My wifes 93 ZJ 5.2 auto will not fire. It turns over great, is sparking, and has 40psi at the fuel rail. I was told that a bad Crank position sensor or Cam Sensor could cause this as they work together. So I went ahead and replaced both, as well as did a full tune up just because i was already in there. well she's all back together and the problem has not changed. what could cause this? If it has spark and fuel, and there is no air restrictions as I currently have the intake off so it breathes straight into the throttle body. It is almost as if the timing has jumped teeth, but it ran fine the day before and we parked it (thankfully in the garage) now the next morning this. Some one please help.???????????????
Could be MAP or TP sensors are at fault as they are used to determine timing at start up. Pcm could have gotten stupid and is no longer able to get the timing right. With key on, wiggle wiring at cam and crank sensors and TPS, if you hear a bunch of clicking of relays, you may have spread terminals at a connector. Your sure you have a good spark while cranking?
hadn't thought of the tps or map. I know how to test tps, but is there a way to test a map without an scope? I'm running pretty short on cash at the moment and would like to not through random parts at it.
Unfortunatly, there's no way to check map calibration without it running. Verify wiring is good and at least 4.5v on supply ckt. Maybe apply vac to sensor while monitoring signal voltage, but map is lleast like of the possibles.
Have you tried starting with throttle open 1/4 or wot? Does it sputter or cough at all?
I have heard a number of guys here have found the wires from the crank sensor ( after having the sensor replaced) were touching the exhaust manifold causing intermittant shorts.
Also swap out the ASD relay.
i just checked the TPS it looks good. and I have a good 5V ref at the MAP. Map has a changing signal voltage when cranking, but as ZombieJeep93 pointed out that I don't have a way to test for a spec. I hooked up a noid light to the #1 injector wire, and a timing light to #1 spark wire and found that the injector appears to be firing just after the spark. Any ideas?
I'm in the same boat, except for the shelter of a garage.
Wife's '97 5.2, running fine when she came home Monday night, Tuesday morning,
cranks but no start.
I picked up cap, rotor, and coil in hopes of something simple.
The sun just poked through the clouds, maybe it will get above freezing
before I finish.
thank you js97. while that is downloading, I thought i would update. I left the noid light installed and pressurized the cylinder to hear the intake/ exhaust strokes as i turned the engine over manually. It seems as though the injector is firing at the beginning of the exhaust stroke????????? after the injector fired i poked a screw driver down the hole and continued to turn it till TDC to verify it was on the low end of piston travel. does this sound possible? I guess i could have been wrong and that could be bottom of compression stroke. does any one have a spec for what degree the injectors should fire?
so for an update, I got it to start by goosing the throttle wide open while cranking, Stuffing more air down its throat. It started up (Very Rough) misses pretty badly, and has raw fuel spitting out of the tail pipe like crazy. it also seems to have "magically" Developed a very bad knock/tick. I think I would have noticed that when we were driving the day before. What could I have possibly done to cause the knock? also I checked compression thinking valve, and comp. was good all around.
Def sounds like it flooded out. Maybe either weak coil or injector leaking. Does noise go away after warming up? Could be enough fuel washed out a cyl getting fuel into oil. this would clear up after running a while. Depends what the noise is. Faulty temp sensors (amb, intake or coolant) can cause pcm to add too much fuel at start up if it thinks its colder than it actually is.
Try to determine which cyl is missing and do a fuel leakdown test.