I spelled that right! Same issue after sitting overnight, will not start first crank. Have to cycle the ignition on and off a couple time to prime the fuel, then will start right up. Any other ideas anyone?http://www.jeepforum.com/ubb/confused.gif
After all of the different things tried, running Berryman's B12 Chemtool through a few tanks in a row finally solved the issue. Apparently, the check valve in the fuel pump was not seating correctly so the fuel system cleaning finally did the trick!